deb-scripts-system-commands

name	deb-scripts-system-commands
description	Use when adding or changing apt, systemctl, ufw, sysctl, curl, rm, or other host-level command execution in deb_scripts. Covers safe subprocess patterns, post-command verification, and what to log versus what to keep in debug output.

System commands

Use this skill whenever a change affects subprocess execution or host state.

Command design

• Prefer explicit argument lists over shell strings.
• Use shell execution when the upstream workflow depends on shell features such as pipes, redirection, or source, for example curl ... | sh or sourcing ~/.local/bin/env.
• Use check=False when you need to inspect return codes and keep control of logging.
• Treat command stdout/stderr as debug material unless the user truly needs to see it.

Safe patterns

• apt: verify success with return code and a follow-up state check when the package/service matters
• systemctl: do not trust a single restart or enable; re-check active state when behavior depends on it
• ufw: preserve safe baseline and SSH access before enablement
• sysctl: re-read the effective value after applying changes
• rm: prefer targeted paths and idempotent flags such as -f where appropriate
• curl: verify both return code and expected file presence when downloading installers

Logging rules

• INFO: operation start and final outcome
• DEBUG: command output, timings, retries, exact return codes
• WARNING: command completed with degraded or uncertain result
• ERROR: command failure that prevents completion

Verification

• Do not report success solely because a command exited 0 if the desired state is easy to verify.
• Prefer a state-based final check:
  • package/version present
  • service active/inactive as expected
  • config file written
  • binary exists

Cleanup

• Clean temporary installers and transient files after successful or safe failure paths.
• Keep cleanup idempotent.

Related skills

• Use deb-scripts-service-pattern for the surrounding service design.
• Use deb-scripts-logging if command telemetry changes what the user sees.