Add items to crontab

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Background

See Cron on Wikipedia

Skills required

You must be able to connect to your QNAP device using SSH and edit using a text editor such as vi or nano.

crontab

The crontab can be used to execute tasks (scripts) based on a recurring schedule. The crontab is used, for example, to restart the webserver during the night.

To view the content of your crontab, login to your QNAP via SSH and type:

crontab -l

You will see a (small) list of crontab entries.


Standard crontab jobs

The following table contains the standard QNAP jobs that run on schedules.

This list is by no means complete. Jobs may depend on the firmware version, start times may vary. If you find a job on your QNAP, that is missing from the table, add it. The list could help to identify unwanted jobs that regularly wake up your harddisk(s).

Default Time
Job
Explanation
0 4 * * *
/sbin/hwclock -s http://linux.die.net/man/8/hwclock
0 3 * * * /sbin/vs_refresh vs_refresh is for share folder space usage calculation (for Network Share Management)
0 3 * * 0
/etc/init.d/idmap.sh dump related to SAMBA Active Directory configuration. Used if security is set to ADS.
0 3 * * *
/sbin/clean_reset_pwd (unclear) might be the new behaviour of the network recycle bin (purging files after a certain amount of days)
0-59/15 * * * *
/etc/init.d/nss2_dusg.sh is a job of the Surveillance Station
10 15 * * * /usr/bin/power_clean -c 2>/dev/null  ?
4 3 * * 3 /etc/init.d/backup_conf.sh does an automatic backup of several config files in /etc/config.
0 3 * * *
/bin/rm -rf /mnt/HDA_ROOT/twonkymedia/twonkymedia.db/cache/*
Will clear the Twonky media cache
5 0 * * 1
/etc/init.d/antivirus.sh scan 1
If Antivirus is enabled, this will scan the files for viruses
0 0 * * *
/etc/init.d/antivirus.sh archive_log
If Antivirus report jobs are enabled
0 0 */1 * *
/etc/init.d/antivirus.sh update_db
If Antivirus is enabled, this will check  clamav.net for updates

/etc/init.d/startup
If a restart/powerof job is configured in power management

/etc/init.d/poweroff
If a restart/powerof job is configured in power management


Adding entries at the command-line

Here are a couple of examples that append new entries to the crontab file:
echo "1 4 * * * /share/custom/scripts/custom1.sh" >> /etc/config/crontab
echo "40 5 * * * /share/custom/scripts/custom2.sh" >> /etc/config/crontab


Modifying entries

Do NOT edit crontab the usual way!

On a desktop or server distribution, you would edit a user's crontab with:

crontab -e

However, due to the way the QNAP firmware updates crontab, it will be overwritten on the next reboot. Obviously, you want your automation to survive reboots, so edit the crontab file directly with your text editor:

vi /etc/config/crontab

or

nano /etc/config/crontab


Restart the daemon

When you're done, reload the crontab file and restart the cron daemon:

crontab /etc/config/crontab && /etc/init.d/crond.sh restart


Notes

Don't forget to make your scripts executable! Otherwise they will silently fail! You tested your script, right?

chmod +x filename.sh


These instructions have been tested on various versions of QNAP firmware from 3.6.0 onwards.