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Friday, June 6, 2008

Unix / Linux commands

Unix / Linux commands

Unix command Description Details
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ALIAS Create abbreviations (aliases) for commands alias abbreviation=command
Displays a list of all aliases, standard arguments can be used (-a, -l, etc.). To cancel the alias use the unalias command. F.e. alias my_command='ls -al'.
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ARCHIE Change the current directory archie filename
Search the Archie database for a file on a FTP site.
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AT Execute a command at a specified time at [-filename][-m] time
-filename - Read the command(s) from the file specified.
-m = Notify the user by mail when the job is completed.
time = The time when the commands are going to be executed.
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BC Use the calculator bc
To use decimals, type scale = number (of decimal digits). End the calculator with Ctrl-D.
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BG Execute processes in the background bg [%n]
%n = Without this parameter it displays the jobs that are currently executed in the background. With a number the process with the given number is executed in the background.
& = At the end of a command starts the process in the background.
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CAL Display the calendar of the current month cal [month][year]
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CANCEL Cancel requests for printing cancel [ -u user] print-request
Requests can be cancelled by using the printer-id or by specifying the printer name.
-u user = Cancel print jobs that are queued for the specified user.
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CAT Display one or more files cat [-sn] [filenames]
If more than one filename is supplied, it is added at the end of the previous file and displayed.
-n = Display numbers in ascending order in front of each line.
-s = Do not comment about nonexistent files.
filenames = The filename(s) in the order that you want them to be displayed.
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CD Change the current directory cd [pathname]
Change the current directory to pathname or to root directory if no pathname is given.
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CHGRP Change group name chgrp groupname filename(s) | directory name(s)
Change group of the named file or directory.
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CHMOD Set file access permissions chmod [ugo,+-,rwx] filename | directory name
Change mode permissions of the named file(s) or directory(ies).
See File permissions for detailed information.

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CHOWN Change owner chown username filename | directoryname
Change the owner of a file or directory.
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CHSH Change shell chsh
Change the Unix shell you log into.
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CLEAR Clears display clear
Clears the display. Only the prompt is displayed.
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CMP Compare files cmp filename filename
Compares the named files. If they are equal nothing is returned, otherwise it returns the first character and line where the two files differ.
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COMPRESS Compress file compress [-v] filename
Compress the named file. The compressed file gets .Z appended to the filename.
-v = Ask for verification after compressing the file.
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CP Copy a file cp oldname newname [-r][-i] pathname (cp index.html index1.html)
The cp command allows you to copy files to new files, or copy files and directories to new directories. The command line cp index.html otherdir will copy the file index.html to the directory otherdir.
-i = Ask before updating a file or directory that exists in the destination with the same name.
-r = To copy a directory including its contents to a new directory, recursive.
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CRONTAB Scheduled files crontab filename [-r][-l][-e] pathname
The crontab command allows you to run, delete or edit scheduled tasks.
-l = lists your currently scheduled tasks.
-r = deletes all currently scheduled tasks.
-e = edit your scheduled tasks.
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DATE List current date and time date
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DF Disk space info df [-k] [filesystem]
Shows disk space available on the system.
-k = Use 1024 byte blocks instead of the default 512.
filesystem = If omitted displays the amount of disk space used and available on all mounted filesystems.
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DU Disk space info du [-aks] [filename | directoryname]
Shows how much disk space is being used up by folders.
-a = Shows counts for all files encountered, not only directories.
-k = Use 1024 byte blocks instead of the default 512.
-s = Don't display space usage of subdirectories.
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DIFF Display the differences between two text files diff textfile1 textfile2
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ECHO Output string echo characterstring
Displays the character string to the standard output device.
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EXIT Exit system exit
Exit the system or logout.
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FG Execute processes in the foreground fg [%n]
%n = Without this parameter it restarts the job that is currently executed in the background. With a number the process with the given number is restarted in the foreground.
& = At the end of a command starts the process in the foreground.
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FILE File classification file filename(s)
Shows information about the file type of the filename(s).
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FIND Search command find directorypath(s) searchpattern action(s)
Search the specified directorie(s) for files that satisfy the search pattern and act on them according to the action(s) parameter.
Search-patterns
-name filename = search for files with the specified filename.
- size n = search for files of n blocks (usually 512 or 1024 bytes).
- links n = search for files with n links.
- atime n = search for files that have been last accessed before n days.
- mtime n = search for files that have been last modified before n days.
- newer filename = search for files that have been modified more recently than the specified file.
Actions
- print = display the path(s) of the files found.
- exec command = run command for each file found
- ok command = as exec, but it asks for approval before the action.
Notes
Search patterns can be combined.
! = negation
-o = logical OR
One or more search patterns are combined using logical AND.
( ) or \ \ = these can be used to define groups of search patterns.
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FINGER User info finger emailaddress
Shows more information about a user.
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FTP FTP to a site ftp hostname (or IP address)
Connects to a FTP site.
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GCC Compile source code gcc option filename
Compile source code into a file.
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GOPHER Connect to Gopher gopher
Use the Gopher database browser.
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GREP Search in a file grep [-c,-n,-i,-v,-w,-y] pattern [filename(s)]
Search for a string in a file or files.
-c = displays only the number of lines that match.
-n = displays the line number in front of every displayed line.
-i = ignore case.
-v = displays all other lines except those lines that match.
-w = matches whole words only.
-y = case independent pattern matching, lower case letters in pattern will also match upper case letters in the input.
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GZIP Compress a file gzip filename
Compress a file.
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HEAD Display head of a file head [-n] filename(s)
Display the first n lines of the named file(s). If no number is given the first 10 lines are displayed.
-n = the number of lines to display from the top of the file.
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HOSTNAME Display hostname hostname
Display the name of the host machine.
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IRC Connect to IRC irc hostname (or IP address)
Connect to an Internet Relay Chat host.
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JOBS Display active processes jobs
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KILL Terminate process kill [-signr] process_ID
Terminate the process with the specified process ID.
-9 = send a definite kill signal.
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LOGOUT Logs off the system logout
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lprint Print a file lprintd Abort a print job lprintq List the print queue
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LS List files in the current directory ls [-CFRR*acdglrstu] [list of filenames or directories]
The -a switch will include hidden files (hidden files in UNIX begin with a dot (.)), the current directory and parent directory entries (. and .. respectively). You can combine switches by placing them one after the other (ls -la, etc..)
-C = list entries in columns.
-F = list directories with /.
-R = list subdirectories as well.
-R* = list subdirectories 2 levels below current directory.
-a = list all entries, including files with a dot (.htaccess, etc..).
-c = sort entries by last modified date.
-d = list directories only.
-g = list hidden files and directories.
-l = list in long format (mode, no of links, owner, group, size, and modified date).
-r = list in reverse order.
-s = list size in 1024 byte blocks.
-t = sort contents by time of last modified date.
-u = use time of last access (not last modified date) for sorting (with -t) or printing onscreen (with -l).
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MAKE Compile source code make command
Compile a source code.
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MAKEFILE Compile source code file make filename
Compile a source code into a file.
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MAN Read the help man command
Shows the help on the entered command, f.e. man ls, man chmod, etc.
To search for some text, press the forward-slash (/) key and type the text you want to search for. If you want to run a program that's in your current directory, you'll need to put a dot-slash (./) in front of the program name.
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MKDIR Create a directory mkdir directoryname, mkdir -i directoryname
To create a directory in the current directory, type mkdir followed by the directory name. To delete a directory and all its contents, use rm -r directoryname. The -i parameter will make the system prompt you before deleting a file or directory. If the directory is empty, you can also delete it using the rmdir command.
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MORE List a file more filename
View a file with a pause after every full screen.
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MV Rename a file mv oldname newname
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PASSWORD Change password password
Change the administrator password.
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PICO Edit a file pico filename
An easy to use text editor.
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PINE A mailer program pine
An easy to use mailer program.
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PWD What is the current directory pwd
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RM Delete/remove a file rm filename
To delete a single file, use rm filename.
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RMDIR Remove a directory rmdir directoryname, rm -r directoryname ( to delete folders with its files).
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RZ Receive a file rz
Receive a file using Zmodem.
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SZ Send a file sz filename
Send a file using Zmodem.
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TAIL Show last lines of a file tail filename
Show the last few lines of a file.
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TALK Page user to chat talk username
Pages the user for a chat, the user is an e-mail address.
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TAR Archive files tar filename
Create or extract multiple file archives. Other methods are lharc, lzh, and lha, but these methods may not be present on your system.
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TIN, TRN Connect to Usenet tin, trn
Connect to Usenet newsgroups.
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TELNET Connect telnet hostname (or IP address)
Connect to an Internet web site.
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DOS2UNIX Conversion of text files dos2unix filename newname
Strips the carriage returns (CR) from the DOS text file.
UNIX2DOS Conversion of text files unix2dos filename newname
Adds the carriage returns (CR) to the Unix text file.
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WHO Who is logged in? who
Shows who is logged into the local system.
W Who is logged in and what are they doing? w
Shows who is logged into the local system and what they are doing.
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WRITE Write to a user write username
Write to a user on the local system (CTRL-C to end it).
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ZIP Compress to zip zip username
Compress to zip for IBM files.





Unix & Linux folder & file permissions

As a webmaster you need to know how to use the CHMOD command to set folder and file permissions (also referred to as 'file attributes') on UNIX and Linux web servers. You need to set the correct file permissions especially with CGI script files when you install them.
On a UNIX web server, every file and folder stored on the hard drive have a set of permissions associated with it, which says who is allowed to do what with the file. Every file (and folder) also has an "owner" and a "group" associated with it. If you created the file, then you are the owner of that file, and your group, or the group associated with the folder you created the file in, will be associated with that file.
There are three types of people that can do things to files - the Owner of the file, anyone in the Group that the file belongs to, and Others (everyone else). In UNIX they are referred to using the letters U (for Owner or User), G (for Group), and O (for Others).
There are three things that can be done to files or folders:
• read the file or folder (this means listing the contents of the file or folder)
• write to the file. For folders this means creating and deleting files in the folder.
• execute (run) the file if it's a program or script. For folders this means accessing files in the folder.
Therefore there are three types of permissions:
r - read the file or directory
w - write to the file or directory
x - execute the file or search the directory
Each of these permissions can be set for any one of three types of user:
u - the user who owns the file (you)
g - members of the group to which the owner belongs
o - all other users
CGI script installation pages will tell you to 'CHMOD 755' or 'Set the file to executable'. This all refers to setting the file permissions or attributes. When you use FTP or Telnet, you'll notice some letters next to the file listings. These letters are the current settings for the file or folder permissions. The details look like this:
15Kb 02/01/02 22:45 drwxrwxrwx
The string of letters, drwxrwxrwx, represents the permissions that are set for this folder.
d r w x r w x r w x
Owner Group Other
Directory Read Write Execute Read Write Execute Read Write Execute


The string of letters breaks down into 3 sections of 3 letters each, representing each of the types of users (the owner, members of the group, and everyone else). There is a 'd' attribute on the left, which tells us if this is a file or a folder (directory). If any of these letters is replaced with a hyphen (-), it means that permission is not granted.
For example:
drwxrwxrwx A folder which has read, write and execute permissions for the owner, the group and for other users.
-rwxr--r-- A file that can be read and written by the user, but only read and executed by the group, and only read by everyone else.

Using numbers
You can also use numbers for setting file and folder permissions. Each of the three numbers corresponds to each of the three sections of letters. The first number determines the owner permissions, the second number determines the group permissions and the third number determines the other permissions. Each number can have one of eight values ranging from 0 to 7. Each value corresponds to a certain setting of the read, write and execute permissions.
These values are added together for any one user category:
1 = execute only
2 = write only
3 = write and execute (1+2)
4 = read only
5 = read and execute (4+1)
6 = read and write (4+2)
7 = read and write and execute (4+2+1)
or in a table format, it would look like this:
Number Read (R) Write (W) Execute (X)
0 No No No
1 No No Yes
2 No Yes No
3 No Yes Yes
4 Yes No No
5 Yes No Yes
6 Yes Yes No
7 Yes Yes Yes

For example:

777 is the same as rwxrwxrwx
755 is the same as rwxr-xr-x
Setting permissions using FTP
Your FTP program will most likely allow you to set file and folder permissions by selecting the file or folder in the remote window and either right-clicking on it and selecting an option such as CHMOD or Set permissions, or by selecting CHMOD / Set permissions from a menu option. Once you've selected the appropriate menu option, you'll see a dialog box similar to the following (this one is from CuteFTP for Windows):

Using the screen of your FTP client, it should be easy to set the read, write and execute permissions for the owner, group and others using the check boxes. If you already know which numbers are needed, you can type the 3 digit number. The FTP client will change (chmod) the permissions for you. The above example of CHMOD 755 will be the one used most, since almost all CGI scripts need to be 755.
Setting permissions using Telnet
The other way to set permissions on your files is using Telnet (or a standard shell). Once you're connected to the server and have logged in, change to the folder containing the files you want to change (cd yourdomain/cgi-bin), You can then use the command chmod to set permissions on your files and folders. You can use the number notation described above, or you can use the letters.
To set permissions with numbers, use the following syntax: chmod xxx filename
where "xxx" is the 3 digit number representing the permissions, and filename is the file you want to change.
chmod 755 mailform.pl
You can use the letters u (owner/user), g (group) and o (other) to set permissions for each of the user types, and r (read), w (write) and x (execute) to represent the permissions to set. You can also use a instead of u, g, and o, to mean all users (u,g,o).
You assign permissions using either the plus sign (+), which means add these permissions, the minus sign (-), which means remove these permissions, or the equals sign (=), which means change the permissions to exactly these.
For example:
chmod a+x mailform.pl adds execute permissions for all users to the file mailform.pl (makes the file executable).
chmod u=rwx mailform.pl sets read, write and execute permission just for the owner (the permissions for the group and for others remain unchanged).
Checking your folder and file permissions
To display the access permissions of a file or directory use the command:
ls -l filename (directory)
This displays a one line summary for each file or directory.
Changing group ownership of files and directories
Every user is a member of one or more groups. To find out which groups you belong to use the command: groups. To find out which groups another user belongs to, use the command: groups username. Your files and directories are owned by the group (or one of the groups) that you belong to. This is known as group ownership. To list the group ownership of your files, use the command: ls -gl. You can change the group ownership of a file or directory with the command: chgrp group_name file/directory_name. You must be a member of the group to which you are changing ownership to.



