linux-tips (Basic command on Linux)

Document created by Jonas52

• Networking
• Security
• Packages
• Files
• System
• Hardware Information
• Users
• File Permission
• Keyboard Shortcuts
• Environment Variable Commands

Networking

---

Get the IP address of all interfaces

networkctl status

Display all IP addresses of the host

hostname -I

show IP addresses and network interfaces

ip addr show

assign an IP address to interface eth0

ip address add
[IP_address]

show IP addresses of all network interfaces

ifconfig

show active (listening) ports

netstat -pnltu 

show tcp and udp ports and their programs

netstat -nutlp

show more information about a domain

whois [domain]

show DNS information about a domain

dig [domain]

reverse lookup on domain

dig -x host

dig -x [ip_address]

reverse lookup of an IP address

do an IP lookup for a domain

host [domain]

download a file from a domain

wget [file_name]

Enable/disable interface

ip link set <interface> up
ip link set <interface> down

Show routes

ip route

Which route will be used to reach a host

ip route get <IP>

List open ports and associated processes

sudo ss -tulpn

Manage firewall rules

Enable firewall: sudo ufw enable
List rules: sudo ufw status
Allow port: sudo ufw allow <port>
Deny port: sudo ufw deny <port>
Disable firewall: sudo ufw disable

Connect remotely through SSH

ssh <user>@<host IP>

Security

---

Show which users are logged in

w

Get user password expiration date

chage -l <user>

Set user password expiration date

chage <user>

Lock a user account

sudo passwd -l <user>

Unlock a user password

sudo passwd -u <user>

Automatically detect and ban abusive IP addresses

sudo apt install fail2ban

Show banned IP addresses

sudo fail2ban-client status
sudo fail2ban-client status <jail>

Packages

---

Search for packages

apt search <string>
snap find <string>

List available package versions

apt-cache policy <package>

List available updates

apt list --upgradable

Apply all available updates

sudo apt update && sudo apt upgrade

Install from the Ubuntu Archive:

sudo apt install <package>

Install from the Snap Store:

sudo snap install <package>

Remove the package

sudo apt remove <package>

Remove the package

sudo snap remove <package>

Remove the package and all its configuration files

sudo apt purge <package>

Reinstall broken package

sudo apt install -f --reinstall
<package>

Which files does this package provide?

dpkg-query -L <package>

Which package provides this file?

dpkg-query -S <path>

Files

---

list files in directory

ls

list all files, including hidden

ls -al

Open a file (or create new one) in nano text editor

nano file

Open a file (or create new one) in vim text editor

vim file

cat file

cat file

show the directory currently working in

pwd

compares two files’ content and their differences.

diff 

displays a file’s first ten lines.

head 

file

file 

create a new directory

mkdir [directory]

remove a file

rm [file_name]

remove a directory recursively

rm -r [directory_name]

remove a directory recursively without requiring confirmation

rm -rf [directory_name]

copy the contents of the first file to the second file

cp [file_name1] [file_name2]

recursively copy the contents of the first directory into the second directory

cp -r [directory_name1] [directory_name2]

rename file_name1 to file_name2

mv [file_name1] [file_name2]
or 
rename [file_name1] [file_name2]

create a symbolic link to a file

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

encrypt a file

gpg -c [file_name]

decrypt a file

gpg [file_name.gpg]

print the number of words, lines,

and bytes in a file

wc

Common file operations

create empty: touch <filename>
create with size: fallocate -l <size>
<filename>
create with content: echo "<content>" >
<filename>

Quick file search

locate <filename>

Search string in file

grep <string> <filename>

Search string recursively in directory

grep -Iris <string> <directory>

Find files modified in the last minutes

find <directory> -mmin -<n> -type
f
eg. find . -mmin -5 -type f

Show only the nth column

col<n> “<separator>” <filename>
eg. col2 “,” foo.csv

Display file paginated

less <filename>

Display first lines

head -n <n> <filename>

Display last lines

tail -n <n> <filename>

Follow file content as it increases

tail -f <filename>

Pack a directory into an archive

tar.gz: tar cvzf <target>.tar.gz
<source dir>
zip: zip -r <target> <source dir>

Unpack an archive

tar.gz: tar xf <tar.gz file>
zip: unzip <zip file>

Copy file to remote server

rsync <filename> <user@
server>:<destination>
eg. rsync config.yaml
admin@192.0.0.0:/config

Copy directory recursively from remote server

rsync -avruz <user@
server>:<source> <destination>
eg. rsync -avruz admin@192.0.0.0:/
config /tmp

System

---

show system information

uname -ar

Reboot the system

reboot

Shut down the system

poweroff

show a snapshot of active processes

ps

shows a command’s manual.

man

lists previously run commands.

history 

manages system services.

