[Bug 2142839] [NEW] crash during installer update while installing 26.04 snapshot4 (on s390x)

[Frank Heimes]

Public bug reported:

While doing a 26.04 snapshot4 test installation (on s390x) I got a notification that an installer update is available.
While doing that the installer crash and I found the following error in the logs:

 2026-02-27 09:52:28,967 DEBUG asyncio:64 Using selector: EpollSelector
 2026-02-27 09:52:28,967 DEBUG subiquitycore.screen:128 KDGKBTYPE returned b'\x02', is_linux_tty True
 2026-02-27 09:52:29,671 DEBUG subiquity.common.errorreport:386 generating crash report
 2026-02-27 09:52:29,675 INFO subiquity.common.errorreport:412 saving crash report 'Installer UI crashed with ServerDisconnectedError' to /var/crash/1772185949.671535730.ui.crash
 2026-02-27 09:52:29,675 INFO subiquity/ErrorReporter/1772185949.671535730.ui/add_info:104 start:
InstallerClientLogInfo:
 2026-02-27 09:52:28,966 INFO subiquity:134 Starting Subiquity TUI revision 7083 of snap /snap/subiquity/7083
 2026-02-27 09:52:28,966 INFO subiquity:135 Arguments passed: ['/snap/subiquity/7083/usr/bin/subiquity']
 2026-02-27 09:52:29,675 INFO subiquity.common.errorreport:412 saving crash report 'Installer UI crashed with ServerDisconnectedError' to /var/crash/1772185949.671535730.ui.crash
 2026-02-27 09:52:29,675 INFO subiquity/ErrorReporter/1772185949.671535730.ui/add_info:104 start:
InstallerJournal:

I'm attaching entire /var/crash and /var/log.

** Affects: ubuntu-z-systems
     Importance: Medium
     Assignee: Skipper Bug Screeners (skipper-screen-team)
         Status: New

** Affects: subiquity (Ubuntu)
     Importance: Medium
         Status: New


** Tags: s390x snapshot4 ubuntu-26.04

** Attachment added: "logs-27.02.2026.tgz"
   https://bugs.launchpad.net/bugs/2142839/+attachment/5948864/+files/logs-27.02.2026.tgz

** Also affects: ubuntu-z-systems
   Importance: Undecided
       Status: New

** Changed in: ubuntu-z-systems
   Importance: Undecided => Medium

** Changed in: ubuntu-z-systems
     Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)

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https://bugs.launchpad.net/bugs/2142839

Title:
  crash during installer update while installing 26.04 snapshot4 (on
  s390x)

Status in Ubuntu on IBM z Systems:
  New
Status in subiquity package in Ubuntu:
  New

Bug description:
  While doing a 26.04 snapshot4 test installation (on s390x) I got a notification that an installer update is available.
  While doing that the installer crash and I found the following error in the logs:

   2026-02-27 09:52:28,967 DEBUG asyncio:64 Using selector: EpollSelector
   2026-02-27 09:52:28,967 DEBUG subiquitycore.screen:128 KDGKBTYPE returned b'\x02', is_linux_tty True
   2026-02-27 09:52:29,671 DEBUG subiquity.common.errorreport:386 generating crash report
   2026-02-27 09:52:29,675 INFO subiquity.common.errorreport:412 saving crash report 'Installer UI crashed with ServerDisconnectedError' to /var/crash/1772185949.671535730.ui.crash
   2026-02-27 09:52:29,675 INFO subiquity/ErrorReporter/1772185949.671535730.ui/add_info:104 start:
  InstallerClientLogInfo:
   2026-02-27 09:52:28,966 INFO subiquity:134 Starting Subiquity TUI revision 7083 of snap /snap/subiquity/7083
   2026-02-27 09:52:28,966 INFO subiquity:135 Arguments passed: ['/snap/subiquity/7083/usr/bin/subiquity']
   2026-02-27 09:52:29,675 INFO subiquity.common.errorreport:412 saving crash report 'Installer UI crashed with ServerDisconnectedError' to /var/crash/1772185949.671535730.ui.crash
   2026-02-27 09:52:29,675 INFO subiquity/ErrorReporter/1772185949.671535730.ui/add_info:104 start:
  InstallerJournal:

  I'm attaching entire /var/crash and /var/log.

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