In the addition to my previous blog https://saifali2017.hashnode.dev/linux-and-common-commands-for-devops I came up with the most useful and important Linux commands for working professionals.

Let me start with

File Management.

To check file permission we have command ls -l here is the example with test.txt file.

 ls -l test.txt
-rw-rw-r-- 1 saif saif 30 Mar 23 13:45 test.txt

I am sure already aware of RWX if not let me tell you.

R refers to Read (Numeric value 4)

W refers to Write (Numeric value 2)

X refers to Execute (Numeric value 1)

--- refers to No Permission (Numerical value 0)

To change the file permission we have the command #chmod Group, Owner, Others.

For example.

$ chmod u+r test.txt  //add read permission to owner
$ chomd g+r test.txt  //add read permission to gropu 
$ chmod o+r test.txt  //add read permission to others

Instead of it, you can set the permission with numerical values refer below.

$ chmod 751 test.txt

Now Let's start with

Searching practices.

We used regular expressions which help us to search data, and match complex patterns.

GREP stands for Global Regular Expression Print

The grep filter searches a file for a particular word or character and displays all lines that contain that pattern.

You can search a word with the below command

$ grep root/ets/test  // will search for test

One of the important command for searching is 'find' and you use it with multiple of various conditions like you can find a file by the file permission, users, group, file type, data, size and many more criteria.

Find the file under the Home directory

$ find /home -name test.txt

Find the file with suid permissions

$ find / -perm 4755

Find the file with suid permissions

$ find /-perm 2644

Find the file with less than 10 MB file in a folder

$ find /tmp -size -10m

Find the file with more than 10 MB file in a folder

$ find /tmp -size +10m

To display the top 10 lines of the file.

$ head /etc/passwd

To Display the bottom 10 lines of the file.

tail /etc/passwd

How to Archive a file to compress the file.

Here are some commonly used options.

c - for create

x - for extracts

v - for verbose

f - for forcefully

t - for test

z - for gzip

j - for bx2

J - for xz

C - for specific destination

To create a tar acrchive file

$ tar -cvf /mnt/backup.tar /var

To show file size in human-readable format.

$ du -sh /var
$ du -sh /mnt/backup.tar

To extract a tar archive file on the default location.

$ tar -xvf/mnt/backup.tar

To extract tar archive file on a specific location.

$ tar -xvf/mnt/backup.tar -C /root/Desktop/

Job automation

Job automation allows us to perform the task automatically in OS by using tools

This feature is very useful for administrators to assign the task to OS whenever he is not present or daily basis work.

There are two types of automation.

at : at command used to execute job only one time.

crontab: crontab command is used to execute jobs multiple times.

To set job with "at" command

#date

#at 8:10 AM

at>useradd saif

at>

///Ctrk+D(write and quit)

To show pending jobs

#atq

To remove at job

$ atrm 2

To restrict the users from accessing at

$ vim /etc/at.deny
Saif(username)
:wq(write& quite)

To start a crond service

$ systemctl start crond

To enable crond service

$ systemctl enable crond

To set cron job

$ crontab -e

To check cron jobs of current user

$ crontab -l

To remove cron jobs

crontab -r

How to set host name

$ hostnamectl set-hostname it.citynet.com

To show host name

$ hostname

Service Management

How to check service status

$ systemctl status servicename

How to start a service

$ systemctl start servicename

How to stop a service

$ systemctl stop servicename

How to restart a service

$ systemctl restart servicename

how to stop permanently.

$ systemctl disable servicename

How to on service permanently

$ systemctl enable servicename

Determine service is enabled

$ systemctl is-enabled servicename

How to check CPU utilisation

$ top
// press 1 then c , high one will on first place
quite - press q

How to check free memory

$ free -g
              total        used        free      shared  buff/cache   available
Mem:              3           1           0           0           1           1
Swap:             1           0           1

How to check disk space.

$ df -kh
Filesystem      Size  Used Avail Use% Mounted on
udev            1.9G     0  1.9G   0% /dev
tmpfs           389M  1.7M  387M   1% /run
/dev/sdb5       234G   11G  212G   5% /
tmpfs           1.9G  180M  1.8G  10% /dev/shm

I hope it will be helpful in your Linux journey.

Happy Learning.

Thanks & Regards,

Saif Raza Khan