Interestingly, '/etc/init.d/dahdi status' and 'systemctl status dahdi' give different results on boot:
[root@freepbx ~]# /etc/init.d/dahdi status
[root@freepbx ~]# echo $?
0
[root@freepbx ~]# systemctl status dahdi
● dahdi.service - LSB: DAHDI kernel modules
Loaded: loaded (/etc/rc.d/init.d/dahdi; bad; vendor preset: disabled)
Active: inactive (dead)
Docs: man:systemd-sysv-generator(8)
[root@freepbx ~]# echo $?
3
[root@freepbx ~]# /etc/init.d/dahdi status
[root@freepbx ~]# echo $?
0
[root@freepbx ~]# systemctl status dahdi
● dahdi.service - LSB: DAHDI kernel modules
Loaded: loaded (/etc/rc.d/init.d/dahdi; bad; vendor preset: disabled)
Active: inactive (dead)
Docs: man:systemd-sysv-generator(8)
[root@freepbx ~]# echo $?
3
[root@freepbx ~]#