Linux Commands Cheat Sheet.

05 Jan 2020 in Others

Linux Commands are categorized into different sections according to its usage. if you want to Download Linux Command Cheat Sheet in pdf format.

What Is The Shell ?

Shell is the textual representation of the operating system. It takes keyboard commands and passes them to the operating system. All Linux distributions came with a Shell program called BASH. Which is the acronym for “Bourne Again Shell.”

What is Terminal Emulators?

To Interact with the Shell, We need a graphical user interface that can allow the user access to a textual representation of the operating system and its application. Most used terminal emulators on Linux are GNOME Terminal on GNOME and GTK-based environments, Konsole on KDE, and xfce4-terminal on Xfce as well as xterm.

Help Commands.

whatis : Search whatis database for complete words. used to find short descriptions of system commands.

$ whatis ls
$ whatis man
$ whatis cd
$ whatis env

which : Show the full path to shell commands.

$ which ls
$ which cd
$ which man

whereis : Locate binary, source and man pages for a command.

$ whereis cd 
$ whereis ls
$ whereis man
$ whereis pwd

apropos: Search through a database of short description to find help and man pages containing certain terms and commands.

$ apropos man
$ apropos ls
$ apropos cd
$ apropos pwd

man : Manual pages for commands.

$ man ls
$ man cd
$ man pwd
$ man man

Bash Variables.

env : List current environment variables.

$ env

echo : Output value of $Name variable.

$ echo "Hello World"
$ echo $USER
$ echo $HOSTNAME
$ echo $PATH
$ echo $HOME
$ echo $BASH_VERSION
# Create a Variable
$ MY_VAR='Hello, from Variable'
$ echo $MY_VAR

# Some other command
$ echo {A..Z}
$ echo {1..100}
$ echo {001..15}
$ echo "Hello World !" > README.txt

export: Set $Name to value in environment.

$ export MY_VAR="Hello, Centos 8"
#show see
$ env

$PATH : Executable search path.

$ echo $PATH

$HOME : Home Directory.

$ echo $HOME

$SHELL : Current Shell.

$ echo $SHELL

System Commands.

uname : Displays Linux system information.

$ uname
$ uname --help
# print all infomation
$ uname -a
# print kernel name
$ uname -s
# print the operating system.
$ uname -o

uptime : Displays how long the system has been running including load average.

$ uptime
$ uptime --help
$ uptime -s
$ uptime -p

hostname : Shows the system host-name.

$ hostname
$ hostname --help
$ hostname -a
$ hostname -A
$ hostname -i
$ hostname -I

last reboot : Shows system reboot history.

$ last reboot

date : Displays current system date and time.

$ date 
$ date -u
$ date --date "10 days ago"
$ date +%T

cal : Displays the current calendar month and day.

$ cal 
$ cal --help
$ cal 08 1991

w : Displays currently logged in users in the system.

$ w
$ w -i 

whoami : Displays who you are logged in as.

$ whoami

id : prints real user id, and various other details related to the account.

$ id
$ id root

Directory Operations

clear : clear your terminal.

$ clear

pwd: Print working directory.

$ pwd

ls : prints the names of the files and directories.

$ ls
$ ls --help
$ ls -a
$ ls -l
$ ls -l -a -h
$ ls -lah

cd : Change directory.

$ cd /etc
$ pwd
$ cd /bin
$ pwd

# This command is used to change directory to the home directory.
$ cd ~

$ cd -
$ cd ..
$ cd ../../

mkdir: Create a new directory.

$ mkdir MyFolder

$ mkdir -p Folder_1/Floder_A

rmdir: Delete an empty directory.

$ rmdir MyFolder

File Operations

cat: Concatenate,It reads data from the file and gives their content as output.

$ cat [file_name]
$ cat README.txt
$ cat /etc/passwd
$ cat /etc/hosts

# Custom end marker and Write Text in File.
$ cat  > longFile.txt << EOF 
> We are Writting in a Long file  
> We can write untile we use wordl of 'EOF'  
> EOF

less :Display the contents of a file one pages at a time.

$ less LongFile.txt
$ less /etc/passwd

head: Print the first 10 line of a file.

