The instructions in this section are intended for experienced administrators with profound knowledge of Kernun UTM and FreeBSD.
The Kernun UTM installer booted from the installation medium can be used to repair the system if all system partitions are unable to boot. The available functions are accessible from the installer main menu:
1. Install Kernun 2. Check for existing Kernun installations 3. Restore backup 4. Start rescue shell 5. Mount Kernun file systems 6. Resize installer's in-memory temporary file system (current size 32m) 7. Halt 8. Power down 9. Reboot 0. Install license
Option 1 is described in
Section 5.1, “Standalone Installer”. Options 7,
8, and 9 are
self-descriptive. Option 2 displays the boot manager
configuration and the disk device names.
System disk is /dev/ad0 Boot manager on ZFS pool 'kernun' F1: Kernun 3.11 2018/06/06 07:36 (031100h00.201806111345.amd64) F2: Unused F3: Unused type=Kernun ZFS boot manager ver. 1.0 current_booted=NONE bootable=1 update=1 default_selection=F1
Option 3 restores a backup selected from a list
of backup files found in /data/backup. If the backup
is stored on another medium, it must be first copied to the
/data/backup directory, using for example the rescue shell
(option 4). For details about backup and restoring, see
Section 6, “Backup and Restoring”.
Option 4 starts a rescue shell
(bash). It provides the environment for emergency
maintenance of a computer with non-bootable Kernun UTM installations. The
rescue shell (as well as the whole standalone installer) runs in a custom
FreeBSD environment. The standard Kernun UTM kernel is used. The root file
system is mounted from the installation medium and is therefore read-only.
A read-write RAM disk for temporary data is mounted under
/tmp, symlinked also from
/var/tmp. The standard size of the RAM disk is
32 MB. It can be resized using option 6 of the
installer main menu.
The content of the RAM disk is lost when the installer is terminated or when the RAM disk is resized.
Do not make the RAM disk too large, because its content is stored in the kernel memory. If the free kernel memory gets too low, the kernel may panic.
Option 5 of the menu mounts any existing Kernun UTM
partitions under the directories /1,
/2, /3 (the system partitions),
and /data (the data partition). The rescue shell
provides many standard FreeBSD command line programs. Programs from a mounted
Kernun UTM system partition can be run as well.
It is often useful to perform a chroot(8) to a mounted Kernun UTM system partition and to run commands in the chrooted environment.