معمل 12.1: Schedule jobs with cron, at and a timer

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الهدف

Plan repeating and one-time jobs with all three tools, and block one user from cron.

User anna must run logger "anna was here" every weekday (Monday to Friday) at 14:23.
As root, write the output of df -h / to /var/tmp/disk.log every 15 minutes, with a file in /etc/cron.d/.
User bob may not use cron.
In 5 minutes, write the text "at works" to /tmp/at-test.txt with at. Then plan a second at job and remove it.
Create a systemd timer cleanup-tmp.timer that runs find /var/tmp -type f -mtime +7 -delete every day at 03:00, also when the machine was off at that time.

#crontab -l -u anna
#cat /etc/cron.d/disk
#su - bob -c 'crontab -l'
#atq
#cat /tmp/at-test.txt
#systemctl list-timers cleanup-tmp.timer

اعرض التلميحات

crontab -e -u anna. Day of week 1-5.
Files in /etc/cron.d need the user field.
/etc/cron.deny.
at now + 5 minutes; atq, atrm.
A .service with Type=oneshot plus a .timer with OnCalendar and Persistent=true; enable the timer.

اعرض الحل

anna's crontab.

#crontab -e -u anna

crontab -e -u anna

23 14 * * 1-5 logger "anna was here"

The system cron file.

#echo '*/15 * * * * root df -h / >> /var/tmp/disk.log' > /etc/cron.d/disk

at jobs.

#echo 'echo "at works" > /tmp/at-test.txt' | at now + 5 minutes
#echo 'reboot' | at 23:59
#atq
#atrm 2

Service and timer.

/etc/systemd/system/cleanup-tmp.service

[Unit]
Description=Delete old files in /var/tmp
 
[Service]
Type=oneshot
ExecStart=/usr/bin/find /var/tmp -type f -mtime +7 -delete

/etc/systemd/system/cleanup-tmp.timer

[Unit]
Description=Daily cleanup of /var/tmp
 
[Timer]
OnCalendar=*-*-* 03:00:00
Persistent=true
 
[Install]
WantedBy=timers.target

#systemctl daemon-reload
#systemctl enable --now cleanup-tmp.timer

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