Linux Cheat Sheet

We are re-doing this page…

Arrow Up: scrolls and edits the command history, press enter to activate.
Shift+pgup: scrolls terminal output up
Shift+pgdown: scrolls terminal output down
CTRL-ALT+DEL reboots the system
Shutdown -h now turns the system off
CTRL C kills the current process
CTRL S Stops the tranfer to the terminal
CTRL Q Resumes the transfer to the terminal
CTRL Z Puts the current process in the background.
Middle Mouse Button Pastes the text that is currently somewhere else.

PWD Shows the current directory
HOSTNAME Shows the host name of the system you are on
WHOAMI Displays your login name
DATE Displays what your machine thinks the date is
WHO Shows who is logged into the machine
RWHO-A Shows all users logged into the server network
FINGER <user name> Shows info on chosen user
LAST Show the last users logged into the machine
UPTIME Shows the systems uptime
PS Shows the current user processes
PS -A Shows all process on the system
UNAME -A Displays all info on your host.
FREE Shows the free memory in KB
DF -H Shows the disk space details
cat/proc/cpuinfo Shows the CPU information
cat/proc/filesystems Shows the file system information in use
cat/etc/printcap Shows if any printers are hooked up
Lsmod Shows the kernel modules loaded
setimore Shows the current user environment
echo $PATH Shows the content on the environment variable path
dmesg Prints the boot messages

Basic Actions

[command] –help – gives syntax for using that command
man [command] – brings up the manual page for the command, if it exists
man [command] > file.txt – dumps the manual page(s) for the command into ‘file.txt’
whatis [command] – gives a short description of the command.
help – gives a list of commands (GNU Bash).
help [command] – gives extra information on the commands listed above. Viewing/editing/creating a text file

vi [filename] – opens VI text editor, if the file doesn’t exist, it’ll be created on saving.
(when inside vi)
– using ‘i’ inserts
– pressing ‘escape’ and then ‘:’ goes back to command mode.
– ‘/searchstring’ searchs for ’searchstring’ using regular expressions.
– ‘:’ followed by ‘w’ writes
– ‘:’ followed by ‘qw’ writes then quits
– ‘:’ followed by ‘q’ quits.
– ‘:’ followed by ‘q!’ quits regardless of whether changes are made.
– ‘:’ followed by ‘z’ undos.
pico [filename] – launches the PICO editor for the filename.
more [filename] – shows one screen’s worth of the file at a time.
less [filename] – similar to more
head [filename] – Shows the first 10 lines of file, or use -n
tail [filename] – Shows the last 10 lines of file, or use -n
cat [filename] | more – works like more, cat concats 2 strings General/System commands

su [user] – changes the login to ‘user’, or to the root if no ‘user’ is given.
date – shows the system date
whoami – tells you who you’re logged in as
uptime – how long the computer has been running, plus other details
w – shows who’s logged on, what they’re doing.
df – how much disk space is left.
du – disk usage by your login, it can also total up directories.
uname -mrs – userful info about the system
uname -a – all details about the system Desktop / X server + client

Switchdesk {manager – gnome, Enlightenment, etc} – Switches your desktop What’s running

ps – what’s running.
ps ax – shows all processes
top – sort of interactive version of ps.
kill [pid] – terminates the named process, which can be name or number or other options.
killall -HUP [command name] – kill a process, running the command specified, by name.
killall -9 [command] – similar to the above
xkill – kills a frozen application in X (gnome,kde etc. desktops), you just click on the frozen app.

File system

ls -la – list all files/directories
dir – simple form of ls
cd [dir] – change directory
cd ~ – go back to the home directory
cdup – similar to using “cd ..”, go up one directory.
pwd – print which directory you’re in.
./[filename] – run the file if it’s executable and in the current directory
rm [filename] – delete a file
rm -R [directory] – delete a directory
mv [oldfilename] [newfilename] – renames the file (or directory)
cp [filename-source] [filename-destination] – copy the file from one place to another
cp -R [dir-source] [dir-destination] – copy a directory an all its subdirectories
mkdir [name] – makes a directory.
cat [sourcefile] >> [destinationfile] – appends sourcefile to the end of destinationfile
df – how much disk space is available, more options available.