$ head /etc/passwd 
$ head longFile.txt 
$ head -3 longFile.txt

tail: print the last 10 line of a file

$ tail /etc/passwd 
$ tail longFile.txt 
$ tail -3 longFile.txt

touch : Create an empty file,

$ touch file1
$ touch file2 file3 file4

cp : copy directory and files.

$ cp file1 copy_file
$ cp file1 [directory_path]
$ cp -r [directory] [copy_directory_path]

mv: Move directory and files.

$ mv file1 New_file
$ mv file1 [directory_path]
$ mv -r [directory] [copy_directory_path]

rm : Remove directory and files.

$ rm MyFile.txt 
$ rm README.txt

$ rm -r MyFloder 
$ rm -r Directory

file: The file utility determines the file type.

$ file /dev/sda 
$ file File.png 
$ file /proc/cpuinfo

wc : count the number of words or characters in a file.

$ wc randomFile.txt
$ wc -l /etc/passwd
$ wc --help

stat : Display file system status.

$ stat file.txt
$ stat /etc/passwd
$ stat /var/log/audit/

cut : Removes sections from lines of input.

$ cut -d ":" -f 1 /etc/passwd

Search Files

grep : Search text files for lines containing a matching pattern.

$ grep [word] [fileName]
$ grep root /etc/passwd

locate : Find files by matching the whole path name.

$ locate [fileName]
$ locate shadow

find : Search fir files in a directory hierarchy.

# $ find [location/directory] -type [file type] -name [Name of the file
$ find / -type f -name passwd 
$ find /etc -type -f -name apache2

Commands to know

sudo : Execute a command as another user,usually with higher permissions.

$ sudo  ls /root 
$ sudo burpsuite

adduser : To add/create a new user.

$ sudo adduser cent

passwd : change password of a user.

$ sudo passwd cent

su : Run a shell as another user or Change the user

$ su cent

shutdown : Bring the system down in a safe way.

$ shutdown -h now

# Will shutdown in 5 minit
$ shutdown -h +5
# Will restart in 5 minit
$ shutdown -r +5

poweroff : Turn off the system.

$ poweroff

init 6 : This command gracefully reboots the system.

$ init 6
	or
$ reboot

Partitions and Disk Management.

df : Report file system disk space usage.

$ df -h

fdisk : lists all the partitions of all the drives

$ fdisk -l

lsblk: It is similar to the output from fdisk-l, but it will also display devices with multiple partitions in a kind of tree

$ lsblk

lsof: Established connections

$ lsof -i

Process Management

ps : Report on current processes

$ ps 
$ ps x 
$ ps aux

top : Show real time processes.

$ top

kill : Terminate a process by PID.

$ kill -9 [PID]

pkill : Lookup of signal processes based on same and other attributes.

$ pkill [service_name]

pgrep : Grep for process information.

$ pgrep [service_name]
$ pgrep sshd
$ pgrep firewalld

jobs : Display all jobs.

$ jobs

Networking

ifconfig : Configure network interface.

# intall net-tools
$ yum install net-tools

$ ifconfig 
$ ifconfig eth0 down 
$ ifconfig eth0 192.168.0.120 netmask 255.255.255.0 broadcast 192.168.0.255 
$ route add defult gw 192.168.0.1 
$ ifconfig eth0 hw ether 00:11:22:33:44:55 
$ ifconfig eth0 up

route : Show/Manipulate the IP routing table.

$ route
# To display routing table in full numeric form.
$ route -n

# To add a default gateway.
$ sudo route add default gw 169.254.0.0
#To reject routing to a particular host or network.
$ sudo route add -host 192.168.1.51 reject
# To delete the default gateway.
$ route del default

ip : Show/M­ani­pulate routing, devices, policy and tunnels; replaces ifconfig, arp, and route.

$ ip a 
	or
$ ip addr

# Only show ipv4
$ ip -4 addr

# Only show ipv6
$ ip -6 addr

# Only show running interfaces.
$ ip link ls up

# Adding an IPv4 address
$ ip addr add 192.168.0.120/24 dev esp0s3

# Delete IP address to interface
$ ip addr del 192.168.0.120/24 dev esp0s3

ifup : Bring network interface up.

$ ifup enp0s3

ifdown : Bring network interface down.

$ ifdown enp0s3

ping : Send ICMP ECHO_R­EQUEST to network hosts

$ ping google.com
$ ping -c 3 google.com