linux-sysadmin

name	linux-sysadmin
description	Diagnose and operate Linux systems, especially Rocky Linux and Ubuntu, including SSH, SELinux, permissions, firewalls, packages, processes, logs, and systemd services. Use when Codex is asked to troubleshoot hosts, prepare commands, write runbooks, fix service failures, or reason about Linux administration.

linux-sysadmin

Workflow

1. Gather host, service, resource, network, and security diagnostics.
2. Determine impact and recent changes.
3. Create rollback for files, packages, service units, and firewall changes.
4. Implement the smallest fix.
5. Validate runtime behavior 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.