– zipping/taring
tar -cvzf mytar.tar.gz sourcefilesordir – creates a new tar file, verbose options on, runs it through gnuzip,f is the filename
tar -xvf mytar.tar.gz destination – extracts a tar file (this example is compressed with gzip), verbosely, f is the filename
gzip fileordir – compresses a file with gzip.
gunzip file.gz – decompresses a file with gzip.
NB gzip only compresses files, it doesn’t collect them into a single file like a tarball does.


locate [filename] – searches the system using an indexed database of files. use updatedb to update the file database
locate [filename] | sort – sorts the files alphabetically
whereis [filename] – locates an application, such as ‘whereis bash’
find [filename] – searches the filesystem as with locate, but without a database so its slower.
find /directory -atime +30 -print – searches for files not used in the past 30 days. Setting up links

ln -s target linkname – creates a symbolic link, like a shortcut to the target directory or filename.
ln target linkname – creates the default hard link. Deleting this will delete the targetted file or directory. Network commands

dig domainname – retrieves information about a domain, such as name servers, mx records
whois domainname – whois info on a domain
finger user – gives info about a user, their group status, but can also be used over a network
netstat -ape – lots of info about whos connected to your machine, what processes are doing what with sockets Piping

Piping to another command is straight forward enough:

locate filename | grep /usr/local > searchresults.txt – searches for filename, runs the results through grep to filter everything without /usr/local in it, and then outputs the results to searchresults.txt

| runs one application via another, and can be used multiple times e.g. cat /usr/group | more | grep root | sort
> creates a new file if once doesn’t already exist, overwrites the contents of the file if it does exist
>> appends to the end of the file, and creates the file if one doesn’t exist.
< sends everything after this to the application, e.g. ./mysql -u bob -p databasename < mysqldump.sql Permissions and directory listing format

groups [username] – shows what groups the user belongs to
id [username] – shows extended information about a user.
finger [user] – give details about a user.
passwd [user] – changes the password for a user, or without the user argument, changes your password.
chsh [user] – changes the shell for a user.
userdel [user] – removes a user from the system, use -r to remove their home directory too.
newgrp [group id] – log into a new group.
useradd -d /home/groupname -g groupname – add a new user with the d being the homedirectory, g the default group they belong to.
groupadd [groupname] – adds a group

Take a look at the users/groups on the system with:

cat /etc/passwd | sort
cat /etc/group | sort

The stuff below is in the man pages also.
The format of passwd is:
password denoted by x (use cat /etc/shadow | sort to list the shadow password file)
uid – user identifier number
gid – group identifier number
misc information such as real name
users home directory
shell for the user

The format of group is:
name of group
password denoted by x (use cat /etc/gshadow | sort to list the shadow group file)
gid – group identifier number
list of additional users assigned to the group

Break down of permissions in a directory listing:
-rw-r–r– 1 mainuser devel 9054 Dec 28 12:42 index.html

The first character indicates whether it is a directory or file (d for directory).
After that, the next 3 (rw-) are owner permissions.
The following 3 (r–) are group permissions
The following 3(r–) are permissions for other users.

After that reads the number of files inside the directory if it’s a directory (which it isn’t so it’s 1) this can also be links to the file, the owner of the file, the group the file belongs to, size in bytes, date and time and then the filename.

Chmod and Chown
Owner,group and other permissions can be r,w,x. Translated into their decimal equivalents (actually octal but…)
owner – read=400,write=200,execute=100
group – read=40,write=20,execute=10
other – read=4,write=2,execute=1

So add them up and you’ve got your user permissions for chmoding:
chmod [mode] fileordirectory – changes the permissions on a file or directory. use -r to recursively change a whole directory and its sub directories.

e.g chmod 755 myfile.txt – changes the permissions on the file to 755 which is : owner read,write,execute; group read,execute; other read,execute.

chown [user:group] fileordirectory – changes the user and group ownership of a file or directory. Use -R to recursively change a whole directory and its sub directories.
chgrp [group] fileordirectory – changes the groupownership of a file or directory. Use -R to recursively change a whole directory and its sub directories.


mysqldump – Dumps a table,database or all databases to a SQL file. Use the –opt argument for best results e.g.
mysqldump -u username -p –opt database > file.sql
mysql – The mySQL query manager. To import/export a database to or from a SQL try:
mysql -u username -p database < file_to_go_in.sql
mysql -u username -p database > file_to_go_to.sql

Basic Commands

man {command}Type man ls to read the manual for the ls command.
man {command} > {filename}Redirect help to a file to download.
whatis {command}Give short description of command. (Not on RAIN?)
apropos {keyword}Search for all Unix commands that match keyword, eg apropos file. (Not on RAIN?)

