Currently, the kill-old-processes command to kill python scripts (like run-webkit-tests) has an unchecked "xargs kill" at the end, which may output an error message if there is no such command to be killed (as it is the case most of the time). Linux' version of xargs has the "-r" option which can be used to avoid running the command.
Created attachment 408362 [details] Patch
Comment on attachment 408362 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=408362&action=review > Tools/ChangeLog:3 > + kill-old-processes: Avoid calling kill command with empty string This is a platform-specific bug and fix. On BSD systems like macOS, xargs already doesn’t do this. But on platforms with GNU xargs this "-r" option is needed.
Created attachment 408402 [details] Patch for landing
Committed r266808: <https://trac.webkit.org/changeset/266808>
<rdar://problem/68612810>
*** Bug 215999 has been marked as a duplicate of this bug. ***