50+ Essential Linux Commands – Saikat Infotech Blog

Top 50 Linux Commands You Must Know as a Regular User

ls – The most frequently used command in Linux to list directories
pwd – Print working directory command in Linux
cd – Linux command to navigate through directories
mkdir – Command used to create directories in Linux
mv – Move or rename files in Linux
cp – Similar usage as mv but for copying files in Linux
rm – Delete files or directories
touch – Create blank/empty files
ln – Create symbolic links (shortcuts) to other files
clear – Clear the terminal display
cat – Display file contents on the terminal
echo – Print any text that follows the command
less – Linux command to display paged outputs in the terminal
man – Access manual pages for all Linux commands
uname – Linux command to get basic information about the OS
whoami – Get the active username
tar – Command to extract and compress files in linux
grep – Search for a string within an output
head – Return the specified number of lines from the top
tail – Return the specified number of lines from the bottom
diff – Find the difference between two files
cmp – Allows you to check if two files are identical
comm – Combines the functionality of diff and cmp
sort – Linux command to sort the content of a file while outputting
export – Export environment variables in Linux
zip – Zip files in Linux
unzip – Unzip files in Linux
ssh – Secure Shell command in Linux
service – Linux command to start and stop services
ps – Display active processes
kill and killall – Kill active processes by process ID or name
df – Display disk filesystem information
mount – Mount file systems in Linux
chmod – Command to change file permissions
chown – Command for granting ownership of files or folders
ifconfig – Display network interfaces and IP addresses
traceroute – Trace all the network hops to reach the destination
wget – Direct download files from the internet
ufw – Firewall command
iptables – Base firewall for all other firewall utilities to interface with
apt, pacman, yum, rpm – Package managers depending on the distribution
sudo – Command to escalate privileges in Linux
cal – View a command-line calendar
alias – Create custom shortcuts for your regularly used commands
dd – Majorly used for creating bootable USB sticks
whereis – Locate the binary, source, and manual pages for a command
whatis – Find what a command is used for
top – View active processes live with their system usage
useradd and usermod – Add a new user or change existing user data
passwd – Create or update passwords for existing user

File and Directory Commands

Command	Description	Example
ls	List directory contents.	`ls`
cd	Change directory.	`cd /path/to/directory`
pwd	Show current directory.	`pwd`
mkdir	Create a new directory.	`mkdir new_directory`
rmdir	Remove an empty directory.	`rmdir empty_directory`
rm	Delete files or directories.	`rm file.txt`
touch	Create an empty file.	`touch new_file.txt`
cp	Copy files or directories.	`cp file.txt /path/to/destination`
mv	Move or rename files.	`mv file.txt /path/to/new_location`
cat	Display file contents.	`cat file.txt`
nano / vim	Edit files in terminal.	`nano file.txt`
find	Search for files in a directory hierarchy.	`find . -name "file.txt"`
grep	Search text using patterns.	`grep "pattern" file.txt`
tar	Archive and compress files.	`tar -cvf archive.tar file1.txt file2.txt`
df	Show disk usage of file systems.	`df`
du	Show directory/file size.	`du -sh /path/to/directory`
chmod	Change file permissions.	`chmod 755 file.txt`
chown	Change file owner.	`chown user:group file.txt`
mount	Mount a filesystem.	`mount /dev/sdb1 /mnt`
umount	Unmount a filesystem.	`umount /mnt`

				
					1. ls – List directory contents
................................

ls → Lists files in the current directory

ls -l → Long listing format (includes permissions, owner, size, date)

ls -a → Shows hidden files (those starting with .)



2. cd – Change directory
.........................

cd /path/to/directory → Go to specific directory

cd .. → Move up one directory

cd ~ or just cd → Go to home directory



3. pwd – Print working directory
.................................

Shows the full path of your current directory
Example: /home/username/Documents


4. mkdir – Make new directory
.............................

mkdir newfolder → Creates a folder named newfolder

mkdir -p folder1/folder2 → Creates nested folders


5. rmdir – Remove an empty directory
....................................

rmdir myfolder → Removes the folder only if it's empty


6. rm – Remove files or directories
....................................

rm file.txt → Deletes a file

rm -r folder/ → Deletes a folder and all contents recursively

rm -rf folder/ → Same as above, but forces deletion without asking (⚠️ dangerous!)



