Basic Linux Commands 

Basic Linux Commands with Examples

Bear with me as this is a work in progress, what started as a basic list turned into a book. I have only added the basic examples here for now. 

Hardware Information

Show boot messages with dmesg:

dmesg

Show CPU information:

cat /proc/cpuinfo

Display free and used memory with:

free -h

List hardware configuration information:

lshw

See information about block devices:

lsblk

Show PCI devices in a tree-like diagram:

lspci -tv

Display USB devices in a tree-like diagram:

lsusb -tv

Show hardware information from the BIOS:

dmidecode

Display disk data information:

hdparm -i /dev/disk

Conduct a read-speed test on device/disk:

hdparm -tT /dev/[device]

Test for unreadable blocks on device/disk:

badblocks -s /dev/[device]

Run a disk check on an unmounted disk or partition:

fsck [disk-or-partition-location]

Searching

Search for a specific pattern in a file with grep:

grep [pattern] [file_name]

Recursively search for a pattern in a directory:

grep -r [pattern] [directory_name]

Find all files and directories related to a particular name:

locate [name]

List names that begin with a specified character [a] in a specified location [/folder/location] by using the find command:

find [/folder/location] -name [a]

See files larger than a specified size [+100M] in a folder:

find [/folder/location] -size [+100M]

File Commands

List files in the directory:

ls

List all files (shows hidden files):

ls -a

Show directory you are currently working in:

pwd

Create a new directory:

mkdir [directory]

Remove a file:

rm [file_name] 

Remove a directory recursively:

rm -r [directory_name]

Recursively remove a directory without requiring confirmation:

rm -rf [directory_name]

Copy the contents of one file to another file:

cp [file_name1] [file_name2]

Recursively copy the contents of one file to a second file:

cp -r [directory_name1] [directory_name2]

Rename [file_name1] to [file_name2] with the command:

mv [file_name1] [file_name2]

Create a symbolic link to a file:

ln -s /path/to/[file_name] [link_name]

Create a new file using touch:

touch [file_name]

Show the contents of a file:

more [file_name]

or use the cat command:

cat [file_name]

Append file contents to another file:

cat [file_name1] >> [file_name2]

Display the first 10 lines of a file with head command:

head [file_name]>

Show the last 10 lines of a file:

tail [file_name]

Encrypt a file:

gpg -c [file_name]

Decrypt a file:

gpg [file_name.gpg]

Show the number of words, lines, and bytes in a file using wc:

wc

List number of lines/words/characters in each file in a directory with the xargs command:

ls | xargs wc

Cut a section of a file and print the result to standard output:

cut -d[delimiter] [filename]

Cut a section of piped data and print the result to standard output:

[data] | cut -d[delimiter]

Print all lines matching a pattern in a file:

awk '[pattern] {print $0}' [filename]

Overwrite a file to prevent its recovery, then delete it:

shred -u [filename]

Compare two files and display differences:

diff [file1] [file2]

Read and execute the file content in the current shell:

source [filename]

Sort file contents and print the result in standard output:

sort [options] filename

Store the command output in a file and skip the terminal output:

[command] | tee [filename] >/dev/null

Directory Navigation

Move up one level in the directory tree structure:

cd ..

Change directory to $HOME:

cd

Change location to a specified directory:

cd /chosen/directory

File Compression

Archive an existing file:

tar cf [compressed_file.tar] [file_name]

Extract an archived file:

tar xf [compressed_file.tar]

Create a gzip compressed tar file by running:

tar czf [compressed_file.tar.gz]

Compress a file with the .gz extension:

gzip [file_name]

File Transfer

Copy a file to a server directory securely using the Linux scp command:

scp [file_name.txt] [server/tmp]

Synchronize the contents of a directory with a backup directory using the rsync command:

rsync -a [/your/directory] [/backup/] 

Users and Groups

See details about the active users:

id

Show last system logins:

last

Display who is currently logged into the system with the who command:

who

Show which users are logged in and their activity:

w

Add a new group by typing:

groupadd [group_name]

Add a new user:

adduser [user_name]

Add a user to a group:

usermod -aG [group_name] [user_name]

Temporarily elevate user privileges to superuser or root using the sudo command:

sudo [command_to_be_executed_as_superuser]

Delete a user:

userdel [user_name] 

Modify user information with:

usermod

Change directory group:

chgrp [group-name] [directory-name]

Package Installation

List all installed packages with yum:

yum list installed

Find a package by a related keyword:

yum search [keyword]

Show package information and summary:

yum info [package_name]

Install a package using the YUM package manager:

yum install [package_name.rpm]

Install a package using the DNF package manager:

dnf install [package_name.rpm]

Install a package using the APT package manager:

apt install [package_name]

Install an .rpm package from a local file:

rpm -i  [package_name.rpm]

Remove an .rpm package:

rpm -e [package_name.rpm]

