After upgrading the glibc packages the root filesystem cannot be mounted ro by /etc/init.d/umountroot during the following shutdown/reboot, resulting in a "mount: / is busy" Error (see also attached screenshot). This is very BAD and may cause data loss.
I have tested this on fresh installed and otherwise unmodified X/K/Ubuntu 7.10 after an upgrade of the packages libc6 and libc6-i686 from version 2.6.1-1ubuntu9 to version 2.6.1-1ubuntu10 in gutsy-updates. It is easily reproducible in a VM as well as on physical hardware (see below).
Steps to Reproduce:
1. install any Ubuntu 7.10 flavour with default settings (in a VM or your hardware)
2. on the first boot use grub's edit function to remove the "quiet" and "splash" options from the kernel line so you can see what's going on during boot/shutdown
3. boot
4. upgrade the libc6 and libc6-i686 packages from version 2.6.1-1ubuntu9 to version 2.6.1-1ubuntu10
5. edit /etc/default/rcS anch change VERBOSE=no to VERBOSE=yes in order to make the init scripts' output more verbose
6. switch to a vt and reboot the system
7. at the end of the shutdown/reboot process observe the following error:
----8<----
* Mounting root filesystem read-only...
mount: / is busy
[fail]
---->8----
I made a small init script in order to see if there are any unusual processess with open filehandles blocking the remount, however I couldn't spot anything on first sight.
I used the following script:
----lsof----
#!/bin/sh
lsof | tee /root/lsof.out
sync; sync
----lsof----
and made it run just before umountfs and umountroot on shutdown/reboot (via "update-rc.d lsof start 35 0 6 .").
The output is attached.