Some Basic Linux Commands, For Beginners...

[Onur]

Some Basic Linux Commands, For Beginners... An A-Z Index of the Linux BASH command line

alias Create an alias
awk Find and Replace text, database sort/validate/index
break Exit from a loop
builtin Run a shell builtin

cal Display a calendar
case Conditionally perform a command
cat Display the contents of a file
cd Change Directory
cfdisk Partition table manipulator for Linux
chgrp Change group ownership
chmod Change access permissions
chown Change file owner and group
chroot Run a command with a different root directory
cksum Print CRC checksum and byte counts
clear Clear terminal screen
cmp Compare two files
comm Compare two sorted files line by line
command Run a command - ignoring shell functions
continue Resume the next iteration of a loop
cp Copy one or more files to another location
cron Daemon to execute scheduled commands
crontab Schedule a command to run at a later time
csplit Split a file into context-determined pieces
cut Divide a file into several parts

date Display or change the date & time
dc Desk Calculator
dd Data Dump - Convert and copy a file
declare Declare variables and give them attributes
df Display free disk space
diff Display the differences between two files
diff3 Show differences among three files
dir Briefly list directory contents
dircolors Colour setup for `ls'
dirname Convert a full pathname to just a path
dirs Display list of remembered directories
du Estimate file space usage

echo Display message on screen
ed A line-oriented text editor (edlin)
egrep Search file(s) for lines that match an extended expression
eject Eject CD-ROM
enable Enable and disable builtin shell commands
env Display, set, or remove environment variables
eval Evaluate several commands/arguments
exec Execute a command
exit Exit the shell
expand Convert tabs to spaces
export Set an environment variable
expr Evaluate expressions

factor Print prime factors
false Do nothing, unsuccessfully
fdformat Low-level format a floppy disk
fdisk Partition table manipulator for Linux
fgrep Search file(s) for lines that match a fixed string
find Search for files that meet a desired criteria
fmt Reformat paragraph text
fold Wrap text to fit a specified width.
for Expand words, and execute commands
format Format disks or tapes
free Display memory usage
fsck File system consistency check and repair
function Define Function Macros

gawk Find and Replace text within file(s)
getopts Parse positional parameters
grep Search file(s) for lines that match a given pattern
groups Print group names a user is in
gzip Compress or decompress named file(s)

hash Remember the full pathname of a name argument
head Output the first part of file(s)
history Command History
hostname Print or set system name

id Print user and group id's
if Conditionally perform a command
import Capture an X server screen and save the image to file
info Help info
install Copy files and set attributes

join Join lines on a common field

kill Stop a process from running

less Display output one screen at a time
let Perform arithmetic on shell variables
ln Make links between files
local Create variables
locate Find files
logname Print current login name
logout Exit a login shell
look Display lines beginning with a given string
lpc Line printer control program
lpr Off line print
lprint Print a file
lprintd Abort a print job
lprintq List the print queue
lprm Remove jobs from the print queue
ls List information about file(s)

m4 Macro processor
man Help manual
mkdir Create new folder(s)
mkfifo Make FIFOs (named pipes)
mknod Make block or character special files
more Display output one screen at a time
mount Mount a file system
mtools Manipulate MS-DOS files
mv Move or rename files or directories

nice Set the priority of a command or job
nl Number lines and write files
nohup Run a command immune to hangups

passwd Modify a user password
paste Merge lines of files
pathchk Check file name portability
ping Test a network connection
popd Restore the previous value of the current directory
pr Prepare files for printing
printcap Printer capability database
printenv Print environment variables
printf Format and print data
ps Process status
pushd Save and then change the current directory
pwd Print Working Directory

quota Display disk usage and limits
quotacheck Scan a file system for disk usage
quotactl Set disk quotas

ram ram disk device
rcp Copy files between two machines.
read read a line from standard input
readonly Mark variables/functions as readonly
remsync Synchronize remote files via email
return Exit a shell function
rm Remove files
rmdir Remove folder(s)
rpm Remote Package Manager
rsync Remote file copy (Synchronize file trees)