7. cp – Copy files and directories
..................................

cp file1.txt file2.txt → Copies file1.txt to file2.txt

cp -r dir1/ dir2/ → Copies an entire directory



8. mv – Move or rename files and directories
............................................

mv file.txt /new/location/ → Moves file

mv oldname.txt newname.txt → Renames file



9. touch – Create an empty file
................................

touch newfile.txt → Creates a blank file
(Also updates timestamp if the file already exists)



10. find – Search for files
...........................

find / -name filename.txt → Searches for a file starting from root

find . -name "*.txt" → Finds all .txt files in current directory and subdirectories



11. cat – View contents of a file
.................................

cat file.txt → Displays file contents

Combine with > to create files: cat > newfile.txt



12. less or more – View long files one page at a time
.....................................................

less file.txt → Scroll up/down with arrow keys

more file.txt → Similar, but less flexible than less



13. stat – Show file or directory status
........................................

stat file.txt → Gives detailed info (size, permissions, timestamps)

Networking Commands

Command	Description	Sample Usage
ping	Test connectivity to a host.	`ping google.com`
ifconfig / ip a	Display network interfaces.	`ifconfig` or `ip a`
netstat / ss	Show network connections.	`netstat -tuln` or `ss -tuln`
wget	Download files via HTTP/FTP.	`wget http://example.com/file.zip`
curl	Transfer data using URL syntax.	`curl -O http://example.com/file.zip`
nc (Netcat)	Network debugging and data transfer.	`nc -zv 192.168.1.1 80`
tcpdump	Capture and analyze network packets.	`tcpdump -i eth0`
iptables	Configure firewall rules.	`iptables -A INPUT -p tcp --dport 22 -j ACCEPT`
traceroute	Trace the path packets take to a network host.	`traceroute example.com`
nslookup	Query DNS to obtain domain name or IP address mapping.	`nslookup example.com`
ssh	Securely connect to a remote host.	`ssh user@example.co`

Basic Networking Commands

Command	Description	Example
`ip a` or `ip addr`	Show IP addresses and interfaces	`ip a`
`ip link`	Show or manage network interfaces	`ip link show`
`ip route`	Display routing table	`ip route`

Connectivity Testing

Command	Description	Example
`ping`	Test if host is reachable	`ping google.com`
`traceroute`	Show route packets take to a host	`traceroute google.com`
`mtr`	Real-time traceroute (advanced)	`mtr google.com`
`telnet`	Test open ports on remote system	`telnet example.com 80`
`nc` (netcat)	Test connections or transfer data	`nc -zv google.com 443`

DNS Tools

Command	Description	Example
`nslookup`	Query DNS for records	`nslookup google.com`
`dig`	Advanced DNS querying	`dig google.com`
`host`	Simple DNS lookup	`host google.com`

Monitoring and Interface Info

Command	Description	Example
`ifconfig`	Show interface info (deprecated)	`ifconfig`
`ip -s link`	Show stats for interfaces	`ip -s link`
`ethtool`	View/set Ethernet device settings	`ethtool eth0`
`iwconfig`	Configure wireless interfaces	`iwconfig wlan0`
`nmcli`	NetworkManager CLI (for desktops)	`nmcli device status`

Port and Socket Monitoring

Command	Description	Example
`netstat`	Show network connections (old)	`netstat -tuln`
`ss`	Show open sockets (modern)	`ss -tuln`
`lsof -i`	List open files using network	`lsof -i`
`nmap`	Port scanner / network mapper	`nmap 192.168.1.1`

Downloading and Transfers

Command	Description	Example
`curl`	Transfer data from URLs	`curl https://example.com`
`wget`	Download files from web	`wget https://file.com/file.zip`
`scp`	Secure copy over SSH	`scp file.txt user@host:/path`
`rsync`	Sync files/directories	`rsync -avz /src user@host:/dest`

Troubleshoot Network Issue

Check your IP: ip a
Test DNS: dig google.com
Ping a site: ping google.com
Check open ports: ss -tuln
Traceroute to a server: traceroute google.com

Process and System Monitoring Commands

Command	Description	Example Command
ps	Show running processes.	`ps aux`
top	Dynamic process viewer.	`top`
htop	Enhanced version of top.	`htop`
kill	Send a signal to a process.	`kill <PID>`
killall	Kill processes by name.	`killall <process_name>`
uptime	System uptime and load.	`uptime`
whoami	Current logged-in user.	`whoami`
env	Display environment variables.	`env`
strace	Trace system calls of a process.	`strace -p <PID>`
systemctl	Manage systemd services.	`systemctl status <service_name>`
journalctl	View system logs.	`journalctl -xe`
free	Display memory usage.	`free -h`
vmstat	Report virtual memory statistics.	`vmstat 1`
iostat	Report CPU and I/O statistics.	`iostat`
lsof	List open files by processes.	`lsof`
dmesg	Print kernel ring buffer messages.	`dmesg`

User and Permission Management Command

Command	Description	Example Command
passwd	Change user password.	`passwd <username>`
adduser / useradd	Add a new user.	`adduser <username>` or `useradd <username>`
deluser / userdel	Delete a user.	`deluser <username>` or `userdel <username>`
usermod	Modify user account.	`usermod -aG <group> <username>`
groups	Show group memberships.	`groups <username>`
sudo	Execute commands as root.	`sudo <command>`
chage	Change user password expiry information.	`chage -l <username>`
id	Display user identity information.	`id <username>`
newgrp	Log in to a new group.	`newgrp <group>`

