linuxexpert-practice-labs/labs/linux-plus/2-3-3-scheduling

Linux+ 2.3.3: Scheduling jobs

A cron job that runs every minute, the environment cron jobs get, and a one-off job with at.

Before you start

Work as root. The lab makes sure cron is installed and running, and removes old copies of the files the tasks create in /tmp. Two of the tasks take a few minutes of waiting.

Tasks

1. Add a job to your crontab that appends the output of date to /tmp/cron-test.txt every minute. When it has run at least twice, remove the job from your crontab again (keep the file).
2. Add a job to your crontab that writes its environment (env) to /tmp/cron-env.txt every minute. When it has run, compare that file with your shell's environment, then remove the job (keep the file).
3. Install at if needed and make sure atd is running and starts at boot. Schedule a one-off job that creates /tmp/at-ran two minutes from now, and wait for it.

Hints

• (crontab -l 2>/dev/null; echo '* * * * * ...') | crontab -, crontab -l | grep -v PATTERN | crontab -.
• diff <(sort /tmp/cron-env.txt) <(env | sort): cron's PATH and SHELL are minimal.
• systemctl enable --now atd, echo 'touch /tmp/at-ran' | at now + 2 minutes, atq.
• The chapter's step 4 (anacron and /etc/crontab) isn't graded.