screen Terminal window manager
sdiff Merge two files interactively
sed Stream Editor
select Accept keyboard input
seq Print numeric sequences
set Manipulate shell variables and functions
shift Shift positional parameters
shopt Shell Options
shutdown Shutdown or restart linux
sleep Delay for a specified time
sort Sort text files
source Run commands from a file `.'
split Split a file into fixed-size pieces
su Substitute user identity
sum Print a checksum for a file
symlink Make a new name for a file
sync Synchronize data on disk with memory

tac Concatenate and write files in reverse
tail Output the last part of files
tar Tape ARchiver
tee Redirect output to multiple files
test Evaluate a conditional expression
time Measure Program running time
times User and system times
touch Change file timestamps
top List processes running on the system
traceroute Trace Route to Host
trap Run a command when a signal is set(bourne)
tr Translate, squeeze, and/or delete characters
true Do nothing, successfully
tsort Topological sort
tty Print filename of terminal on stdin
type Describe a command

ulimit Limit user resources
umask Users file creation mask
umount Unmount a device
unalias Remove an alias
uname Print system information
unexpand Convert spaces to tabs
uniq Uniquify files
units Convert units from one scale to another
unset Remove variable or function names
unshar Unpack shell archive scripts
until Execute commands (until error)
useradd Create new user account
usermod Modify user account
users List users currently logged in
uuencode Encode a binary file
uudecode Decode a file created by uuencode

v Verbosely list directory contents (`ls -l -b')
vdir Verbosely list directory contents (`ls -l -b')
vi Text Editor

watch Execute/display a program periodically
wc Print byte, word, and line counts
whereis Report all known instances of a command
which Locate a program file in the user's path.
while Execute commands
who Print all usernames currently logged in
whoami Print the current user id and name (`id -un')

xargs Execute utility, passing constructed argument list(s)
yes Print a string until interrupted

.period Run commands from a file
### Comment / Remark

[Onur]

This is a practical selection of the commands we use most often. Press <Tab> to see the listing of all available command (on your PATH). On my small home system, it says there are 2595 executables on my PATH. Many of these "commands" can be accessed from your favourite GUI front-end (probably KDE or Gnome) by clicking on the right menu or button. They can all be run from the command line. Programs that require GUI have to be run from a terminal opened under a GUI.
Legend:
<> = single special or function key on the keyboard. For example <Ctrl> indicates the "control" key.
italic = name of the file or variable you probably want to substitute with your own.
fixed width = in-line Linux commands and filenames.
Notes for the UNIX Clueless:
1. LINUX IS CASE-SENSITIVE. For example: Netscape, NETSCAPE and nEtscape are three different commands. Also my_filE, my_file, and my_FILE are three different files. Your user login name and password are also case sensitive. (This goes with the tradition of UNIX and the "c" programming language being case sensitive.)
2. Filenames can be up to 256 characters long and can contain letters, numbers, "." (dot), "_" (underscore), "-" (dash), plus some other not recommended characters.
3. Files with names starting with "." are normally not shown by the ls (list) or dir commands. Think of these files as "hidden". Use ls -a (list with the option "all") to see these files.
4. "/" is an equivalent to DOS "\" (root directory, meaning the parent of all other directories).
5. Under Linux, all directories appear under a single directory tree (there are no DOS-style drive letters).
6. In a configuration file, a line starting with # is a comment.
7.1 Linux essential shortcuts and sanity commands

