Unix/Linux Commands

File Commands
ls Displays directory listing

ls -al

Displays formatted listing with hidden files
cd Change to home directory

cd dir

Change directory to  dir
pwd Show current directory
mkdir dir Create a directory  dir
rm file Delete  file

rm -r dir

Delete directory  dir

rm -f file

Force remove  file

rm rf dir

Force remove directory  dir
Note: Use with extreme caution
cp file1 file2 Copy  file1 to  file2

cp -r dir1 dir2 

Copy  dir1 to  dir2
Creates  dir2 if it does not exist
mv file1 file2  Rename or move  file1 to  file2
ln -s file link Create symbolic link link to file
touch file Create or update  file
cat > file Places standard input into  file
more file Outputs the content of  file
head file Outputs the first 10 lines of  file
tail file Outputs the last 10 lines of  file

tail -f file

Outputs the contents of  file at is grows, starting with the last 10 lines


Process Management
ps Displays currently active processes
top Display all running processes
kill pid Kills process id  pid
killall proc* Kills all processes named  proc
Note: Use with extreme caution
bg Lists stopped or background jobs
Resume a stopped job in background 
fg Brings most recent job to foreground

fg jobname

Brings job  jobname to foreground


File Permissions
chmod octal file

Change the permissions of  file to  octal , which can be found separately for user, group, and world by adding: 

  • 4 - read (r)
  • 2 - write (w)
  • 1 - execute (x)

To form the  octal add the values of r, w, or x. The first digit stands for the user, the second stands for the group, and the last digit stands for world.

Ex: chmod 777 file - read, write, execute (rwx) for all

Ex: chmod 755 file - rwx for user, rw for group and world


ssh user@host Connect to  host as  user

ssh -p port user@host

Connect to  host on port  port as  user

ssh -copy -id user@host

Add you key to  host for  user to enable a keyed or passwordless login


grep pattern files Search for  pattern in  files
grep -r pattern dir Search recursively for  pattern in  dir
command | grep pattern Search for  pattern in the output of  command
locate file Find all instances of  file


System Info
date Shows the current date and time
cal Shows this month's calendar
uptime Shows current uptime
w Displays who is online
whoami Displays who you are logged in as
finger user Displays information about  user
uname -a Shows kernel information
cat /proc/cpuinfo cpu information
cat /proc/meminfo memory information 
man command Shows the manual for the  command
df Shows disk usage
du Shows directory space usage
free Shows memory and swap usage
whereis app Shows possible locations of  app
which app Shows which  app will be run by default


tar cf file.tar files Creates a tar named  file.tar containing  files
tar xf file.tar Extract the files from  file.tar
tar czf file.tar.gz files Creates a tar named  file.tar.gz containing  files with Gzip compression
tar xzf file.tar.gz Extract the files from  file.tar with Gzip
tar cjf file.tar.bz2 files Creates a tar named  file.tar.gz containing  files with Bzip2 compression
tar xjf file.tar.bz2 Extract the files from  file.tar with Bzip2
gzip file Compresses  file and renames it to  file.gz
gzip -d file.gz Decompresses  file.gz back to  file


ping host Pings  host and outputs results
whois domain Gets whois information for  domain
dig domain Gets DNS information for  domain

dig -x host

Reverse lookup  host
wget file Downloads  file

wget -c file

Continue a stopped download


Install from source:
make install
dpkg -i pkg.deb Install a package (Debian)
rpm -Uvh pkg.rpm Install a package (RPM)


Ctrl + C Halts the current command
Ctrl + Z Stops the current command
Ctrl + D Log out of current session; similar to exit
Ctrl + W Erases one word in the current line
Ctrl + U Erases the whole line
Ctrl + R Type to bring in recent command
!! Repeats the last command
exit Log out of current session