👤 1. User Management Commands

Command	Description	Example
`adduser`	Add a new user (interactive, preferred)	`sudo adduser john`
`useradd`	Add user (non-interactive, more control)	`sudo useradd -m john`
`passwd`	Set/change a user’s password	`sudo passwd john`
`usermod`	Modify a user account	`sudo usermod -aG sudo john`
`deluser`	Delete a user	`sudo deluser john`
`userdel`	Delete a user (and optionally their home dir)	`sudo userdel -r john`
`id`	Show user ID and group info	`id john`
`whoami`	Show the current logged-in username	`whoami`

👥 2. Group Management Commands

Command	Description	Example
`addgroup`	Add a new group	`sudo addgroup developers`
`groupadd`	Add group (alternative command)	`sudo groupadd staff`
`groupdel`	Delete a group	`sudo groupdel staff`
`usermod -aG`	Add a user to a group	`sudo usermod -aG developers john`
`groups`	Show groups of a user	`groups john`
`gpasswd`	Administer group membership	`sudo gpasswd -a john developers`

🗂️ 3. File Ownership and Permissions

Command	Description	Example
`chown`	Change ownership of a file/directory	`sudo chown john:developers file.txt`
`chmod`	Change file/directory permissions	`chmod 755 script.sh`
`chgrp`	Change group ownership	`chgrp developers file.txt`
`ls -l`	View file permissions and ownership	`ls -l /home/john/`
`umask`	Show or set default permission mask	`umask`

4. Understanding `chmod` (Permissions)

Permission format: rwxr-xr--

Symbol	Meaning	Binary
`r`	Read	4
`w`	Write	2
`x`	Execute	1

Example:

chmod 755 file.sh
→ Owner: read/write/execute
→ Group: read/execute
→ Others: read/execute

Numeric	Meaning
`7`	read + write + execute
`6`	read + write
`5`	read + execute
`4`	read only
`0`	no permissions

5. Useful Combinations

Task	Command
Add user and assign to a group	`sudo adduser john developers`
Add user to sudoers	`sudo usermod -aG sudo john`
Change file to be executable	`chmod +x script.sh`
Give read/write to user only	`chmod 600 file.txt`
Change owner to root	`sudo chown root:root file.txt`

6. Audit User Activity

Command	Description	Example
`last`	Show recent logins	`last`
`who`	Show who is logged in	`who`
`w`	Show logged in users + what they’re doing	`w`
`history`	Show command history	`history`
`sudo`	Execute as another user (usually root)	`sudo apt update`

Summary Cheat Table

Area	Key Commands
User	`adduser`, `useradd`, `passwd`, `userdel`
Group	`addgroup`, `usermod -aG`, `groups`, `groupdel`
Permissions	`chmod`, `chown`, `chgrp`, `ls -l`
Audit	`last`, `who`, `w`, `history`

				
					How to change pemisson ownership?
..................................
sudo chown -R username:group directory
centos - chown :groupnamr <filename>
         chown	<username> <filename>



How to show  users?
...................
getent passwd


How to show  group?
...................
getent group


How to check user which group join?
...................................
groups <username>


How to show all gropus?
.......................
compgen -g


How to show all users?
......................
compgen -u


How to List All Groups in Linux?
................................
cat /etc/group


How to List All Members of a Group on Ubuntu ?
.............................................
getent group <group_name>


How to add User in a Group on Ubuntu?
......................................
sudo usermod -aG <group_name> <user_name>


How to remove User from a Group on Ubuntu ?
...........................................
sudo gpasswd -d <user_name> <group_name>


How to change password users self ?
...................................
passwd


How to normal users permisson to root privilage?
................................................
usermod -aG sudo <username>
sudo some-command
sudo visudo
sudo passwd -e bob
sudo passwd --expire sumita


How to Account Lokking Unlokking?
.................................
sudo passwd -l bob
sudo passwd -u bob
skill -u USERNAME


How to delete user forcefully kill?
....................................
sudo killall -u username
sudo userdel -f username
How to del group?
delgroup -f <group name>

Text Processing Commands

Command	Description	Example Command
awk	Pattern scanning and processing.	`awk '{print $1}' file.txt`
sed	Stream editor for filtering/modifying text.	`sed 's/old/new/g' file.txt`
cut	Remove sections from lines of text.	`cut -d':' -f1 /etc/passwd`
sort	Sort lines of text.	`sort file.txt`
grep	Search for patterns in text.	`grep 'pattern' file.txt`
wc	Count words, lines, and characters.	`wc -l file.txt`
paste	Merge lines of files.	`paste file1.txt file2.txt`
join	Join lines of two files on a common field.	`join file1.txt file2.txt`
head	Output the first part of files.	`head -n 10 file.txt`
tail	Output the last part of files.	`tail -n 10 file.txt`

Command	Description	Example Command
alias	Create shortcuts for commands.	`alias ll='ls -la'`
unalias	Remove an alias.	`unalias ll`
history	Show previously entered commands.	`history`
clear	Clear the terminal screen.	`clear`
reboot	Reboot the system.	`reboot`
shutdown	Power off the system.	`shutdown now`
date	Display or set the system date and time.	`date`
echo	Display a line of text.	`echo "Hello, World!"`
sleep	Delay for a specified amount of time.	`sleep 5`
time	Measure the duration of command execution.	`time ls`
watch	Execute a program periodically, showing output fullscreen.	`watch -n 5 df -h`

Linux LVM Commnds

What is LVM?

