GPT on Question 14, Sep 29

I'm writing a bash script to purge orphaned children after the parent dies. What's the idiomatic way?

There are two cases:

Normal script exit: trap and reap direct children

#!/usr/bin/env bash

children=()

cleanup() {
    trap - EXIT INT TERM
    ((${#children[@]})) && kill -TERM "${children[@]}" 2>/dev/null
    wait "${children[@]}" 2>/dev/null
}
trap cleanup EXIT INT TERM

worker1 & children+=("$!")
worker2 & children+=("$!")

wait

This handles ordinary exit and catchable signals. wait is important: killing children is not the same as reaping them.

Parent is killed or crashes

A Bash trap cannot run after SIGKILL, machine failure, etc. The idiomatic robust solution is to use an external supervisor/cgroup, such as a systemd service:

[Service]
ExecStart=/path/to/script
KillMode=control-group

That lets systemd terminate every process remaining in the service’s cgroup, including grandchildren.

On Linux, another option is to launch each child with a parent-death signal:

setpriv --pdeathsig TERM -- worker1 &

This uses PR_SET_PDEATHSIG, but applies to the direct child, not automatically to its descendants.

Avoid relying on PPID, kill -0 "$parent", or broad pkill matching: they have races and PID-reuse hazards. If you must clean up an entire descendant tree after an uncatchable parent death, cgroup-based supervision is generally the best approach.

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There are two cases:
### Normal script exit: trap and reap direct children
```bash
#!/usr/bin/env bash
children=()
cleanup() {
    trap - EXIT INT TERM
    ((${#children[@]})) && kill -TERM "${children[@]}" 2>/dev/null
    wait "${children[@]}" 2>/dev/null
}
trap cleanup EXIT INT TERM
worker1 & children+=("$!")
worker2 & children+=("$!")
wait
```
This handles ordinary exit and catchable signals. `wait` is important: killing children is not the same as reaping them.
### Parent is killed or crashes
A Bash `trap` cannot run after `SIGKILL`, machine failure, etc. The idiomatic robust solution is to use an external supervisor/cgroup, such as a systemd service:
```ini
[Service]
ExecStart=/path/to/script
KillMode=control-group
```
That lets systemd terminate every process remaining in the service’s cgroup, including grandchildren.
On Linux, another option is to launch each child with a parent-death signal:
```bash
setpriv --pdeathsig TERM -- worker1 &
```
This uses `PR_SET_PDEATHSIG`, but applies to the direct child, not automatically to its descendants.
Avoid relying on `PPID`, `kill -0 "$parent"`, or broad `pkill` matching: they have races and PID-reuse hazards. If you must clean up an entire descendant tree after an uncatchable parent death, cgroup-based supervision is generally the best approach.

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