Cron job on my Droplet does not run, but works when I run it by hand

Question

Hi, I have a bash script that backs up my database to a file. If I run ./backup.sh in the terminal it works fine. I added it to crontab -e to run every night at 2 AM, but nothing happens. No backup file, no error. What am I missing?

Bobby · Answer

Hi there, This is one of the most common cron problems. Cron runs with a very small environment. It has no PATH like your normal shell, a different working directory, and no output on screen, so errors just disappear. First, check if cron even tried to run the job: grep CRON /var/log/syslog | tail -20 If you see your line there, cron ran it and the script failed. If not, check the crontab syntax and that the cron service is running (systemctl status cron). Then fix the usual causes: Use full paths for everything, in the crontab and inside the script. Use /usr/bin/pg_dump instead of pg_dump. Find the path with which pg_dump. Make the script executable (chmod +x backup.sh) and use the full path to it in the crontab. Don’t use relative paths for the output file. Use /var/backups/db.sql, not ./db.sql, because cron does not start in your home folder. Set PATH at the top of the crontab if you need it: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin Make sure the script has a shebang on the first line, like #!/bin/bash. To see the real error, send the output to a log file: 0 2 * * * /home/user/backup.sh >> /var/log/backup.log 2>&1 Now check /var/log/backup.log after the next run. You can also test with a job that runs every minute (* * * * *) while you debug, then change it back. Also, if you use % in the crontab line (for example in a date +%F command), you must escape it as \%, or cron will break the line. Easier fix: put the date logic inside the script, not in the crontab. One more tip for backups: make the script exit with an error if the dump fails (set -euo pipefail at the top) and test a restore from time to time. A backup you never restored is only a guess. If you want to check your schedule before you save it, this cron expression simulator shows when a job will run next.

alexdo · Answer

Hi there, Bobby covered the environment and path side well. Here are a few other things that produce exactly “no backup file, no error”. Timezone. Cron runs on the server’s timezone, not yours, and a fresh Droplet is usually set to UTC. So “2 AM” may be running hours earlier or later than you expect, and if you checked right after your local 2 AM, the job may not have run yet. Check with: timedatectl Either write the schedule in UTC, or change the timezone with sudo timedatectl set-timezone Your/Zone and then restart cron with sudo systemctl restart cron, so it picks up the new zone. Database credentials. When you run the script by hand, pg_dump or mysqldump often gets the password from something your login shell provides, like a PGPASSWORD export in ~/.bashrc, or it simply prompts you. Cron doesn’t load .bashrc and has no terminal to prompt on, so the dump fails or hangs. Put the credentials somewhere cron can read them, for example a ~/.pgpass file with chmod 600 for PostgreSQL, or a ~/.my.cnf with a [client] section for MySQL, owned by the same user whose crontab runs the job. Which crontab. crontab -e and sudo crontab -e are two different crontabs. If the script needs root, for example to write into /var/backups, but you added it to your own user’s crontab, it will fail on permissions. You can check both with: crontab -l sudo crontab -l Where the cron logs are. If grep CRON /var/log/syslog returns nothing, it may be because the image doesn’t use rsyslog. The systemd journal has the same entries: journalctl -u cron --since "today" Regards

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Cron job on my Droplet does not run, but works when I run it by hand

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Cron job on my Droplet does not run, but works when I run it by hand

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