January 1, 2021 12 min to read

Linux Cheat Sheet 101

Linux,where a true freedom is !

Linux is a kernel, on which lots of Operating systems like andriod, Debian, Arch are runnig.

The Linux “core” (called a kernel) was born in 1991 in Finland, and it has come a really long way from its humble beginnings. It went on to be the kernel of the GNU Operating System, creating the duo GNU/Linux.

What makes Linux special is,Distro !

Eg of linux distro are:-Ubuntu, Debian, kali, Parrot,openSUSE,Fedora

System

Commands	Descriptions
uname	Display the Linux information
uname-r	Display the kernel information
utime	Display how long the system has been running including the load average
hostname	shows the system hostname
hostname-i	display the IP address of the system
last reboot	shows the system reboot history
date	Display the current system date & time
timedatectl	Query and change the system clock
cal	Display the current calendar month and day
w	Display currently logged in users in the system
whoami	Display who you are logged in
finger username	Display the information about the user

Hardware

Commands	Descriptions
dmseg	Display bootup messages
cat/proc/cpuinfo	Displays more information about CPU eg. model, model name,cores,vendor id
cat/proc/meminfo	Display the more information about hardware memory e.g total and free memory
lshw	Display information about system's hardware configuration
lsblk	Display the block device related information
free -m	Display free and used memory in the system (-m flag indicates memory in MB )
lspci -tv	Display PCI devices in a tree-like diagram
lsusb -tv	Display USB devices in a tree-like diagram
dmidecode	Display hardware information from the BIOS
hdparm -i /dev/xda	Display information about the disk data
hdparm -tT/dev/xda	Conducts a read speed test on device xda
badblocks -s/dev/xda	Test for unreadable blocks on disk

User

Commands	Descriptions
id	Displays the details of the active user e.g uid,gid, and groups
Last	Shows the last logins in the System
who	Shows who is logged into the System
groupadd "admin"	Adds the group "admin"
adduser"Shubham"	Adds user Shubham
userdel"Sam"	Deletes user Sam
usermod	used for changing/modifying user information

File commands

Commands	Descriptions
ls -al	List files both regular and hidden along with their permission
pwd	Display the path of the current directory
mkdir <directory_name>	Creates a directory
rm <file_name>	Delete file
rm -r <directory_name>	Delete directory recursively
rm -f <file_name>	Forcefully remove file
rm -rf <directory_name>	Forcefully remove the directory
cp file1 file2	copy file1 to file2
cp -r dir1 dir2	copy dir1 to dir2 ,creates dir2 if it doesn't exits
mv file1 file2	Rename source to Destination/move source to directory
ln -s /path/to/file-name link name	Creates symbolic link to the file-name
touch file	Creates/ Update file
cat > file	Place standard input into filel
more file	Output contents of file
head file	Output first 10 lines of file
tail file	Output last 10 lines of file
tail -f file	Output contents of file as it grows starting with the last 10 lines
gpg -c file	Encrypt file
gpg file.gpg	Decrypt file
wc	print the number of bytes,words,and lines in files
xargs	Execute command lines from standard input

File Permission Related

Commands	Descriptions
chmod octal < file_name>	Change the permission of the file to local
Eg: -
chmod 777 /data/test.c	Set rwx permission for owner,group,world
chmod 755/data/test.c	Set rws permission for the owner, rx for group and world
chmod 766/data/test.c	Sets rwx for the owner,rw for the group and everyone

chown owner user-file	Changes the ownership of the file
chown owner-user:owner-group < file_name>	change owner and group owner of the file
chown owner-user:owner-group -directory	change owner and group owner of the directory

Process Related

Commands	Descriptions
ps	Display the current active processes
ps aux \| grep 'telnet'	Searches for the id of the process 'telnet'
pmap	Display memory map of the process
top	Displays all running processes
kill pid	Terminates process with a given pid
killall proc	kills/Terminates all processes named proc
pkill process-name	Sends a signal to a process with its a name
bg	Resume suspended jobs in the background
fg	Brings suspended jobs to the foreground
fg n	Brings job n to the foreground
lsof	Lists files that are open by processes
renic 19 PID	Makes a process run with very low priority
pregp firefox	find Firefox process ID
pstree	Visualizing processess in tree model

Network Related

Commands	Descriptions
ip addr show	Displays IP addresses and all the network interfaces
ip address add 192.1.20 dev eth0	Set Ip address
ifconfig	Displays Ip addresses of all network interfaces
ping host	ping command sends an ICMP echo request to establish a connection to server/Pc
whois domain	Retrievs more information about a domain name
dig domain	Retrievs DNS infromation about the domain
dig-x host	Performs reverse lookup on a domain
host google.com	perfroms an Ip lookup for the domain name
hostname-i	Display all local Ip address
wget <file_name>	Downloads a file from an online source
netstat-pnltu	Displays all active listening port

Compression/Archives

Commands	Descriptions
tar -cf home.tar home	creates archive file called 'home.tar' from file 'home'
tar -Xf files.tar	Extracct archive file 'files.tar'
tar -ZCVf home.tar.gz Source-folder	Creates gzipped tar archive file from source folder
gzip file	Compression a file with .gz extension

Install packages

Commands	Descriptions
rpm -i pkg_name.rpm	Install an rpm package
rpm -e pkg_name	Removes an rpm package
dnf install pkg_name	Install package using dnf utility

Install Source (Compilation)

./ configure
make
make install

Search

Commands	Descriptions
grep 'pattern' files	Search for a given pattern in files
grep -r pattern dir	Search recursively for a pattern in a given directory
locate file	Find all instances of the file
find /home/ -name "index"	Find file names that begin with 'index in /home folder
find /home/ -size +10000k	Find files greater than 10000k in the home folder

Login

Commands	Descriptions
ssh user@host	Securely connect to host as user
ssh -p <port_number> user@host	Securely connect to host using a specified port
ssh host	Securely connect to the system via SSH default port 22
telnet host	Connect to host via telnet default port 23

File Transfer

Commands	Descriptions
scp file1.txt server2/tmp	Securely copy file1.txt to server2 in /tmp diretory
rsync -a/home/apps /backup	Synchronize contents in /home/apps directory with directory

Disk usages

Commands	Descriptions
df -h	Displays free space on mounted systems
df -i	Displays free inodes on filesystems
fdisk -l	Shows disk partitions, sizes,and types
du -sh	Displays disk usage in the current directory in a human readable format
findmnt	Displays target mount points for all filesystems
mount device-path mount-point	Mount a device