LVM (Logical Volume Manager) allows you to manage disk space flexibly by abstracting physical storage into logical volumes. You can resize, combine, and manage volumes more easily than with traditional partitions.

1. Install LVM (if not already installed)

2. Basic LVM Workflow Overview

Step	Task	Command
1	Create physical volume (PV)	`pvcreate /dev/sdX`
2	Create volume group (VG)	`vgcreate my_vg /dev/sdX`
3	Create logical volume (LV)	`lvcreate -L 10G -n my_lv my_vg`
4	Format LV with a file system	`mkfs.ext4 /dev/my_vg/my_lv`
5	Mount the LV	`mount /dev/my_vg/my_lv /mnt`

3. Physical Volume (PV) Commands

Command	Description
`pvcreate /dev/sdX`	Initialize a physical volume
`pvdisplay`	Show detailed info about PVs
`pvs`	Show a summary of all PVs
`pvscan`	Scan all disks for PVs
`pvremove /dev/sdX`	Remove a physical volume (wipe LVM data)

4. Volume Group (VG) Commands

Command	Description
`vgcreate my_vg /dev/sdX`	Create a volume group
`vgextend my_vg /dev/sdY`	Add PV to VG
`vgreduce my_vg /dev/sdY`	Remove PV from VG
`vgs`	Show summary of all VGs
`vgdisplay`	Detailed info about VGs
`vgremove my_vg`	Remove a VG
`vgchange -a y`	Activate all volume groups
`vgchange -a n`	Deactivate all volume groups

5. Logical Volume (LV) Commands

Command	Description
`lvcreate -L 10G -n my_lv my_vg`	Create a logical volume
`lvextend -L +5G /dev/my_vg/my_lv`	Extend a logical volume
`lvresize -L 15G /dev/my_vg/my_lv`	Resize LV to specific size
`lvreduce -L 8G /dev/my_vg/my_lv`	Reduce LV size (⚠️ careful!)
`lvremove /dev/my_vg/my_lv`	Remove an LV
`lvdisplay`	Detailed info about LVs
`lvs`	Show summary of all LVs
`lvscan`	Scan for logical volumes

6. Resizing File Systems with LVM

⚠️ Always backup before resizing!

Extend Logical Volume and File System:

⚠️ Shrink Logical Volume and File System:

7. Removing LVM Components

Task	Command
Unmount the LV	`umount /mnt`
Remove LV	`lvremove /dev/my_vg/my_lv`
Remove VG	`vgremove my_vg`
Remove PV	`pvremove /dev/sdX`

8. Useful Monitoring and Status Commands

Command	Description
`lsblk`	Lists all block devices (including LVMs)
`df -h`	Disk space usage (mounted volumes)
`mount`	Check mounted file systems
`blkid`	Display block device UUIDs and types
`lvs`, `vgs`, `pvs`	Show LVM components in summary

				
					How To Cheking Linux Ubantu Disk Status?
.........................................
lsblk
fdisk -l
df -hT
lsblk -f                                              <Cheking Formating Partition >
mount -av                                             <cheking Mounting>


How To Create Linux Ubantu LVM?
...............................
Step#01 fdisk /dev/sdb                                        <Go To HDD >
Step#02 n, p, t, 8e, w                                        <New Partion Create>
Step#03 partprobe /dev/sdb                                    <Karnel Infom For New HDD Partition>
Step#04 pvcreate /dev/sdb1                                    <Create Pv>
Step#05 vgcreate nextcloud /dev/sdb1                          <Create VG>
Step#06 lvcreate -L 500G -n nextcloud nextcloudlv             <Create LV>
Step#07 mkfs.ext4 /dev/mapper/nextcloud-nextcloudlv           <Formating> 
Step#08 mount /dev/mapper/nextcloud-nextcloudlv /var/www/html <Create Mount Point For Use Disk Space>
Step#09 df -hT                                                <For Checking Mount>
Step#10 cat/etc/mtab                                          <Copy Full Path nextcloud-nextcloudlv For Entry Fstab>
Step#11 nano /etc/fstab
Step#11 /dev/mapper/nextcloud-nextcloudlv /var/www/html ext4   errors=remount-ro 0 1 <Paste This Line Fstab Then Save>



How To Cheking Linux Ubantu LVM Status?
........................................
pvdisplay              
vgdisplay
lvdisplay
lvs
vgs
pvs
lvscan
pvscan
vgscan



How To Remove Linux Ubantu LVM?
...............................
lvremove /dev/nextcloud/nextcloudlv

				
					Ubantu LVM Root Partion Extend
...............................

