FreeBSD periodic(8)
periodic is nothing more than a shell script that
wraps the execution of other scripts.
Sorry to be harsh, but that’s it!
Why is so many time cited when dealing with FreeBSD? Well, because the operating system delegates to
periodic a lot of manainance activities.
But, again, to be straight:
periodic is not a replacement for cron, it is something that
runs based on cron.
First of all, let’s inspect the
root crontab:
joey# cat /etc/crontab
# /etc/crontab - root's crontab for FreeBSD
#
#
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin
#
#minute hour mday month wday who command
#
# Save some entropy so that /dev/random can re-seed on boot.
*/11 * * * * operator /usr/libexec/save-entropy
#
# Rotate log files every hour, if necessary.
0 * * * * root newsyslog
#
# Perform daily/weekly/monthly maintenance.
1 3 * * * root periodic daily
15 4 * * 6 root periodic weekly
30 5 1 * * root periodic monthly
...
As you can see,
cron runs three instances of this
periodic thing with different schedules.
Now,
periodic lies in
/usr/sbin and is a shell script that accepts a directory name (
daily,
weekly,
monthly). Those directories are stored into
7etc/periodic and
/usr/local/etc/periodic:
joey# ls /etc/periodic
daily monthly security weekly
joey# ls /usr/local/etc/periodic
daily security weekly
Within each subdirectory, there are shell scripts that execute tasks:
oey# ls /etc/periodic/daily
100.clean-disks 222.backup-gmirror 408.status-gstripe 480.status-ntpd
110.clean-tmps 223.backup-zfs 409.status-gconcat 500.queuerun
120.clean-preserve 300.calendar 410.status-mfi 510.status-world-kernel
130.clean-msgs 310.accounting 420.status-network 800.scrub-zfs
140.clean-rwho 400.status-disks 430.status-uptime 801.trim-zfs
150.clean-hoststat 401.status-graid 440.status-mailq 999.local
200.backup-passwd 404.status-zfs 450.status-security
210.backup-aliases 406.status-gmirror 460.status-mail-rejects
221.backup-gpart 407.status-graid3 480.leapfile-ntpd
When
periodic is called, either interactively or via
cron, and receives a directory argument like in
periodic daily, it opens the
daily directory and executes the scripts in a lexicographic order (that’s why they are named after a progressive number).
In order to understand what the scripts do, let’s examine one really simple:
#!/bin/sh
#
#
# If there is a global system configuration file, suck it in.
#
if [ -r /etc/defaults/periodic.conf ]
then
. /etc/defaults/periodic.conf
source_periodic_confs
fi
case "$daily_status_uptime_enable" in
[Yy][Ee][Ss])
rwho=$(echo /var/rwho/*)
if [ -f "${rwho%% *}" ]
then
echo ""
echo "Local network system status:"
prog=ruptime
else
echo ""
echo "Local system status:"
prog=uptime
fi
rc=$($prog | tee /dev/stderr | wc -l)
if [ $? -eq 0 ]
then
[ $rc -gt 1 ] && rc=1
else
rc=3
fi;;
*) rc=0;;
esac
exit $rc
The script is named
430.status-uptime and the first (well, not very first) thing it does it to evaluate a variable named
daily_status_uptime_enabled.
Every
periodic script is enabled by a variable named after the script (without the leading number) with an underscore substituting every dash and with the
enabled suffix. Therefore the script
222.backup_gmirror is enabled via the value
daily_backup_gmirror_enabled.
Clearly, there are other variables to substitute
daily to
monthly and
weekly.
Once the enabling variable is set to
YES like
daily_status_uptime_enabled=YES, the script continues to run and performs its job. In the above example, the script tries to understand the correct
program to run, e.g.,
uptime. Then it runs the command and returns a normalized valued as follows:
0 means the script did nothing, e.g., it was not enabled;1 the script produced some output;2 the script has something misconfigured;3 or a greater value, there has been an error.
Please note: the script has to return 1 in the case of success!
But where is configured the variable that enables a script?
There is a script
/etc/periodic.conf that contains a list of variables that enable/disable the set of scripts.
For example,
/etc/defaults/periodic.conf contains something like:
# cat /etc/defaults/periodic.conf
...
# 550.ipfwlimit
security_status_ipfwlimit_enable="YES"
security_status_ipfwlimit_period="daily"
...
There are other variables that can be set for each script, and that are usually dependent on the script itself.
It is possible to override the default configuration by means of editing
/etc/periodic.conf or
/usr/local/etc/periodic.conf.
Logs of the periodic system go into
/var/log/daily and similar files.