Command grouping and signals

This is part of the Semicolon&Sons Code Diary - consisting of lessons learned on the job. You're in the unix category.

Last Updated: 2022-05-26

I had the following Procfile

web: rails server -p 3000
docservices: (cd ../oxnotes-docservices && APP_ENV=development bundle exec rackup config.ru)

I planted an un-rescued exception in web.1 (rails server) and the foreman output was as follows:

14:50:52 web.1         | exited with code 1
14:50:52 system        | sending SIGTERM to all processes
14:50:52 docservices.1 | terminated by SIGTERM

However, running ps shows there are remnants still running!

13360 ttys000    0:00.00 sh -c (cd ../oxnotes-docservices && APP_ENV=development bundle exec rackup config.ru)
13361 ttys000    0:00.67 /Users/jack/.rbenv/versions/2.6.4/bin/rackup config.ru

pstree shows these two have a parent child relationship

 |-+- 13360 jack sh -c (cd ../oxnotes-docservices && APP_ENV=development bundle exec rackup config.ru)
 | \--- 13361 jack /Users/jack/.rbenv/versions/2.6.4/bin/rackup config.ru

Let's run it again get more info from ps e.g. process group id pgid

# ask ps for pgid specifically
ps o pid,ppid,pgid,sess,comm,arg

# running Foreman again - unfortunately pids different to above

  PID  PPID  PGID   SESS COMM             ARGS
28590 17478 28590      0 foreman: master  foreman: master
28603 28590 28590      0 puma 4.1.1 (tcp: puma 4.1.1 (tcp://localhost:3000) [oxnotes4]
28604 28590 28590      0 redis-server 127 redis-server 127.0.0.1:6379
28605 28590 28590      0 /Library/Java/Ja /Library/Java/JavaVirtualMachines/jdk1.8.0_192.jdk/Contents/Home
28606 28590 28590      0 sh               sh -c (cd ../oxnotes-docservices && APP_ENV=development bundle e
# It seems odd that these lines are repeated. What I believe is happened is that
# the previous one was `sh -c ""` and the subsequent one is `()`
28608 28606 28590      0 sh               sh -c (cd ../oxnotes-docservices && APP_ENV=development bundle e
28609 28608 28590      0 /Users/jack/.rbe /Users/jack/.rbenv/versions/2.6.4/bin/rackup config.ru
28610 28590 28590      0 /Users/jack/.rbe /Users/jack/.rbenv/versions/2.6.4/bin/rake jobs:work

What do we see?

So what's going on with the process staying around after being killed? Basically we have too much indirection with sh -c and () and, since child processes do not get passed along signals, the actual server does not get shut down.

Aside

Solutions

cd ../oxnotes-docservices || echo "DocServices directory not found" || exit
# Keep the same process ID, but run what follows.
# This allows signals to be passed forwards.
exec bundle exec rackup config.ru

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