Linux Operations Hub

Overview

This hub collects practical Linux notes you can reference during on-call and project work. The two nested folders cover shell essentials and systemd troubleshooting with longer walkthroughs to exercise the navigation and TOC.

What’s inside

• cli/essentials — Daily driver shell commands, file ops, networking, and process inspection.
• systemd/troubleshooting — Service checks, log review, and restart strategies.

Quick sanity checks

• uname -a — confirm kernel and architecture
• lsb_release -a or /etc/os-release — confirm distro
• whoami && id — confirm user and group membership
• df -h and lsblk — confirm disks and mounts

Common tasks

Package management

• Debian/Ubuntu: sudo apt update && sudo apt upgrade
• RHEL/Fedora: sudo dnf check-update && sudo dnf upgrade
• Alpine: sudo apk update && sudo apk upgrade

Logs to grab first

• journalctl -p err -b — errors since last boot
• dmesg -T | tail -n 30 — kernel hints
• /var/log/auth.log or /var/log/secure — auth anomalies

Networking triage

• ip a — addresses
• ip r — routes
• ss -tulpn | head — listening sockets
• dig example.com @resolver — DNS sanity

File permissions refresher

• chmod u+rwx,g+rx,o-rwx file — explicit mode
• chown appuser:appgroup /srv/app — ownership
• setfacl -m u:deploy:rw /srv/app — ACL for one user

Troubleshooting checklist

1. Reproduce and timestamp the issue.
2. Check service status and logs.
3. Validate dependencies (network, disk, env vars).
4. Apply smallest safe change; capture the diff/command.
5. Re-test, roll back if needed, and document the fix.