LINUX Day2Day Job Description for a DevOps Engineer [Very Imoprtant]

Manually set up a repository

create a .repo file within /etc/yum.repos.d using a text editor. Here I am creating the repository file for MySQL 5.7

Step1 :

• cd /etc/yum.repos.d/

Step2:

• vim mysql57-community.repo
• [mysql57-community]
• name=MySQL 5.7 Community Server
• baseurl=http://repo.mysql.com/yum/mysql-5.7-community/el/7/$basearch/
• enabled=1
• gpgcheck=1
• gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql

Step4:

• yum install mysql

YUM CONFIGURTION

• YUM stands for Yellow Dog Updater Manager.
• Yum is the default package management utility in RHEL/Centos.
• Yum uses repository to get the necessary rpm files.
• A repository is collection of rpm files.
• Repository may contain multiple versions of the same RPM package.
• Repository may contain different builds for different architectures for example one for i686 and other for x86_64.
• A repository can be configured locally or remotely.

Repository configuration files are stored in /etc/yum.repos.d/ directory with an extension .repo

vi /etc/yum.repos.d/example.repo

• [examplerepo] // label of the repository
• name=examplerepo // name of the repository.
• baseurl=file:///rhcelab/repo // define the location of rpm files.
• enabled=1 // value = 1 means enabled. or, 0 means the repository is disabled.
• gpgcheck=0 // value = 1 means integrity will be checked. or, 0 means integrity will not be checked.
• :wq! // save and quit from the file.

CONFIGURE IP NETWORKING WITH NMCLI

• yum install NetworkManager
• systemctl start NetworkManager
• systemctl enable NetworkManager (make sure it is up 24/7)
• nmcli connection show --active
• nmcli device status
• nmcli connection add type ethernet ifname eth0
• nmcli connection show
• nmcli connection up ethernet-eth0
• nmcli connection show --active

To Change the Linux system IP ADDRESS:

• nmcli connection modify ethernet-eth0 ipv4.address 172.31.16.0/24
• nmcli connection modify ethernet-eth0 ipv4.method manual

To modify IPV4 Gateway:

• nmcli connection modify ethernet-eth0 ipv4.gateway “172.31.16.2”

To modify the DNS:

• nmcli connection modify ethernet-eth0 ipv4.dns “172.31.16.101”

Reset Root Password in Linux CentOS:

• Boot to Recovery Mode. When system restarts, press “ESC” key to interrupt the boot process.
• Select the kernel from the GRUB/Boot menu; press the arrow keys.
• Pressing ‘e’ from your keyboard will open the editing menu.
• In the editing menu, locate the “ro” kernel parameter and replace it with “rw”.
• Add an additional parameter “init=/sysroot/bin/sh”
• Press Ctrl + X to enter into single-user mode
• Run the “chroot /sysroot” command to convert the root file to read and write mode
• Set a new password for root, command: passwd root (Changing the password for user root)
• SELinux relabelling (to set the permissions for files or folders)
• Exit from terminal
• Hit reboot

Create a .tar backup

• tar -cvf backup.tar finaldraft.sh
• tar -czf backup.tar.gz finaldraft.sh
• tar -xvfz backup.tar.gz

Exclude files when creating a tar backup

• tar --exclude file.txt --exclude file.sh -cvfz backup.tar.gz

Extract content from a tar (.gz) backup

• tar -xvfz backup.tar.gz

Here:

• c -> Create the archive
• v -> Show the process verbosely
• f -> Name the archive
• x -> Extract the content
• z -> Compressed gzip archive file

Tunning Linux system

Profile tuned are divided into power-saving profiles, and performance-boosting profiles. The performance-boosting profiles include profiles focus on the following aspects:

• low latency for storage and network
• high throughput for storage and network
• virtual machine performance
• virtualization host performance

TuneD recommends the most suitable profile for your system, commands:

