THIS ARTICLE HAS BEEN RETRACTED.

The bug described in this page is of /usr/local/bin/pkill from proctools, not of macOS’s built-in /usr/bin/pkill.

This article is remain unremoved just for web pages which refer this article.

Original Contents

• pkill on macOS kills its parent process if a invalid parameter for a option is passed
• Verified on OS X 10.11.6 (El Capitan) and macOS 10.12.6 (Sierra)
• Seems to be fixed on macOS High Sierra (10.13)

First, let’s look through the usage of pkill:

$ pkill --help
pkill: illegal option -- h
Usage: pkill [-<signal>] [-finvVx] [-g <pgrplist>] [-G <gidlist>] [-P <ppidlist>] [-s <signal>] [-t <termlist>] [-u <euidlist>] [-U <uidlist>] [<pattern>]

Create test-pkill.sh which passes a invalid option -g foo to pkill:

echo 'Executing pkill'
pkill -g foo
echo 'Done'

Execute it.

$ sh test-pkill.sh
Executing pkill
pkill: unable to parse pid: foo
Terminated: 15

$ echo $?
143

Note that Done is not printed; test-pkill.sh was crashed! Terminated: 15 is printed by the shell (here, I used bash) and exit code 143 implies test-pkill.sh is killed with SIGTERM (143 = 128 + 15 = 128 + SIGTERM, see here for details). The message and exit code vary by shell:

$ csh
[wsh5:~/work] wsh% sh test-pkill.sh
Executing pkill
pkill: unable to parse pid: foo
Terminated
[wsh5:~/work] wsh% echo $?
143
[wsh5:~/work] wsh% exit
exit

$ ksh
$ sh test-pkill.sh
Executing pkill
pkill: unable to parse pid: foo
Terminated
$ echo $? # 271 = 256 = 15
271
$ exit

$ zsh
wsh5% sh test-pkill.sh
Executing pkill
pkill: unable to parse pid: foo
zsh: terminated  sh test-pkill.sh
wsh5% echo $?
143
wsh5% exit

$ fish
wsh@wsh5 /U/w/work> sh test-pkill.sh
Executing pkill
pkill: unable to parse pid: foo
fish: Job 1, 'sh test-pkill.sh' terminated by signal SIGTERM (Polite quit request)
wsh@wsh5 /U/w/work> echo $status
143
wsh@wsh5 /U/w/work> exit

I confirmed other options -G, -P, -t, -u, and -U also causes this crash.

This bug was found on Mac OS X 10.11.6 (El Capitan) while investigating a bug in the extension for Visual Studio Code, which crashes Visual Studio Code. This issue argues that the crash occurs on macOS 10.12.6 (Sierra).

Although there’s a room for further investigation (for example, sudo dtruss pkill -P foo reveals that it calls kill(2) to many unrelated processes), I won’t do that since the bug seems to be fixed on macOS 10.12 (High Sierra):

$ sh test-pkill.sh
Executing pkill
usage: pkill [-signal] [-ILfilnovx] [-F pidfile] [-G gid]
             [-P ppid] [-U uid] [-g pgrp]
             [-t tty] [-u euid] pattern
Done