run-in-separate-pgrp: launch a console command in a newly created foreground process group

This wrapper tool launches an arbitrary command (and all its future child processes) in a newly created process group. The new process group also becomes foreground (interactive in terminal) if you ran the tool in an interactive session.

Usage

run-in-separate-pgrp
  [--forward-signals-to-group [--wait-timeout=N] | --forward-signals-to-child]
  [--print-signals]
  [--if-absent-path=PATH [--if-absent-cleanup=COMMAND]]
  command [arg ...]

Use Case 1: Limit Ctrl-C Impact

Use the tool if you want to limit the scope of Ctrl-C SIGINT propagation to only the hierarchy of that new process group.

Motivation: terminals send SIGINT to ALL processes of a foreground process group when Ctrl-C is pressed (not only to one process), which may kill some intermediate parent processes like yarn. As an example, the tool can be used to let interactive psql run in a yarn script (without the tool, yarn dies on SIGINT, which effectively closes STDIN for psql).

With the tool, you can use Ctrl-C when running yarn psql:

Without the tool, pressing Ctrl-C kills yarn and thus kills psql on stdin EOF:

See details here:

• https://www.postgresql.org/message-id/flat/271520.1713052173%40sss.pgh.pa.us#6ebc31cdb0365b0de9e0a2e7e5cb2268
• https://www.cons.org/cracauer/sigint.html

Use Case 2: Fanout Incoming Signals to All Processes in the New Group

If --forward-signals-to-group flag is passed, and the tool's process ID receives some signal, this signal is forwarded to all children processes subtree (in fact, to the processes of the new group). This is useful in e.g. GitHub Actions which send a SIGINT to the currently running shell process ONLY. Shells ignore that SIGINT, so the running jobs continue running until they are cruelly killed by the action runner in ~10 seconds. In this mode, the tool also waits until all the processes in the new group subtree exit (not only one immediate child); the wait timeout is controlled by --wait-timeout option (defaults to 10 seconds).

Alternatively, when --forward-signals-to-child is passed, the tool forwards the signals to the command's process only (no fanout). This is less useful of course.

See details here:

• https://github.com/ringerc/github-actions-signal-handling-demo

If --if-absent-path=PATH is passed and the path (file or directory) disappears, the tool sends itself a SIGINT. Once the children processes are terminated according to the mode above, it optionally runs --if-absent-cleanup=COMMAND command. This is e.g. when a work directory is removed externally, and we want the final cleanup to happen.

Installation

You can download the tool file run-in-separate-pgrp and put it anywhere you want (it's a stand-alone Perl script with no dependencies):

wget https://raw.githubusercontent.com/dimikot/run-in-separate-pgrp/main/run-in-separate-pgrp
chmod +x run-in-separate-pgrp

Alternatively, you can install it as a Node module to be available in your PATH:

npm install run-in-separate-pgrp
yarn add run-in-separate-pgrp
pnpm install run-in-separate-pgrp