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Linux Administration

Status

Master Plan - Comprehensive init.md complete, ready for SKILL.md implementation

Linux administration remains critical in the cloud-native era. This skill covers systemd service management, process monitoring, filesystem operations, networking fundamentals, and production troubleshooting patterns.

Scope​

This skill teaches:

  • Systemd Service Management - Creating units, service lifecycle, timers (modern cron)
  • Process Management - Monitoring (ps, top, htop), control (kill, nice), resource limits
  • Filesystem Operations - Mount management, disk usage, permissions, quotas
  • Networking Fundamentals - Interface config, routing, firewall basics, DNS resolution
  • Log Management - journalctl, log rotation, log aggregation
  • Performance Tuning - CPU, memory, disk I/O optimization
  • Troubleshooting - Systematic debugging for production issues

Key Components​

Systemd Service Management​

Core Concepts:

  • Units: Services, timers, targets, sockets, mounts
  • Unit Files: /etc/systemd/system/ (custom), /lib/systemd/system/ (package)
  • Service Lifecycle: start, stop, restart, reload, enable, disable
  • Timers: Modern replacement for cron with better logging

Common Commands:

systemctl start service
systemctl status service
systemctl enable service  # Start on boot
journalctl -u service -f  # Follow service logs
systemctl list-timers     # List scheduled tasks

Process Management​

Monitoring:

  • ps aux - List all processes
  • top/htop - Interactive process viewer
  • pgrep/pidof - Find process IDs
  • /proc/[pid]/ - Process information filesystem

Control:

  • kill - Send signals (SIGTERM, SIGKILL)
  • nice/renice - Process priority
  • nohup - Run process immune to hangups
  • systemd-run - Run transient services

Filesystem Operations​

Disk Management:

  • df -h - Disk free space
  • du -sh * - Directory sizes
  • lsblk - List block devices
  • mount/umount - Mount filesystems

Permissions:

  • chmod - Change file permissions (755, 644)
  • chown - Change file ownership
  • setfacl/getfacl - Access control lists

Quotas:

  • User/group disk quotas
  • Soft/hard limits
  • Grace periods

Networking Fundamentals​

Configuration:

  • ip addr - Show/configure IP addresses
  • ip route - Show/configure routing table
  • ss - Socket statistics (modern netstat)
  • nmcli - NetworkManager CLI

Diagnostics:

  • ping - Test connectivity
  • traceroute - Trace network path
  • dig/nslookup - DNS queries
  • tcpdump - Packet capture

Firewall:

  • firewalld (RHEL/CentOS/Fedora)
  • ufw (Ubuntu/Debian)
  • iptables (legacy, still used)

Decision Framework​

Which Init System?

2025 Reality:
  Almost all distributions use systemd
  Exceptions: Alpine (OpenRC), some containers

Use systemd unless:
  - Alpine Linux (lightweight containers)
  - Legacy system (pre-2015)
  - Embedded systems (custom init)

Performance Tuning Priority:

Where's the bottleneck?
  CPU bound? → nice/renice, CPU affinity
  Memory bound? → Swap tuning, memory limits
  Disk I/O? → I/O scheduler, filesystem tuning
  Network? → TCP tuning, NIC ring buffers

Monitor first:
  top/htop → CPU/memory
  iostat → Disk I/O
  sar → Historical trends
  netstat/ss → Network connections

Tool Recommendations​

System Monitoring​

Process Monitoring:

  • top - Classic process viewer
  • htop - Interactive, color-coded
  • atop - Advanced with history

Performance Analysis:

  • vmstat - Virtual memory stats
  • iostat - I/O statistics
  • sar - System activity reporter
  • perf - Performance profiling

Log Management​

journalctl - Systemd journal

journalctl -u service    # Service logs
journalctl -f            # Follow all logs
journalctl --since today # Filter by time
journalctl -p err        # Error priority and above

Traditional Logs:

  • /var/log/syslog or /var/log/messages
  • /var/log/auth.log - Authentication
  • logrotate - Log rotation automation

Package Management​

RHEL/CentOS/Fedora: dnf/yum, rpm Debian/Ubuntu: apt, dpkg Arch: pacman Universal: snap, flatpak (sandboxed)

Integration Points​

With Other Skills:

  • managing-configuration - Automate Linux configuration at scale (Ansible)
  • security-hardening - Apply CIS benchmarks, SELinux, AppArmor
  • operating-kubernetes - Understand K8s node OS layer
  • shell-scripting - Automate administrative tasks
  • implementing-observability - Integrate with monitoring (Prometheus, Grafana)

Workflow Example:

Manual Admin → Script → Ansible → IaC
     │            │        │        │
     ▼            ▼        ▼        ▼
Learn system  Automate  Scale to  Provision
commands      tasks     100s      infrastructure

Learn More​