systemctl 

show processes as a tree

pstree

shows a memory usage map of processes

pmap

show all running processes

top

kill all processes labelled proc

killall [proc_name]

list and resume stopped jobs in the background

bg

list files opened by processes

lsof

show how long the system has been running, including load average

uptime

show system hostname

hostname

show the IP address of the system

hostname -i

show system reboot history

last reboot

show current time and date

date

query and change the system clock

timedatectl

show current calender month and day

cal

Get root disk usage

df -h

Get memory usage

cat /proc/meminfo

Get system time

timedatectl status

Set system timezone

timedatectl list-timezones
sudo timedatectl set-timezone <zone>

connexion db mysql

mysql -u root -p

displays the status of a service

systemctl status <service>

Get all running/failing services

systemctl --state running
systemctl --state failed

Start, stop or restart a service

systemctl start/stop/restart <service>

Get the full content of a systemd unit including overrides

systemctl cat <service>

Edit a systemd avoiding conflicts with package updates

systemctl edit <service>

Monitor new logs for a service

journalctl -u <service> --since now -f

Monitor all logs since boot

journalctl --boot 0

Get the list of recent logins

last

Display running processes

htop

Kill process by id

kill <process id>

Kill process by name

pkill <process name>

Run command in the background

<command> &
# staying alive after hangup and logging to file
nohup <command> >> /var/log/yourcommand.log 2>&1 &

Display background commands

jobs

Bring command to the foreground

fg <n>

Hardware Information

---

show bootup messages

dmesg

show free and used space on mounted systems

df -h

show free inodes on mounted filesystems

df -i

show disk partitions, sizes, and types

fdisk -l

show disk usage for all files and directory

du -ah

show disk usage of current directory

du -sh

show target mount point for all filesystems

findmnt

mount a device

mount [device_path] [mount_point]

show CPU information

cat /proc/cpuinfo

show free and used memory (-m flag indicates memory in MB)

free -h

list information about hardware configuration

lshw

list information about block devices

lsblk

show PCI devices in a tree-like diagram

lspci -tv

show USB devices in a tree-like diagram

lsusb -tv

show hardware information from the BIOS

dmidecode

show information about disk data

hdparm -i /dev/[disk]

conduct a read speed test on disk

hdparm -tT /dev/[disk]

test for unreadable blocks on disk

badblocks -s /dev/[disk]

See general information about host bridge, VGA controller, ethernet controller, USB controller, SATA controller, etc.

lspci

See some information about BIOS, motherboard, chassis, etc.

dmidecode	

Retrieve processor type, socket, speed, configured flags, etc.

cat /proc/cpuinfo	

See information about the CPU

x86info or x86info -a	

See detailed information about system RAM

cat /proc/meminfo

List all hardware components and see their configuration details

lshw	

Detect number of RAM slots used, speed, and size

lshw -C memory -short	

List details for all hardware, including their device files and configuration options

hwinfo

Get some general information about your system’s BIOS

biosdecode

Retrieve the name of your BIOS vendor with this simple command

dmidecode -s bios-vendor	

Get a list of USB devices plugged into your system

lsusb	

Retrieve a list of USB device files

ls -la /dev/disk/by-id/usb-*	

Retrieve a list of USB device files

hdparm -I /dev/sdx	

Show the speed of an installed hard drive – including cached reads and buffered disk reads

hdparm -tT /dev/sdx

wodim --devices

Locate CD or DVD device file

Users

---

show user you are using

whoami

show information about a user

finger[username]

show details of the active user

id

show the last logins onto the system

last

show who is logged into the system

who

show who is logged in and their activity

w

add a new group

groupadd [group_name]

add new user

adduser [user_name]

add a user to a group

usermod -aG [group_name] [user_name]

add a user sudo

sudo usermod -a -G sudo user

delete a user

userdel [user_name]

use for changing / modifying user information

usermod

Switch to another user account.

su username

Set or change the password for a user account.

passwd username

File Permission

---

The user (owner) of the file can change its permissions with the command

chmod {ugo}{+-=}{rwx} <files>

give read, write, and execute permission to everyone

chmod 777 [file_name]

give full permission to owner, and read and execute permission to group and others

chmod 755 [file_name]

give full permission to owner, and read and write permission to group and others

chmod 766 [file_name]

change the file ownership

chown [user] [file_name]

change the owner and group

connect to host as user ownership of a file

chown [user]: [group] [file_name]

Keyboard Shortcuts

---

kill current process running in the terminal

Ctrl + C

stop current process (can be resumed in the foreground with fg or in the background with bg)

Ctrl + Z

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

repeat the last command

!!

log out of current session

exit

Environment Variable Commands

List all environment variables on a Linux system, or a specific one

printenv or printenv variable_name

Find where a command in PATH is located

whereis and which

Set a temporary environment variable (just an example, but use the same syntax)

export MY_SITE="yourwebsite.com"

echo $VARIABLE

echo $VARIABLE

Remove a variable

unset