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I have a process that spawn a bash command with system() while the signal mask has all the signals blocked. This cannot be fixed easily.

The bash command eventually execs into a process. The all blocked signal mask is inherited from the original process through bash to the final process, so in the end I get a process that is "immune" to all the signals (except of course SIGKILL, SIGSTOP, etc).

The workaround would be resetting sigprocmask from bash, but I cannot find any related command. Is it possible to do?

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  • Is there a bash script that you can modify? What is the exact call to system involved? Commented Apr 8, 2014 at 17:42
  • It seems to me that this is not possible (whyever): "Non-builtin commands run by bash have signal handlers set to the values inherited by the shell from its parent." Commented Apr 8, 2014 at 18:01
  • @chepner I can modify the bash command that is invoked, but not the fact that when it's invoked the process has an all blocked signals set. Commented Apr 8, 2014 at 20:01
  • I don't think this is possible with bash. Can you use ksh93 or mksh instead? Or call the final process via yet another process (ksh, perl, python, …)? Commented Apr 8, 2014 at 23:26
  • @Gilles python and perl are possible Commented Apr 9, 2014 at 18:44

2 Answers 2

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There doesn't seem to be a pure bash solution.

Ksh (both ksh93 and mksh) unblock all signals (tested on Debian wheezy), so if you can use ksh instead of bash, it will solve your problem.

If you can't change the fact that bash is invoked, you might be able to make bash execute ksh and make ksh execute the child process: replace

bash -c '…; exec child_process'

by

bash -c '…; exec ksh -c "exec child_process"'

Beware of quoting issues!

Ksh is fast and easy to use, but often not part of the default installation. If that is an issue, you can use Perl instead, which is part of the default installation in most non-embedded Linux systems.

perl -e ' use POSIX; $s = POSIX::SigSet->new(); $s->fillset(); sigprocmask(1, $s, $s) or die $!; # 1 = SIG_UNBLOCK exec "child_process"'
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env in coreutils >= v8.31 will have this functionality

env --default-signal your_prog
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