1.sudo fdisk -l : find new drive
or lsblk or df -h

2.sudo pvscan

3.sudo fdisk /dev/sdb
n
p
1
[enter]
[enter]
t
8e
w

5.lsblk and see /dev/sdb1 added
if /dev/sdb1 is not seen then reboot before continuing further

6.sudo pvcreate /dev/sdb1

7.sudo vgdisplay : look for VG Name value (ubuntu-vg, vg00 etc)

8.sudo vgextend ubuntu-vg /dev/sdb1

9.sudo pvscan

10.sudo lvdisplay : look for LV Path value

11.sudo lvextend /dev/ubuntu-vg/ubuntu-lv /dev/sdb1
OR
sudo lvextend -L +5G /dev/my_vg/my_lv sudo resize2fs /dev/my_vg/my_lv # For ext4


12.sudo resize2fs /dev/ubuntu-vg/ubuntu-lv

lsblk will now show your size increase

Disk Management

				
					How to check hdd?
.................
sudo fdisk -l

How to check partition MBR/GPT
..............................
gdisk /dev/sda
lsblk


How to create partition?
........................
sudo fdisk /dev/sda
help- m
n
enter
enter
+20G
p- print
w-save
fdisk -l

How to format partition?
........................
mkfs.ext4 /dev/sda
lsblk -f -chcek format or not partition



How to mount partiton?
......................
sudo mount /dev/sda /<mount folder>
check - sudo mount
        lsblk

Tool	Command	Output Tells You
`parted`	`sudo parted /dev/sdX print`	`gpt` or `msdos`
`gdisk`	`sudo gdisk -l /dev/sdX`	MBR or GPT
`fdisk`	`sudo fdisk -l /dev/sdX`	Disklabel type
`lsblk`	`lsblk -f`	Filesystem info
`blkid`	`sudo blkid`	UUIDs/labels

				
					Convert MBR to GPT using gdisk
...............................
sudo apt update
sudo apt install gdisk


Step 2: Identify the target disk
.................................
List available disks:lsblk
Find your disk (e.g., /dev/sda, /dev/sdb, etc.)


Step 3: Run gdisk to convert MBR to GPT
.......................................
sudo gdisk /dev/sdX
Replace /dev/sdX with your actual disk (not a partition, e.g., /dev/sda)
You’ll see a message like:MBR detected. Do you want to convert it? (Y/N)
Enter Y to proceed with the conversion.



Step 4: Write the new partition table
.....................................
Type the following in gdisk:

w → Write changes to disk

Y → Confirm

This writes the GPT structure and exits.



Step 5: Verify the new partition table
.......................................
sudo parted /dev/sdX print
It should now say: Partition Table: gpt



1. Using lsblk -f + blkid (to check GPT UUIDs)
...............................................
sudo lsblk -f
sudo blkid


2. Using fdisk (Shows Partition Type)
.....................................
sudo fdisk -l /dev/sdX

				
					How to create multiplefile touch commend?
.........................................
for i in {1..10}; do touch file$i.txt; done


How to create tar file?
......................
tar cvf <filename>.tar <filename> then enter


How to create tar file untar?
..............................
tar xvf <filename>.tar <filename> then enter
tar –xvzf <filename>.tar <filename> then enter



How to create compress reduce size tar file?
.............................................
tar cjf <filename>.tar.gz cvf <filename> then enter


How to create gzip?
....................
gzip <filename>


How to create gzip extarct ?
............................
gunzip <filename>
zcat   <filename>



How to view file size check?
............................
du -sh <filename>

VPS Server Install Apache WordPress

				
					
1. Install Apache

sudo apt update && sudo apt install apache2
............................................
2. Configure Firewall

sudo ufw allow OpenSSH

sudo ufw allow in "Apache Full"

sudo ufw enable

sudo ufw status


3. Test Apache
...............

sudo service apache2 status


4. Install MySQL
................

sudo apt update && sudo apt install mysql-server

sudo service mysql status


5. MySQL Security
..................

sudo mysql_secure_installation

-> ENTER | Y | Y | Y | Y

sudo mysqladmin -p -u root version



6. Install PHP
...............

sudo apt update && sudo apt install php libapache2-mod-php php-mysql

php -version


7. Installing phpMyAdmin
........................

sudo apt update && sudo apt install phpmyadmin php-mbstring

sudo ln -s /etc/phpmyadmin/apache.conf /etc/apache2/conf-available/phpmyadmin.conf

sudo a2enconf phpmyadmin.conf

sudo service apache2 reload


8. Create MySQL User
....................

sudo mysql

CREATE USER 'newuser'@'localhost' IDENTIFIED BY 'password';

GRANT ALL PRIVILEGES ON * . * TO 'newuser'@'localhost';

FLUSH PRIVILEGES;
CREATE USER 'username'@'ip_address' IDENTIFIED BY 'password';
exit


