Comment 0 for bug 1777149

Even if DASD devices of an already installed Ubuntu Server on s390x system got properly specified during the configuration phase of booting and using d-i's rescue (aka recovery) mode,
d-i does not identify the DASD partitions, hence doesn't list them for selection:

   ┌──────────────────────┤ [!!] Enter rescue mode ├───────────────────────┐
   │ │
   │ The installer could not find any partitions, so you will not be able │
   │ to mount a root file system. This may be caused by the kernel failing │
   │ to detect your hard disk drive or failing to read the partition │
   │ table, or the disk may be unpartitioned. If you wish, you may │
   │ investigate this from a shell in the installer environment. │
   │ │
   │ No partitions found │
   │ <Go Back> <Continue> │
   │ │
   └───────────────────────────────────────────────────────────────────────┘

If proceeding without specifying a root partition and executing a shell, one can see that the DASD disks are online and the partitions are available:

~ # lszdev --online
TYPE ID ON PERS NAMES
dasd-eckd 0.0.162a yes no dasda
dasd-eckd 0.0.2625 yes no dasdb
qeth 0.0.c000:0.0.c001:0.0.c002 yes no encc000
~ # fdasd -ps /dev/dasda

WARNING:
Disk /dev/dasda is online on operating system instances in 3 different LPARs.
Ensure that the disk is not being used by a system outside your LPAR.
Note: Your installation might include z/VM systems that are configured to
automatically vary on disks, regardless of whether they are subsequently used.

          /dev/dasda1 2 24415 24414 1 Linux native
          /dev/dasda2 24416 450762 426347 2 Linux native
                          450763 450764 2 unused
~ # fdasd -ps /dev/dasdb

WARNING:
Disk /dev/dasdb is online on operating system instances in 3 different LPARs.
Ensure that the disk is not being used by a system outside your LPAR.
Note: Your installation might include z/VM systems that are configured to
automatically vary on disks, regardless of whether they are subsequently used.

          /dev/dasdb1 2 450762 450761 1 Linux native
                          450763 450764 2 unused
~ # mkdir /mnt/boot
~ # mkdir /mnt/root
~ # mkdir /mnt/home
~ # mount /dev/dasda1 /mnt/boot
~ # mount /dev/dasda2 /mnt/root
~ # mount /dev/dasdb1 /mnt/home
~ # mount | grep ^\/dev\/
/dev/dasda1 on /mnt/boot type ext2 (rw,relatime,block_validity,barrier,user_xattr,acl)
/dev/dasda2 on /mnt/root type ext4 (rw,relatime,data=ordered)
/dev/dasdb1 on /mnt/home type ext4 (rw,relatime,data=ordered)
~ # ls -a /mnt/boot
. initrd.img-4.15.0-23-generic
.. initrd.img-4.15.0-24-generic
System.map-4.15.0-23-generic initrd.img.old
System.map-4.15.0-24-generic lost+found
abi-4.15.0-23-generic retpoline-4.15.0-23-generic
abi-4.15.0-24-generic retpoline-4.15.0-24-generic
bootmap vmlinuz
config-4.15.0-23-generic vmlinuz-4.15.0-23-generic
config-4.15.0-24-generic vmlinuz-4.15.0-24-generic
initrd.img vmlinuz.old
~ # ls -a /mnt/root
. dev lost+found proc snap sys
.. etc media root space tmp
bin home mnt run srv usr
boot lib opt sbin swapfile var
~ # ls -a /mnt/home
. .. lost+found ubuntu

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Furthermore I came across some more issues:

   - default ssh cmd-line with ipv6 (for 2nd d-i stage) does not work:
     workstation:~$ ssh installer@fe80::ff:feff:abc
     ssh: connect to host fe80::ff:feff:abc port 22: Invalid argument
     (however using ipv4 works)
   - not all screens are titled with 'Rescue Mode' in the upper left
     especially not the initial d-i screen of the 2nd (ssh) stage: 'Configuring d-i'
     which is a bit confusing (but just cosmetic)
   - if DASD AND FCP devices are specified during the configuration
     (installations might have both)
     only FCP devices are listed for the mounting of the root device, no DASDs
     but I only see the raw devices, not the multipath devices
     (hope that this is not by intention)
   - I expected (for safety reasons) NOT to see entries like:
      - Partition disks
      - Install the base system
     in 'Ubuntu installer main menu'
     and also not the options to low-leve format the DASDs, like:
     "The DASD 0.0.1234 is already low-level formatted."