Mac OS Sierra 10.12.4
smsd v3.1.20, compiling from source
Wavecom GSM modem M1306B, USB interface

Has anyone successfully compiled version 3.1.20 from source? I'm running into this error on make:
smsd.c:35:10: fatal error: 'sys/inotify.h' file not found #include <sys/inotify.h>

Any particular package I need to install?

BTW, 3.1.15 compiles fine.

I do not know if Mac has inotify available, but if you disable it in the src/Makefile, you should get this compiled:

# Uncomment this to disable usage of inotify
#CFLAGS += -D DISABLE_INOTIFY

Remove the #.

Got it. What feature do I lose if I did this, though?

By default smsd checks once per 10 seconds if there are outgoing files to send. This means that it may take up to 10 seconds until a new file is handled, because main process of smsd sleeps to save system resources. Delaytime can be set to lower value, but in some environments it may cause higher server load.

With inotify library and a setting notifier = yes smsd continues spooling immediately after a new outgoing file is created, because notifier process sends a signal CONT to the main process. This same can be done if external program is monitoring the outgoing folder, or if the program which creates outgoing messages sends the signal after a new file is created. When signalling is used, delaytime can be very high, and still messages are picked up without remarkable delays.