Disk usage,

tar command to Compress and Extract Files

Here’s what those flags (-cvf) actually mean
-c, --create– create a new archive
-x, --extract, --get– extract files from an archive
-f, --file ARCHIVE– use archive file or device ARCHIVE

Now see the file

Create a new archive

now see new archive created

Now extract file; no normal directory found

Now extract Desktop dir

Gzip compression

Extract gz file

Remove a .gz file

Grep

grep installation

Search word hi

Case insensitive search: The -i option enables to search for a string case insensitively in the given file. It matches the words like “UNIX”, “Unix”, and “unix”.

See the content 1.txt

Display a matching word

Display a matched word line number

Display a matched words

Display a ending with letter a

Display a matched letter without case sensitive -i [a-c]

word count

Display a line without hi

Search by word

Ethernet down

Ethernet up

Date

Set date

View last Sunday's date

Calendar

Display current month

Display a specified month

Display a 5month of 2024

Display 2024

display current month,previous,before month

Word count

Count line, words,letters

Count word

Count letters

Count line

How to create, delete, and modify groups in Linux

Groups are an essential part of the Linux permission structure and a powerful way to manage file access on your system.

know groups command groups

cat /etc/group/

To add a group in Linux, use the `groupadd` command:

sudo groupadd java

You can verify that the group appears (and see its group ID) by looking in the /etc/group file.

now java group added

If you want to create a group with a specific group ID (GID), use the `--gid` or `-g` option:

sudo groupadd -g 1009 demo1

Change the group ID

sudo groupmod -g 1012 demo1

Rename a group

sudo groupmod -n test demo1

before see the group id for demo1

now will be changing

See the groups

Now see the same group id changed from demo1 to test

Add and remove users from a group

Suppose you have existing users named user1 and user2, and you want to add them to the demo group. Use the usermod command with the --append --groups options (-a and -G for short):

sudo usermod --append --groups demo user1

sudo usermod -aG demo user2

Look in the /etc/group file or use the id command to confirm your changes:

id user1

Add a user

Delete a user

Delete a group

sudo groupdel user1

SSH

sudo apt-get install openssh-server

sudo service ssh status

edit sshd_config file

sudo vi /etc/ssh/sshd_config

Head and tail command

The head is used for displaying the first 10 lines of the file

tail is used for displaying the last 10 lines of the file

First see test1 file content

reading from firstline

Read a first line

show the first 3 lines

shows the multiple files

tail command

Normal fiel view

Read from last line tail file.txt

tail -n1 file.txt

It display last three lines

tail file.txt file2.txt

How to find IP address

ip address

hostname -i

ip a

ip add

ifconfig

Now see the file test1

remove a test1 file

Now see test1 not found

Remove morethan one file

list

remove a 1 2

now see found not found 1 2

Create a directory

now see sun directory has created

Remove a directory

now see sun directory not found

Create a directory inside ; this means b directory created inside a directory

Now see b directory created inside a

Delete a inside directory

Options: 1. -i (Interactive Deletion): the -i option makes the command ask the user for confirmation before removing each file, you have to press y for confirm deletion, any other key leaves the file un-deleted.

-f (Force Deletion): rm prompts for confirmation removal if a file is write protected. The -f option overrides this minor protection and removes the file forcefully.