Public bug reported:
Summary
-------
Booting the ubuntu-26.04.1-desktop-amd64 live image on a machine whose
hardware clock is in the past (here 2023-01-02) hangs forever at the
Ubuntu logo. The hang is in casper-bottom/41apt_build_cache_cdrom
(reintroduced for LP: #2145807): "apt-get update" completes all
downloads, then the APT::Update::Post-Invoke-Success hook
"appstreamcli refresh --source=os" never returns. There is no timeout,
and the splash screen and the hook's /dev/null redirection hide all
output, so the machine just looks frozen on the logo. That makes the
problem easy to mistake for a graphics issue: "nomodeset" and
"safe graphics" do not help.
Environment
-----------
- Image: ubuntu-26.04.1-desktop-amd64.iso (SHA256 verified)
- Hardware: Apple MacBook Pro Early 2015 (Intel Core i7)
- RTC at boot: 2023-01-02 00:55 UTC (actual date: 2026-10-22)
- Index files on the medium: Last-Modified Wed, 26 Aug 2026
- Medium: ISO contents copied to a FAT32 partition of a USB disk.
Other users report the same hang on the same line with regular
dd-written USB sticks (see "Related reports").
Steps to reproduce
------------------
1. Set the hardware clock to a date before the ISO build date
(e.g. 2023-01-01).
2. Boot the 26.04.1 desktop live image.
3. Remove "quiet splash" to see the console.
Expected: the live session starts (or the step fails or times out
and the boot continues).
Actual: the boot never gets past
Begin: Generating APT cache for cdrom ...
Ign:1 file:/cdrom resolute InRelease
Get:2 file:/cdrom resolute Release [664 B]
Get:3 file:/cdrom resolute Release.gpg [228 B]
Get:4 file:/cdrom resolute/main amd64 Packages [32.0 kB]
Get:5 file:/cdrom resolute/restricted amd64 Packages [14.5 kB]
and stays there indefinitely. systemd is never reached.
Analysis
--------
I used break=casper-bottom, then reproduced the exact environment of
41apt_build_cache_cdrom (same /etc/apt overlay, only cdrom.sources
kept) and ran:
chroot /root timeout -k 5 90 apt-get update --no-list-cleanup \
-o Debug::RunScripts=true -o Debug::pkgAcquire::Worker=true
- cdrom.sources has "Check-Date: no", so APT itself accepts the
"future" Release file, and every index file is fetched and stored
correctly.
- The hooks then run in this order:
touch /var/lib/apt/periodic/update-success-stamp ...
[ ! -f /var/run/dbus/system_bus_socket ] || dbus-send ...
/usr/bin/test -e .../org.freedesktop.PackageKit.service && ...
if /usr/bin/test -w /var/cache/swcatalog -a -e /usr/bin/appstreamcli;
then appstreamcli refresh --source=os > /dev/null || true; fi
The appstreamcli hook never returns, so the next two hooks
(cnf-update-db, update-motd-updates-available) never run.
- 80 s in, the process chain is apt-get -> sh -> sh (all in wait4),
and the leaf process, most likely appstreamcli, is blocked in:
do_poll -> do_sys_poll -> __x64_sys_poll
- The timeout fired: apt-get exit code 124.
- Setting the correct date fixes the boot.
Full diagnostic output attached (diag.txt).
Workaround
----------
Fix the hardware clock before booting the live image. Alternatively,
boot with break=casper-bottom, empty
/scripts/casper-bottom/41apt_build_cache_cdrom, then "exit".
Suggested fixes
---------------
1. casper: this boot-time "apt-get update" does not need the APT::Update
hooks. They could be disabled for this call, e.g. by dropping a
snippet into the temporary /etc/apt overlay the script already
mounts (named to sort last, e.g. zz-casper-no-hooks):
#clear APT::Update::Pre-Invoke;
#clear APT::Update::Post-Invoke;
#clear APT::Update::Post-Invoke-Success;
2. casper: wrap the call in "timeout" so that a misbehaving hook can
never block the boot forever.
3. appstream: find out why "appstreamcli refresh --source=os" never
returns when the system clock is earlier than the metadata
timestamps.
Related reports (same hang at "Get:5 file:/cdrom", fixed by
correcting the clock / firmware date):
-
https://community.frame.work/t/ubuntu-26-04-install-hangs-logo-freeze-then-stuck-at-get-5-file-cdrom/83392
- https://community.frame.work/t/struggling-to-boot-ubuntu/82993?page=2
** Affects: casper (Ubuntu)
Importance: Undecided
Status: New
--
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https://bugs.launchpad.net/bugs/2171937
Title:
Live boot hangs forever at "Generating APT cache for cdrom" when the
system clock is in the past (appstreamcli refresh hook never returns)
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