Untar a Unix / Linux file

How to untar a Unix / Linux file
Unzipping files is an important part of downloading Linux files from the Internet. In Linux a majority of the files that are downloaded are in tgz format (a gnu zipped tar file), although there are other common extensions, as shown here:

[filename].tgz
[filename].tar
[filename].tar.gz
[filename].tar.z
[filename].z
Extraction
First you upload the .tgz, .tar .tar.gz or .tar.z file to the directory on your web server designated for public Internet use. Typically this directory is named 'www', 'htdocs' or 'web'. The file should be uploaded in BINARY format using any FTP program.

Once the installation file has been uploaded, connect to your web server using a terminal emulation program. One of the most popular of these programs is Telnet. Enter your username and password when prompted, then change to the directory on your web server designated for Internet use. If this directory is named 'www', you should type the following command at the prompt:

cd /usr/dom/www or cd /home/sites/me/web
Always start from the root directory (/).
With files that have the .tgz, tar.gz, or tar.z extension use this command:

tar -zxvf [filename with all extensions]

example: tar -zxvf yourfile.tar.gz

This will extract the file for you in the directory you are currently in. Using the above command will save you from having to redirect the output for gzip or anything else (because the z option automatically decompresses the file for you), otherwise without the z argument, you would have to do a command like this:

uncompress [filename with all extensions]

tar -xvf [filename with only tar extension]

Other ways to decompress files are to use:

gunzip [filename with .gz extension] - f.e. gunzip yourfile.gz

zcat [filename with .gz extension] - f.e. zcat yourfile.gz

uncompress [filename with .z extension] - f.e. uncompress yourfile.z
Not all Unix systems extract archive files with all the necessary permissions intact, therefore you should set the proper permissions on the program as required.
Using Telnet type the following at the prompt:

chmod -R 777 "directoryname"
cd "directoryname"
chmod 755 cgi-bin
cd cgi-bin
chmod 755 *.cgi
chmod 755 *.pl
You can also use most FTP clients to change the file attributes. 777 (RWX-RWX-RWX) and 755 (RWX-RX-RX) are the most widely used attributes for files relating to running most CGI scripts on a server.


VI Unix editor

The vi editor is a shell editor for Unix systems. It makes use of a regular keyboard with an Escape key. On a DEC station the Escape key is the F11 key. It works on all Unix computers. Use a Telnet or SSH client and login to your web server. Enter your username and password, then type
su -
at the command line. Enter your root password to get access to root.
Complete documentation is available by typing: man vi

START SESSION
vi filename - filename is the file to be edited
UNDO
u - undo the last command

SCREEN COMMANDS (CTRL-X means pressing the CTRL key and the X key simultaneously)
CTRL-l - reprint current screen
CTRL-L - expose one more line at the top of the screen
CTRL-E - expose one more line at the bottom of the screen
CTRL-F - go forward one screen
CTRL-B - go back one screen
CTRL-D - page down half a screen
CTRL-U - page up half a screen

CURSOR POSITIONING COMMANDS
j - move cursor down one line, same column
k - move cursor up one line, same column
h - move cursor back one character
l - move cursor forward one character
RET - move cursor to beginning of next line (RET is the Return key)
0 - move cursor to beginning of current line
$ - move cursor to end of current line
SPACE - move cursor forward one character (SPACE is the Space bar)
nG - move cursor to the beginning of line n (Default is the last line of the file)
:n - move cursor to the beginning of line n
b - move the cursor backward to the beginning of the previous word
e - move the cursor backward to the end of the previous word
w - move the cursor forward to the next word
/pattern - move cursor forward to the next occurrence of a pattern
?pattern - move cursor backward to the next occurrence of a pattern
n - repeats the last / or ? pattern search.

TEXT INSERTION COMMANDS
a - append text after the cursor (press ESC key to terminate the command)
A - append text at the end of the line (press ESC key to terminate the command)
i - insert text before the cursor (press ESC key to terminate the command)
I - insert text at the beginning of the line (press ESC key to terminate the command)
o - open a new line below the current line for text insertion (press ESC key to terminate the command)
O - open a new line above the current line for text insertion (press ESC key to terminate the command)
DEL - overwrite the last character during text insertion (DEL is the Delete key)
ESC - stop text insertion. (ESC is the Escape key, on a DEC station this is the F11 key)

TEXT DELETION COMMANDS
x - delete the current character
dd - delete the current line
dw - delete the current word
d) - delete the rest of the current sentence
D or d$ - delete from cursor to end of line
P - put text back from previous delete

TEXT MODIFICATION COMMANDS
cw - change characters of current word (until terminated with the ESC key)
c$ - change text up to the end of the line
C or cc - change remaining text on current line (until terminated with the ESC key)
~ - change case of the current character
xp - transpose current and following characters
J - join current line with next line
s - delete the current character and go into insertion mode
rx - replace the current character with x
R - replace the following characters (until terminated with the ESC key)

CUT AND PASTE COMMANDS
yy - put the current line in a buffer (does not delete the line from its current position)
p - places the line in the buffer after the current position of the cursor

APPEND FILE COMMANDS
:R filename - insert the file filename where the cursor was before the : was typed

EXIT COMMANDS
ZZ - exit vi and save changes
:wq - write changes to current file and quit editing session
:q! - quit editing session (no changes are made)


Telnet commands

telnet [-8ELadr] [-S tos] [-e escapechar] [-l user] [-n tracefile] [host [port]]


DESCRIPTION
The telnet command is used for interactive communication with another host using the TELNET protocol. It begins in command mode, where it prints a telnet prompt ("telnet> "). If telnet is invoked with a host argument, it performs an open command implicitly; see the description below.

OPTIONS
-8 Request 8-bit operation. This causes an attempt to negotiate the TELNET BINARY option for both input and output. By default Telnet is not 8-bit clean.
-E Disables the Escape character functionality; sets the Escape character to ``no character''.
-L Specifies an 8-bit data path on output. This causes the TELNET BINARY option to be negotiated on just output.
-a Attempt automatic login. This sends the user name via the USER variable of the ENVIRON option if supported by the remote system. The username is retrieved via getlogin(3).
-d Sets the initial value of the debug toggle to TRUE.
-r Emulate rlogin(1). In this mode, the default escape character is a tilde. The interpretation of the escape character is changed: an escape character followed by a dot causes telnet to disconnect from the remote host. A ^Z instead of a dot suspends telnet, and a ^] (the default telnet escape character) generates a normal telnet prompt. These codes are accepted only at the beginning of a line.
-S tos : Sets the IP type of service (TOS) option for the telnet connection to the value tos.
-e escapechar : Sets the escape character to escapechar. If no character is supplied, no escape character will be used. Entering the escape character while connected causes telnet to drop to command mode.
-l user : Specify user as the user to log in as on the remote system. This is accomplished by sending the specified name as the USER environment variable, so it requires that the remote system supports the TELNET ENVIRON option. This option implies the -a option, and may also be used with the open command.
-n tracefile : When LINEMODE is enabled, character processing is done on the local system, under the control of the remote system. When input editing or character echoing is to be disabled, the remote system will relay that information. The remote system will also relay changes to any special characters that happen on the remote system, so that they can take effect on the local system. In ``character at a time'' mode, most text typed is immediately sent to the remote host for processing.
In ``old line by line'' mode, all text is echoed locally, and only completed lines are sent to the remote host. The ``local echo character'' (initially ``^E'') may be used to turn off and on the local echo (this would mostly be used to enter passwords without the password being echoed). If the LINEMODE option is enabled, or if the localchars toggle is TRUE (the default for ``old line by line``), the user's quit, intr, and flush characters are trapped locally, and sent as TELNET protocol sequences to the remote side. If LINEMODE has ever been enabled, then the user's susp and eof are also sent as TELNET protocol sequences, and quit is sent as a TELNET ABORT instead of BREAK. There are options (see toggle autoflush and toggle autosynch) which cause this action to flush subsequent output to the terminal (until the remote host acknowledges the TELNET sequence) and flush previous terminal input (in the case of quit and intr).
TELNET COMMANDS

The following telnet commands are available. Unique prefixes are understood as abbreviations.

auth argument ...
The auth command controls the TELNET AUTHENTICATE protocol option. If telnet was compiled without authentication, the auth command will not be supported.
Valid arguments are:
disable type
Disable the specified type of authentication. To obtain a list of available types, use the auth disable ? command.

enable type
Enable the specified type of authentication. To obtain a list of available types, use the authenable ? command.
status
List the current status of the various types of authentication.
Valid arguments are:
disable type [input|output]
Disable the specified type of encryption. If you do not specify input or output, encryption of both is disabled. To obtain a list of available types, use ``encrypt disable ?''.

enable type [input|output]
Enable the specified type of encryption. If you do not specify input or output, encryption of both is enabled. To obtain a list of available types, use ``encrypt enable ?''.
input
This is the same as ``encrypt start input''.

-input
This is the same as ``encrypt stop input''.

output
This is the same as ``encrypt start output''.

-output
This is the same as ``encrypt stop output''.

start [input|output]
Attempt to begin encrypting. If you do not specify input or output, encryption of both input and output is started.

status
Display the current status of the encryption module.

stop [input|output]
Stop encrypting. If you do not specify input or output, encryption of both is stopped.

type type
Sets the default type of encryption to be used with later ``encrypt start'' or ``encrypt stop'' commands.
environ arguments...
The environ command is used to propagate environment variables across the telnet link using the TELNET ENVIRON protocol option. All variables exported from the shell are defined, but only the DISPLAY and PRINTER variables are marked to be sent by default. The USER variable is marked to be sent if the -a or -l command line options were used.

Valid arguments are:
define variable value

unexport variable
Do not mark the specified variable for propagation to the remote host. The remote host may still ask for variables that are not exported.

list
List the current set of environment variables. Those marked with a * will be propagated to the remote host. The remote host may still ask for the rest.

?
Prints out help information for the environ command.
logout
Send the TELNET LOGOUT protocol option to the remote host. This command is similar to a close command. If the remote host does not support the LOGOUT option, nothing happens. But if it does, this command should cause it to close the connection. If the remote side also supports the concept of suspending a user's session for later reattachment, the logout command indicates that the session should be terminated immediately.

mode type
Type is one of several options, depending on the state of the session. Telnet asks the remote host to go into the requested mode. If the remote host says it can, that mode takes effect.
character
Disable the TELNET LINEMODE option, or if the remote side does not understand the LINEMODE option, then enter ``character at a time`` mode.

line
Enable the TELNET LINEMODE option, or if the remote side does not understand the LINEMODE op tion, then attempt to enter ``old-line-by-line`` mode.

isig (-isig)
Attempt to enable (disable) the TRAPSIG mode of the LINEMODE option. This requires that the LINEMODE option be enabled.

edit (-edit)
Attempt to enable (disable) the EDIT mode of the LINEMODE option. This requires that the LINEMODE option be enabled.

softtabs (-softtabs)
Attempt to enable (disable) the SOFT_TAB mode of the LINEMODE option This requires that the LINEMODE option be enabled.

litecho (-litecho)
Attempt to enable (disable) the LIT_ECHO mode of the LINEMODE option. This requires that the LINEMODE option be enabled. It is possible to connect to services that do not support the telnet protocol without creating problems. Protocol negotiation can be forced by placing a dash before the port number. After establishing a connection, any commands associated with the remote host in the user's .telnetrc file are executed. The format of the .telnetrc file is as follows: Lines beginning with a #, and blank lines, are ignored. The rest of the file should consist of hostnames and sequences of telnet commands to use with that host. Commands should be one per line, indented by whitespace lines beginning without whitespace are interpreted as hostnames. Upon connecting to a particular host, the commands associated with hat host are executed.
quit
Close any open session and exit telnet. An end of file condition on input, when in command mode, will trigger this operation as well.

send arguments
Send one or more special telnet protocol character sequences to the remote host. The following are the codes which may be specified (more than one may be used in one command):
abort
Sends the TELNET ABORT (Abort Processes) sequence.

ao
Sends the TELNET AO (Abort Output) sequence, which should cause the remote system to flush all output from the remote system to the user's terminal.

ayt
Sends the TELNET AYT (Are You There?) sequence, to which the remote system may or may not choose to respond.

brk
Sends the TELNET BRK (Break) sequence, which may have significance to the remote system.

ec
Sends the TELNET EC (Erase Character) sequence, which should cause the remote system to erase the last character entered.

el
Sends the TELNET EL (Erase Line) sequence, which should cause the remote system to erase the line currently being entered.

eof
Sends the TELNET EOF (End Of File) sequence.

eor
Sends the TELNET EOR (End of Record) sequence.

escape
Sends the current telnet escape character.

ga
Sends the TELNET GA (Go Ahead) sequence, which likely
susp
Sends the TELNET SUSP (Suspend Process) sequence.

synch
Sends the TELNET SYNCH sequence. This sequence causes the remote system to discard all previously typed but not yet read input. This sequence is sent as TCP urgent data and if it doesn't work, a lower case ``r'' may be echoed on the terminal.

do cmd

dont cmd

will cmd

wont cmd
Sends the TELNET DO cmd sequence. Cmd can be either a decimal number between 0 and 255, or a symbolic name for a specific TELNET command. Cmd can also be either help or ? to print out help information, including a list of known symbolic names.

