loading...
Cover image for Useful Linux commands

Useful Linux commands

laxmanvijay profile image Vijay Updated on ・3 min read

This is a list of useful Linux commands. Most of them are basic and they can be used as a reference for developers.

files and directories

  • ls => list all files
  • ls -a => list all files along with hidden ones
  • ls -R => list all files and folders recursively
  • ls -l => list in long format (shows more info)

  • rm {filename} => deletes a file

  • mv {filename} {directory path} => moves a file

  • mv {srcFileName} {destFileName} => renames a file

  • cp {srcFileName} {destFileName} => copies file

  • cp -R {srcDir} {destDir} => copies directory

  • cat {filename} => read contents of a file

  • cat > {filename} => writes to file

  • touch {filename} => creates a file, touch is basically used to change file timestamps. Refer here

  • mkdir {directory name} => makes a directory

  • rmdir {directory name} => removes a directory

  • rm -rf {directory name} => removes a directory recursively along with the files

  • mv {dirname1} {path or dirname} => moves or renames directory

  • history => list all commands used in the current session

  • clear => clears the terminal screen

  • pwd => displays the path of the current working directory.

file permissions

File permissions will be provided to users, groups and others (in the same order). They can be provided as numbers or letters.

r - read, w - write, x - execute
u - user, g - group, o - other, a - all

0 - no permission
1 - execute
2 - write
3 - execute + write
4 - read
5 - read + execute
6 - read + write
7 - all

  • chmod {number} {filename} => gives permissions to user,group and others.

Eg: chmod 777 ex.txt => gives all permissions to all users, groups and others.

'+' - gives permission
'-' - removes permission
'=' - assigns the given permission

Eg: chmod u=rw ex.txt => gives read/write to user
Eg: chmod a= ex.txt => removes all permission to all users.

  • chgrp {group name} {filename} => changes group for a file
  • chown {user} {filename} => changes owner of a file

input/ output directions

  • '>' write (stdout)
    Eg: ls -al > {filename} => writes the output of "ls -al" to the file. If the file already exists, it is overwritten.

  • '>>' append (stdout)
    Eg: echo "hi" >> {filename} => appends to the file

  • '<' input

File descriptors : 0 - stdin, 1 - stdout, 2 - stderr

Error redirection:

This is used to redirect errors to a log file, rather than cluttering the terminal.

Eg: cat ex.txt 2> error.log => tries to read the file, if there is any error, it is written to error.log

Here, '2' is the file descriptor for stderr.

working with pipes

pg, more and less

Show large text in the terminal as scrollable chunks by piping it to the pg, more or less commands.

Eg: cat large_file.txt | less => gives a scrollable viewer.

grep

Search for a string in the output by piping to grep.

Eg: ls | grep key => shows files that have a string "key".

Flags:

  • -i => case insensitive
  • -c => displays only count
  • -n => displays matching line and number
  • -v => displays output that didn't match

Eg: ls | grep -cv key => displays count to output that didn't match

  • grep can also accept regular expressions. Refer here
sort

Sort the contents

Eg: ls | sort => displays in alphabetic order

Flags:

  • -r => reverse
  • -n => numerical
  • -f => case insensitive

Eg: ls -l | sort -nk2 => displays content numerically sorted on the second column. (number of hard links in this case)

variables

  • VARIABLE=value => Set variables in the session.
  • $VARIABLE => gets the value of a variable.
  • unset VARIABLE => unsets the variable.

networking commands

  • ping {ip} => checks the connection
  • dig {hostname} => performs a dns lookup
  • ssh -i {key} {username@ip} => connects to a remote computer securely. key is the private key file.
  • scp -i {key.pem} {source} {dest} => copies a file. remote location should be host:file.
  • lsof -i {protocol:port} => list all processes listening on a port.

Eg: lsof -i tcp:3000 lists all processes listening to port 3000

process management

  • top => lists all running process
  • kill {pid} => kills a process with the given process id

mount device

  • lsblk => list all block devices
  • mount {device id} {directory} => mount a device to a directory

Eg: mount /dev/sda4 /ex/mnt

Flags:

  • -a => mounts all devices in /etc/fstab
  • -l => lists all mounted devices
  • -t => type of filesystem (eg: ext4)

  • umount {device id} => unmounts a device

manual

  • man {command name} => shows usage of a command

cover image by Sai Kiran Anagani

Discussion

pic
Editor guide
Collapse
jonrandy profile image
Jon Randy

touch {filename} => creates a file

Not really - touch is a command used to update the access date and/or modification date of a computer file or folder. The fact that it creates the file if it doesn't exist is purely a side effect. There are many ways to create a new file

Collapse
laxmanvijay profile image
Vijay Author

Really? I thought creating a file was its purpose, thanks for your valuable feedback Jon.
Will update it :)

Collapse
fultonbrowne profile image
Fulton Browne

Note: this should also apply to mac and bsd

Collapse
laxmanvijay profile image
Vijay Author

Yeah most of them should

Collapse
henryonsoftware profile image
Henry Bui

Is cat large_file.txt | less same with less large_file.txt?

Collapse
laxmanvijay profile image
Vijay Author

Yeah it is

Collapse
kadawatha profile image
Luke Fe

thanx