[Bug 828895] Re: Bash loses track of background children sometimes

[Ben Harris]

Just a quick note: having moved some affected systems back to Ubuntu,
this bug has just manifested in production on Ubuntu 16.04 LTS:

/opt/dump/bin/dump_multi: line 11: wait: pid 56652 is not a child of
this shell

My test script above no longer demonstrates it though.  I'll see if I
can come up with one that does.

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Title:
  Bash loses track of background children sometimes

Status in bash package in Ubuntu:
  Confirmed

Bug description:
  Under some circumstances (I've not worked out precisely what), bash
  can forget about background child processes.  For instance, if the
  file "simpletest" contains:

  #! /bin/bash

  count=0

  while [ $count -lt 51 ]; do
      count=$((count+1))
      /nonexist
      true &
      bgpids="$bgpids $!"
  done

  for pid in $bgpids; do
      wait $pid
  done

  then running "bash simpletest", seems to reliably report "simpletest:
  line 13: wait: pid 28850 is not a child of this shell" (with different
  PIDs each time, obviously).  Increasing the "51" in the script
  increases the number of errors.  Curiously, removing the call to a
  nonexistent program causes the problem to stop manifesting.

  "getconf CHILD_MAX" returns "undefined", which I think means that Bash
  should support an unlimited number of unwaited children.

  I've observed this on two different amd64 boxes running Ubuntu 10.04
  LTS, and it persisted after I upgraded the bash package to
  4.2-0ubuntu4.  I couldn't reproduce it on an i386 box running Ubuntu
  11.04.

  ProblemType: Bug
  DistroRelease: Ubuntu 10.04
  Package: bash 4.1-2ubuntu3
  ProcVersionSignature: Ubuntu 2.6.32-33.72-server 2.6.32.41+drm33.18
  Uname: Linux 2.6.32-33-server x86_64
  Architecture: amd64
  Date: Thu Aug 18 17:04:23 2011
  InstallationMedia: Ubuntu-Server 10.04.3 LTS "Lucid Lynx" - Release amd64 (20110719.2)
  ProcEnviron:
   LANG=en_GB.UTF-8
   SHELL=/bin/bash
  SourcePackage: bash

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