?
Prints out help information for the send command.
set argument value

unset argument value
The set command will set any one of a number of telnet variables to a specific value or to TRUE. The special value off turns off the function associated with the variable. This is equivalent to using the unset command. The unset command will disable or set to FALSE any of the specified variables. The values of variables may be interrogated with the display command. The variables which may be set or unset, but not toggled, are listed here. In addition, any of the variables for the toggle command may be explicitly set or unset.
ayt
If telnet is in localchars mode, or LINEMODE is enabled, and the status character is typed, a TELNET AYT sequence is sent to the remote host. The initial value for the "Are You There" character is the terminal's status character.

echo
This is the value (initially ``^E'') which, when in ``line by line'' mode, toggles between doing local echoing of entered characters for normal processing, and suppressing echoing of entered characters (f.e. a password).

eof
If telnet is operating in LINEMODE or ``old line by line'' mode, entering this character as the first character on a line will cause this character to be the end of file.

flushoutput
If telnet is in localchars mode and the flushoutput character is typed, a TELNET AO sequence is sent to the remote host. The initial value for the flush character is taken to be the terminal's flush character.

forw1

forw2
If TELNET is operating in LINEMODE, these are the characters that, when typed, cause partial lines to be forwarded to the remote system. The initial value for the forwarding characters are taken from the terminal's eol and eol2 characters.

interrupt
If telnet is in localchars mode and the interrupt character is typed, a TELNET IP sequence is sent to the remote host. The initial value for the interrupt character is taken to be the terminal's intr character.

kill
If telnet is in localchars mode and if telnet is operating in ``character at a time'' mode, then when this character is typed, a TELNET EL sequence is sent to the remote system. The initial value for the kill character is taken to be the terminal's kill character.

lnext
If telnet is operating in LINEMODE or ``old line by line`` mode, then this character is taken to be the terminal's lnext character. The initial value for the lnext character is taken to be the terminal's lnext character.

quit
If telnet is in localchars mode and the quit character is typed, a TELNET BRK sequence is sent to the remote host. The initial value for the quit character is taken to be the terminal's quit character.

reprint
If telnet is operating in LINEMODE or ``old line by line`` mode, then this character is taken to be the terminal's reprint character. The initial value for the reprint character is taken to be the terminal's reprint character.

rlogin
This is the rlogin mode escape character. Setting it enables rlogin mode, as with the r command-line option.

susp
If telnet is in localchars mode, or LINEMODE is enabled, and the suspend character is typed, a TELNET SUSP sequence is sent to the remote host. The initial value for the suspend character is taken to be the terminal's suspend character.

tracefile
This is the file to which the output, caused by netdata or option tracing being TRUE, will be written. If it is set to ``-'', then tracing information will be written to standard output.

worderase
If telnet is operating in LINEMODE or ``old line by line`` mode, then this character is taken to be the terminal's worderase character. The initial value for the worderase character is taken to be the terminal's worderase character.

?
Displays the legal set (unset) commands.
slc state
The slc command (Set Local Characters) is used to set or change the state of the the special characters when the TELNET LINEMODE option has been enabled. Special characters are characters that get mapped to TELNET commands sequences (ip or quit) or line editing characters (erase and kill). By default, the local special characters are exported.
check
Verify the current settings for the current special characters. The remote side is requested to send all the current special character settings, and if there are any discrepancies with the local side, the local side will switch to the remote value.

export
Switch to the local defaults for the special characters. The local default characters are those of the local terminal at the time when telnet was started.

import
Switch to the remote defaults for the special characters. The remote default characters are those of the remote system at the time when the TELNET connection was established.

?
Prints out help information for the slc command.
status
Show the current status of telnet. This includes the name of the remote host, as well as the current mode.

toggle arguments ...
Toggle (between TRUE and FALSE) various flags that control how system acknowledges (via a TELNET TIMING MARK option) that it has processed those TELNET sequences. The initial value for this toggle is TRUE if the terminal user had not done an "stty noflsh", otherwise FALSE (see stty(1)).
autodecrypt
When the TELNET ENCRYPT option is negotiated, by default the actual encryption (decryption) of the data stream does not start automatically. The autoencrypt (autodecrypt) command states that encryption of the output (input) stream should be enabled as soon as possible. This flag exists only if encryption support is enabled.

autologin
If the remote side supports the TELNET AUTHENTICATION option, telnet attempts to use it to perform automatic authentication. If the TELNET AUTHENTICATION option is not supported, the user's login name is propagated using the TELNET ENVIRON option. Setting this flag is the same as specifying the a option to the open command or on the command line.

autosynch
If autosynch and localchars are both TRUE, then when either the intr or quit characters is typed, the resulting telnet sequence sent is followed by the TELNET SYNCH sequence. This procedure should cause the remote system to begin discarding all previously typed input until both of the telnet sequences have been read and acted upon. The initial value of this toggle is FALSE.

binary
Enable or disable the TELNET BINARY option on both input and output.

inbinary
Enable or disable the TELNET BINARY option on input.

outbinary
Enable or disable the TELNET BINARY option on output.

crlf
If this is TRUE, then carriage returns will be sent as . If this is FALSE, then carriage returns will be send as . The initial value for this toggle is FALSE.

crmod
Toggle carriage return mode. This flag only exists if encryption support is available.

localchars
If this is TRUE, then the flush, interrupt, quit, erase, and kill characters are recognized locally, and transformed into appropriate TELNET control sequences (respectively ao, ip, brk, ec, and el). The initial value for this toggle is TRUE in ``old line by line'' mode, and FALSE in ``character at a time'' mode. When the LINEMODE option is enabled, the value of localchars is ignored, and assumed to always be TRUE. If LINEMODE has ever been enabled, then quit is sent as abort, and eof and are sent as eof and susp.

netdata
Toggles the display of all network data in hexadecimal format. The initial value for this toggle is FALSE.

options
Toggles the display of some internal telnet protocol processing. The initial value for this toggle is FALSE.

prettydump
When the netdata toggle is enabled, if prettydump is enabled the output from the netdata command will be formatted in a more user readable format. Spaces are put between each character in the output, and the beginning of telnet escape sequences are preceded by a '*' to aid in locating them.

skiprc
When the skiprc toggle is TRUE, telnet does not read the .telnetrc file. The initial value for this toggle is FALSE.

termdata
Toggles the display of all terminal data (in hexadecimal format). The initial value for this toggle is FALSE.

verbose_encrypt
When the verbose_encrypt toggle is TRUE, TELNET prints out a message each time encryption is enabled or disabled. The initial value for this toggle is FALSE. This flag only exists if encryption support is available.

?
Displays the legal toggle commands.
z
Suspend telnet. This command only works when the user is using Telnet uses at least the HOME, SHELL, DISPLAY, and TERM environment variables. Other environment variables may be propagated to the other side via the TELNET ENVIRON option.

NOTE: on some remote systems, echo has to be turned off manually when in ``old line by line'' mode. In ``old line by line'' mode or LINEMODE the terminal's eof character is only recognized and sent to the remote system when it is the first character on a line.


1 Introduction
This is my own summary of useful Linux abbreviations, directories, files, and commands. I use my own annotations to recall useful options and arguments that are not necessarily documented in easy-to-find places. I quite often call up this file when I can't remember the syntax of a command that I use often (but not often enough to remember the syntax!). I also editorialize on the relative usefulness of different types of programs.
This document is work in progress. Send suggested changes and corrections to ambler.steven@uqam.ca
O'Reilly has just published online an alphabetical list of commands from Linux in a Nutshell. It is available here. It contains more detailed explanations of many of the commands listed here.
2 Shorthand at the Command Prompt
Some of these are specific to the bash shell. I have not experimented enough with other shells to know which are common to all shells. See also the ``Bash Reference Card'', SSC (2000), available online.
• / - root directory
• ./ - current directory
• ./command_name - run a command in the current directory when the current directory is not on the path
• ../ - parent directory
• ~ - home directory
• $ - typical prompt when logged in as ordinary user
• # - typical prompt when logged in as root or superuser
• ! - repeat specified command
• !! - repeat previous command
• ^^ - repeat previous command with substitution
• & - run a program in background mode
• [Tab][Tab] - prints a list of all available commands. This is just an example of autocomplete with no restriction on the first letter.
• x[Tab][Tab] - prints a list of all available completions for a command, where the beginning is ``x''
• [Alt][Ctrl][F1] - switch to the first virtual text console
• [Alt][Ctrl][Fn] - switch to the nth virtual text console. Typically, there are six on a Linux PC system.
• [Alt][Ctrl][F7] - switch to the first GUI console, if there is one running. If the graphical console freezes, one can switch to a nongraphical console, kill the process that is giving problems, and switch back to the graphical console using this shortcut.
• [ArrowUp] - scroll through the command history (in bash)
• [Shift][PageUp] - scroll terminal output up. This also works at the login prompt, so you can scroll through your boot messages.
• [Shift][PageDown] - scroll terminal output down
• [Ctrl][Alt][+] - switch to next X server resolution (if the server is set up for more than one resolution)
• [Ctrl][Alt][-] - change to previous X server resolution
• [Ctrl][Alt][BkSpc] - kill the current X server. Used when normal exit is not possible.
• [Ctrl][Alt][Del] - shut down the system and reboot
• [Ctrl]c - kill the current process
• [Ctrl]d - logout from the current terminal
• [Ctrl]s - stop transfer to current terminal
• [Ctrl]q - resume transfer to current terminal. This should be tried if the terminal stops responding.
• [Ctrl]z - send current process to the background
• reset - restore a terminal to its default settings
• [Leftmousebutton] - Hold down left mouse button and drag to highlight text. Releasing the button copies the region to the text buffer under X and (if gpm is installed) in console mode.
• [Middlemousebutton] - Copies text from the text buffer and inserts it at the cursor location. With a two-button mouse, click on both buttons simultaneously. It is necessary for three-button emulation to be enabled, either under gpm or in XF86Config.
3 Typical Dot Files
There is some redundancy across these programs. For example, the look and behavior of emacs can be customized by usinng the .emacs file, but also by adding the appropriate modifications to the .Xdefaults file. Default versions of these files are often installed in users' home directories when the software packages that use them are installed. If a program doesn't find its configuration file in the user's home directory, it will often fall back on a sytem-wide default configuration file installed in one of the subdirectories that the package lives in.
• .bash_logout - file executed by bash shell on logout
• .bash_profile - initialization of bash shell run only on login. Bash looks first for a .bash_profile file when started as a login shell or with the -login option. If it does not find .bash_profile, it looks for .bash_login. If it doesn't find that, it looks for .profile. System-wide functions and aliases go in /etc/bashrc and default environment variables go in /etc/profile.
• .bashrc - initialization command run when bash shell starts up as a non-login shell
• .cshrc - initialization commands that are run automatically (like autoexec.bat) when C shell is initiated

• .emacs - configuration file for emacs editor

• .fvwmrc - configuration file for fvwm window manager

• .fvwm2rc - configuration file for fvwm2 window manager

• .jedrc - configuration file for the jed text editor

• .lessrc - typically contains key bindings for cursor movement with the less command

• .login - initialization file when user logs in

• .logout - commands run when user logs out

• .wm_style - gives choice of default window manager if one is not specified in startx

• .Xdefaults - sets up X resources for individual user. The behavior of many different application programs can be changed by modifying this file.

• .xinitrc - initialization file when running startx. Can be used to activate applications, run a given window manager, and modify the appearance of the root window.

• .xsession - configuration file for xdm

4 Useful Files

• /boot/vmlinuz - the typical location and name of the Linux kernel. In the Slackware distribution, the kernel is located at /vmlinuz.

• /dev/fd0 - first floppy disk drive

• /dev/fd0H1440 - driver for the first floppy drive in high density mode. Generally, this is invoked when formatting a floppy drive for a particular density. Slackware comes with drivers that allow for formatting a 3.5" diskette with up to 1.7MB of space. Red Hat and Mandrake do not contain these device driver files by default.

• /dev/fd1 - second floppy disk drive

• /dev/hda - first IDE hard drive

• /dev/hdc - on many machines, the IDE cdrom drive. Most often, there is a symbolic link called /dev/cdrom which is just a link to the true cdrom driver file.

• /dev/null - used when you want to send output into oblivion

• /etc/aliases - file containing aliases used by sendmail and other MTAs (mail transport agents). After updating this file, it is necessary to run the newaliases utility for the changes to be passed to sendmail.

• /etc/bashrc - system-wide default functions and aliases for the bash shell

• /etc/conf.modules - aliases and options for configurable modules

• /etc/crontab - shell script to run different commands periodically (hourly, daily, weekly, monthly, etc.)

• /etc/DIR_COLORS - used to store colors for different file types when using ls command. The dircolors command uses this file when there is not a .dir_colors file in the user's home directory. Used in conjunction with the eval command (see below).

• /etc/exports - specifies hosts to which file systems can be exported using NFS. Man exports contains information on how to set up this file for remote users.

• /etc/fstab - contains information on partitions and filesystems used by system to mount different partitions and devices on the directory tree

• /etc/HOSTNAME - stores the name of the host computer

• /etc/hosts - contains a list of host names and absolute IP addresses.

• /etc/hosts.allow - hosts allowed (by the tcpd daemon) to access Internet services

• /etc/hosts.deny - hosts forbidden (by the tcpd daemon) to access Internet services

• /etc/group - similar to /etc/passwd but for groups

• /etc/inetd.conf - configures the inetd daemon to tell it what TCP/IP services to provide (which daemons to load at boot time). A good start to securing a Linux box is to turn off these services unless they are necessary.

• /etc/inittab - runs different programs and processes on startup. This is typically the program which is responsible for, among other things, setting the default runlevel, running the rc.sysinit script contained in /etc/rc.d, setting up virtual login terminals, bringing down the system in an orderly fashion in response to [Ctrl][Alt][Del], running the rc script in /etc/rc.d, and running xdm for a graphical login prompt (only if the default runlevel is set for a graphical login).