• yum install tuned
• systemctl enable --now tuned
• yum install tuned-profiles-realtime
• tuned-adm active (Verify that a TuneD profile is active and applied)
• tuned-adm verify
• tuned-adm recommend
• tuned-adm profile powersave

Create Group

• useradd //adds accounts
• usermod //modifies accounts
• userdel //deletes accounts
• groupadd //adds groups
• groupmod //modifies groups
• groupdel //deletes groups
• groupadd [-g gid [-o]] [-r] [-f] groupname

Create Account

useradd -d /home/example/ -g testers -s /bin/bash -m example

SELinux [Security Enhanced Linux]

It is an access control system built into the Linux kernel. It enforces resource policies according to the level of user access, programs, and services.

SELINUX=enforcing|permissive|disabled //It Defines the top-level state of SELinux on a system.

• enforcing — The SELinux security policy is enforced.
• permissive — The SELinux system prints warnings but does not enforce the policy.
• disabled — SELinux is fully disabled. SELinux hooks are disengaged from the kernel and the pseudo-file system is unregistered.

SELINUXTYPE=targeted|strict //It Specifies which policy SELinux should enforce.

• targeted — Only targeted network daemons are protected.
• strict — Full SELinux protection, for all daemons. Security contexts are defined for all subjects and objects, and every action is processed by the policy enforcement server.

To check SELinux:

• sestatus
• cat /etc/selinux/config

To Change SELinux Mode:

• vi /etc/sysconfig/selinux
• SELINUX=enforcing
• SELINUXTYPE=targeted
• :wq!

Create Cron Job

Example: send an email every Monday at 5 pm, how to exec in a cron job in Linux?

Enter the command to edit the crontab file:

crontab -e

In the crontab file, add the following line to schedule the cron job:

0 17 * * MON /sh/opt/script.sh

Save the crontab file and exit the text editor.

SWAP PARTITION

For Prioritization and Hibernation, and if your RAM fills up completely, then AWAP Partition comes in the picture!

1st way:

Use fdisk command to create a disk partition of type 82 (Linux swap)

Initialize the partition (for example, /dev/sda2) as a swap partition:

mkswap /dev/sda2

Enable swapping to the swap partition:

swapon /swapfile

Add an entry to /etc/fstab for the swap partition so that the system uses it following the next reboot:

/dev/sda2 swap swap defaults 0 0

2nd way:

Create a swap partition fdisk /dev/vda

Press n [for new ]

+512 M

t [type for SWAP partition number is 82]

:wq! [quit]

partprobe /dev/vda3 [To hit the kernel about new partition]

mkswap /dev/vda3 [To use the swap partition]

mount –a [To check errors]

vi /etc/fstab [For permanent mount]

/dev/vda3 swap swap

swapon -s

df -h [Recheck file]

Logical Volume Management (LV)

It combines multiple individual hard drives and/or disk partitions into a single volume group (VG). New VG can be subdivided into logical volumes (LV) or used as a single large volume.

fdisk -l [to see mapper]

Steps:

Install a new hard disk drive

Designate Physical Volumes

pvcreate /dev/vda1

Manage Volume Groups

vgcreate vgname /dev/vda1

Manage Logical Volumes, VG can be subdivided into one or more LVs

lvcreate -L size -n lvname vgname [size maybe anything like 500MB..]

Logical volumes- 8e

fdisk /dev/vda

n

+500M

t ->8e

:wq!

Reboot the VM

pvcreate /dev/vdb

vgcreate –s 16 test /dev/vdb

lvcreate –l 30 –n new test

Mkdir /mnt/storage

MAKE VFAT FILE SYSTEM:

A virtual file allocation table (VFAT) is an extension to the file allocation table (FAT) from Windows 95 and onward for creating, storing, and managing files with long names.

Mkfs.vfat /dev/test/new

Vim /etc/fstab

/dev/test/new /mnt/storage vfat

/dev/test/new

Thank YOU!

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