Useful Linux Commands (Red Hat)
- man commandname
- display the manual page for a particular command named
- man -S sectionnumber commandname
- display the manual page under a specific section numbered
sectionnumber for the command named
commandname. Sometimes the same command will exist in
more than one section. man alone will display
the lowest-numbered section only. To see other sections, you'll
need to use the -s flag. The different sections
- 1 - user commands
- 2 - system calls
- 3 - libc calls
- 4 - devices
- 5 - file formats and protocols
- 6 - games
- 7 - conventions, macro packages, etc.
- 8 - system administration
- man -l commandname
- list all the man pages available for commandname
- man -l intro
- interesting reading-- when you have the time
- man -K keyword
- searches all man pages for keywords
- the other major way to find information about commands.
Somewhat obscure to navigate, but quite useful. Basically,
navigate using tab key to select a node, return key to enter a
node, 'l' key to go back, 'q' to quit. Useful information available through info include:
- which commandname
- find the path to a commandname
- whatis commandname
- tells you what a command is and does. works sometimes.
- Some file notations
- . (current directory)
- ./myfile.txt (a file in current directory)
- ./mydirectory/myfile.txt (a file in a subdirectory of current directory)
- mydirectory/myfile.txt (same as above, a file in a subdirectory of current directory)
- .. (parent directory of current directory)
- ../otherdirectory (a sibling subdirectory of current directory [go back one level and down another directory])
- / (the ultimate root directory)
- ~ (my home directory)
- ~/mydirectory (a subdirectory of my home directory)
- ~otheruser (another user's home directory)
- filename*.txt ("*" is the wildcard character)
- cp fromfilename tofilename
- copy from fromfilename tofilename
- mv fromfilename tofilename
- Move from fromfilename to tofilename.
- remove a file (DANGER: this is permanent!)
- rm -i
- asks you before removing a file
- rm -R
- recursively remove a directory and every file in it (DANGER)
- > filename
- redirect output to a file named filename. Overwrites that file. Example: ls > directory.txt
- >> filename
- redirect output to a file named filename. Appends to the end of that file.
- < redirect in
- redirect input to a program. Example: myprogram < myfile.txt
- | mycommand
- pipe output so it goes through a certain command. Example: ls -l | less
- | grep myword
- pipe output through grep. grep
searches for "myword" and displays only those lines containing that
word. Example (to search for all files containing ".cc": ls -l | grep
- find mydirectory -name "nametolookfor"
- searches mydirectory and all its subdirectories for a file named "nametolookfor"
- find . -name "proj3*"
- searches the current directory and all its subdirectories for a file begining with "proj3".
- shows which directory you are currently in
- cd newdirectory
- changes to a new directory
- cd ~
- change to your home directory.
- cd [tab key]
- change to your home directory.
- cd -
- changes to the last directory you were in.
- mkdir directoryname
- Make a new directory.
Executing commands (some are tcsh-specific)
- ^Z (Control-Z)
- This suspends a currently running command. You can then use "bg" or "fg" on it.
- Sends your suspended command to run in the background.
- Resumes execution of your currently suspended command.
- fg jobnumber
- Resumes execution of your suspended command with job number jobnumber.. Use "sps" or "jobs" to see job numbers.
- mycommand &
- runs the command named mycommand in the background
- repeats the last command you ran beginning with the word "foo"
- shows background jobs that were spawned from this current shell.
- nice +nicelevel commandname
- runs a command with
a lower priority. Priorities range from 0 to +19, +19 being the lowest
priority available. If you are going to run a cpu-intensive command, it
is nice to nice it.
- renice +nicelevel jobnumber
- resets a particular command to a different priority level
- shows your current processes attached to this terminal. Use "ps -aux" to see everything.
- show the processes that are using the most resources
- top -Uusername
- show a user's processes in order of resource usage.
- kill jobnumber
- kill off a particular process (BE CAREFUL)
- kill -9 jobnumber
- kill off a particularly troublesome process if the above doesn't work (BE VERY CAREFUL)
Using Text Files
- cat filename
- outputs content of a file to the screen
- cat filename1 filename2 > filename3
- concatenates filename1 and filename2 into a new file named filename3
- more filename
- displays a file page by page
- less filename
- does the same thing as more, but a little cooler
- head filename
- shows the first 10 lines of a file.
- head -numberoflines filename
- shows the first specified number of lines of a file. Ex. tail -50 filename
- tail filename
- shows the last 10 lines of a file.
- tail -numberoflines filename
- shows the last specified number of lines of a file. Ex. tail -50 filename
- nl filename
- sticks line numbers in front of each line in your file and redirects output to the screen
Using Other Files
- file filename
- find out what type of file filename is
- gzip filename
- compress a file
- gunzip filename
- uncompress a file
- tar cvf tarfilename file1 file2 file3 etc.
- archive a bunch of files or directories into one tar file.
- tar xvf tarfilename
- un-archive a tar file into its constituent files
- zcat filename
- like gunzip, but sends output to stdout.
- zcat filename | tar -xvf -
- unzips a compressed, tar'ed file, and untars it directly without creating an intermediate file
- eject the cd tray
- play audio CD's in the cdrom drive.
- cat .au > /dev/audio
- play an au sound file.
- play MP3 files.
- view pdf files
- view ps files
- view dvi files
- view gif, jpeg, png files
Spying and Surveillance on Other Users
- Check to see if someone is logged into your system.
- .plan files
- If you put text into a file named ".plan" in your home directory, people will see it when they finger you.
- in case you forget.
- who is on
- who is on
- who is on, and what they're doing
- this directory has files that show the biggest user of the /scratch directory
- talk username
- start chat session with another user
- ytalk username
- start chat session with multiple users
Learning about the Machine
- see the system load
- quota -v
- How much of your disk and file quota you are using up.
- How much disk space is free on various drives.
- How much space files are taking up in this current directory.
- display a clock
- log into a different machine securely. We
recommend using "ssh" over telnet and rlogin. May interfere with Java
Swing GUI stuff.
- set autolist
- Auto-suggest commands you type on the command line.
- mesg n
- Turns messages off so you won't be disturbed.
- Tells you who your new mail is from.
- A text-based program which will show a message when you receive new mail.
- shows a picture of a mailbox on your screen. The flag goes up and it beeps when you get new mail.
- set nobeep = 1
- Turns off that annoying beep.
- text-based web browser
(most of these commands must be executed as root)
- view and play with your ethernet and tcp/ip settings
- su username
- change your current shell to one owned by username
- mount and unmount file systems
- brings up the Red Hat control panel
- shutdown time
- shuts down the system at time
- manually edit routing table (warning: careful)
- init #
- manually tell init to go to runlevel #
- check the hard disk for errors
- can greatly increase the performance of your hard disk (careful)
- utility to help configure Plug'N'Play devices