• /etc/issue - pre-login message. This is often overwitten by the /etc/rc.d/rc.S script (in Slackware) or by the /etc/rc.d/rc.local script (in Mandrake and Red Hat, and perhaps other rpm-based distributions). The relevant lines should be commented out (or changed) in these scripts if a custom pre-login message is desired.

• /etc/lilo.conf - configuration file for lilo boot loader

• /etc/motd - message of the day file, printed immediately after login. This is often overwritten by /etc/rc.d/rc.S (Slackware) or /etc/rc.d/rc.local (Mandrake/Red Hat) on startup. See the remarks in connection with /etc/issue.

• /etc/mtab - shows currently mounted devices and partitions and their status

• /etc/passwd - contains passwords and other information concerning users who are registered to use the system. For obvious security reasons, this is readable only by root. It can be modified by root directly, but it is preferable to use a configuration utility such as passwd to make the changes. A corrupt /etc/passwd file can easily render a Linux box unusable.

• /etc/printcap - shows the setup of printers

• /etc/profile - sets system-wide defaults for bash shell. It is this file in Slackware that sets up the DIR_COLORS environment variable for the color ls command. Also sets up other system-wide environment variables.

• /etc/resolv.conf - contains a list of domain name servers used by the local machine

• /etc/securetty - contains a list of terminals on which root can login. For security reasons, this should not include dialup terminals.

• /etc/termcap - ASCII database defining the capabilities and characteristics of different consoles, terminals, and printers

• /etc/X11/XF86Config - X configuration file. The location in Slackware is /etc/XF86Config.

• /proc/cpuinfo - cpu information

• /proc/filesystems - prints filesystems currently in use

• /proc/interrupts - prints interrupts currently in use

• /proc/ioports - contains a list of the i/o addresses used by various devices connected to the computer

• /proc/kcore - The command ls -l /proc/kcore will give the amount of RAM on the computer. It's also possible to use the free command to get the same information (and more).

• /proc/version - prints Linux version and other info

• /var/log/messages - used by syslog daemon to store kernel boot-time messages

• /var/log/lastlog - used by system to store information about last boot

• /var/log/wtmp - contains binary data indicating login times and duration for each user on system

5 Important Directories
Different distributions have different directory structures, despite attempts at standardization such as the the Linux Filesystem Hierarchy Standard (FHS) organization.

• /bin - essential UNIX commands such as ls, etc. Should contain all binaries needed to boot the system or run it in single-user mode

• /boot - files used during booting and possibly the kernel itself are stored here

• /dev - contains device files for various devices on system

• /etc - files used by subsystems such as networking, NFS, and mail. Includes tables of disks to mount, processes to run on startup, etc.

• /etc/profile.d - contains scripts that are run by /etc/profile upon login.

• /etc/rc.d - contains a number of shell scripts that are run on bootup at different run levels. There is also typically an rc.inet1 script to set up networking (in Slackwar), an rc.modules script to load modular device drivers, and an rc.local script that can be edited to run commands desired by the administrator, along the lines of autoexec.bat in DOS.

• /etc/rc.d/init.d - contains most of the initialization scripts themselves on an rpm-based system.

• /etc/rc.d/rc*.d - where ``*'' is a number corresponding to the default run level. Contains files for services to be started and stopped at that run level. On rpm-based systems, these files are symbolic links to the initialization scripts themselves, which are in /etc/rc.d/init.d.

• /etc/skel - directory containing several example or skeleton initialization shells. Often contains subdirectories and files used to populate a new user's home directory.

• /etc/X11 - configuration files for the X Window system

• /home - home directories of individual users

• /lib - standard shared library files

• /lib/modules - modular device driver files, most with .o extensions

• /mnt - typical mount point for many user-mountable devices such as floppy drives, cd-rom readers, etc. Each device is mounted on a subdirectory of /mnt.

• /proc - virtual file system that provides a number of system statistics

• /root - home directory for root

• /sbin - location of binaries used for system administration, configuration, and monitoring

• /tmp - directory specifically designed for programs and users to store temporary files.

• /usr - directory containing a number of subdirectory with programs, libraries, documentation, etc.

• /usr/bin - contains most user commands. Should not contain binaries necessary for booting the system, which go in /bin. The /bin directory is generally located on the same disk partition as /, which is mounted in read-only mode during the boot process. Other filesystems are only mounted at a later stage during startup, so putting binaries essential for boot here is not a good idea.

• /usr/bin/X11 - most often a symbolic link to /usr/X11R6/bin, which contains executable binaries related to the X Window system

• /usr/doc - location of miscellaneous documentation, and the main location of program documentation files under Slackware

• /usr/include - standard location of include files used in C programs such as stdio.h

• /usr/info - primary location of the GNU info system files

• /usr/lib - standard library files such as libc.a. Searched by the linker when programs are compiled.

• /usr/lib/X11 - X Window system distribution

• /usr/local/bin - yet another place to look for comon executables

• /usr/man - location of manual page files

• /usr/sbin - other commands used by superuser for system administration

• /usr/share - contains subdirectories where many installed programs have configuration, setup and auxiliary files

• /usr/share/doc - location of program documentation files under Mandrake and Red Hat

• /usr/src - location of source programs used to build system. Source code for programs of all types are often unpacked in this directory.

• /usr/src/linux - often a symbolic link to a subdirectory whose name corresponds to the exact version of the Linux kernel that is running. Contains the kernel sources.

• /var - administrative files such as log files, used by various utilities

• /var/log/packages - contains files, each of which has detailed information on an installed package in Slackware. The same file can also be found at /var/adm/packages, since the adm subdirectory is a symbolic link to log. Each package file contains a short description plus a list of all installed files.

• /var/log/scripts - package installation scripts in Slackware are stored here. You can inspect these scripts to see what special features are included in individual packages.

• /var/spool - temporary storage for files being printed, mail that has not yet been picked up, etc.

6 Important Bash Shell Variables
These variables are most often inherited or declared when a shell is started. A great reference for bash shell variable, bash builtin commands, and bash in general is SSC (2000).

• HOME - home directory, abbreviated as ~

• MAIL - name of file that mail is stored in (mailbox)

• MAILCHECK - sets the frequency at which bash checks for mail

• PATH - directory paths to search for executable files. According to A Practical Guide to Linux, p.329, the PATH is set in /etc/profile. On my Linux box, /etc/profile adds /usr/X11R6/bin to the path, which means that the path must be set before by another configuration file. The .bash_profile file in my home directory adds /home/ambler/bin to the path. On my Linux box, the first command to set the path would seem to be in /etc/rc.d/rc.sysinit, which is one of the shell scripts invoked by the init process (inittab). Then, /etc/profile adds /usr/X11R6/bin. Finally, .bash_profile adds /home/ambler/bin.

• PS1 - prompt string. Things that can be put in the prompt string include \h (hostname), \u (username), \w (absolute pathname of working directory), \W (name of working directory w/o path), \d (date), \t (time). See p.331 of A Practical Guide to Linux for more details. On my Red Hat boxes, the primary prompt string is set in the /etc/bashrc file. The prompt is also set in /etc/profile, but the setting in bashrc seems to take precedence. I also have a .bashrc file, which in turn runs /etc/bashrc, which sets the prompt. This means that the same prompt is used by xterm and rxvt in X sessions. On my Slackware box, the command line prompt is set in /etc/profile. The xterm and rxvt prompts are different, since I don't have a .bash_profile file which is run when an xterm is started. In fact, I don't know where the prompt is set in X sessions. It is not set by /usr/X11R6/lib/X11/app-defaults/XTerm.

• PS2 - secondary prompt string.

7 Important Daemons and Startup Services
These are programs or processes which are run at boot time. Some remain in memory to execute various tasks when required (daemons). Most are started and stopped with scripts in the /etc/rc.d/init.d directory (see above). The exact contents of this directory will depend on which packages from a particular distribution are installed. For example, installing the Apache package will cause an httpd script to be placed in /etc/rc.d/init.d.
There are man pages on most of these. The Red Hat program tksysv (ntsysv is the non graphical version) allows root to automatically configure which of these are started automatically at boot time. The linuxconf program does the same thing, although I haven't tried it. The utility chkconfig is also designed to query and configure runtime services for different runlevels. The www.mandrakeuser.org site has a good page on common services/daemons, especially those included in recent versions of the Mandrake distribution.
A good source of information on daemons and services is the ``Linux Devices, Daemons, Services'' chapter of the CTDP (2000a) document.

• amd - runs the automount daemon for remote filesystem mounting such as nfs

• anacron - checks delayed `cron' tasks (see below) at boot time and executes them. Useful if you have cron jobs scheduled but don't run your machine all the time.

• apmd - Advanced Power Management BIOS daemon. For use on machines, especially laptops, that support apm. Monitors battery status and can shut down the system if power is too low.

• arpwatch - keeps watch for ethernet IP address pairings that are resolved using the ARP protocol.

• atd - runs jobs queued by `at'

• autofs - control the operation of automount daemons, used to mount and unmount devices on demand

• bootparamd - allows computers to boot from a Linux machine using the BOOTP network protocol. A server process that provides information to diskless clients necessary for booting

• crond - automatic task scheduler. Manages the execution of tasks that are executed at regular but infrequent intervals, such as rotating log files, cleaning up /tmp directories, etc.

• cups - daemon for print services under the Common Unix Printer System, a replacement for lpd

• dhcpd - implements the Dynamic Host Configuration Protocol (DHCP) and the Internet Bootstrap Protocol (BOOTP). Used to lease out IP addresses to remote machines.

• drakfont - font server in Mandrake

• fetchmail - daemon to fetch mail at regular intervals from mail servers

• ftpd - ftp server daemon

• gated - routing daemon that handles multiple routing protocols and replaces routed and egpup

• gpm - useful mouse server for applications running on the Linux console.

• httpd - the Apache webserver hypertext transfer protocol daemon

• identd - The identd server provides a means to determine the identity of a user of a particular TCP connection. Given a TCP port number pair, it returns a character string which identifies the owner of that connection on the server's system.

• inetd - listens for service requests on network connections, particularly dial-in services. This daemon can automatically load and unload other daemons (ftpd, telnetd, etc.), thereby economizing on system resources. In the latest version of Red Hat (7.0 at the time of writing), it has been replaced by xinetd. A partial list of services controlled by inetd is listed below. Under many distributions, inetd will execute scripts in the file /etc/inetd.conf.

• innd - Usenet news server daemon

• ipchains - daemon for packet forwarding. Used for configuring a gateway/firewall.

• isdn provides ISDN network interfacing services

• isdn4linux - for users of ISDN cards

• kerneld - automatically loads and unloads kernel modules

• keytable - loads the appropriate keyboard map from /etc/sysconfig/ keyboard

• kheader -

• kudzu - detects and configures new or changed hardware during boot

• linuxconf - ``startup hook'' needed for the linuxconf system configuration tool

• lpd - line printer and print spooler daemon

• mcserv - server program for the Midnight Commander networking file system. It provides access to the host file system to clients running the Midnight file system (currently, only the Midnight Commander file manager). If the program is run as root the program will try to get a reserved port otherwise it will use 9876 as the port. If the system has a portmapper running, then the port will be registered with the portmapper and thus clients will automatically connect to the right port. If the system does not have a portmapper, then a port should be manually specified with the -p option (see below).

• mysql - database server daemon

• named - provides DNS services

• netfs - network filesystem mounter. Used for mounting nfs, smb and ncp shares on boot.

• network -activates all network interfaces at boot time by calling scripts in /etc/sysconfig/network-scripts

• nfsd - used for exporting nfs shares when requested by remote systems

• nfslock - starts and stops nfs file locking service

• numlock - locks numlock key at init runlevel change

• pcmcia - generic services for pcmcia cards in laptops

• portmap - needed for Remote Procedure Calls

• postfix - mail transport agent which is a replacement for sendmail. Now the default on desktop installations of Mandrake.

• postgresql - database server daemon

• random - random number generating daemon, related to security and encryption

• routed - manages routing tables

• rstatd - kernel statistics server. Allows users on a network to get performance statistics for any connected machine.

• rusersd - provides services that allow users to find one another over the network

• rwalld - allows users to use rwall to write messages on remote terminals

• rwhod - server which maintains the database used by the rwho(1) and ruptime(1) programs. Its operation is predicated on the ability to broadcast messages on a network.

• sendmail - mail transfer agent. This is the agent that comes with Red Hat. Others, such as smtpd, are not included.

• smb - needed for running SAMBA

• snmpd - provides Simple Network Management Protocol support

• sound - daemon for managing sound

• squid - web page proxy server daemon

• syslogd - manages system log files

• smtpd - Simple Mail Transfer Protocol, designed for the exchange of electronic mail messages. Several daemons that support SMTP are available, including sendmail, smtpd, rsmtpd, qmail, zmail, etc.

• tcpd - from the tcp_wrappers package. Intercepts requests normally handled by inetd and filters them through the files hosts.allow and hosts.deny files, which can restrict access to services based on type of service, origin of request, destination, etc. Requests are intercepted because calls to particular services are replaced with calls to tcpd in /etc/inetd.conf.

• telnetd - telnet server daemon

• usb - daemon for devices on Universal Serial Bus

• xfs - X font server

• xinetd - more modern replacement for inetd. It apparently allows for similar kinds of access filters to the ones used by tcpd in conjunction with inetd. xinetd replaces inetd as the default network services daemon in Red Hat 7.0.

• xntpd - Network Time Protocol daemon. Provides a means to syncronize time over the network.

• webmin - daemon for webmin web-based system administration program

• ypbind - NIS binder. Needed if computer is part of Network Information Service domain.

8 Window Managers
The ``Window Managers for X'' site is extremely useful for keeping track of new Linux window managers. See http://winman.org.

• Afterstep - Based on Fvwm. Designed to give a similar look and feel to the NextStep interface.

• AnotherLevel - a custom configuration for fvwm2 which mimics the look and feel of Windows95.

