Fix a cron job that is not running

(CRON) info (No MTA installed, discarding output)

Common causes

• Commands like php, node or wp are not on cron's short PATH (/usr/bin:/bin)
• Relative paths that only work from your home or project directory
• The script is not executable or lacks a #! shebang line
• An unescaped % in the command, which cron converts to a newline
• Wrong schedule syntax, a missing trailing newline, or the job was added to the wrong user's crontab
• The server time zone differs from what you expect, so the job runs at another hour

How to fix it

1. Confirm cron fired the job. Check grep CRON /var/log/syslog (Debian/Ubuntu), /var/log/cron (RHEL) or journalctl -u cron (cron.service on Debian/Ubuntu, crond.service on RHEL). A CMD line at the expected time means cron ran it and the command itself failed.
2. Capture the output. Append >> /var/log/myjob.log 2>&1 to the crontab line. The "No MTA installed" message means output was being discarded, so this log will show the real error.
3. Use absolute paths. Find binaries with which php and write them in full, for example /usr/bin/php /var/www/app/artisan schedule:run. cd into the project directory first if the script uses relative paths.
4. Make scripts executable. Run chmod +x /home/user/backup.sh and make sure the first line is a shebang such as #!/usr/bin/env bash or #!/bin/bash.
5. Escape percent signs. Write date +\%F instead of date +%F inside crontab, or move the command into a script file.
6. Check schedule and user. View the active crontab with crontab -l (or sudo crontab -u www-data -l). Confirm the server time zone with timedatectl and use CRON_TZ= where supported.

crontab -e

SHELL=/bin/bash
PATH=/usr/local/bin:/usr/bin:/bin

# Laravel scheduler every minute, with output logged
* * * * * cd /var/www/app && /usr/bin/php artisan schedule:run >> /var/log/app-cron.log 2>&1

# Nightly backup at 02:30, escaping %
30 2 * * * /home/user/backup.sh > /home/user/backup-$(date +\%F).log 2>&1

How to stop it happening again

• Always log cron output to a file or monitoring service
• Use absolute paths and set PATH at the top of the crontab
• Test the exact command with env -i /bin/sh -c '...' to mimic cron's environment
• Run jobs as the same user that owns the files they touch