9. Secure PhpMyAdmin
....................

sudo nano /etc/apache2/conf-available/phpmyadmin.conf

Alias /your_url /usr/share/phpmyadmin

sudo service apache2 reload



10. Install ZIP/Unzip
......................

apt-get update

apt-get install zip unzip



11. Enable .htaacess
.....................

sudo apt-get update

sudo a2enmod rewrite

systemctl restart apache2

sudo nano /etc/apache2/sites-enabled/000-default.conf

<Directory "/var/www/html">
  AllowOverride All
</Directory>


12. Configure Apache File
..........................

sudo nano /etc/apache2/apache2.conf

<Directory /var/www/>
    Options Indexes FollowSymLinks
    AllowOverride All
    Require all granted
 </Directory>

 <Directory /var/www/html>
    Options -Indexes
 </Directory>

 ServerSignature Off
 ServerTokens Prod


13. install SSL Certificate
............................

sudo apt update && sudo apt install certbot python3-certbot-apache

sudo certbot --apache

service apache2 restart

Redhat RHEL,Cent-OS User Group Commnds

1. Add / Create Users

Command	Description
`sudo adduser username`	Add a user (interactive)
`sudo useradd username`	Add user (scriptable, non-interactive)
`sudo passwd username`	Set password for a user
`sudo useradd -m -s /bin/bash username`	Create user with home directory and shell

Example:

2. Delete / Remove Users

Command	Description
`sudo userdel username`	Delete a user
`sudo userdel -r username`	Delete user and home directory

3. Modify Existing Users

Command	Description
`sudo usermod -l newname oldname`	Rename user
`sudo usermod -d /new/home -m username`	Move home directory
`sudo usermod -s /bin/zsh username`	Change user’s shell
`sudo usermod -aG groupname username`	Add user to a group (append)

Example:

4. Lock / Unlock User Accounts

Command	Description
`sudo usermod -L username`	Lock account (disable login)
`sudo usermod -U username`	Unlock account
`sudo passwd -l username`	Lock password
`sudo passwd -u username`	Unlock password

5. Add / Manage Groups

Command	Description
`sudo groupadd groupname`	Add new group
`sudo groupdel groupname`	Delete a group
`sudo groupmod -n newname oldname`	Rename a group
`sudo gpasswd -a username groupname`	Add user to group
`sudo gpasswd -d username groupname`	Remove user from group

Example:

6. View User & Group Info

Command	Description
`id username`	Show UID, GID, and groups
`groups username`	List groups a user belongs to
`getent passwd username`	Show user entry
`getent group groupname`	Show group entry
`cat /etc/passwd`	List all users
`cat /etc/group`	List all groups

7. Sudo (Admin) Access

Add user to sudo group (Red Hat uses `wheel`):

Check sudo access:

8. Change User Shell

Command	Description
`chsh -s /bin/bash username`	Change user’s default shell
`cat /etc/shells`	List available shells

Example:

9. Account Expiry and Password Aging

Command	Description
`chage -l username`	Show password aging info
`sudo chage -E 2025-12-31 username`	Set account expiration date
`sudo chage -M 90 username`	Set max password age to 90 days
`sudo chage -m 7 username`	Set min password age to 7 days
`sudo chage -W 10 username`	Warn 10 days before expiry

11. Switch Users and Become Root

Command	Description
`su - username`	Switch to another user
`sudo su -`	Become root user
`sudo -i`	Open a root login shell

Quick Summary Table

Task	Command
Add user	`adduser` / `useradd`
Delete user	`userdel -r`
Add group	`groupadd`
Add user to group	`usermod -aG`
Set password	`passwd`
Lock/unlock user	`usermod -L/-U`
View groups	`groups` / `id`
Give sudo access	Add to `wheel` group

Ubantu Server Firewall UFW Commnds

1. What is UFW?

UFW (Uncomplicated Firewall) is a frontend for iptables that makes it easier to manage firewall rules on Ubuntu. It’s ideal for most users who want simple, secure, and readable firewall configurations.

2. Enable or Disable UFW

Task	Command
Enable firewall	`sudo ufw enable`
Disable firewall	`sudo ufw disable`
Check firewall status	`sudo ufw status`
Verbose status	`sudo ufw status verbose`
Reset firewall (clear all rules)	`sudo ufw reset`

3. Allow or Deny Services and Ports

Allow Traffic

Task	Command
Allow specific port	`sudo ufw allow 22`
Allow service by name	`sudo ufw allow ssh`
Allow port with protocol	`sudo ufw allow 80/tcp`
Allow port range	`sudo ufw allow 1000:2000/tcp`
Allow IP access to port	`sudo ufw allow from 192.168.1.100 to any port 22`

Deny Traffic

Task	Command
Deny specific port	`sudo ufw deny 23`
Deny service	`sudo ufw deny telnet`

4. Managing Incoming/Outgoing Rules

Task	Command
Allow outgoing traffic	`sudo ufw default allow outgoing`
Deny all incoming by default	`sudo ufw default deny incoming`
Allow all incoming	`sudo ufw default allow incoming`
Deny all outgoing	`sudo ufw default deny outgoing`

5. Deleting Rules

Task	Command
Delete by rule	`sudo ufw delete allow 22`
Delete by number (from `ufw status numbered`)

6. Logging & Monitoring

Command	Description
`sudo ufw logging on`	Enable logging
`sudo ufw logging off`	Disable logging
`sudo ufw status verbose`	Show with logging info
Logs are stored in	`/var/log/ufw.log`

7. Application Profiles

Many services define UFW profiles (e.g., OpenSSH, Apache, Samba, etc.)