• Blackbox - a light, fast, window manager. It doesn't clutter the screen with too much junk, but it gets the job done efficiently.

• CDE - Common Desktop Environment. This is the default window manager on many commercial Unix systems. There is no free version.

• Enlightenment - Very configurable, and probably the coolest looking window manager, but a bit of a resource hog.

• Flwm - Fast, Light Window Manager. It has very few features, but is very small.

• Fvwm - F (?) Virtual Window Manager. This, along with Fvwm2, are old standbies in the Linux world. They are quite configurable, but configuration involves editing text files which are sometimes obscure.

• Fvwm2 - newer version of above.

• Fvwm95 - implementation of Fvwm2 configured to look and feel like Windows 95.

• Gnome - Gnome desktop environment. A themable collection of desktop utilities that can be used with different window managers. The current default window manager for a gnome session is Sawfish.

• Icewm - Ice Window Manager. Very small, very fast, quite configurable. On low memory/small hard drive machines, this one is my favorite. Configuration involves editing text files, but the syntax is extremely easy to understand. There are also a couple of third-party programs available which allow the user to configure Icewm using a graphical interface.

• KDE - K Desktop Environment. Many of the desktop utilities can be run under different window managers. I may be wrong, but I believe kikbd is the only program out there that allows the user to reconfigure the keyboard layout to different national keyboards on the fly, with one-click switching from one to the other. Unfortunately, this utility is no longer available under KDE 2.x.

• Kwm - the window manager that comes with the KDE desktop environment.

• Mwm - Motif window manager.

• Olwm - Open Look window manager.

• Sawfish - a small, efficient, configurable window manager that is now the default window manager with Gnome.

• Twm - Tab window manager.

• UDE - Unix Desktop Environment. In early development stages. An attempt to create a new type of desktop environment for Unix machines, including Linux.

• Windowmaker - One of the more popular window managers. Highly configurable and themable.

• XFce - ``Cholesterol-Free Desktop Environment''. Includes its own window manager, a toolbar, a sound manager, a background manager, and a file manager. It has tearoff menus, up to twelve virtual desktops, etc. It is completely configurable with menus. Its toolbar looks like the one in CDE. I find it easy to use and to configure, and easy on system resources.

9 Alphabetical List of Principal Commands
In the following command list, the distinction between upper case and lower case letters is important. Most of the commands are utilities that are run by invoking their own executable files. In some cases, they are commands which are internal to a shell such as bash (shell builtins). The shell builtins are indicated. There are now many utilities that are included with either the Gnome or the KDE desktop environments, so many that it would be difficult to include them all here. In many cases, they duplicate the functionality of one or more of the programs listed below. I would suggest consulting the online documentation for these packages.
Another good source of information on commands is the CTDP (2000b) document. There are different chapters which group commands in different categories.
On rpm-based systems, to find out which package owns the command foo (where foo is a standalone executable), use the command rpm -q -f foo.

• a2p - translation utility from awk to Perl

• a2ps - translation utility from ``any'' to Postscript

• ac - print statistics concerning user connect time

• access - determine whether a file can be accessed

• acroread - Adobe utility for viewing pdf files

• adduser - used by root to add user to system
o usage: adduser userid

• afio - utility to copy or restore files to an archive file. This utility is not part of the basic internal and external programs under Red Hat Linux. It is available as an rpm on the rpmfind.net site.

• agetty - enables login on terminals. See getty, mgetty, and uugetty.

• ali - list mail aliases

• alias - assign name to specified command list. This is actually a shell builtin. On my Red Hat system, I have global alias commands in my /etc/bashrc file and in my /.bashrc file. On my Slackware box, I have made the rm command a little bit safer with
o alias rm='rm -i'
so that you can't recursively delete your /dev directory without telling the system you're sure you want to do it.

• alien - utility to convert to and from different Linux package formats. Can handle Debian (deb), Stampede (stp), Red Hat (rpm) and Slackware (tgz) packages.

• apropos - display command names based on keyword search
o usage: apropos keyword

• apsfilter - printer filter called by lpd to deal with printing different types of files. This is a fairly sophisticated print filter. It is not set up by default in Slackware. It used to be available on the second cd of a Slackware distribution. Since 4.0, it is available as one of the main packages in the ap set. Read the mail that the installation program sends to the root user. I believe that Red Hat uses its own printer filters.

• ar - create, modify and extract from archives

• arch - print machine architecture type

• as - the portable GNU assembler

• asapm - AfterStep laptop advanced power management utility

• ash - a shell, a very simple shell program sometimes used on boot diskettes since it takes up much less space than bash, tcsh, zsh, etc.

• asload - AfterStep cpu load monitor

• asmail - AfterStep mail checking utility

• asmodem - AfterStep utility to monitor modem status

• aspell - a spell checking program along the lines of ispell

• aspostit - X Window postit note utility

• at - executes a shell script at specified time. Use atq to show pending jobs, and atrm to remove jobs from the queue.
o usage: at time
o or: at -f file time

• atq - shows pending jobs queued by at. If run by root, shows everybody's pending jobs.

• atrm - removes pending jobs queued by at. Use atq to determine the identities of various jobs.
o usage: atrm job

• awk - searches for and process patterns in a file

• banner - print banner to standard output. Syntax is
o banner [option] [characters]

• bash - Bourne again shell. This is the default shell in the Red Hat installation.

• batch - queue, examine, or delete jobs for later execution. See at.

• bc - a language (compiler) similar to C, with unlimited precision arithmetic

• bg PID - send process with pid ``PID'' to the background. This is the same as executing [Ctrl]z while interacting with the running process. This is a shell builtin.

• bh - puts a job in the background. This is a shell builtin.

• biff - mail notification utility. Notifies user of mail arrival and sender's name.

• bind - displays or redefines key bindings. This is a shell builtin.

• bison - parser generator similar to yacc

• bru - a powerful backup utility program. Commercial. Demonstration versions are often included with Linux distributions such as Red Hat.

• bsh - equivalent to ash

• bunzip2 - used to uncompress files compressed with bzip2

• byacc - parser generator

• bzip2 - compresses with algorithm different from gzip

• bzless - view bzipped files

• c++ - invokes GNU C and C++ compiler

• cal - displays a 12-month calendar for the given year or a one-month calendar of the given month
o usage: cal month year

• cat - combine, copy standard input to standard output. Used to join or display files.

• cd - change working directory. This is a shell builtin in bash, tcsh and zsh.

• cdplay - command line utility for playing audio cds

• cfdisk - similar to fdisk, but menu-driven

• chat - used to interact with a modem via a chat script

• chgrp - changes group associated with file. Can be used to change the group associated with subdirectories and files of a directory.
o usage: chgrp group files
o or: chgrp -R group files

• chkconfig - Query or update system services/daemons for different runlevels. Manipulates the various symbolic links in /etc/rc.d. This utility is included with many rpm-based distributions such as RedHat and Mandrake. It is designed to work with System V initialization scripts. Graphical tools for configuring system services include ntsysv, tksysv and ksysv (the latter is a KDE utility).

• chmod - set permissions (modes) of files or directories. A value of 4 is used for read permission. A value of 2 is used for write permission. A value of 1 is used for execute permission. See umask for default file permissions upon file creation. Chmod can also be used to change the suid bit on files. The syntax for the symbolic version is
o chmod [options] who operation permission file-list
The syntax for the absolute version is
o chmod [options] mode file-list
To set the uid to the owner's permissions, use
o chmod u +s file-name
To set the uid to the group's permissions, use
o chmod g +s file-name
There are lots of security issues related to allowing a program to have root's permissions when run by an ordinary user. I don't pretend to understand all of these issues.

• chown - changes ownership of a file. Can be used recursively.
o usage: chown userid files
o or: chown -R userid files

• chsh - change default shell

• ci - creates or records changes in an RCS file

• clear - clear screen command

• cmp - compares two files for differences
o usage: cmp file1 file2

• co - retrieves an unencoded version of an RCS file

• comm - compares sorted files

• configure - automatically configures software source code

• color-xterm - color xterm program. Under Red Hat, this is just a link to xterm-color.

• control-panel - graphical system configuration tool under Red Hat.

• cp - copies on or more files. Recursive copying is one simple way of archiving part of a directory structure. Use the command as follows:
o cp -r /sourcedirectory /targetdirectory

• cpio - direct copy of files to an output device. Allows creation of archive file spanning multiple diskettes. Allows one directory structure to be mirrored elsewhere on the partition or on another partition. In order to back up an entire directory structure on diskettes, cd to the directory and use the following command:
o find . -depth -print | cpio -ov > /dev/fd0
To restore from diskettes, use:
o cpio -iv < /dev/fd0
The cpio command will prompt the user to insert more diskettes as they are needed. The command for mirroring a directory structure is the following:
o find . -depth -print | cpio -pv /destinationdirectory
This copies the working directory and its contents, including subdirectories, into /destinationdirectory. In order to copy an individual file which is larger than a floppy, use:
o find . -name nameoffile -print | cpio -iv > /dev/fd0

• cpkgtool - Slackware tool to install, uninstall and query packages. Front end to installpkg, removepkg, makepkg. This is the graphical version that uses ncurses.

• cpp - GNU C-compatible compiler preprocessor

• crontab - schedules command to run at regularly specified time

• csh - run C shell

• csplit - separate files into sections. See also split.

• cvs - manages concurrent acces to files in a hierarchy. Stands for concurrent version system. Is built on RCS. It stores successive revisions of files efficiently and ensures that access to files by multiple developers is done in a controlled manner. Useful when many developers are working on the same project.

• cut - selects characters or TAB-separated fields from lines of input and writes them to standard output

• date - displays or sets date and time
o usage: date
o or: date date

• dd - direct copy of file from one device to another. Can be used to make copies of boot or root diskettes for installing Linux. It can be used, for example, to make and exact copy of a floppy disk, as follows. First, place the diskette to be copied in the floppy drive. Then,
o dd if=/dev/fd0 ibs=512 > floppy.copy
o Replace the diskette with a fresh diskette.
o dd if=floppy.copy bs=512 of=/dev/fd0
The ibs and bs options specify the block sizes for input and for both input and output. A boot disk image can be directly copied to a floppy using the second of the two dd commands above.

• declare - declares attributes for a variable (same as typeset). This is a shell builtin.

• df - displays capacity and free capacity on different physical devices such as hard drive partitions and floppy drives that are mounted on the file system. Gives free space in blocks. With the (undocumented) option -h, the program gives free space in Mb or Gb. This is useful for those accustomed to thinking of the capacity of a high-density 3.5 inch diskette as 1440k.

• diff - displays differences between two files
o usage: diff file1 file2

• diff3 - compares three files and reports on differences

• dip - used to set up a SLIP or PPP connection. It can be used to set up an outgoing SLIP connection or an incoming connection.

• diplogin - used for setting up incoming dip connections. See the man page for dip.

• dir - a variation of the GNU ls command that defaults to printing file names in columns

• dircolors - set colors for GNU ls command. In Slackware, this command is run by the /etc/profile script. Then, whenever xterm is run with the -ls (login shell) option, ls displays different colors for different types of files. Typical usage is eval `dircolors -b`. In Red Hat and Mandrake, I get color directories by aliasing the ls command (see below).

• display - set display for output of programms under X Windows. Can be used to run a program on a remote machine while displaying the output on a local machine. The remote machine must have permission to send output to the local machine. This is actually an environment variable. See the more detailed discussion in connection with the xhost command below.

• dmesg - displays messages from /var/log relative to the most recent boot

• dos - invoke the DOSEMU DOS emulator

• du - displays information on disk usage. The command
o du / -bh | less
will display detailed disk usage for each subdirectory starting at root, giving files sizes in bytes.

• dumpkeys - print information about the keyboard driver's translation tables to standard output

• dvilj - send a dvi file to a Laserjet printer. There are specialized versions for individual models of Laserjet printer.

• dvilj2p - specialized version of dvilj for the IIp series of printers. See above.

• dvips - send a dvi file to a Postscript printer, to a Postscript capable Laserjet printer, or to a file (with the -o option). There is a switch to print only a subset of the pages, and another switch to print in landscape mode. Use -t landscape, which is one of the arguments to the paper type switch. If you have one page of a document that is a wide table, and you wish to print this in landscape mode, use
o dvips filename -pp pagenumber -t landscape

• e2fsck - check an ext2 filesystem. The syntax is
o e2fsck /dev/devicename
where the filesystem is on /dev/devicename. The device should not be mounted, and this program must be run as root.

• echo - write arguments to standard output. One use is to print out information about environment variables, as in
o echo $PATH - list paths to search
o echo $HOME or echo ~ - list name of home directory
This is a shell builtin.

• editres - a dynamic resource editor for X Toolkit applications. Allows the user to change X resources for individual applications.

• efax - fax program

• efix - convert between fax, text, bit-map and gray-scale formats

• egrep - search files for lines that match regular expressions. Runs faster than grep and fgrep.

• elm - an interactive mail system

• elvis - a version of the vi text editor

• emacs - screen oriented text editor

• env - desplay the current environment or set a variable equal to a new value

• eval - scans and evaluates the command line. See dircolors command. This is a shell builtin.

• ex - interactive command-based editor. The man page lists it as being the same as vim, an improved version of vi.

• exec - system call which creates a subshell to execute a binary or a script. This is a shell builtin.

• execve - a variation of the exec command.

• exit - exit a shell. This is a shell builtin.

• expand - convert tabs in files to spaces and write to standard output

• expect - a program that ``talks'' to other interactive programs according to a script. Following the script, Expect knows what can be expected from a program and what the correct response should be. An interpreted language provides branching and high-level control structures to direct the dialogue. In addition, the user can take control and interact directly when desired, afterward returning control to the script.

• export - place the value of a variable in the calling environment (makes it global). This is a shell builtin.

