As a Linux administrator, managing systems effectively involves a variety of tasks, from automating jobs with Cron to securing applications. This guide walks you through 24 essential tasks with practical use cases and instructions.

1. Create a Cron Job

Cron automates repetitive tasks. Example: Schedule a backup every day at midnight.

Steps:

1. Edit crontab:

   crontab-e

1. Add the job:

   0 0*** /path/to/backup.sh

1. Verify:

   crontab-l

2. Linux Banner

Display a custom message on login using/etc/motd.

Steps:

1. Edit/etc/motd:

echo"Welcome to Linux Server" |sudo tee /etc/motd

3. Linux Collaborative Directories

Set up a shared directory with proper permissions.

Steps:

1. Create directory:

mkdir /shared

1. Set group ownership and permissions:

chgrpdevelopers /sharedchmod2775 /shared

4. Linux String Substitute (sed)

Modify files usingsed. Example: Replace "error" with "warning".

Command:

sed-i's/error/warning/g' logfile.txt

5. Linux SSH Authentication

Set up key-based authentication for secure remote access.

Steps:

1. Generate keys:

   ssh-keygen

1. Copy the public key to the server:

   ssh-copy-id user@server

6. Linux Find Command

Locate files quickly. Example: Find.log files larger than 10MB.

Command:

find /path-type f-name"*.log"-size +10M

7. Install a Package

Installhtop as an example.

Command:

sudoaptinstallhtop

8. Install Ansible

Automate IT tasks with Ansible.

Steps:

1. Install Ansible:

sudoaptinstallansible

1. Verify:

   ansible--version

9. Configure Local Yum Repos

Set up a local YUM repository.

Steps:

1. Create a repo file:

sudovi /etc/yum.repos.d/local.repo

1. Add content:

   [local-repo]   name=Local Repository   baseurl=file:///mnt/repo   enabled=1   gpgcheck=0

10. Linux Services

Manage services. Example: Start and enable Apache.

Commands:

sudosystemctl start httpdsudosystemctlenablehttpd

11. Linux Configure sudo

Grant sudo privileges.

Steps:

1. Edit sudoers file:

sudovisudo

1. Add user:

   username ALL=(ALL) NOPASSWD:ALL

12. DNS Troubleshooting

Diagnose DNS issues.

Commands:

nslookup domain.comdig domain.com

13. Linux Firewalld Setup

Set up and manage firewalld.

Commands:

sudofirewall-cmd--add-port=80/tcp--permanentsudofirewall-cmd--reload

14. Linux Postfix Mail Server

Set up Postfix for email delivery.

Steps:

1. Install:

sudoaptinstallpostfix

1. Configure via/etc/postfix/main.cf.

15. Linux Postfix Troubleshooting

Check logs:

sudo tail-f /var/log/mail.log

16. Install and Configure HAProxy LBR

Load balance traffic with HAProxy.

Steps:

1. Install HAProxy:

sudoaptinstallhaproxy

1. Configure/etc/haproxy/haproxy.cfg.

17. HAProxy LBR Troubleshooting

Check status:

sudosystemctl status haproxy

Debug logs:

sudojournalctl-u haproxy

18. MariaDB Troubleshooting

Check MariaDB logs:

sudo tail-f /var/log/mysql/error.log

19. Linux Bash Scripts

Automate tasks. Example: Disk usage report.

#!/bin/bashdf-h> disk_report.txt

20. Add Response Headers in Apache

Enhance security by adding headers.

Steps:

1. Edit.htaccess or/etc/httpd/conf/httpd.conf:

   Header set X-Frame-Options "DENY"

1. Restart Apache:

sudosystemctl restart httpd

21. Apache Troubleshooting

Check configuration:

sudoapachectl configtest

View logs:

sudo tail-f /var/log/httpd/error_log

22. Linux GPG Encryption

Encrypt files with GPG.

Commands:

gpg--encrypt--recipient email@example.com file.txtgpg--decrypt file.txt.gpg

23. Linux Log Rotate

Automate log rotation.

Steps:

1. Configure/etc/logrotate.conf.
2. Test:

   logrotate-d /etc/logrotate.conf

24. Application Security

Implement security measures like SELinux, AppArmor, or Fail2Ban.

Commands:

sudoaptinstallfail2bansudosystemctlenablefail2ban

Happy Learning !!!