Most shells (including bash, zsh) have a built-in for kill so it's done internally. Some shells don't so it executes /bin/kill instead which has this issue.
One comment noted this was fixed at some point in 2013 in version 3.3.4 but it apparently broke again at some point and is broken at least in 20.04 Focal's v3.3.16. This was recently fixed again upstream here: https://gitlab.com/procps-ng/procps/-/merge_requests/77 Upstream v3.3.16 (in 20.04 Focal and 20.10 Hirsute) was released Dec 2019 without this fix. That fix was submitted upstream 3 years ago but only merged 11 months ago and was included in the v3.3.17 release which was made in Feb 2021 so not included in 20.04 Focal. 3.3.17 with the fix is already in 21.10 Impish. -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to procps in Ubuntu. https://bugs.launchpad.net/bugs/1077796 Title: /bin/kill no longer works with negative PID Status in procps package in Ubuntu: Triaged Bug description: Incorrectly gives a usage message, eg: /bin/kill -1 -4321 ==> /bin/kill: invalid option -- '4' A workaround appears to be to use "--" before the PID, but this is unsatisfactory, as existing scripts would have to be modified when they shouldn't have to be. This problem has only appeared recently in 12.10. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/procps/+bug/1077796/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
