Cron Initialization Order: Why It Matters on macOS
Cron Initialization Order: Why It Matters
On macOS, cron jobs run through launchd, and launchd does not guarantee execution order. If you have three cron jobs scheduled at the same time, they might run in any order. For most tasks this does not matter. For stats collection and agent initialization, it matters a lot.
The Stats Collection Problem
Imagine you have a cron job that collects system metrics and another that processes those metrics into reports. If the processing job runs before the collection job, it processes stale data from the previous cycle. You get a report that is always one cycle behind, and the error is completely silent.
On Linux with systemd, you can define ordering dependencies between timer units. On macOS with launchd, you cannot. Launchd treats each plist as independent. There is no built-in way to say "run job B after job A finishes."
Workarounds That Actually Work
The most reliable fix is chaining: have job A trigger job B when it completes. Instead of scheduling both at the same time, schedule only job A and have its last step be launchctl kickstart for job B.
Another approach is using a lock file. Job B checks for a file that job A creates when it finishes. If the file does not exist yet, job B waits or exits and tries again on the next cycle.
The worst approach is adding time offsets - schedule A at :00 and B at :05. This works until A takes longer than five minutes, and then you are back to the same race condition.
For Desktop Agents
AI agents that rely on cron for periodic tasks - memory consolidation, stats rollup, cache cleanup - need to be especially careful. A memory consolidation job that runs before the stats collection job will miss the most recent data. Get the ordering right from the start.
Fazm is an open source macOS AI agent. Open source on GitHub.