Public bug reported:
# Summary
GDM fails to start at boot because `/usr/share/gdm/generate-config`
cannot write to `/var/lib` due to a read-only root filesystem. Manually
remounting the root filesystem read-write immediately before starting
GDM always fixes the problem.
## Problem
After installing recent Ubuntu 26.04 updates and rebooting, the
graphical login screen no longer appears.
The system boots to a black screen, but switching to a text console
(Ctrl+Alt+F3) works and login is possible.
`gdm.service` repeatedly fails with:
```
generate-config:
install: /var/lib: chmod failed with error Read-only file system (os error 30)
```
Journal:
```
Starting gdm.service - GNOME Display Manager...
generate-config: install: /var/lib: chmod failed with error Read-only file
system (os error 30)
gdm.service: Control process exited, code=exited, status=1/FAILURE
Failed to start gdm.service - GNOME Display Manager.
```
GDM retries several times and eventually gives up.
## Workaround
The following commands always recover the system:
```bash
sudo mount -o remount,rw /
sudo systemctl restart gdm
```
GDM starts immediately afterwards and the desktop works normally.
## Root cause observed
`/usr/share/gdm/generate-config` executes:
```sh
install -d /var/lib
install -m711 -ogdm -ggdm -d /var/lib/gdm3
```
The first command fails because the filesystem is still read-only:
```
install: /var/lib: chmod failed with error Read-only file system
```
After manually remounting `/` read-write, the exact same script succeeds
without errors.
## Temporary workaround
Creating the following systemd override makes the system boot correctly
every time:
`/etc/systemd/system/gdm.service.d/override.conf`
```ini
[Service]
ExecStartPre=
ExecStartPre=/bin/mount -o remount,rw /
ExecStartPre=/usr/share/gdm/generate-config
```
After:
```bash
sudo systemctl daemon-reload
```
and rebooting, GDM starts normally.
This suggests that `generate-config` is being executed before the root
filesystem is effectively writable, or that the root filesystem
unexpectedly remains read-only until an explicit remount.
## Additional information
Distribution:
* Ubuntu 26.04 LTS
Kernel:
* Linux 7.0.0-28-generic
Filesystem:
* ext4
* root on `/dev/nvme0n1p5`
Observed diagnostics:
* `systemd-remount-fs.service` reports success.
* After manual recovery:
* `/proc/mounts` shows `/` mounted as `rw`.
* `/var` and `/var/lib` permissions are normal.
* `generate-config` itself is unmodified.
* The failure is fully reproducible on every boot.
## Expected result
GDM should start normally after boot without requiring a manual remount
of the root filesystem.
## Actual result
GDM fails because `generate-config` cannot modify `/var/lib` due to
"Read-only file system". Manually remounting `/` read-write immediately
before starting GDM resolves the problem every time.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: gdm3 50.1-0ubuntu0.1
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Fri Jul 24 11:24:17 2026
InstallationDate: Installed on 2022-03-08 (1599 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
SourcePackage: gdm3
UpgradeStatus: Upgraded to resolute on 2026-05-20 (65 days ago)
---
ProblemType: Bug
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
DistroRelease: Ubuntu 26.04
InstallationDate: Installed on 2022-03-08 (1599 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
Package: gdm3 50.1-0ubuntu0.1
PackageArchitecture: amd64
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Tags: resolute wayland-session
Uname: Linux 7.0.0-28-generic x86_64
UpgradeStatus: Upgraded to resolute on 2026-05-20 (65 days ago)
UserGroups: adm cdrom dialout dip disk input lpadmin lxd plugdev sambashare
sudo tty vboxusers
_MarkForUpload: True
** Affects: gdm3 (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug apport-collected resolute wayland-session
** Tags added: apport-collected
** Description changed:
# Summary
GDM fails to start at boot because `/usr/share/gdm/generate-config`
cannot write to `/var/lib` due to a read-only root filesystem. Manually
remounting the root filesystem read-write immediately before starting
GDM always fixes the problem.
## Problem
After installing recent Ubuntu 26.04 updates and rebooting, the
graphical login screen no longer appears.
The system boots to a black screen, but switching to a text console
(Ctrl+Alt+F3) works and login is possible.
`gdm.service` repeatedly fails with:
```
generate-config:
install: /var/lib: chmod failed with error Read-only file system (os error 30)
```
Journal:
```
Starting gdm.service - GNOME Display Manager...
generate-config: install: /var/lib: chmod failed with error Read-only file
system (os error 30)
gdm.service: Control process exited, code=exited, status=1/FAILURE
Failed to start gdm.service - GNOME Display Manager.
```
GDM retries several times and eventually gives up.
## Workaround
The following commands always recover the system:
```bash
sudo mount -o remount,rw /
sudo systemctl restart gdm
```
GDM starts immediately afterwards and the desktop works normally.
## Root cause observed
`/usr/share/gdm/generate-config` executes:
```sh
install -d /var/lib
install -m711 -ogdm -ggdm -d /var/lib/gdm3
```
The first command fails because the filesystem is still read-only:
```
install: /var/lib: chmod failed with error Read-only file system
```
After manually remounting `/` read-write, the exact same script succeeds
without errors.
## Temporary workaround
Creating the following systemd override makes the system boot correctly
every time:
`/etc/systemd/system/gdm.service.d/override.conf`
```ini
[Service]
ExecStartPre=
ExecStartPre=/bin/mount -o remount,rw /
ExecStartPre=/usr/share/gdm/generate-config
```
After:
```bash
sudo systemctl daemon-reload
```
and rebooting, GDM starts normally.
This suggests that `generate-config` is being executed before the root
filesystem is effectively writable, or that the root filesystem
unexpectedly remains read-only until an explicit remount.
## Additional information
Distribution:
* Ubuntu 26.04 LTS
Kernel:
* Linux 7.0.0-28-generic
Filesystem:
* ext4
* root on `/dev/nvme0n1p5`
Observed diagnostics:
* `systemd-remount-fs.service` reports success.
* After manual recovery:
* `/proc/mounts` shows `/` mounted as `rw`.
* `/var` and `/var/lib` permissions are normal.
* `generate-config` itself is unmodified.
* The failure is fully reproducible on every boot.
## Expected result
GDM should start normally after boot without requiring a manual remount
of the root filesystem.
## Actual result
GDM fails because `generate-config` cannot modify `/var/lib` due to
"Read-only file system". Manually remounting `/` read-write immediately
before starting GDM resolves the problem every time.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: gdm3 50.1-0ubuntu0.1
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Fri Jul 24 11:24:17 2026
InstallationDate: Installed on 2022-03-08 (1599 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
SourcePackage: gdm3
UpgradeStatus: Upgraded to resolute on 2026-05-20 (65 days ago)
+ ---
+ ProblemType: Bug
+ ApportVersion: 2.34.1-0ubuntu0.1
+ Architecture: amd64
+ CasperMD5CheckResult: unknown
+ CurrentDesktop: ubuntu:GNOME
+ DistroRelease: Ubuntu 26.04
+ InstallationDate: Installed on 2022-03-08 (1599 days ago)
+ InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
+ Package: gdm3 50.1-0ubuntu0.1
+ PackageArchitecture: amd64
+ ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
+ Tags: resolute wayland-session
+ Uname: Linux 7.0.0-28-generic x86_64
+ UpgradeStatus: Upgraded to resolute on 2026-05-20 (65 days ago)
+ UserGroups: adm cdrom dialout dip disk input lpadmin lxd plugdev sambashare
sudo tty vboxusers
+ _MarkForUpload: True
--
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https://bugs.launchpad.net/bugs/2161707
Title:
GDM fails to start at boot
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