Task	Command
List available profiles	`sudo ufw app list`
Show details of a profile	`sudo ufw app info Apache`
Allow a profile	`sudo ufw allow 'Apache Full'`

8. Enable UFW on Boot

UFW is usually enabled to start at boot automatically once you enable it:

9. Disable UFW Temporarily

Task	Command
Disable firewall	`sudo ufw disable`
Re-enable firewall	`sudo ufw enable`

10. Common Examples

Task	Command
Allow SSH	`sudo ufw allow ssh` or `sudo ufw allow 22`
Allow HTTP & HTTPS	`sudo ufw allow 80,443/tcp`
Allow MySQL from local network	`sudo ufw allow from 192.168.1.0/24 to any port 3306`
Block all except SSH

Check Summary

Important Tips

Always allow SSH before enabling the firewall remotely:

sudo ufw allow ssh sudo ufw enable

Redhat,Cent-OS Server Firewall Commnds

Basics of firewalld on CentOS / RHEL

Service: firewalld
Command-line tool: firewall-cmd
Zones: Used to define trust levels for network connections (e.g., public, internal, external, etc.)
Default zone: Usually public

				
					Start/Enable/Disable firewalld
...............................
sudo systemctl start firewalld       # Start the firewall
sudo systemctl enable firewalld      # Enable at boot
sudo systemctl stop firewalld        # Stop the firewall
sudo systemctl disable firewalld     # Disable at boot
sudo systemctl status firewalld      # Check status


Check firewall status & rules
.............................
firewall-cmd --state                             # Running or not
firewall-cmd --get-active-zones                  # Shows active zones
firewall-cmd --get-default-zone                  # Default zone
firewall-cmd --list-all                          # List all rules for default zone
firewall-cmd --list-all --zone=public            # List rules for a specific zone
firewall-cmd --list-services                     # List allowed services


Add / Remove Ports and Services
................................
Add service (permanent and runtime)
# Runtime (immediate)
sudo firewall-cmd --zone=public --add-service=http

# Permanent (persists after reboot)
sudo firewall-cmd --zone=public --add-service=http --permanent
sudo firewall-cmd --reload    # Reload to apply permanent rules



Remove service
...............
sudo firewall-cmd --zone=public --remove-service=http --permanent
sudo firewall-cmd --reload



Add port
.........
sudo firewall-cmd --zone=public --add-port=8080/tcp --permanent
sudo firewall-cmd --reload


Remove port
...........
sudo firewall-cmd --zone=public --remove-port=8080/tcp --permanent
sudo firewall-cmd --reload



Rich Rules (Advanced)
Example: Allow IP through firewall
...................................
sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="192.168.1.100" accept'
sudo firewall-cmd --reload

Example: Block an IP
sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="192.168.1.200" reject'
sudo firewall-cmd --reload


Reload / Reset Firewall
.......................
sudo firewall-cmd --reload                         # Reload after changes
sudo firewall-cmd --complete-reload                # Full reload (drops runtime configs)
sudo firewall-cmd --permanent --reset-default-zone # Reset default zone


Lockdown Mode
..............
sudo firewall-cmd --lockdown-on                   # Enable lockdown
sudo firewall-cmd --lockdown-off                  # Disable lockdown
sudo firewall-cmd --query-lockdown                # Check lockdown status


Predefined Services
...................
firewall-cmd --get-services

File Transfer Linux Server SCP Commnds

				
					SCP stands for Secure Copy Protocol
...................................

Copy from local to remote
..........................
scp /path/to/local/file username@remote_host:/path/to/remote/destination

Example:

scp file.txt root@192.168.1.100:/home/root/



Copy from remote to local
.........................
scp username@remote_host:/path/to/remote/file /path/to/local/destination

Example:

scp file.txt root@192.168.1.100:/home/root/



Copy a directory recursively
............................
scp -r /local/dir username@remote_host:/remote/dir

Example:

scp -r myfolder user@192.168.1.101:/var/www/



Specify a non-default port
..........................
scp -P 2222 file.txt user@host:/path/


Upload file to remote server
............................
scp index.html root@192.168.1.10:/var/www/html/


Download file from remote server
.................................
scp root@192.168.1.10:/var/log/messages ~/logs/


Copy folder to remote server with port
......................................
scp -P 2200 -r website/ user@host:/home/user/


Transfer a ZIP file via SCP
............................
From Local to Remote
scp website_backup.zip root@192.168.1.10:/home/root/backups/


From Remote to Local
.....................
scp root@192.168.1.10:/home/root/website_backup.zip ~/Downloads/


Combine zip and scp in one line (local to remote)
.................................................
zip -r myfolder.zip myfolder && scp myfolder.zip user@host:/destination/


SSH uses a non-default port (e.g., port 2222)
.............................................
scp -P 2222 myfile.zip user@host:/remote/path/


Common Options:
-r: Recursively copy entire directories.
-P: Specify a custom SSH port (note the uppercase P).
-i: Specify a private key file for authentication.
-v: Enable verbose mode to see more detailed output for debugging.
-C: Enable compression to speed up the transfer for large files.

