Scheduling Tasks

Cron

crontab -l

crontab -e

crontab -u user -l

cat /etc/crontab

# cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * user-name command to be executed

Crontab settings per user location /var/spool/cron

Job definition	Description
`1 2 3 4 5`	Elke vrijdag (5) die op 3 april (4) valt om 1 minuut over 2
`30 4 * * *`	Every day at 4:30am
`30 4-6 * * *`	Every day at 4:30am, 5:30am and 6:30am
`30 4-8/2 * * *`	Every day at 4:30am, 6:30am, 8:30am
`30 4,6,8 * * *`	Every day at 4:30am, 6:30am and 8:30am
`0 15,20 * */2 1-5`	Every workday during an even month at 15:00 and 20:00
`/10 8-16,22 * *`	Every 10 minutes between 8am and 5pm and between 10pm and 11pm

At

at [-V] [-q queue] [-f file] [-mMlv] timespec...

at [-V] [-q queue] [-f file] [-mMkv] [-t time]

at -c job [job...]

atq [-V] [-q queue]

at [-rd] job [job...]

atrm [-V] job [job...]

batch

at -b

Systemd timers

$ systemctl --user stop schedule-test.timer
$ systemctl --user disable schedule-test.timer
$ systemctl --user stop schedule-test.service
$ systemctl --user disable schedule-test.service
$ systemctl --user daemon-reload
$ systemctl --user reset-failed

[Unit]
Description=Schedule a message every 1 minute
RefuseManualStart=no  # Allow manual starts
RefuseManualStop=no   # Allow manual stops

[Timer]
#Execute job if it missed a run due to machine being off
Persistent=true
#Run 120 seconds after boot for the first time
OnBootSec=120
#Run every 1 minute thereafter
OnUnitActiveSec=60
#File describing job to execute
Unit=schedule-test.service

[Install]
WantedBy=timers.target

$ systemctl list-timers
NEXT                        LEFT          LAST                        PASSED       UNIT                         ACTIVATES
Wed 2021-11-17 02:00:00 CET 15s left      Wed 2021-11-17 01:50:34 CET 9min ago     sysstat-collect.timer        sysstat-collect.service
Wed 2021-11-17 03:19:18 CET 1h 19min left Wed 2021-11-17 01:22:46 CET 36min ago    dnf-makecache.timer          dnf-makecache.service
Wed 2021-11-17 21:30:46 CET 19h left      Tue 2021-11-16 11:17:42 CET 14h ago      systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.service
Thu 2021-11-18 00:00:00 CET 22h left      Wed 2021-11-17 00:45:27 CET 1h 14min ago logrotate.timer              logrotate.service
Thu 2021-11-18 00:00:00 CET 22h left      Wed 2021-11-17 00:45:27 CET 1h 14min ago mlocate-updatedb.timer       mlocate-updatedb.service
Thu 2021-11-18 00:00:00 CET 22h left      Wed 2021-11-17 00:45:27 CET 1h 14min ago unbound-anchor.timer         unbound-anchor.service
Thu 2021-11-18 00:07:00 CET 22h left      Wed 2021-11-17 00:45:27 CET 1h 14min ago sysstat-summary.timer        sysstat-summary.service
Mon 2021-11-22 01:07:18 CET 4 days left   Mon 2021-11-15 01:00:34 CET 2 days ago   fstrim.timer                 fstrim.service
n/a                         n/a           Mon 2021-11-15 00:00:35 CET 2 days ago   rdiff-backup.timer           rdiff-backup.target

9 timers listed.
Pass --all to see loaded but inactive timers, too