Line vs expression
A cron expression is five fields. A crontab line adds a command, and in `/etc/cron.d` a user column between them.
User crontab vs cron.d
Personal `crontab -e` files must not include a user token. System drop-ins do. Toggle the format on this page rather than guessing.
PATH, MAILTO, redirects
Jobs fail because `backup.sh` is not on cron’s PATH. The snippet sets a conservative PATH and optional MAILTO. Redirects append >> log 2>&1.
HTTP monitoring is painful in crontab
curl in cron has no execution UI. If the command is really an HTTP call, migrate it to CronFox for logs and retries.
macOS note
Launchd is the modern macOS scheduler. This tool still emits crontab lines for Linux and for macOS users who keep cron enabled.