• expr - utility evaluates an expression and displays the result

• f2c - FORTRAN to C translator

• f77 - FORTRAN 77 compiler

• false - null command that returns an unsuccessful exit status

• fax - simple user interface to efax and efix programs

• fc - views, edits, and executes commands for the history list. This is a shell builtin.

• fdformat - low level format of a floppy device

• fetchmail - retrieve mail from a remote mail server and pass it to local SMTP agents on the local machine

• fdisk - used to partition hard drives
o usage: fdisk device

• fg PID - bring a background or stopped process with pid ``PID'' to the foreground. This is a shell builtin. If only one process is running in background mode, fg with no argument is sufficient to bring it to the foreground

• fgrep - search for patterns in files

• file - displays classification of a file or files according to the type of data they contain

• find - find files according to a large variety of search criteria. The find command that I use the most is
o find . -name filename -print
in order to find files matching a particular name on the working directory and all subdirectories. Find can be incredibly powerful, but it is incredibly obscure.

• finger - display information about a specified userid or userids

• fmt - simple text formatting utility. Tries to make all nonblank lines nearly the same length.

• fold - break lines of specified files so they are no wider than a specified lengths

• fortune - available in the bsdgames package in Slackware and other distributions. Put a call to fortune in /etc/profile and get something inspirational or amusing every time you fire up an xterm as a login shell.

• free - gives used and free memory on system along with other useful information

• fromdos - takes a DOS text file from stdin and sends a UNIX file to stdout.

• fsck - file system check and repair

• ftp - file transfer over network

• g++ - C++ compiler

• g77 - GNU Fortran 77 compiler

• gawk - GNU awk, mostly for processing delimited text files

• gcc - invoke C, C++ compiler

• getipts - parses arguments to a shell script. This is a shell builtin.

• getkeycodes - print kernel's scancode-to-keycode mapping table

• ghostscript - set of printing utilities. It seems to be obligatory to have this if a TEX installation such as teTEX is installed. How they communicate with one another is somewhat obscure.

• ghostview - Aladdin ghostscript interpreter/previewer

• gimp - image manipulation and paint program

• glint - Red Hat graphical front end for the rpm package installer and manager.

• grep - used to find a string within a file. The -i option returns matches without regard to case. The -n option means that each line of output is preceded by file name and line number. The -v option causes non-matched lines to be printed.
o usage: grep pattern files
o or: grep -i pattern files
o or: grep -n pattern files
o or: grep -v pattern files

• groupadd - create a new group on the system

• groups - shows which groups you are in

• grub - Gnu grand unified bootloader. Can be used instead of lilo to boot multiple operating systems. I encountered a couple of snafus trying to install grub on my home machine after installing Mandrake 8.0 and choosing the lilo bootloader during the initial install. The Mandrake installation program set up /boot/vmlinuz as a symlink to the actual kernel, vmlinuz-2.4.3-20mdk. It took me a while to figure out that grub doesn't understand symbolic links. The documentation suggests installing grub on a diskette using the ``dd'' command. This refused to work, but
o grub-install '(fd0)'
did work. The single quotes are necessary. The files necessary to run grub are normally located in /boot/grub. Once the file menu.lst has been edited and appropriated entries added to boot the different operating systems on one's hard disk(s), the following sequence of commands can be used to install grub in the master boot record (MBR) sector of the hard disk:
o root (hd0,x)
o setup (hd0)
Here, the x should be replaced by the partition where the /boot/grub directory is located, which is probably the root partition of the Linux system. Note that grub has its own conventions for naming devices and numbering partitions, so that for example a partition which is called hda6 under Linux will be called (hd0,5) by grub.

• grub-install - command to install grub on the hard drive (or floppy drive).

• gunzip - used to uncompress files compressed with gzip

• gv - PostScript and PDF previewer, based on ghostview

• gvim - see vi

• gzexe - compresses executables

• gzip - used to compress or decompress files

• halt - shut down system as root, without reboot, immediately

• hash - remembers the location of commands in the search path. This is a shell builtin.

• head - displays first part of a file

• history - command for viewing and manipulating the shell command history list

• host - look up host names using domain server

• hostname - used to get or set hostname. Typically, the host name is stored in the file /etc/HOSTNAME.

• hwclock - used to query and set the hardware clock

• hylafax - commercial fax program

• id - display userid and groupid

• inetd - daemon which starts up other daemons on demand. Configured in /etc/inetd.conf.

• ifconfig - display (as root) information on network interfaces that are currently active. First ethernet interface should be listed as eth0, second as eth1, etc. First modem ppp connection should be listed as ppp0, etc. The ``lo'' connection is ``loopback'' only.

• ifdown - shut down the network interface

• ifup [interface_name] - start up the interface

• info - display system information. This is the GNU hypertext reader.

• init - the mother of all processes, run at bootup, executes commands in /etc/inittab. Can be used (with root privileges) to change the system run level.
o usage: init run_level

• insmod - used (by root) to install modular device drivers

• installpkg - Slackware command to install one of the packages from the program sets

• intr - interrupt key, usually [Ctrl-C]

• ispell - checks files for spelling errors
o usage: ispell files

• jed - programmer's file editor. Behaves like emacs. Has modes for TEX, FORTRAN, C, etc.

• jobs - displays list of current jobs in the background. This is a shell builtin.

• joe - simple WordStar-like text editor. It can be invoked in emacs emulation mode with jemacs and in WordStar emulation mode with jstar.

• jove - Joseph's Own Version of Emacs. A simple emacs clone.

• kbd_mode - print current keyboard mode

• kernelcfg - GUI to add/remove kernel modules (as root in X terminal).

• kerneld - kernel daemon, a process that stays in memory and does all sorts of useful stuff, like automatic loading of device driver modules

• kikbd - a utility program that comes with KDE that allows users to switch on the fly among different international keyboards. It can be used under different window managers than kfm.

• kill - sends a signal to (especially to terminate) a job or process. This is a shell builtin in bash, tcsh and zsh.

• killall - kill processes by name. Kill all processes which are instances of the speciffied program. Also used to send signals to processes or restart them.

• killall5 - kill all processes except the ones on which it depends

• last - generate a listing of user logins

• lastlog - prints the last login times of all users

• latex - compile a LATEX file

• ldconfig - creates the necessary links and cache (for use by the run-time linker, ld.so) to the most recent shared libraries found in the directories specified on the command line, in the file /etc/ld.so.conf, and in the trusted directories (/usr/lib and /lib). Ldconfig checks the header and file names of the libraries it encounters when determining which versions should have their links updated. Ldconfig ignores symbolic links when scanning for libraries.

• ldd - list the shared libraries on which a given executable depends, and where they are located

• leave - display reminder at specified time

• less - Linux alternative to ``more'' command. Displays text files, one screenful at a time. When less pauses, there is a large number of available commands to tell it what to do next. One can scroll both forwards and backwards.

• let - evaluates a numeric expression. This is a shell builtin.

• lilo - installs boot loader on the boot sector of a hard drive, of a diskette, or in another location. My 486 has a hard drive that is too large for the machine's BIOS, so I have to boot from a floppy. To create a boot diskette, I do the following (as root):
o /sbin/fdformat /dev/fd0H1440
o /sbin/mkfs.ext2 /dev/fd0
o mount -t ext2 /dev/fd0 /mnt/floppy
o cp -dp /boot/* /mnt/floppy
o /sbin/lilo -C /etc/lilo.flop
The -C option to lilo has lilo use the lilo.flop file instead of the default lilo.conf.

• linuxconf - interactive tool for configuring Linux system. Uses X if loaded. This is a Gnome tool. It comes with my Red Hat distribution, and is not included with Slackware. It would seem to be the easiest way to configure Linux under Slackware. Version 1.15 is available for Slackware. There is a pretty good introduction to the use of linuxconf in the Red Hat 5.2 installation manual, which is available online at their web site.

• ln - creates a link to a file. Used to create hard links and, with the -s option, symbolic links which can link files on different disk partitions. The syntax is
o ln [options] source [dest]

• locate filename - find the file name which contains the string ``filename''. The syntax is easier than the find command.

• lock - temporarily lock terminal

• lockfile - create semaphore file(s), used to limit access to a file

• - log in to system

• logname - consult /etc/utmp for user's login name

• logout - execute logout as individual user and bring up login: prompt

• look - look for strings in files

• lpq - show print jobs that are waiting

• lpr - send file to be printed

• lprm - cancel a job from print queue

• ls - list directory contents. To get colored directory listings under Red Hat, Mandrake, etc., use
o ls -color
To get this all the time, add
o alias ls='ls -color=auto'
to .bashrc. The following command
o alias ls='ls -Fskb -color=auto'
will give directory listings in color, with file sizes in kilobytes, and append a character to the file to indicate its type.

• lsattr - list attributes of files in ext2 file system

• lsmod - used (by root) to show kernel modules currently loaded

• lspci - utility to display information on pci buses and hardware devices attached to them. Part of the pciutils package that comes with many Linux distributions.

• lspnp - utility to display information about pnp devices. Part of the pcmcia or kernel-pcmcia package, depending on the distribution.

• m4 - an implementation of the traditional UNIX macro processor. It can be used with the sendmail configuration package in Red Hat (and Slackware) to generate a sendmail.conf configuration file without having to edit the configuration file directly.

• magicfilter - general purpose printer filter. See apsfilter above. apsfilter is the printer filter that comes with the Red Hat and Slackware distributions.

• mail - sends or reads electronic mail

• make - keeps a set of programs current. This is a utility that helps when developing a set of programs. It works by executing a script called makefile, Makefile or GNUmakefile in the working directory. It is very often used in combination with configure when compiling and installing noncompiled software packages.

• makebootdisk - command in Slackware to do just what the name says

• MAKEDEV - executable script to make device files on /dev

• makeswap - configures swap space

• man - displays information from online Unix reference manual

• manpath - attempt to determine path to manual pages

• mc - Midnight Commander file manager and visual shell

• mesg - enables/disables reception of messages

• minicom - terminal program

• mkdir - create a directory

• mkfs - create a file system (format) on a device or partition. Should be invoked after lowlevel formatting of the disk using fdformat. It has several versions which are all links to the basic program, such as mkfs.ext2 and mkfs.msdos.

• mkswap - creates a Linux swap space on the specified hard disk parition (root privileges neede)
o usage: mkswap device

• more - list file contents, stopping after each full screen

• mount -t [fstype] [device] [mountpoint] - mount device using filesystem of type [fstype] with device name [device] at the location [mountpoint] in the filesystem directory tree

• mount -a - mount all filesystems according to the specifications in /etc/fstab

• mouseconfig - mouse configuration utility under Red Hat. Located in /usr/sbin.

• mpage - print multiple pages per sheet on a Postscript printer. Can also be used to print a page in landscape mode.

• Mtools - package of MS-DOS utilities. Includes the following commands.
o mcd - changes working directory on DOS disk
o mcopy - copies DOS files from one directory to another
o mdel - deletes DOS files
o mdir - lists contents of DOS directories
o mformat - adds DOS formatting information to a disk
o mtype - displays contents of a DOS file
The default device for execution of these commands is /dev/fd0 and can be referred to as ``a:''.

• mv - moves (renames) files

• netconf - used (as root) to set up network

• newaliases - rebuilds the /etc/aliases database used by sendmail. Must be rerun every time /etc/aliases is modified for the changes to take effect.

• newgrp - similar to login. Changes user's identification

• nice program_name - sets the priority of the program ``program_name''.

• nm - lists the symbols from object files objfile. If no object files are given as arguments, nm assumes `a.out'.

• nohup - runs a command that keeps running after logout. The command is in principle immune to hangups, and must have output to a non tty. According to Linux in a Nutshell, this is necessary only in the Bourne shell, since modern shells preserve background processes by default.

• ntsysv - run level editor under Red Hat. This is the equivalent of tksysv, but does not require a graphical interface.

• nxterm - color xterm program. The man page for nxterm under Red Hat brings up the same page as xterm.

• od - dumps contents of a file

• passwd - change login password

• paste - joins corresponding lines from files

• patch - updates source code. Attempts to update a file from a file of change information, or pathces, created by diff.

• pathchk - determine validity and portability of filenames

• pdflatex - part of the pdftex program suite. Produces pdf output from a LATEX file.

• pdftex - produces pdf output from a TeX file. See also pdflatex. This program is part of the tetex 0.9 distribution that is included with Red Hat 5.2 and above, and with Slackware 4.0 and above. It is also available as a separate program.

• perl - practical extraction and report language

• pg - display data one screenful at a time

• pico - simple screen oriented text editor. It is included as part of the Pine program.

• ping - check if Internet computer is responding. Can also measure the time it takes the queried computer to respond.

• pkgtool - Slackware tool to install, uninstall and query packages. Front end to installpkg, removepkg, makepkg. The cpkgtool is the ncurses graphical version of this program.

• popclient - retrieve mail via the Post Office Protocol. Supports POP2 and POP3.

• popd - pops the top directory of the directory stack and uses cd to change to that directory. This is a shell builtin.

• pr - paginates files for printing

• printenv - display list of environment variables

• printtool - run (as root) in an X terminal to configure your printer(s)

• ps - displays status of processes. Use the -a option for processes for all users. Use the -x option to include processes not attached to a terminal.

• pstree - display processes in the form of a tree structure. Killing a parent process will also kill all the children and their descendants.

• pushd - pushes the argument onto the top of the directory stack and uses cd to change to that directory. This is a shell builtin.

• pwd - print absolute path of working directory. This is a shell builtin.

• pwchk - checks the integrity of password and shadow files

• pwconv - converts passwords to the shadow password format

• pwunconv - unconverts passwords from the shadow password format. Generates a standard Unix password file.

• python - interpreted, interactive, object-oriented programming language

• rcp - copy one or more files to or from remote computer. The syntax is poorly explained in the documentation that I have, including the man pages. Usage is:
o rcp filename username@remotehost:path
The user's home directory on the remote system must contain the file .rhosts with a list of users (preceded by the full domain name or exact IP address of their machine) with access privileges.
o localhostname username

• rcs - creates or changes the attributes of an RCS file. Stands for Revision Control System.

