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Unix/Linux Command Reference

File Commands

  • ls – directory listing
  • ls -al – formatted listing with hidden files
  • cd dir – change directory to dir
  • cd – change to home
  • 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 *
  • cp file1 file2 – copy file1 to file2
  • cp -r dir1 dir2 – copy dir1 to dir2; create dir2 if it doesn’t exist
  • mv file1 file2 – rename or move file1 to file2 if file2 is an existing directory, moves file1 into directory 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 – output the contents of file
  • head file – output the first 10 lines of file
  • tail file – output the last 10 lines of file
  • tail -f file – output the contents of file as it grows, starting with the last 10 lines

Process Management

  • ps – display your currently active processes
  • top – display all running processes
  • kill pid – kill process id pid
  • killall proc – kill all processes named proc *
  • bg – lists stopped or background jobs; resume a stopped job in the background
  • fg – brings the most recent job to foreground
  • fg n – brings job n to the 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)
Examples:
chmod 777 – read, write, execute for all
chmod 755 – rwx for owner, rx for group and world
For more options, see man chmod.

SSH

  • 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 your key to host for user to enable a keyed or passwordless login

Searching

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

Compression

  • tar cf file.tar files – create a tar named file.tar containing files
  • tar xf file.tar – extract the files from file.tar
  • tar czf file.tar.gz files – create a tar with Gzip compression
  • tar xzf file.tar.gz – extract a tar using Gzip
  • tar cjf file.tar.bz2 – create a tar with Bzip2 compression
  • tar xjf file.tar.bz2 – extract a tar using Bzip2
  • gzip file – compresses file and renames it to file.gz
  • gzip -d file.gz – decompresses file.gz back to file

Network

  • ping host – ping host and output results
  • whois domain – get whois information for domain
  • dig domain – get DNS information for domain
  • dig -x host – reverse lookup host
  • wget file – download file
  • wget -c file – continue a stopped download

Installation

Install from source:
./configure
make
make install

dpkg -i pkg.deb – install a package (Debian)

rpm -Uvh pkg.rpm – install a package (RPM)

Shortcuts

  • Ctrl+C – halts the current command
  • Ctrl+Z – stops the current command, resume with fg in the foreground or bg in the background
  • 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 up a recent command
  • !! – repeats the last command
  • exit – log out of current session

* use with extreme caution.

About Amit Raj

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