Linux System Administration

 What is Linux System Administration?

Linux System Administration involves installing, configuring, maintaining, securing, and troubleshooting Linux servers and systems to ensure reliability, performance, and security.

🔹 Core Responsibilities

• User & group management
• File system & storage management
• Package & software management
• Process & service management
• Network configuration
• System monitoring & troubleshooting
• Security & access control
• Backup & recovery
• Automation & scripting

🔹 Essential Linux Admin Skills

1️⃣ User & Group Management

useradd user1

passwd user1

usermod -aG sudo user1

groupadd developers

Files:

• /etc/passwd
• /etc/shadow
• /etc/group

2️⃣ File System & Permissions

ls -l

chmod 755 file.sh

chown user:group file

df -h

du -sh *

mount /dev/sdb1 /mnt

Permissions: r (4) | w (2) | x (1)

3️⃣ Package Management

Debian/Ubuntu

apt update

apt install nginx

apt remove nginx

RHEL/CentOS

yum install httpd

dnf update

4️⃣ Process & Service Management

ps aux

top

htop

kill -9 PID

systemctl start nginx

systemctl enable nginx

systemctl status nginx

5️⃣ Networking Basics

ip a

ip r

ping google.com

netstat -tulnp

ss -tulnp

nmcli device status

Config files:

• /etc/network/interfaces
• /etc/netplan/*.yaml

6️⃣ Disk & Storage Management

lsblk

fdisk /dev/sdb

mkfs.ext4 /dev/sdb1

mount /dev/sdb1 /data

LVM:

pvcreate /dev/sdb

vgcreate vg_data /dev/sdb

lvcreate -L 10G -n lv_data vg_data

7️⃣ Logs & Monitoring

journalctl

journalctl -u nginx

tail -f /var/log/syslog

uptime

free -h

vmstat

8️⃣ Security & Access Control

ufw enable

ufw allow 22

iptables -L

SELinux:

getenforce

setenforce 0

SSH:

ssh user@server-ip

9️⃣ Backup & Compression

tar -czvf backup.tar.gz /data

rsync -av /data /backup

crontab -e

🔟 Shell Scripting (Automation)

#!/bin/bash

df -h >> disk_report.txt

Make executable:

chmod +x script.sh

🔹 Important Configuration Files

FilePurpose/etc/fstabMount points/etc/hostsHostname mapping/etc/resolv.confDNS/etc/ssh/sshd_configSSH/etc/crontabScheduled jobs

🔹 Common Linux Admin Interview Questions

• Difference between soft link & hard link
• What happens during Linux boot process
• How to check high CPU usage
• How to recover root password
• Difference between systemctl and service
• How permissions work in Linux