• rdev - query/set image root device, swap device, RAM disk size, or video mode in kernel

• read - reads line from standard input. This is a shell builtin.

• readonly - declares a variable to be read only. This is a shell builtin.

• reboot - in Slackware, reboots the system. Seems to be equivalent to shutdown -r now in generic Linux.

• renice program_name - resets the priority of process ``program_name''.

• reset - used to reset the screen characteristics. This is useful if the screen gets messed up from, for example, trying to display a binary file in an xterm.

• return - exits from a function. This is a shell builtin.

• rlog - prints a summary of the history of an RCS file

• rlogin - log in to remote computer. The general syntax is as follows, using the UQAM Nobel machine as an example:
o rlogin -l userid nobel.si.uqam.ca
The remote computer must recognize the local user and the local machine. See the rcp command for how to set up the .rhosts file on the remote machine.

• rm - remove files or directories. With the -r (recursive) option (very dangerous!), can be used to remove the contents of a specified directory including all subdirectories.

• rmail - interpret and handle remote mail received via uucp

• rmdir - remove empty directories

• rmmod - used to remove modular device drivers

• route -n - show routing table. The n option returns numerical addresses rather than names.

• rpm - invokes the Red Hat package manager in command line mode. I often use this command in query mode to query packages about what files they contain and to find out which package owns a particular file. Examples are
o rpm -qil foo. Gives package information and a file list for the package foo.
o rpm -qfil foo. Gives package information and a file list for the package that owns the file foo. Foo must be in the working directory, or the full path to foo must be specified.
We need to find out about installing the rpm package on a Slackware box. It's probably better to use a package converter such as alien.

• rpm2tgz - an extremely useful utility on Slackware systems that converts rpm packages to tgz format. They can then be installed using the installpkg command (or pkgtool).

• rsh - execute shell command on a remote computer. See rcp and rlogin.

• rstat - summarize host's status: uptime, load averages, and current time

• ruptime - show host status of local machines

• rusers - list who is logged on local machines

• rwall - write to all users over a network

• rwho - show who is logged in on a LAN. The rwho service must be enabled for this command to run. If it isn't, run ``setup'' as root. I don't understand this last remark, which comes from ``Linux Newbie Administrator Guide''.

• rxvt - a terminal program similar to xterm, but which has less features and uses less memory

• sed - edits a file (not interactively). Also a tool for processing text files.

• set - set or display value of shell variables. This is a shell builtin. The command
o set | less
prints the current user environment, giving the values of currently defined variables.

• setenv - set or display value of environment variables

• setserial - used by root to configure a serial port

• setterm - set terminal attributes for a virtual console

• setuid - set the id of a program when it is run. Used, for example, to give root privileges to a program run by an ordinary user. This is actually done by running the chmod program as root. See the chmod command for the syntax.

• setup - Slackware program to set up program sets and configure system. Setup devices and file systems, mount root file system

• sh - standard UNIX shell. On Linux, just another name for bash.

• shift - promotes each command-line argument. This is a shell builtin.

• showmount - show information about an nfs server

• shutdown - reboot or shut down system as root, after specified amount of time. With the -r option, reboot. With the -h option, halt the system.
o usage: shutdown -r minutes

• sleep - creates process that sleeps for specified interval

• sliplogin - attaches a SLIP interface to standard input. Used to allow dialin SLIP connections.

• sort - sorts and/or merge files

• split - split file into specified number of segments

• ssh - secure shell. Apparently has many of the same functionalities as rlogin, telnet, ftp, rsh, etc., with better security and encryption features. We may want to learn how to set this up and use it.

• startx - front end to xinit in Linux. This is a script which starts up X clients and shuts down the X server on exit from the window manager.

• startx -- :1 - start the next X window session on the display 1 (the default is opened on display 0). One can switch between different graphical displays using [Ctrl][Alt][F7], [Ctrl][Alt][F8], etc.

• stty - sets or displays operating options for terminal

• su - log in as another user, including root

• sudo - allows individual users to have root permission to perform specified tasks

• swapoff - disables swap disk

• swapon - enables swap disk

• symlinks - provide list of and information about symbolic links

• sync - writes memory buffers to physical devices

• systat - query host for system information

• tac - print file in reverse

• tail - displays the last part of a file

• talk - visual communication program that copies lines from one terminal to that of another user

• tar - file compression and archiving utility. I find the syntax of this command to be frustratingly opaque. The following works for me. To use this command to unzip gzipped tarballs in verbose mode, use
o tar -xvzf filename.tgz
To create a tarball from files in a given directory and its subdirectories, use
o tar -cvzf filename.tgz sourcename
Sourcename can be the name of a single file, a wildcard such as *, or the name of a subdirectory. There seem to be two different conventions concerning gzipped tarballs. One often encounters .tar.gz. The other popular choice is .tgz. Slackware packages use the latter convention. The command can also be used to archive a file, a group of files, or a directory (with its subdirectories) on tape or onto floppies. If the material to be archived exceeds the capacity of the backup medium, the program will prompt the user to insert a new tape or diskette. Use the following command to back up to floppies:
o tar -cvf /dev/fd0 filename(s) or directoryname(s)
The backup can be restored with
o tar -xvf /dev/fd0
Tar can be used for other things. To mirror all the files and subdirectories in from-stuff to to-stuff, use the commands
o cd from-stuff
o tar cf - . | (cd ../to-stuff; tar xvf -)
No tar file is ever written to disk. The data is sent by pipe from one tar process to another. This example is taken from Running Linux, p.177. To list the table of contents of a tar archive, use
o tar tvf tarfile
To extract individual files from a tar archive, use
o tar xvf tarfile files
where files is the list of files to extract. When extracting files, tar creates missing subdirectories underneath the current directory in which the cammand is invoked.

• tcl - scripting language

• tcsh - extended version of the C shell

• tee - copy standard input to standard output and one or more files

• telinit - used to change run level. Exact run level that corresponds to single-user, multi-user, and X levels depends on distribution.

• telnet - remote login over network

• test - evaluates an expression or compares arguments. This is a shell builtin in bash, tcsh and zsh.

• tftp - user interface to TFTP protocol

• time - displays times for the current shell and its children. This is a shell builtin. Strange, because there is also a /usr/bin/time program on my Red Hat system.

• tin - Netnews reader

• tkdesk - graphical desktop file manager for X

• tksysv - graphical runlevel editor under Red Hat. Allows root to configure the services that are started at each run level.

• tload - display system load average in graph format

• top - dynamically displays process status

• touch - update access and modification times of a file. If the file does not exist on disk, an empty file is created.

• tr - translation utility that can be used, for example, to replace specified characters in a text file

• trap - traps a signal. This is a shell builtin.

• true - null command that returns a successful exit status

• tset - initializes terminal

• tty - shows special file that represents your terminal. Displays the terminal pathname.

• type - displays how each argument would be interpreted as a command. This is a shell builtin.

• typeset - declares attributes for a variaable (same as declare). This is a shell builtin.

• ul - translate underscores to underlining

• umask - establishes the file-creation permissions mask. Usage is
o umask xyz
The system subtracts x, y and z from the owner, group and other file permissions that it would otherwise assign to new files. This is a shell builtin.

• umount [device] - finish writing to the device and remove it from the active filesystem. The command umount -a will (re)mount all file systems listed in /etc/fstab.

• unalias - remove name previously defined by alias. This is a shell builtin.

• uname - displays information about the system. With no arguments, it displays the name of the operating system. With the -a option, it displays information about the operating system, the host name, and hardware.

• uniq - displays lines of a file that are unique

• unset - removes a variable or function. This is a shell builtin.

• unzip - uncompress files compressed with the zip utility, compatible with DOS PKzip

• updatedb - update file database used by locate command

• uptime - shows the time, how long the system has been up, the number of users, and average load.

• useradd - same as adduser

• userdel - remove an account (as root). The user's home directory and undelivered mail must be dealt with separately.

• users - prints list of users on the system

• vdir - variant of the GNU version of the ls command. Defaults to printing out the long version of directory entries.

• vi - standard screen oriented Unix editor

• view - vi in read-only mode

• vim - improved vi editor

• vrfy - query remote host to verify the accuracy of an email address

• w - display info about userids and active processes

• wait - waits for a background process to terminate. This is a shell builtin.

• wc - displays number of lines, characters and words in a file

• Wharf - the AfterStep application dock module

• whatis - display one-line summary of specified command

• whereis - use to find utilities in standard locations

• which - used to find utilities in search path. Will return the absolute directory path of the named utility program.

• who - display information about currently logged in userids

• whoami - display information about userid that is currently logged in

• wish - front end to tk, an X window extension of tcl

• workbone - console based cd player

• workman - graphical cd player program

• write - send messages to another local user

• X - starts up the X server. Can be invoked with
o X -quiet -query remotemachineaddress
in order to get a graphical login screen on the remote machine. See the discussion in connection with xdm below.

• xadm - display advanced power management BIOS information

• xargs - converts standard output of one command into arguments for another. This is one of those powerful but obscure commands. Xargs reads arguments from the standard input, delimited by blanks (which can be protected with double or single quotes or a backslash) or newlines, and executes the command (default is /bin/echo) one or more times with any initial-arguments followed by arguments read from standard input. Blank lines on the standard input are ignored.

• xbiff - graphical mail delivery notification utility

• xcalc - simple calculator program

• xclipboard - name says it all

• Xconfigurator - Red Hat utility for configuring settings for X

• xdm - used to start an X login session. This can be used to start a login session on a remote system. See the discussion on the following site:
o http://www.menet.umn.edu/~kaszeta/unix/xterminal/index.html
See the man pages for X, xdm, and Xserver. As usual, the man pages are pretty obscure. The best single source seems to be the Xserver man pages. After X is configured, X needs to be started at bootup with the command (in /etc/rc.d/init.d/xterm):
o X -quiet -query remotemachineaddress
If the address of a nameserver is not configured, then the numeric address of the remote machine rather than its name should be entered. If the machines are connected through ethernet cards and the net, then obviously basic networking has to be set up. Gnome and KDE come with their own versions of X display/login managers, called respectively gdm and kdm.

• xdvi - view a dvi file compiled under LATEX

• xedit - a simple text editor for X

• xf86config - graphical configuration tool for X

• XF86Setup - graphical configuration tool for X

• xfd - display an available font in X. Creates a grid in an x-term with one character per rectangle.

• xfig - utility for interactive generation of figures

• xfm - graphical file manager for X

• xhost - tell X server that remote computer has access to your machine and that you will use the remote computer. This can be used to set up remote X sessions. To set up a remote X session on the UQAM Nobel machine, run the following command on the local machine (one doesn't have to be root to do this)
o xhost +nobel.si.uqam.ca
Then, log onto the remote machine using rlogin (see above) or telnet. Once logged in, use the following command to get the remote X server to open an X terminal on the local machine:
o setenv DISPLAY localhostname:0 ; xterm &
This is valid for csh, which is the default login shell on Nobel. For ksh, (and I think bash) replace with
o DISPLAY=localhostname:0
o export DISPLAY ; xterm
Other X-based programs such as Netscape or Gauss (graphical version) can also be run on a remote machine with display on the local machine with little trouble. The local X server is the program that has all of the information concerning the properties of the graphics card and terminal, so it must be necessary to have X running on the local machine. The following should also work. After using xhost to give permission to the remote machine to display on the local machine, use
o netscape -display localhostname:0.0
Question: can one start the X session on the local machine and then run a remote copy of a window manager?

• xinit - start X Window. The command startx is a front end to xinit in Linux, including Slackware.

• xload - displays a graphic of the system load

• xlpq - graphical interface to print manager. This is included on one of the XFCE menus, but does not seem to be a part of the base Red Hat distribution.

• xlsfonts - list fonts available under the X Window system.

• xman - browsable command reference. Displays manual pages under X.

• xmh - graphical front end under X to the nmh mail handling system. This program is part of the XFree86 package in Red Hat.

• xmodmap - utility for modifying keymaps and pointer button mappings in X. Can be used to install a French Canadian keyboard. Download the Xmodmap.cf file from www.linux-quebec.org, and insert the command
o xmodmap /etc/X11/Xmodmap.cf &
into the .xession (with xdm) or the .xinitrc (with startx) file.

• xosview - displays bar graphs of system load, load average, memory usage, and swap usage

• xpaint - simple paint program for X

• xpdf - GPL'd utility for previewing dvi files. Doesn't seem to work too well on texts with a lot of math.

• xplaycd - X Window audio cd player utility

• xsetroot - utility to configure root window of an X terminal

• xsysinfo - graphical display of load and memory usage

• xterm - start an X Window terminal session

• xterm-color - color version of xterm

• xv - utility for viewing and manipulating many types of image files. This is a shareware program.

• xvidtune - utility for fine tuning of monitor settings under X

• yacc - parser generator

• ytalk - multi-user program similar to talk

• zcat - read one or more files that have been compressed with gzip or compress and write to standard output

• zcmp - read compressed files and pass them to cmp

• zdiff - read compressed files and pass them to diff

• zgrep - read compressed files and pass them to grep

• Zharf - AfterStep button panel module

• zip - zip utility compatible with DOS PKzip

• zless - view zipped files

• zmore - print contents of compressed files one screen at a time

• znew - uncompress Z files and recompress in .gz format

Eventually, we want to be able to distinguish between commands that are an intrinsic part of the kernel, commands that are executable binaries that come with every distribution of Linux, executable binaries that are not provided with all distributiions of Linux, and executable shell scripts. We also want to point out the typical location of these commands on different Linux distributions. Finally, we want to distinguish between shell commands and Linux commands.

10 Notes on Applications

10.1 Mail Transfer Agents (MTAs)
The Linux distributions I know come with sendmail, except for Mandrake, which as of version 7.1 uses Postfix as its default MTA. There are several competing programs available. Even the simplest don't seem to be that easy to configure.

