service-conditions

Service conditions

condition-file-exists and condition-file-missing gate a service on the state of a file: the first runs the process only if the path exists, the second only if it doesn't. Setting both means both must hold. The classic use is a preparation oneshot that must run only when its work is not done yet — no sh -c 'if [ ! -e ... ]' wrapper needed.

condition-file-exists: /etc/app/enable    # run only if present
condition-file-missing: /etc/app/done     # run only if absent

Rules and semantics:

• Paths must be absolute; a relative path is rejected at load.
• The condition is re-evaluated at every start attempt: initial startup, on-failure/on-success restarts, each scheduled cron tick, and manual start via the control socket. A restart loop therefore stops on its own once the watched file state changes.
• An unmet condition skips the start: it is logged with the reason, shown by status <name> as skipped (...), and counts as success — services with after:/requires: on it start normally, and no on-success/ on-failure action fires (nothing ran).
• Symlinks are followed (os.Stat), so a k8s configmap/secret key resolved through ..data/ gives the right answer; a dangling symlink counts as missing. A stat error other than not-exist (e.g. permission denied) leaves the condition unmet with the error in the skip reason, so it never silently masquerades as a missing file.
• The check is advisory, not a lock: the file state can change between the probe and the exec.

Config

processes:
  - name: aux-cfg
    condition-file-missing: /etc/haproxy/haproxy-aux.cfg
    command: /bin/sh
    args:
      - -c
      - |
        touch /etc/haproxy/haproxy-aux.cfg
        chmod g+w /etc/haproxy/haproxy-aux.cfg
    startup: oneshot
  - name: app
    command: /usr/sbin/haproxy
    requires: [aux-cfg]

Expected behavior

• First boot: the file is missing, aux-cfg runs and creates it, app starts after it completes.
• Later boots: the file exists, aux-cfg is skipped (aux-cfg skipped (condition-file-missing: ... exists)), and app still starts — skip satisfies requires:.
• status aux-cfg reports skipped (condition-file-missing: ... exists); a manual start aux-cfg reports the same instead of running it.

Test

Run level. Boots the daemon twice against the same directory and asserts the run/skip split above. SIGTERM yields a clean exit 0.

go test ./documentation/service-conditions/ -v