Cron and scheduling

cron runs commands on a schedule on Linux servers. Bash scripts are common cron targets—keep them idempotent and log output.

Crontab format

# min hour dom month dow command
0 2 * * * /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1

Fields: minute, hour, day-of-month, month, day-of-week. Use crontab -e for your user table.

Script hygiene for cron

#!/usr/bin/env bash
export PATH="/usr/local/bin:/usr/bin:/bin"
cd /opt/app || exit 1
./run-job.sh

Cron environments are minimal—set PATH and cd explicitly.

Alternatives

systemd timers, GitHub Actions schedules, and cloud schedulers replace cron in many stacks—Bash glue scripts stay the same pattern: exit codes and logs.

Important interview questions and answers

1. Q: Why set PATH in cron scripts?
   A: Cron provides a sparse environment—commands may not be found otherwise.
2. Q: Redirect cron output?
   A: Capture stdout/stderr to log files for debugging silent failures.

Self-check

1. How many time fields does a cron line have?
2. Why cd to the app directory first?

Tip: Log cron output somewhere visible—silent failures are hard to debug.