[Bug 534211] Re: Cannot umount /proc after using update-binfmts in a chroot

[Launchpad Bug Tracker]

This bug was fixed in the package binfmt-support - 2.2.0-1

---------------
binfmt-support (2.2.0-1) unstable; urgency=medium

  * New upstream release.
    - Sort formats by name in the output of "update-binfmts --display".
    - Add a new --unimport action, which is the inverse of --import.
    - Don't enable formats on import or disable them on unimport unless
      /proc/sys/fs/binfmt_misc is already mounted.  This avoids causing
      cleanup problems in chroots (closes: #847788, LP: #534211).
    - "--fix-binary yes" is incompatible with detectors.  Warn the user if
      they try to use both at once (closes: #918901).
  * Document recommended maintainer script use of --unimport in
    README.Debian.
  * Stop building with V=1; debhelper configures with --disable-silent-rules
    as of 9.20150501.

 -- Colin Watson <cjwatson at debian.org>  Fri, 25 Jan 2019 00:25:54 +0000

** Changed in: binfmt-support (Ubuntu)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/534211

Title:
  Cannot umount /proc after using update-binfmts in a chroot

Status in binfmt-support package in Ubuntu:
  Fix Released
Status in ltsp package in Ubuntu:
  Fix Released

Bug description:
  Binary package hint: binfmt-support

  As part of LTSP fat client installations, the following instructions
  are performed (cut down version):

  $ chroot "$ROOT" mount -t proc proc /proc
  $ chroot "$ROOT" update-binfmts --import wine
  $ umount "$ROOT/proc"

  At this point we get:
  $ umount: /opt/ltsp/i386/proc: device is busy.
  $         (In some cases useful info about processes that use
  $         the device is found by lsof(8) or fuser(1))
  ...and we're forced to resort to `umount -l` to work around this problem.

  Is the any way to call update-binfmts in a chroot (e.g. to install
  wine) without having to resort to `umount -l`?

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