Re: potential exec/nohup/timeout improvement for Linux: prctl(PR_SET_PDEATHSIG)

[Richard W.M. Jones]

On Thu, Aug 31, 2017 at 07:59:41AM -0500, Eric Blake wrote:
> Rich Jones just taught me about Linux' prctl(PR_SET_PDEATHSIG), which
> allows you to run a helper executable that will automatically be killed
> if its parent process dies.  I'm trying to figure out if coreutils
> should provide support for that API via any of its existing wrapper
> utilities (in fact, it sounds somewhat like the opposite of nohup -
> instead of spawning a child process that survives the shell's death, we
> want to be able to spawn a child process that automatically cleans
> itself up on the shell's death).  Or maybe we make a new wrapper
> utility.  However, since the functionality is currently Linux-only, I'm
> also wondering if coreutils is still a good choice for this
> functionality, or if we should pursue exposing it in some other package
> of useful shell utilities.

My idea (I'll leave it to someone else to implement) would be some
kind of cleanup wrapper for shell scripts, like:

  autocleanup [-s TERM] someprog &

If the main script exits, someprog gets killed automatically.  No need
for traps etc.

Note that ‘PR_SET_PDEATHSIG’ is passed through exec to non-setuid
processes so this is fairly simple to implement.  For setuid it would
fail silently, and testing for setuid might be problematic or racy I
suppose.

Of course this is all Linux-only.  Do other kernels implement anything
like this?  We could use it for nbdkit:

https://github.com/libguestfs/nbdkit/commit/370b554fb38be7360815af70d5e0175842c451c6

Rich.

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