What is the "H" switch for in `pkill`

teachernightowl

The final example on this page about signals says that pkill -HUP rsyslogd will make rsyslog re-read its configuration file.

I have checked man pkill on Ubuntu 18.04, CentOS 7, and OpenSUSE Tumbleweed and I cannot find anything about an uppercase "H" option.

coop

That's because "HUP" is a signal, not options (shorthand for SIGHUP). For some more explanation one link I found quickly is:

https://linuxize.com/post/pkill-command-in-linux/#:~:text=pkill is a command-line,the process, or other attributes.