Skip to main content

Administering Linux

Comprehensive Linux system administration for managing servers, deploying applications, and troubleshooting production issues in modern cloud-native environments.

When to Use​

Use when:

  • Deploying custom applications to Linux servers
  • Troubleshooting slow systems or service failures
  • Optimizing server performance and resource usage
  • Managing users, SSH access, and security
  • Configuring systemd services and timers
  • Monitoring disk space and system resources
  • Scheduling tasks with cron or systemd timers
  • Diagnosing network connectivity issues

Key Features​

Systemd Service Management​

  • Create and manage systemd unit files
  • Configure automatic restarts and dependencies
  • Security hardening with PrivateTmp, ProtectSystem
  • Journal logs with journalctl filtering

Process Management​

  • Monitor processes with top/htop
  • Process states and signal handling (SIGTERM, SIGKILL)
  • Process priority with nice/renice
  • Resource limits with ulimit

Filesystem Operations​

  • ext4, XFS, Btrfs, ZFS filesystem selection
  • LVM for flexible volume management
  • Disk usage monitoring with df, du, ncdu
  • File permissions and ACLs

Package Management​

  • apt (Ubuntu/Debian) and dnf (RHEL/Fedora)
  • System updates and security patches
  • snap/flatpak for cross-distribution packages

Network Configuration​

  • Interface management with ip command
  • Firewall setup (ufw, firewalld)
  • Socket statistics with ss
  • DNS configuration and troubleshooting

Performance Tuning​

  • sysctl for kernel parameter tuning
  • I/O scheduler configuration
  • TCP/BBR congestion control
  • Memory swappiness and cache pressure

Quick Start​

Creating a Systemd Service​

# /etc/systemd/system/myapp.service
[Unit]
Description=My Web Application
After=network.target postgresql.service
Requires=postgresql.service

[Service]
Type=simple
User=myapp
Group=myapp
WorkingDirectory=/opt/myapp
Environment="PORT=8080"
ExecStart=/opt/myapp/bin/server
ExecReload=/bin/kill -HUP $MAINPID
Restart=on-failure
RestartSec=5s
StandardOutput=journal

# Security hardening
PrivateTmp=true
NoNewPrivileges=true
ProtectSystem=strict
ReadWritePaths=/var/lib/myapp

[Install]
WantedBy=multi-user.target

Deploy service:

sudo systemctl daemon-reload
sudo systemctl enable myapp.service
sudo systemctl start myapp.service
sudo systemctl status myapp.service

SSH Hardening​

# /etc/ssh/sshd_config
PermitRootLogin no
PasswordAuthentication no
PubkeyAuthentication yes
MaxAuthTries 3
AllowUsers admin deploy
X11Forwarding no

# Apply changes
sudo sshd -t
sudo systemctl restart sshd

Performance Tuning​

# /etc/sysctl.d/99-custom.conf
# Network tuning
net.core.rmem_max = 134217728
net.core.wmem_max = 134217728
net.ipv4.tcp_congestion_control = bbr

# Memory management
vm.swappiness = 10
vm.vfs_cache_pressure = 50

# Apply changes
sudo sysctl -p /etc/sysctl.d/99-custom.conf

Essential Commands​

Service Management​

systemctl start nginx              # Start service
systemctl stop nginx               # Stop service
systemctl restart nginx            # Restart service
systemctl status nginx             # Check status
systemctl enable nginx             # Enable at boot
journalctl -u nginx -f             # Follow service logs

Process Monitoring​

top                                # Interactive process monitor
htop                               # Enhanced process monitor
ps aux | grep process_name         # Find specific process
kill -15 PID                       # Graceful shutdown (SIGTERM)
kill -9 PID                        # Force kill (SIGKILL)

Disk Management​

df -h                              # Filesystem usage
du -sh /path/to/dir                # Directory size
ncdu /path                         # Interactive disk analyzer
lsblk                              # List block devices

Network Tools​

ip addr show                       # Show interfaces
ip route show                      # Show routing table
ss -tunap                          # All TCP/UDP connections
ss -tlnp                           # Listening TCP ports
ping -c 4 8.8.8.8                  # Test connectivity
dig example.com                    # DNS query

Troubleshooting Workflows​

Performance Issues​

  1. Identify bottleneck:

    top                             # Quick overview
    uptime                          # Load averages

  2. CPU Issues (usage >80%):

    top                             # Press Shift+P to sort by CPU
    ps aux --sort=-%cpu | head

  3. Memory Issues (swap used):

    free -h                         # Memory usage
    top                             # Press Shift+M to sort by memory

  4. Disk I/O Issues (high wa%):

    iostat -x 1                     # Disk statistics
    iotop                           # I/O by process

References​

  • Full Skill Documentation
  • Systemd Guide: references/systemd-guide.md
  • Performance Tuning: references/performance-tuning.md
  • Filesystem Management: references/filesystem-management.md
  • Network Configuration: references/network-configuration.md
  • Security Hardening: references/security-hardening.md
  • Troubleshooting Guide: references/troubleshooting-guide.md