I'm sorry, I'm a bit late to the party, but on aarch64 I consistently
have to increase kern.seminfo.semmns in order to get PostgreSQL 18.1 to
not miserably fail to start with the following error message (strangely,
reducing max_connections even down to 5 does not help and doesn't change
the failing call), where notably max_connections was 20 by default and
not 100 as the pkg-readme claims:
FATAL:  could not create semaphores: No space left on device
DETAIL:  Failed system call was semget(388807, 17, 03600).
HINT:  This error does *not* mean that you have run out of disk space.
       It occurs when either the system limit for the maximum number of
       semaphore sets (SEMMNI), or the system wide maximum number of
       semaphores (SEMMNS), would be exceeded.  You need to raise the
       respective kernel parameter. Alternatively, reduce PostgreSQL's
       consumption of semaphores by reducing its "max_connections"
       parameter.

I am more specifically on a Raspberry Pi 4B, if that has any influence
on some defaults I'm not aware of

In any case, the package README surely has to be updated to reflect the
actual default, but considering that this is the first release when I
encountered this problem *with the default sysctls*, I wonder what gives