<Ctrl><Alt><F1>
Switch to the first text terminal. Under Linux you can have several (6 in standard setup) terminals opened at the same time. <Ctrl><Alt><Fn> (n=1..6)
Switch to the nth text terminal.
tty
Print the name of the terminal in which you are typing this command.
<Ctrl><Alt><F7>
Switch to the first GUI terminal (if X-windows is running on this terminal).
<Ctrl><Alt><Fn> (n=7..12)
Switch to the nth GUI terminal (if a GUI terminal is running on screen n-1). On default, nothing is running on terminals
8 to 12, but you can run another server there.
<Tab>
(In a text terminal) Autocomplete the command if there is only one option, or else show all the available options.
THIS SHORTCUT IS GREAT! It even works at LILO prompt!
<ArrowUp>
Scroll and edit the command history. Press <Enter> to execute.
<Shift><PgUp>
Scroll terminal output up. Work also at the login prompt, so you can scroll through your bootup messages.
<Shift><PgDown>
Scroll terminal output down.
<Ctrl><Alt><+>
(in X-windows) Change to the next X-server resolution (if you set up the X-server to more than one resolution). For multiple resolutions on my standard SVGA card/monitor, I have the following line in the file /etc/X11/XF86Config (the first resolution starts on default, the largest determines the size of the "virtual screen"):
Modes "1024x768" "800x600" "640x480" "512x384" "480x300" "400x300" "1152x864"
<Ctrl><Alt><->
(in X-windows) Change to the previous X-server resolution.
<Ctrl><Alt><BkSpc>
(in X-windows) Kill the current X-windows server. Use if the X-windows server crushes and cannot be exited normally.
<Ctrl><Alt><Del>
Shut down the system and reboot. This is the normal shutdown command for a user at the text-mode console. Don't just press the "reset" button for shutdown!
<Ctrl>c
Kill the current process (mostly in the text mode for small applications).
<Ctrl>d
Log out from the current terminal. See also the next command.
<Ctrl>d
Send [End-of-File] to the current process. Don't press it twice else you also log out (see the previous command).
<Ctrl>s
Stop the transfer to the terminal.
<Ctrl>q
Resume the transfer to the terminal. Try if your terminal mysteriously stops responding.
<Ctrl>z
Send the current process to the background.
exit
Logout. I can also use logout for the same effect. (If you have started a second shell, e.g., using bash the second shell will be exited and you will be back in the first shell, not logged out.)
reset
Restore a screwed-up terminal (a terminal showing funny characters) to default setting. Use if you tried to "cat" a binary file. You may not be able to see the command as you type it.
<MiddleMouseButton>
Paste the text which is currently highlighted somewhere else. This is the normal "copy-paste" operation in Linux. (It doesn't work with Netscape and WordPerfect which use the MS Windows-style "copy-paste". It does work in the text terminal if you enabled "gpm" service using "setup".) Best used with a Linux-ready 3-button mouse (Logitech or similar) or else set "3-mouse button emulation").
~
(tilde) My home directory (normally the directory /home/my_login_name). For example, the command cd ~/my_dir will change my working directory to the subdirectory "my_dir" under my home directory. Typing just "cd" alone is an equivalent of the command "cd ~".
.
(dot) Current directory. For example, ./my_program will attempt to execute the file "my_program" located in your current working directory.
..
(two dots) Directory parent to the current one. For example, the command cd .. will change my current working directory one one level up.
7.2 Common Linux commands--system info

