Checkmk

Other restart currently in progress. Aborting

When this is shown for a long time, the helper which locks the main.mk died.
The solution is to find and kill that worker using the fuser command.

OMD[cmk]:~/etc/check_mk$ fuser main.mk
/opt/omd/sites/cmk/etc/check_mk/main.mk: 233324
OMD[cmk_core]:~/etc/check_mk$ ps -ef | grep 233324
cmk_cor+  186370  184646  0 09:27 pts/0    00:00:00 grep --color=auto 233324
cmk_cor+  233324       1  0 Feb20 ?        00:00:15 gunicorn: worker [automation-helper]
OMD[cmk]:~/etc/check_mk$ kill -9 233324
OMD[cmk]:~/etc/check_mk$ fuser main.mk
OMD[cmk]:~/etc/check_mk$

Then the Activate Changes will work again