Install software from source code:

tar zxvf [source_code.tar.gz]
cd [source_code]
./configure
make
make install

Process Related

See a snapshot of active processes:

ps

Show processes in a tree-like diagram:

pstree

Display a memory usage map of processes:

pmap

See all running processes:

top

Terminate a Linux process under a given ID:

kill [process_id]

Terminate a process under a specific name:

pkill [proc_name]

Terminate all processes labelled “proc”:

killall [proc_name]

List and resume stopped jobs in the background:

bg

Bring the most recently suspended job to the foreground:

fg

Bring a particular job to the foreground:

fg [job]

List files opened by running processes with lsof command:

lsof

Catch a system error signal in a shell script:

trap "[commands-to-execute-on-trapping]" [signal]

Pause terminal or a Bash script until a running process is completed:

wait

Run a Linux process in the background:

nohup [command] &

System Management and Information

Show system information:

uname -r 

See kernel release information:

uname -a  

Display how long the system has been running, including load average:

uptime 

See system hostname:

hostname

Show the IP address of the system:

hostname -i 

List system reboot history:

last reboot 

See current time and date:

date

Query and change the system clock with:

timedatectl 

Show current calendar (month and day):

cal

List logged in users:

w

See which user you are using:

whoami

Show information about a particular user:

finger [username]

View or limit system resource amounts:

ulimit [flags] [limit]

Schedule a system shutdown:

shutdown [hh:mm]

Shut Down the system immediately:

shutdown now

Add a new kernel module:

modprobe [module-name]

Disk Usage

You can use the df and du commands to check disk space in Linux.

See free and used space on mounted systems:

df -h

Show free inodes on mounted filesystems:

df -i

Display disk partitions, sizes, and types with the command:

fdisk -l

See disk usage for all files and directory:

du -ah

Show disk usage of the directory you are currently in:

du -sh

Display target mount point for all filesystem:

findmnt

Mount a device:

mount [device_path] [mount_point]

SSH Login

Connect to host as user:

ssh user@host

Securely connect to host via SSH default port 22:

ssh host

Connect to host using a particular port:

ssh -p [port] user@host

Connect to host via telnet default port 23:

telnet host

File Permission

Chown command in Linux changes file and directory ownership.

Assign read, write, and execute permission to everyone:

chmod 777 [file_name]

Give read, write, and execute permission to owner, and read and execute permission to group and others:

chmod 755 [file_name]

Assign full permission to owner, and read and write permission to group and others:

chmod 766 [file_name]

Change the ownership of a file:

chown [user] [file_name]

Change the owner and group ownership of a file:

chown [user]:[group] [file_name]

Network

List IP addresses and network interfaces:

ip addr show

Assign an IP address to interface eth0:

ip address add [IP_address]

Display IP addresses of all network interfaces with:

ifconfig

See active (listening) ports with the netstat command:

netstat -pnltu

Show tcp and udp ports and their programs:

netstat -nutlp

Display more information about a domain:

whois [domain]

Show DNS information about a domain using the dig command:

dig [domain] 

Do a reverse lookup on domain:

dig -x host

Do reverse lookup of an IP address:

dig -x [ip_address]

Perform an IP lookup for a domain:

host [domain]

Show the local IP address:

hostname -I

Download a file from a domain using the wget command:

wget [file_name]

Receive information about an internet domain:

nslookup [domain-name]

Save a remote file to your system using the filename that corresponds to the filename on the server:

curl -O [file-url]

Variables

Assign an integer value to a variable:

let "[variable]=[value]"

Export a Bash variable:

export [variable-name]

Declare a Bash variable:

declare [variable-name]= "[value]"

List the names of all the shell variables and functions:

set

Display the value of a variable:

echo $[variable-name]

Shell Command Management

Create an alias for a command:

alias [alias-name]='[command]'

Set a custom interval to run a user-defined command:

watch -n [interval-in-seconds] [command]

Postpone the execution of a command:

sleep [time-interval] && [command]

Create a job to be executed at a certain time (Ctrl+D to exit prompt after you type in the command):

at [hh:mm]

Display a built-in manual for a command:

man [command]

Print the history of the commands you used in the terminal:

history

Linux Keyboard Shortcuts

Kill process running in the terminal:

Ctrl + C

Stop current process:

Ctrl + Z

The process can be resumed in the foreground with fg or in the background with bg.

Cut one word before the cursor and add it to clipboard:

Ctrl + W

Cut part of the line before the cursor and add it to clipboard:

Ctrl + U

Cut part of the line after the cursor and add it to clipboard:

Ctrl + K

Paste from clipboard:

Ctrl + Y

Recall last command that matches the provided characters:

Ctrl + R

Run the previously recalled command:

Ctrl + O

Exit command history without running a command:

Ctrl + G

Run the last command again:

!!

Log out of current session:

exit