List a directory
ls {path}It’s ok to combine attributes, eg ls -laF gets a long listing of all files with types.
ls {path_1} {path_2}List both {path_1} and {path_2}.
ls -l {path}Long listing, with date, size and permisions.
ls -a {path}Show all files, including important .dot files that don’t otherwise show.
ls -F {path}Show type of each file. “/” = directory, “*” = executable.
ls -R {path}Recursive listing, with all subdirs.
ls {path} > {filename}Redirect directory to a file.
ls {path} | moreShow listing one screen at a time.
dir {path}Useful alias for DOS people, or use with ncftp.

Change to directory
cd {dirname}There must be a space between.
cd ~Go back to home directory, useful if you’re lost.
cd ..Go back one directory.
cdupUseful alias, like “cd ..”, or use with ncftp.

Make a new directory
mkdir {dirname}

Remove a directory
rmdir {dirname}Only works if {dirname} is empty.
rm -r {dirname}Remove all files and subdirs. Careful!

Print working directory
pwdShow where you are as full path. Useful if you’re lost or exploring.

Copy a file or directory
cp {file1} {file2}
cp -r {dir1} {dir2}Recursive, copy directory and all subdirs.
cat {newfile} >> {oldfile}Append newfile to end of oldfile.

Move (or rename) a file
mv {oldfile} {newfile}Moving a file and renaming it are the same thing.
mv {oldname} {newname}

Delete a file
rm {filespec}? and * wildcards work like DOS should. “?” is any character; “*” is any string of characters.
ls {filespec}
rm {filespec}
Good strategy: first list a group to make sure it’s what’s you think…
…then delete it all at once.

Download with zmodem(Use sx with xmodem.)
sz [-a|b] {filename}-a = ascii, -b = binary. Use binary for everything. (It’s the default?)
sz *.zipHandy after downloading with FTP. Go talk to your spouse while it does it’s stuff.

Upload with zmodem(Use rx with xmodem.)
rz [-a|b] (filename}Give rz command in Unix, THEN start upload at home. Works fine with multiple files.

View a text file
more {filename}View file one screen at a time.
less {filename}Like more, with extra features.
cat {filename}View file, but it scrolls.
cat {filename} | moreView file one screen at a time.
page {filename}Very handy with ncftp.
pico {filename}Use text editor and don’t save.

Edit a text file.
pico {filename}The same editor PINE uses, so you already know it. vi and emacs are also available.

Create a text file.
cat > {filename}Enter your text (multiple lines with enter are ok) and press control-d to save.
pico {filename}Create some text and save it.

Compare two files
diff {file1} {file2}Show the differences.
sdiff {file1} {file2}Show files side by side.

Other text commands
grep ‘{pattern}’ {file}Find regular expression in file.
sort {file1} > {file2}Sort file1 and save as file2.
sort -o {file} {file}Replace file with sorted version.
spell {file}Display misspelled words.
wc {file}Count words in file.

Find files on system
find {filespec}Works with wildcards. Handy for snooping.
find {filespec} > {filename}Redirect find list to file. Can be big!

Make an Alias
alias {name} ‘{command}’Put the command in ’single quotes’. More useful in your .cshrc file.

Wildcards and Shortcuts
*Match any string of characters, eg page* gets page1, page10, and page.txt.
?Match any single character, eg page? gets page1 and page2, but not page10.
[…]Match any characters in a range, eg page[1-3] gets page1, page2, and page3.
~Short for your home directory, eg cd ~ will take you home, and rm -r ~ will destroy it.
.The current directory.
..One directory up the tree, eg ls ...

Pipes and Redirection(You pipe a command to another command, and redirect it to a file.)
{command} > {file}Redirect output to a file, eg ls > list.txt writes directory to file.
{command} >> {file}Append output to an existing file, eg cat update >> archive adds update to end of archive.
{command} < {file}Get input from a file, eg sort < file.txt
{command} < {file1} > {file2}Get input from file1, and write to file2, eg sort < old.txt > new.txt sorts old.txt and saves as new.txt.
{command} | {command}Pipe one command to another, eg ls | more gets directory and sends it to more to show it one page at a time.