Linux Server File Compression

				
					ls -lh
Compressing a Big file
.......................
gzip myfile.txt           # Produces myfile.txt.gz


Unompressing a Big file
.......................
gunzip myfile.txt


Directory Compress
...................
mkdir backup        <Create a Folder>
tar -cvf backup.tar backup/ <Backup/ Means Folder Name>
ls -ltr              <Show File>
gzip backup.tar      <Compress For Backup.tar File>
ls


D Compress
..........
tar -xzvf backup.tar.gz
ls -ltr

Without backup.tar.gz Extrat File Show
.......................................
tar -tzvf backup.tar.gz
Or
zcat backup.tar


Single Step Commnd Compress
............................
tar -czvf backup.tar.gz backup
tar -xzvf backup.tar.gz backup <Extract Commnd>


Zip Commnd
..........
Example- file1 file2
Compress:- zip file.zip file1 file2 
ls -ltr


Without file.zip Extrat File Contain Show
..........................................
zipinfo files.zip
unzip -l files.zip

UnZip Commnd
.............
unzip file.zip



scp -v backup.tar.gz user@192.168.1.100:/home/user/backups/


Check the File on Remote
........................
ssh user@192.168.1.100
ls -lh /home/user/backups/

rsync on Linux Server

What is `rsync`?

rsync is a powerful, efficient tool used to copy and sync files/directories between locations, either locally or over a network (e.g., between two servers). It only transfers changed parts of files, making it much faster than scp for repeated syncs.

				
					1. Installing rsync on Ubuntu
.............................
Open a terminal and run:
sudo apt update
sudo apt install rsync

Check the version to confirm installation
..........................................
rsync --version


2. Basic rsync Usage
.....................
Local Sync (Directory to Directory):

rsync -av /source/folder/ /destination/folder/


-a: Archive mode (preserves permissions, timestamps, etc.)

-v: Verbose (shows progress)


Remote Sync (Over SSH)
......................
From Local to Remote:
rsync -av /local/folder/ user@remote_ip:/remote/folder/


You can add -z for compression if sending over the internet:
rsync -avz /local/folder/ user@remote:/remote/folder/

Example

rsync -av backup.tar.gz user@192.168.1.100:/home/user/backups/


Using SSH Key (Optional, Recommended)
.....................................
To avoid typing the password every time:

1.Generate SSH key (if you don’t have one):
ssh-keygen


2.Copy it to remote server:
ssh-copy-id user@remote_ip


3.Now rsync will work without asking for a password.

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File and Directory Commands

Networking Commands

Basic Networking Commands

Connectivity Testing

DNS Tools

Monitoring and Interface Info

Port and Socket Monitoring

Downloading and Transfers

Troubleshoot Network Issue

Process and System Monitoring Commands

User and Permission Management Command

👤 1. User Management Commands

👥 2. Group Management Commands

🗂️ 3. File Ownership and Permissions

4. Understanding chmod (Permissions)

5. Useful Combinations

6. Audit User Activity

Summary Cheat Table

Text Processing Commands

Linux LVM Commnds

What is LVM?

1. Install LVM (if not already installed)

2. Basic LVM Workflow Overview

3. Physical Volume (PV) Commands

4. Volume Group (VG) Commands

5. Logical Volume (LV) Commands

6. Resizing File Systems with LVM

Extend Logical Volume and File System:

⚠️ Shrink Logical Volume and File System:

7. Removing LVM Components

8. Useful Monitoring and Status Commands

Disk Management

VPS Server Install Apache WordPress

Redhat RHEL,Cent-OS User Group Commnds

1. Add / Create Users

2. Delete / Remove Users

3. Modify Existing Users

4. Lock / Unlock User Accounts

5. Add / Manage Groups

6. View User & Group Info

7. Sudo (Admin) Access

Add user to sudo group (Red Hat uses wheel):

Check sudo access:

8. Change User Shell

11. Switch Users and Become Root

Quick Summary Table

Ubantu Server Firewall UFW Commnds

1. What is UFW?

2. Enable or Disable UFW

3. Allow or Deny Services and Ports

Allow Traffic

Deny Traffic

4. Managing Incoming/Outgoing Rules

5. Deleting Rules

6. Logging & Monitoring

7. Application Profiles

8. Enable UFW on Boot

9. Disable UFW Temporarily

10. Common Examples

Check Summary

Important Tips

Redhat,Cent-OS Server Firewall Commnds

Basics of firewalld on CentOS / RHEL

File Transfer Linux Server SCP Commnds

Linux Server File Compression

rsync on Linux Server

What is rsync?

4. Understanding `chmod` (Permissions)

Add user to sudo group (Red Hat uses `wheel`):

What is `rsync`?