Bug 266901

What is happening?
I get daily mails from inside my jails with content like "Backup of
partitions information for" or "Backup of MBR record" with the error
message "No such file or directory". I think this is because there is
no MBR to backup inside a jail. I disabled backing up MBR in
periodic.conf but it seems to run nevertheless. This seems to start
after the last patch level update.

What do I expect to happen?
Not to run if it is disabled.

How to reproduce?
Set daily_backup_gpart_enable to NO in /etc/periodic.conf inside a jail
and monitor the periodic script output.

Further information

$ grep -R "Backup of partitions information for" /etc/periodic/
/etc/periodic/daily/221.backup-gpart: echo "Backup of partitions information for:";

$ grep -R "Backup of MBR record" /etc/periodic/
/etc/periodic/daily/221.backup-gpart: echo "Backup of MBR record:"

$ grep backup_gpart /etc/periodic.conf
daily_backup_gpart_enable="NO"

--- Periodic output --- 
Dump of kern.geom.conftxt:

Backup of partitions information for:
mmcsd0
mmcsd0s2

Backup of MBR record:
mmcsd0
mv: rename /var/backups/boot.mmcsd0.tmp to /var/backups/boot.mmcsd0.bak: No such file or directory