linux-administration

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---
name: linux-administration
description: System administration for Linux servers. Manage packages, services, and system configuration. Use when administering Linux systems.
license: MIT
metadata:
  author: devops-skills
  version: "1.0"
---

# Linux Administration

Core Linux system administration skills for managing production servers, development environments, and infrastructure hosts across Debian/Ubuntu and RHEL/CentOS distributions.

## When to Use

- Provisioning and maintaining Linux servers in any environment
- Installing, updating, or removing software packages
- Managing filesystems, disk usage, and mount points
- Investigating runaway processes or high resource consumption
- Scheduling recurring tasks with cron or systemd timers
- Analyzing system and application logs for troubleshooting

## Prerequisites

- Root or sudo access on the target system
- SSH access configured (see `ssh-configuration` skill)
- Familiarity with a terminal text editor (vim, nano)
- Package manager available (`apt` on Debian/Ubuntu, `dnf` on RHEL 8+/Fedora)

## Package Management

### Debian / Ubuntu (apt)

```bash
# Update package index and upgrade all installed packages
apt update && apt upgrade -y

# Search for a package by keyword
apt search nginx

# Show detailed package info including dependencies
apt show nginx

# Install a specific version of a package
apt install nginx=1.24.0-1ubuntu1

# Install multiple packages in one command
apt install -y nginx certbot python3-certbot-nginx

# Remove a package but keep its config files
apt remove nginx

# Remove a package and purge all config files
apt purge nginx

# Remove unused dependency packages
apt autoremove -y

# List all installed packages
dpkg -l | grep nginx

# Pin a package to prevent automatic upgrades
cat <<'EOF' > /etc/apt/preferences.d/pin-nginx
Package: nginx
Pin: version 1.24.0-1ubuntu1
Pin-Priority: 1001
EOF

# Add an external repository (example: Docker CE)
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" \
  > /etc/apt/sources.list.d/docker.list
apt update
```

### RHEL / CentOS / Fedora (dnf)

```bash
# Update all packages
dnf update -y

# Search for a package
dnf search nginx

# Show package details
dnf info nginx

# Install a package
dnf install -y nginx

# Install a specific version
dnf install nginx-1.24.0-1.el9

# Remove a package
dnf remove nginx

# List installed packages
dnf list installed | grep nginx

# Enable a module stream (example: Node.js 20)
dnf module enable nodejs:20
dnf install -y nodejs

# Add an external repository
dnf install -y epel-release

# View repository list
dnf repolist --all

# Clean cached package data
dnf clean all
```

## System Information

```bash
# Kernel and OS release
uname -a
cat /etc/os-release

# Hostname and system metadata
hostnamectl

# CPU information
lscpu
nproc                      # Number of processing units

# Memory usage (human-readable)
free -h

# Disk usage summary
df -hT                     # Include filesystem type
du -sh /var/log/*          # Summarize directory sizes

# Network interfaces and IP addresses
ip addr show
ip route show              # Routing table

# Uptime and load average
uptime
w                          # Who is logged in and load
```

## Filesystem Management

```bash
# List block devices and partitions
lsblk
fdisk -l

# Create a new ext4 filesystem on a partition
mkfs.ext4 /dev/sdb1

# Mount a filesystem temporarily
mount /dev/sdb1 /mnt/data

# Add a persistent mount via fstab
echo '/dev/sdb1  /mnt/data  ext4  defaults,noatime  0  2' >> /etc/fstab
mount -a                   # Mount everything in fstab

# Check and repair a filesystem (unmount first)
umount /dev/sdb1
fsck.ext4 -y /dev/sdb1

# Monitor disk I/O in real time
iostat -xz 2

# Find files larger than 100 MB
find / -xd