[Bug 571444] Re: Boot hangs and unable to continue when automount disk in fstab is not available (Off or Disconnected)

[Tim Cutts]

We've also been bitten by this.  We run approximately 2000 servers
(currently mostly Debian, but increasing numbers of Ubuntu Lucid).
We're finding our servers hang if, for example, a SAN disk has failed,
for whatever reason.  Now, yes, we usually have some sort of remote
console access, but it's a royal PITA to use, and if I have several
hundred machines affected because of a mistake in SAN zoning or
something, it's really impractical to start a console session on each
server to press S.  I'd be there for weeks.  Of course in reality I'd
just power cycle them all again.

There needs to be some sort of remote administration access using ssh or
something similar, presumably started from the initrd, from which people
can recover from this sort of situation.  In the meantime I think I'll
probably use kumy's mountall that proceeds anyway, which restores the
Debian behaviour.  At least then I get a booted system which I can log
into and diagnose.

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https://bugs.launchpad.net/bugs/571444

Title:
  Boot hangs and unable to continue when automount disk in fstab is not
  available (Off or Disconnected)

Status in “mountall” package in Ubuntu:
  Confirmed

Bug description:
  On 10.04 Lucid server installations, if a filesystem that is specified in /etc/fstab cannot be mounted for some reason (USB disk not connected, partition deleted, samba share not availible etc.) the boot process hangs displaying
  "mountall: Filesystem could not be mounted: ..."
  Screenshot: http://launchpadlibrarian.net/48612932/Screenshot%20mountall%20hang.png
  The user is not informed what to do at this point.

  == WORKAROUND ==
  Press "s" to skip the missing filesystem and continue booting.
     - This workaround only works for the first missing drive. For more missing drives press alt-sysrq-i and edit your fstab to remove missing drives

  == ORIGINAL DESCRIPTION ==
  I have attached an external drive to mount on boot up of 10.04 server (Lucid).
  It's label is "WAD" and is located and mounted via the following fstab entry:

  LABEL=WAD          /mnt/WAD         auto         relatime,errors
  =remount-ro      0       2

  It's pretty generic and usually mounts either a ext3 or ext4 file
  system.

  However, If this drive is detached or powered down for some reason - Then the entire boot process hangs!
  There is no way to continue. You can switch terminals, But can not drop to any command line or even login.
  So you can't easily fix the problem either. ctrl-alt-del will initiate a shutdown/restart.
  Also booting into recovery mode exhibits the same problem.

  The only way I could recover this server (As I had no live cd available) was to hit alt-sysreq-i (Kill all tasks)
  The process's it killed are as follow: (This may give a hint to where it is hanging!?)
  udev
  portmap
  statd
  mountall
  plymouth
  Then it stated: General error mounting filesystems.
  And droped into a terminal (Thank God), So I could fix fstab (remove the external drive entry).

  I feel this is a pretty serious issue. It almost forced me to reinstall the server.
  (Only chance made me press Alt-SysRq-ScrollLock to give me Magic Key Help)

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