Every-Minute Cron Job Won't Run
The shortest interval standard cron supports is one minute — * * * * * (or */1 * * * *). If it isn't firing, the cause is almost always a bad command, a wrong PATH, or the cron service being down, not the schedule. Check the cron log first.
The correct expression
* * * * * /path/to/job.sh runs every minute. */1 is identical to * — both mean 'every minute'; there is no sub-minute cron.
Confirm cron launched it
grep CRON /var/log/syslog or journalctl -u cron -f. If you see the launch line every minute but nothing happens, the job's command is the problem (PATH, permissions, or a crash) — not the schedule.
Common real causes
Missing absolute path to the binary; script not executable (chmod +x); no output redirect so errors vanish into mail; or the cron daemon isn't running (systemctl status cron).
Need every few seconds?
Cron can't. Use a systemd timer with OnUnitActiveSec, or a small loop script with sleep that cron starts once a minute.
FAQ
Is */1 the same as * in cron?
Yes. Both mean every minute. The smallest interval standard cron supports is one minute; there is no sub-minute schedule.
Why isn't my every-minute cron job running?
Usually not the schedule. Check the cron log (grep CRON /var/log/syslog). If cron launches it but nothing happens, fix the command: absolute paths, chmod +x, output redirect.
How do I run a job every 30 seconds with cron?
Cron can't go below one minute. Use a systemd timer, or have a once-a-minute cron job run the task twice with a sleep 30 between.