Linux Administration Quick Reference
April 24, 2026
A compact reference for Linux files, permissions, services, storage, networking, security, and automation.
Files and permissions
| Need |
Useful command or record |
| Inspect owner and mode |
ls -l |
| Change owner or group |
chown, chgrp |
| Change mode bits |
chmod |
| Inspect or manage POSIX ACLs |
getfacl, setfacl |
| Find files |
find, grep, distribution-specific locate databases |
| Grant narrow administrative access |
sudo policy and an approved sudoers drop-in |
Services and processes
| Need |
Useful check |
| Inspect a process |
ps, top, pidstat, and logs |
| Inspect a systemd service |
systemctl status service and journalctl -u service |
| Start now and at boot on systemd |
systemctl start service, then systemctl enable service when appropriate |
| Investigate a port conflict |
Current listener, service configuration, firewall, and security-policy logs |
| Run scheduled work |
cron or systemd timers, with explicit paths and logging |
systemctl and journalctl apply to systemd-based systems; use the init and logging tools supplied by another platform when systemd is absent.
Storage and networking
| Need |
Useful first check |
| Filesystem free space |
df -h |
| Directory consumption |
du -sh |
| Persistent mount |
/etc/fstab, a stable identifier such as UUID, and a tested mount |
| Logical volumes |
Physical volume, volume group, logical volume, filesystem, and resize order |
| Host connectivity |
Interface state, address, route, gateway, DNS, and link |
| Service reachability |
Listener, local firewall, remote policy, route, service configuration, and logs |
Security and automation
- Use individual accounts and narrow
sudo permissions.
- Protect SSH private keys and restrict SSH access according to policy.
- Inspect SELinux or AppArmor denials before disabling enforcement.
- Patch from trusted repositories and assess service impact.
- In scripts, quote variables, validate input, use explicit paths, record failures, and check exit status.
- Test filesystem, firewall, service, and scheduled-task changes before relying on them after a restart.
Revised on Friday, September 11, 2026