pwd
Print working directory, i.e., display the name of my current directory on the screen. hostname
Print the name of the local host (the machine on which you are working). Use netconf (as root) to change the name of the machine.
whoami
Print my login name.
id username
Print user id (uid) and his/her group id (gid), effective id (if different than the real id) and the supplementary groups.
date
Print or change the operating system date and time. E.g., I could change the date and time to 2000-12-31 23:57 using this command:
date 123123572000
To set the hardware (BIOS) clock from the system (Linux) clock, use the command (as root) setclock
time
Determine the amount of time that it takes for a process to complete + other info. Don't confuse it with the date command. E.g. I can find out how long it takes to display a directory content using:
time ls
who
Determine the users logged on the machine.
rwho -a
(=remote who) Determine all users logged on your network. The rwho service must be enabled for this command to run. If it isn't, run setup as root to enable "rwho".
finger user_name
System info about a user. Try: finger root
last
Show listing of users last logged-in on your system.
history | more
Show the last (1000 or so) commands executed from the command line on the current account. The "| more" causes the display to stop after each screenful.
uptime
Show the amount of time since the last reboot.
ps
(=print status) List the processes currently run by the current user.
ps axu | more
List all the processes currently running, even those without the controlling terminal, together with the name of the user that owns each process.
top
Keep listing the currently running processes, sorted by cpu usage (top users first). In KDE, you can get GUI-based Ktop from "K"menu under "System"-"Task Manager" (or by executing "ktop" in an X-terminal).
uname -a
(= Unix name with option "all") Info on your (local) server. I can also use guname (in X-window terminal) to display the info more nicely.
free
Memory info (in kilobytes).
df -h
(=disk free) Print disk info about all the filesystems (in human-readable form)
du / -bh | more
(=disk usage) Print detailed disk usage for each subdirectory starting at the "/" (root) directory (in human legible form).
cat /proc/cpuinfo
Cpu info--it show the content of the file cpuinfo. Note that the files in the /proc directory are not real files--they are hooks to look at information available to the kernel.
cat /proc/interrupts
List the interrupts in use.
cat /proc/version
Linux version and other info
cat /proc/filesystems
Show the types of filesystems currently in use.
cat /etc/printcap
Show the setup of printers.
lsmod
(As root. Use /sbin/lsmod to execute this command when you are a non-root user.) Show the kernel modules currently loaded.
set|more
Show the current user environment.
echo $PATH
Show the content of the environment variable "PATH". This command can be used to show other environment variables as well. Use "set" to see the full environment.
dmesg | less
Print kernel messages (the content of the so-called kernel ring buffer). Press "q" to quit "less". Use less /var/log/dmesg to see what "dmesg" dumped into this file right after the last system bootup.

[Onur]

