Securelevel is a security mechanism implemented in the kernel.

To check current ‘secure level’:

$ sysctl kern.securelevel
kern.securelevel: 2

To change / raise ‘secure level’:

$ sysctl kern.securelevel=2

To enable ‘secure level’ on boot:

$ sysrc kern_securelevel_enable="YES"
kern_securelevel_enable:  -> YES

$ sysrc kern_securelevel="2"
kern_securelevel:  -> 2

FreeBSD security levels