https://wiki.plecko.hr/ 2026-04-04T01:26:28+00:00 https://wiki.plecko.hr/ https://wiki.plecko.hr/lib/tpl/bootstrap3/images/favicon.ico text/html 2019-10-31T09:14:00+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.plecko.hr/doku.php?id=linux:misc:cron:best_practices_for_cron&rev=1572509640&do=diff Best practices for cron Cron is a wonderful tool, and a standard part of all sysadmins toolkit. Not only does it allow for precise timing of unattended events, but it has a straightforward syntax, and by default emails all output. What follows are some best practices for writing crontabs I’ve learned over the years. In the following discussion, “cron” indicates the program itself, “crontab” indicates the file changed by “crontab -e”, and “entry” begin a single timed action specified inside the … text/html 2019-10-31T09:14:00+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.plecko.hr/doku.php?id=linux:misc:cron:bug&rev=1572509640&do=diff How a cron bug became the de-facto standard While testing some scheduling edge cases, an old bug was discovered in cron. As long as your crontab schedules' day-of-month and day-of-week fields' values are just simple asterisks (*) or don't contain a * at all, you'll be fine. Otherwise, definitely keep on reading. text/html 2019-10-31T09:14:00+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.plecko.hr/doku.php?id=linux:misc:cron:configuring_schedule&rev=1572509640&do=diff Configuring cron task schedule * * * * * task Fields * * * * * /path/to/task minute hour day of month month day of week full path to command 0-59 0-23 1-31 1-12 JAN-DEC 0-6 SUN-SAT 7 (Non-standard) can be binary, or any script Legend text/html 2020-06-01T10:35:00+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.plecko.hr/doku.php?id=linux:misc:cron:diskspace_zulip_notify&rev=1591000500&do=diff Send Zulip notification on low disk space in Linux #/bin/bash free_percent=$(df -h | grep /data | awk '{print $5}') free_percent_no=$(df -h | grep /data | awk '{print $5}' | sed 's/%//') free_no=$(df -h | grep /data | awk '{print $4}') FILE=/root/cron_diskspace_notification if [ "$free_percent_no" -gt "95" ]; then if [[ ! -f "$FILE" ]]; then curl -X POST https://chat.example.com.hr/api/v1/messages \ -u name-bot@chat.example.com.hr:<key> \ … text/html 2019-10-31T09:14:00+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.plecko.hr/doku.php?id=linux:misc:cron:start&rev=1572509640&do=diff Cron * Best practices for cron * Configuring cron task schedule * Cron tips * How a cron bug became the de-facto standard * Send Zulip notification on low disk space in Linux text/html 2019-10-31T09:14:00+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.plecko.hr/doku.php?id=linux:misc:cron:tips&rev=1572509640&do=diff Cron tips Tips for writing crontab expressions: * If the day-of-month or day-of-week part starts with a *, they form an intersection. Otherwise they form a union. * * 3 * 1 runs on the 3rd day of the month and on Monday (union), whereas * * */2 * 1 runs on every second day of the month only if it's also a Monday (intersection). The