• Exim -

• Fetchmail - seemingly one of the few ways (Pine is able to do this as well) to download mail automatically from a POP or IMAP server and pass it to local mail handling agents. Use the following line in /.fetchmailrc:
o poll pop.uqam.ca proto pop3 user USERNAME pass PASSWORD
Use the following to have fetchmail loaded as a daemon that will download mail at regular intervals:
o fetchmail -d 6000
The interval is specified in seconds. Fetchmail will poll all of the pop servers listed in /.fetchmailrc.

• Getmail - Designed as a replacement for Fetchmail.

• MMDF -

• Postfix - a mail transport agent and potential replacement for sendmail. Mandrake 7.1 and up uses this as its default MTA.

• Qmail - a ``modern'' replacement for sendmail. It is reputed to be more secure than sendmail. Since it doesn't have a GPL license, it is not the default MTA of any Linux distributions that I know of.

• Sendmail - this one gets my vote for the most complicated and obscure configuration file, /etc/sendmail.cf. Most individual Linux users will be using machines connected to the Internet via an ISP or on networks (such as university networks) with centralized mail processing and access to the net. I have to change the following lines in sendmail.cf to be able to send mail with emacs.
o DMuqam.ca # masquerade the domain name
o DNambler.steven # masquerade username
o DSnobel.si.uqam.ca # relay all mail through nobel server
The problem comes from the fact that, as a user on a local network, I don't have my own domain name. I want return mail to be routed to UQAM's mail server and I want the server to handle all my mail for me, even mail to other UQAM users. If I send mail to UQAM users using their normalized usernames, the net does not know who or where they are. I have managed to get a configuration that works by writing a sendmail.mc file and processing it with the m4 macro interpreter, following the Address-Rewriting mini-HOWTO. I now have something that works, but which mysteriously complains about ``dangerous write permissions'' every time the system boots up.

• Smail - seems to be a popular choice on smaller systems. It would appear that at one point in its history, Red Hat shipped with smail, but this has been replaced with sendmail.

• Zmailer - apparently designed for mail servers with a large number of users.

10.2 Mail User Agents (MUAs)

• Acmemail - Web-based mail agent. Allows you to access your mail with any browser. Involves setting up a Perl CGI script on the server side.

• Archimedes - A successor program to XFmail (see below)

• Arrow -

• Balsa - the default Gnome mail program

• Blitzmail -

• Elm -

• Emumail - Web-based mail agent. Allows you to use any browser to check your POP mail account. The Web site of the company that makes this one can be used to check your mail on a Unix system without setting up any CGI script on the server side.

• Evolution - mail reader and contact manager/calendar designed for use under Gnome

• Exmh - graphical front end for Mh

• Kmail - mail reading program included with KDE

• M - for ``Mahogany''. Seems similar to XFmail (see below). I haven't been able to figure out from the description whether it runs independently of or in conjunction with sendmail and procmail.

• Mh -

• Mumail -

• Mutt - text based mail program, which is highly configurable.

• Nmh - mail handling system. This system includes a large number of binary commands that are kept in /usr/bin. See the man page for nmh for details. Red Hat 5.1 and 5.2 come with exmh and xmh, which are graphical front ends for nmh. The exmh front end is a separate package, while xmh is owned by XFree86.

• Pine - text based mail and news utility. Features now include:
o MIME support
o ability to read and post network news
o maintenance of an address book of mail recipients
o spell checking during message composition
o mouse support when using xterm on an X Window system
o a highly configurable environment
Pine can be used to download mail from one or more POP3 mail servers. See Tip of the Week (http://tipoftheweek.darkelf.net) for the fourth week of February 1999. First, set up multiple configuration files (pine -p localmail, pine -p popserver 1, pine -p popserver 2, etc.). Then, to configure Pine to use a POP3 server, use the Setup Config command. Set something like this in the inbox-path:
o {pop.server.com/pop3/user=myid}INBOX
When Pine is restarted, it should ask for your password, connect to the remote server, and use it is if it were accessing local mail. The article is unclear on whether there is the option of leaving copies of the downloaded mail on the server.

• Sylpheed -

• XCmail -

• XFmail - This one seems very promising. It's a GUI-based mail tool that seems to offer most of the features of Netscape's mail module. It runs without using sendmail and procmail, which is a major advantage.

10.3 Editors

• cooledit - a pretty powerful GUI text editor

• emacs - powerful text editor that includes modules for reading and sending mail and postings to newsgroups, and a browser module. For editing TEX and LATEX files, the AucTEX addon package is invaluable, and makes emacs pretty hard to beat as an editor with LATEX.

• jed - has pretty good emacs emulation (it can even read mail like emacs!). It does simple syntax highlighting for TeX files, including giving positioning of parentheses. It would seem to be pretty configurable and takes up much less disk space than emacs, although more than joe and muemacs. It works well in console mode, and still manages to use colors for menu bars and syntax highlighting. The program xjed which comes with some versions starts up its own X terminal when invoked.

• joe - "Joe's Own Editor", a fairly powerful editor with a compact binary and an ability to emulate Wordstar, Emacs, Pico, and a few other editors.

• jove - "Joe's Own Version of Emacs". I tried this out a couple of times and managed to crash it when making some minor errors in command syntax.

• microemacs (JASSPA) - spinoff of muemacs. Pretty powerful and configurable, while not taking up too much disk space or memory.

• muemacs - a fairly powerful emacs clone whose binary is actually smaller than that of the Joe editor.

• nedit - an X Window based text editor. Of all text editors for Linux that I've seen, it has commands which are closest to Windows text editors, for cursor movement, highlighting, marking text, etc. It has very good syntax highlighting for both LATEX and HTML.

• pico - simple text editor. It often comes packaged with the Pine mail user agent.

• vi - included with most Linux distributions. If you're not used to the syntax, it can be pretty hard to understand.

• vim - improved version of vi

• xedit - simple text editor included with many Linux distributions

10.4 Other

• dfm - Desktop File Manager. Allows the user to place program icons on the desktop.

• gmc - Gnome Midnight Commander. Gnome version of Midnight Commander. Includes a graphical interface and allows the user to place icons on the desktop.

• mc - Midnight Commander file manager. Runs in console mode and in an xterm.

• scilab - a free matrix programming language. May be a good substitute for GAUSS and/or MATLAB.

11 Some Nifty Slogans
Linux: the choice of a GNU generation.
Windows: where do you want to go today? Linux: where do you want to go tomorrow?
This program has performed an illegal operation and will be shut down: please reboot using Linux.
``When you say `I wrote a program that crashed Windows', people just stare at you blankly and say `Hey, I got those with the system, for free'.'' - Linus Torvalds
Windows 2000, from the company that brought you EDLIN!
Linux: because rebooting is for adding new hardware.
Your mouse has moved. Windows NT must be restarted for the change to take effect. Reboot now [OK]?
Linux: transforms your microcomputer into a workstation. Windows NT: transforms your workstation into a microcomputer.

12 References
Computer Technology Documentation Project (CTDP) (2000a), ``How Linux Works'', http://ctdp.tripod.com/os/linux/howlinuxworks/index.html
Computer Technology Documentation Project (CTDP) (2000b), ``Linux Files and Command Reference'', http://ctdp.tripod.com/os/linux/commands/index.html
Klimas, Piotr et. al. (1999), ``Linux Newbie Administrator Guide'', http://sunsite.dk/linux-newbie/
Siever, Ellen, Stephen Spainhour, Jessica P. Hekman, and Stephen Figgins (2000), Linux in a Nutshell. third edition, O'Reilly
Sobell, Mark G. (1998), A Practical Guide to Linux. Addison-Wesley
SSC (2000), ``Bash Reference Card'', http://www.ssc.com/ssc/bash/ bash.pdf
Welsh, Matt, Matthias Kalle Dalheimer and Lar Kaufman (1999), Running Linux. third edition, O'Reilly and Associates













The C shell provides the following built-in commands:
# Marks a command.
alias Displays alias.
bg Resumes job in the background.
break Resumes execution after the loop.
breaksw Breaks from a switch command; resumes after the endsw command.
case Defines a label in a switch command.
cd Changes directory.
chdir Changes directory, same as cd.
continue Continues a loop.
default Specifies the default case in a switch.
dirs Displays the directory stack.
echo Writes arguments to the standard output of the shell.
eval Evaluates a command.
exec Executes the command in the current shell.
exit Exits the shell.
fg Brings a job in the foreground.
foreach Specifies a looping control statement and execute a sequence of commands until reaching an end command.
glob Writes arguments to the standard output of the shell, like the echo command, but without the new line.
goto Continues execution after the specified label.
hashstat Displays hash table statistics.
history Displays the history list.
if Executes a command if condition met.
jobs Lists active jobs.
kill Sends a signal to a process. term (terminate) is the default signal.
limit Sets or list system resource limits.
login Logs on.
logout Logs out.
nice Changes the priority of commands run in the shell.
nohup Ignores the hangup signal.
notify Notifies the user about changes in job status.
onintr Tells the shell what to do on interrupt.
popd Pops the top directory off the directory stack and changes to the new top directory.
pushd Exchanges the top two elements of the directory stack.
rehash Re-computes the hash table of the contents of the directories in the path shell variable.
repeat Repeats the execution of a command.
set Displays or set the value of a shell variable.
setenv Sets environment variables.
shift Shifts shell arguments.
source Reads commands from a script.
stop Stops a background job.
suspend Stops the current shell.
switch Starts a switch.
time Displays the time used to execute commands.
umask Shows or set file permissions.
unalias Removes command alias.
unhash Disables the internal hash table.
unlimit Removes limitations on system Resource.
unset Deletes shell variables.
unsetenv Deletes environment variables.
wait Waits for background jobs to complete.
while …end Executes the commands between the while and matching end statements repeatedly.
@ Displays or set the values of all the shell variables.
Unix commands reference card
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Environment Control
Command Description

cd d Change to directory d

mkdir d Create new directory d

rmdir d Remove directory d

mv f1 [f2...] d Move file f to directory d

mv d1 d2 Rename directory d1 as d2

passwd Change password

alias name1 name2 Create command alias (csh/tcsh)

alias name1="name2" Create command alias (ksh/bash)

unalias name1[na2...] Remove command alias na

ssh nd Login securely to remote node

exit End terminal session

setenv name v Set env var to value v (csh/tcsh)

export name="v" set environment variable to value v (ksh/bash)


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Output, Communication, & Help
Command Description

lpr -P printer f
or
lp -d printer f Output file f to line printer

script [f] Save terminal session to f

exit Stop saving terminal session

mailx username Send mail to user

man name Unix manual entry for name

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Process Control
Command Description

CTRL/c * Interrupt processes

CTRL/s * Stop screen scrolling

CTRL/q * Resume screen output

sleep n Sleep for n seconds

jobs Print list of jobs

kill % Kill job n

ps Print process status stats

kill -9 n Remove process n

CTRL/z * Suspend current process

stop %n Suspend background job n

cmmd& Run cmmd in background

bg [%n] Resume background job n

fg [%n] Resume foreground job n

exit Exit from shell
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Environment Status
Command Description

ls [d] [f...] List files in directory

ls -1 [f...] List files in detail

alias [name] Display command aliases

printenv [name] Print environment values

quota Display disk quota

date Print date & time

who List logged in users

whoami Display current user

finger [username] Output user information

chfn Change finger information

pwd Print working directory

history Display recent commands

! n Submit recent command n
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File Manipulation
Command Description

vi [f] Vi fullscreen editor

emacs [f] Emacs fullscreen editor

ed [f] Text editor

wc f Line, word, & char count

cat f List contents of file

more f List file contents by screen

cat f1 f2 >f3 Concatenates f1 & f2 into f3

chmod mode f Change protection mode of f

cmp f1 f2 Compare two files

cp f1 f2 Copy file f1 into f2

sort f Alphabetically sort f

split [-n] f Split f into n-line pieces

mv f1 f2 Rename file f1 as f2

rm f Delete (remove) file f

grep 'ptn' f Outputs lines that match ptn

diff f1 f2 Lists file differences

head f Output beginning of f

tail f Output end of f
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Compiler
Command Description

cc [-o f1] f2 C compiler

lint f Check C code for errors

f77 [-o f1] f2 Fortran77 compiler

pc [-o f1] f2 Pascal compiler
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Working with NFS files
Files saved on the UITS central Unix computers Steel, the Parallel PC cluster, Solar/Lunar, and the Research SP are stored on the Network File Server (NFS). That means that your files are really on one disk, in directories named for the central Unix hosts on which you have accounts.
No matter which of these computers you are logged into, you can get to your files on any of the others. Here are the commands to use to get to any system directory from any other system:
cd /N/u/username/PPPC/
cd /N/u/username/Cobalt/
cd /N/u/username/Solar/
cd /N/u/username/Steel/
cd /n/u/username/SP/
Be sure you use the capitalization just as you see above, and substitute your own username for "username".
For example, if Jessica Rabbit is logged into her account on Steel, and wants to get a file on her SP account, she would enter:
cd /N/u/jrabbit/SP/
Now when she lists her files, she'll see her SP files, even though she's actually logged into Steel.
You can use the ordinary Unix commands to move files, copy files, or make symbolic links between files. For example, if Jessica Rabbit wanted to move "file1" from her Steel directory to her SP directory, she would enter:
mv -i /N/u/jrabbit/Steel/file1 /N/u/jrabbit/SP/
This shared file system means that you can access, for example, your SP files even when you are logged into Steel, and vice versa. However, if you are logged into the SP, you can only use the software installed on SP -- only users' directories are linked together, not system directories.
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Abbreviations used in this document

CTRL/x hold down control key and press x

d directory

env environment

f filename

n number

nd computer node

prtr printer

ptn pattern

var variable

[y/n] yes or no

[] optional arg

... list
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some useful links