UCS uses GRUB2 as bootloader. If the installation of GRUB2 is inconsistent, the UCS system might not boot or GRUB2 shows a rescue shell. In some cases the UCS system can be started by booting the Super GRUB2 Disk.
The Super GRUB2 Disk is available at http://www.supergrubdisk.org/super-grub2-disk/ and may be used on i386, amd64 and UEFI systems. For booting the UCS system, usually the following steps have to be performed:
- Download the latest ISO file
- In virtualization environments the ISO file may be directly added as CD-ROM drive to a virtual machine. On hardware systems it is required to write the ISO file to a USB stick or CDROM/DVD.
- Boot the system from ISO/USB stick/CDROM. After booting the Super GRUB2 Disk shows a text menu.
- If RAID or LVM is used for the UCS system, the menu entry “Enable GRUB2’s RAID and LVM support” has to be selected. Activating the RAID/LVM support may take a moment. This step may be omitted and can be catched up on later if neccessary.
- Select the entry “Detect and show boot methods”. Please note: depending on the complexity of your setup, this might take a moment. A black screen is shown while detecting.
- The next menu shows all available boot options. Select an appropriate entry containing the text “Univention Corporate Server”.
- Now, the existing GRUB configration from /boot is automatically used to boot the UCS system.
If the boot of the UCS system was successful, the GRUB configuration should be fixed.
The SDB article 1356 contains information on how to (re)configure GRUB.