7.3 Basic operations

any_command --help |more
Display a brief help on a command (works with most commands). "--help" works similar to DOS "/h" switch. The "more" pipe is needed if the output is longer than one screen. man topic
Display the contents of the system manual pages (help) on the topic. Try man man first. Press "q" to quit the viewer. The command info topic works similar and may contain more up-to-date information. Manual pages can be hard to read. Try any_command --help for short, easy to digest help on a command. If more info needed, have a look to the directory /usr/doc. To display manual page from a specific section, I may use something like in this example: man 3 exit (this displays an info on the command exit from section 3 of the manual pages).
apropos topic
Give me the list of the commands that have something to to do with my topic.
help command
Display brief info on a bash (shell) build-in command.
ls
List the content of the current directory. Under Linux, the command "dir" is an alias to ls. Many users have "ls" to be an alias to "ls --color".
ls -al |more
List the content of the current directory, all files (also those starting with a dot), and in a long form. Pipe the output through the "more" command, so that the display pauses after each screenful.
cd directory
Change directory. Using "cd" without the directory name will take you to your home directory. "cd -" will take you to your previous directory and is a convenient way to toggle between two directories. "cd .." will take you one directory up.
cp source destination
Copy files. E.g., cp /home/stan/existing_file_name . will copy a file to my current working directory. Use the "-r" option (for recursive) to copy the contents of whole directories, e.g. , cp -r my_existing/dir/ ~ will copy a subdirectory under my current working directory to my home directory.
mcopy source destination
Copy a file from/to a DOS filesystem (no mounting necessary). E.g., mcopy a:\autoexec.bat ~/junk . See man mtools for related commands: mdir, mcd, mren, mmove, mdel, mmd, mrd, mformat ....
mv source destination
Move or rename files. The same command is used for moving and renaming files and directories.
ln source destination
Create a hard link called destination to the file called source. The link appears as a copy of the original files, but in reality only one copy of the file is kept, just two (or more) directory entries point to it. Any changes the file are automatically visible throughout. When one directory entry is removed, the other(s) stay(s) intact. The limitation of the hard links are: the files have to be on the same filesystem, hard links to directories or special files are impossible.
ln -s source destination
Create a symbolic (soft) link called "destination" to the file called "source". The symbolic link just specifies a path where to look for the file. In contradistinction to hard links, the source and destination don't not have to tbe on the same filesystem. In comparison to hard links, the drawback of symbolic links are: if the original file is removed, the link is "broken", symbolic links can also create circular references (like circular references in spreadsheets or databases, e.g., "a" points to "b" and "b" points back to "a").
rm files
Remove (delete) files. You must own the file in order to be able to remove it. On many systems, you will be asked or confirmation of deleation, if you don't want this, use the "-f" (=force) option, e.g., rm -f * will remove all files in my current working directory, no questions asked.
mkdir directory
Make a new directory.
rmdir directory
Remove an empty directory.
rm -r files
(recursive remove) Remove files, directories, and their subdirectories. Careful with this command as root--you can easily remove all files on the system with such a command executed on the top of your directory tree, and there is no undelete in Linux (yet). But if you really wanted to do it (reconsider), here is how (as root): rm -rf /*
cat filename | more
View the content of a text file called "filename", one page a time. The "|" is the "pipe" symbol (on many American keyboards it shares the key with "\") The pipe makes the output stop after each screenful. For long files, it is sometimes convenient to use the commands head and tail that display just the beginning and the end of the file. If you happened to use "cat" a binary file and your terminal displays funny characters afterwards, you can restore it with the command "reset".
less filename
Scroll through a content of a text file. Press q when done. "Less" is roughly equivalent to "more" , the command you know from DOS, although very often "less" is more convenient than "more".
pico filename
Edit a text file using the simple and standard text editor called pico.
pico -w filename
Edit a text file, while disabling the long line wrap. Handy for editing configuration files, e.g. /etc/fstab.
find / -name "filename"
Find the file called "filename" on your filesystem starting the search from the root directory "/". The "filename" may contain wildcards (*,?).
locate filename
Find the file name of which contains the string "filename". Easier and faster than the previous command but depends on a database that normally rebuilds at night.
./program_name
Run an executable in the current directory, which is not on your PATH.
touch filename
Change the date/time stamp of the file filename to the current time. Create an empty file if the file does not exist.
xinit
Start a barebone X-windows server (without a windows manager).
startx
Start an X-windows server and the default windows manager. Works like typing "win" under DOS with Win3.1
startx -- :1
Start another X-windows session on the display 1 (the default is opened on display 0). You can have several GUI terminals running concurrently. Switch between them using <Ctrl><Alt><F7>, <Ctrl><Alt><F8>, etc.
xterm
(in X terminal) Run a simple X-windows terminal. Typing exit will close it. There are other, more advanced "virtual" terminals for X-windows. I like the popular ones: konsole and kvt (both come with kde) and gnome-terminal (comes with gnome). If you need something really fancy-looking, try Eterm.
xboing
(in X terminal). Very nice, old-fashioned game. Many small games/programs are probably installed on your system. I also like xboard (chess).
shutdown -h now
(as root) Shut down the system to a halt. Mostly used for a remote shutdown. Use <Ctrl><Alt><Del> for a shutdown at the console (which can be done by any user).
halt
reboot
(as root, two commands) Halt or reboot the machine. Used for remote shutdown, simpler to type than the previous command.

[Onur]

Accessing drives/partitions

mount
See here for details on mounting drives. Examples are shown in the next commands. mount -t auto /dev/fd0 /mnt/floppy
(as root) Mount the floppy. The directory /mnt/floppy must exist, be empty and NOT be your current directory.
mount -t auto /dev/cdrom /mnt/cdrom
(as root) Mount the CD. You may need to create/modify the /dev/cdrom file depending where your CDROM is. The directory /mnt/cdrom must exist, be empty and NOT be your current directory.
mount /mnt/floppy
(as user or root) Mount a floppy as user. The file /etc/fstab must be set up to do this. The directory /mnt/floppy must not be your current directory.
mount /mnt/cdrom
(as user or root) Mount a CD as user. The file /etc/fstab must be set up to do this. The directory /mnt/cdrom must not be your current directory.
umount /mnt/floppy
Unmount the floppy. The directory /mnt/floppy must not be your (or anybody else's) current working directory. Depending on your setup, you might not be able to unmount a drive that you didn't mount.

