linux-sysadmin

Workflow

1. Gather host, service, resource, network, and security diagnostics.
2. Determine whether the failure is host-level or primarily belongs to a specialized application, container, or cross-system infrastructure skill.
3. Identify impact and recent changes, then create rollback for files, packages, service units, and firewall changes.
4. Implement the smallest host-level fix and validate runtime behavior, remote access, security policy, and boot persistence.

Diagnostics

cat /etc/os-release
uname -a
uptime
free -h
df -h
lsblk
systemctl status <unit>
journalctl -xeu <unit>
ss -tulpn
getenforce
firewall-cmd --list-all
ufw status verbose

Safety Rules

• Never disable SELinux as a default fix.
• Never rotate SSH keys or change sshd_config without rollback.
• Never modify firewall rules without confirming active firewall stack.
• Prefer systemd drop-ins over editing packaged unit files.
• Preserve ownership, permissions, ACLs, mount options, and labels.

Validation

• Service starts now and after reboot.
• Logs show no new errors.
• Expected ports listen and unexpected ports do not.
• SSH access still works.
• SELinux and firewall state match the intended policy.