[Bug 672177] Re: libc6 upgrade causes umount to fail on shutdown because init cannot be restarted

[Clint Byrum]

Oops, I'm still learning my way around the shutdown process and, indeed,
I missed umountroot.

I went ahead and added another lsof right after the call to telinit u,
right before MOUNT_FORCE_OPT=, and one *after* the remount of /.

It doesn't seem to make any difference:

clint at natty-alpha1:~$ grep DEL /lastlsof-umountroot-post 
init         1 root  DEL       REG              251,0          399637 /lib/libnss_files-2.12.2.so
init         1 root  DEL       REG              251,0          399636 /lib/libnss_nis-2.12.2.so
init         1 root  DEL       REG              251,0          399630 /lib/libnsl-2.12.2.so
init         1 root  DEL       REG              251,0          399643 /lib/libnss_compat-2.12.2.so.dpkg-new
init         1 root  DEL       REG              251,0          399644 /lib/libc-2.12.2.so
init         1 root  DEL       REG              251,0          390256 /lib/librt-2.12.2.so
init         1 root  DEL       REG              251,0          399646 /lib/libpthread-2.12.2.so
init         1 root  DEL       REG              251,0          399647 /lib/ld-2.12.2.so
clint at natty-alpha1:~$ grep DEL /lastlsof-umountroot
init         1 root  DEL       REG              251,0          399637 /lib/libnss_files-2.12.2.so
init         1 root  DEL       REG              251,0          399636 /lib/libnss_nis-2.12.2.so
init         1 root  DEL       REG              251,0          399630 /lib/libnsl-2.12.2.so
init         1 root  DEL       REG              251,0          399643 /lib/libnss_compat-2.12.2.so.dpkg-new
init         1 root  DEL       REG              251,0          399644 /lib/libc-2.12.2.so
init         1 root  DEL       REG              251,0          390256 /lib/librt-2.12.2.so
init         1 root  DEL       REG              251,0          399646 /lib/libpthread-2.12.2.so
init         1 root  DEL       REG              251,0          399647 /lib/ld-2.12.2.so

I even tried forcing the telinit u by doing 'touch
/var/run/init.upgraded', and verified that it ran by adding -x and a
sleep at the end of umountroot.

This makes sense, because telinit u just sends SIGTERM to upstart, which
has no handler, as it was removed by revision 977, and doesn't seem to
have been added back. Since SIG_DFL signals are not delivered to init,
I'm not sure how umountroot's call to 'telinit u' can help in this case.

Unless I'm missing something in upstart's code (quite likely) I think
there may still potentially need to be a change in upstart to support
re-executing.

Another option if this can't be pushed into upstart is to mount a
special readonly filesystem at boot just for init's libraries. However,
it seems that re-execcing would be simpler than trying to get that
right.

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https://bugs.launchpad.net/bugs/672177

Title:
  libc6 upgrade causes umount to fail on shutdown because init cannot be restarted