7.6 Network administration tools

netconf
(as root) A very good menu-driven setup of your network. pingmachine_name
Check if you can contact another machine (give the machine's name or IP), press <Ctrl>C when done (it keeps going).
route -n
Show the kernel routing table.
nslookup host_to_find
Query your default domain name server (DNS) for an Internet name (or IP number) host_to_find. This way you can check if your DNS works. You can also find out the name of the host of which you only know the IP number.
traceroute host_to_trace
Have a look how you messages trave to host_to_trace (which is either a host name or IP number).
ipfwadm -F -p m
(for RH5.2, seen next command for RH6.0) Set up the firewall IP forwarding policy to masquerading. (Not very secure but simple.) Purpose: all computers from your home network will appear to the outside world as one very busy machine and, for example, you will be allowed to browse the Internet from all computers at once.
echo 1 > /proc/sys/net/ipv4/ip_forward
ipfwadm-wrapper -F -p deny
ipfwadm-wrapper -F -a m -S xxx.xxx.xxx.0/24 -D 0.0.0.0/0
(three commands, RH6.0). Does the same as the previous command. Substitute the "x"s with digits of your class "C" IP address that you assigned to your home network. See here for more details. In RH6.1, masquarading seems broken to me--I think I will install Mandrake Linux.
ifconfig
(as root) Display info on the network interfaces currently active (ethernet, ppp, etc). Your first ethernet should show up as eth0, second as eth1, etc, first ppp over modem as ppp0, second as ppp1, etc. The "lo" is the "loopback only" interface which should be always active. Use the options (see ifconfig --help) to configure the interfaces.
ifup interface_name
(/sbin/ifup to it run as a user) Startup a network interface. E.g.:
ifup eth0
ifup ppp0
Users can start up or shutdown the ppp interface only when the right permission was checked during the ppp setup (using netconf ). To start a ppp interface (dial-up connection), I normally use kppp available under kde menu "internet".
ifdown interface_name
(/sbin/ifdown to run it as a user). Shut down the network interface. E.g.: ifdown ppp0 Also, see the previous command.
netstat | more
Displays a lot (too much?) information on the status of your network.

Music-related commands

cdplay play 1
Play the first track from a audio CD. eject
Get a free coffee cup holder )). (Eject the CD ROM tray).
play my_file.wav
Play a wave file.
mpg123 my_file.mp3
Play an mp3 file.
mpg123 -w my_file.wav my_file.mp3
Create a wave audio file from an mp3 audio file.
knapster
(in X terminal) Start the program to downolad mp3 files that other users of napster have displayed for downloading. Really cool!
cdparanoia -B "1-"
(CD ripper) Read the contents of an audio CD and save it into wavefiles in the current directories, one track per wavefile. The "1-"
means "from track 1 to the last". -B forces putting each track into a separate file.
playmidi my_file.mid
Play a midi file. playmidi -r my_file.mid will display text mode effects on the screen.
sox
(argument not given here) Convert from almost any audio file format to another (but not mp3s). See man sox.

Graphics-related commands

kghostview my_file.ps
Display a postscript file on screen. I can also use the older-looking ghostview or gv for the same end effect. ps2pdf my_file.ps my_file.pdf
Make a pdf (Adobe portable document format) file from a postscript file.
gimp
(in X terminal) A humble looking but very powerful image processor. Takes some learning to use, but it is great for artists, there is almost nothing you can't do with gimp. Use your mouse right button to get local menus, and learn how to use layers. Save your file in the native gimp file format *.xcf (to preserve layers) and only then flatten it and save as png (or whatever). There is a large user manual /usr/
gphoto
(in X terminal) Powerful photo editor.
giftopnm my_file.giff > my_file.pnm
pnmtopng my_file.pnm > my_file.png
Convert the propriatory giff graphics into a raw, portable pnm file. Then convert the pnm into a png file, which is a newer and better standard for Internet pictures (better technically plus there is no danger of being sued by the owner of giff patents).

[MHJ]

Thanks! That is a really resourceful list that is loaded with a whole number of info worth archiving