#Lists all files and directories in the present working directory
$ ls
#Lists files in sub-directories as well
$ ls -R
#Lists hidden files as well
$ ls -a
#Lists files and directories with detailed information like permissions,size, owner, etc.
$ ls -al
#Navigate to HOME directory
$ cd
$ cd ~
#Move one level up
$ cd ..
#To change to a particular directory
$ cd
#Move to the root directory
$ cd /
#Creates a new file
$ cat > filename
#Displays the file content
$ cat filename
#Joins two files (file1, file2) and stores the output in a new file (file3)
$ cat file1 file2 > file3
#Moves the files to the new location
$ mv file "new file path"
#Renames the file to a new filename
$ mv filename new_file_name
#Allows regular users to run programs with the security privileges of the superuser or root
$ sudo
#Deletes a file
$ rm filename
#Gives help information on a command
$ man
#Gives a list of all past commands typed in the current terminal session
$ history
#Clears the terminal
$ clear
#Creates a new directory in the present working directory or a at the specified path
$ mkdir directoryname
#Deletes a directory
$ rmdir
#Renames a directory
$ mv
#Divides the file into x columns
$ pr -x
#Assigns a header to the file
$ pr -h
#Denotes the file with Line Numbers
$ pr -n
#Prints “c” copies of the File
$ lp -nc , lpr c
#Specifies name of the printer
$ lp-d lp-P
#Command used to install and update packages
$ apt-get
#Command to send email
$ mail -s 'subject' -c 'cc - address' -b ' bcc - address' 'to - address'
#Command to send email with attachment
$ mail -s "Subject" to - address < Filename
File Permission Commands
#To show file type and access permission
$ ls -l
r - Read permission
w - Write Permission
x - execute permission
#Giving permission to any file
$chmod 755 file_name
#Changing ownership of user and group for any file
$ chown user:group filename
Environment Variables Command
#To display value of a variable
$ echo $VARIABLE
#Displays all environment variables
$ env
#Create a new variable
$ VARIABLE_NAME= variable_value
#Remove a variable
$ Unset
#To set value of an environment variable
$ export Variable=value
User management Commands of linux
#To add a new user
$ sudo adduser username
#To change the password of a user
$ sudo passwd -l 'username'
#To remove a newly created user
$ sudo userdel -r 'username'
#To add a user to a group
$ sudo usermod -a -G GROUPNAME USERNAME
#To remove a user from a group
$ sudo deluser USER GROUPNAME
#Shows information of all the users logged in
$ finger
#Give information of a particular user
$ finger username
Networking Command
#Login into a remote Linux machine using SSH
$SSH username@ip - address or hostname
#To ping and Analyzing network and host connections
$ Ping hostname="" or =""
#Display files in the current directory of a remote computer
$ dir
#Change directory to "dirname" on a remote computer
$ cd "dirname"
#Upload 'file' from local to remote computer
$ put file
# Download 'file' from remote to local computer
$ get file
#Logout
$ quit
Process Command
bg - To send a process to the background
fg - To run a stopped process in the foreground
top - Details on all Active Processes
ps - Give the status of processes running for a user
# Gives the status of a particular process
$ ps PID
#Give the process ID (PID) of a process
$ pidof
#Kills a process
$ kill PID
#Starts a process with a given priority
$ nice
#Changes priority of an already running process
$ renice
#Gives free hard disk space on your system
$ df
#Gives free RAM on your system
$ free
VI Editing Commands
i - Insert at cursor (goes into insert mode)
a - Write after cursor (goes into insert mode)
A - Write at the end of line (goes into insert mode)
ESC - Terminate insert mode
u - Undo last change
U - Undo all changes to the entire line
o - Open a new line (goes into insert mode)
dd - Delete line
3dd - Delete 3 lines
D - Delete contents of line after the cursor
C - Delete contents of a line after the cursor and insert new text. Press ESC key to end insertion
dw - Delete word
4dw - Delete 4 words
cw - Change word
x - Delete character at the cursor
r - Replace character
R - Overwrite characters from cursor onward
s - Substitute one character under cursor continue to insert
S - Substitute entire line and begin to insert at the beginning of the line
~ - Change case of individual character
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