config root man

This menu allows you to configure the Securelevel mechanism in FreeBSD.

Securelevels may be used to limit the privileges assigned to the
root user in multi-user mode, which in turn may limit the effects of
a root compromise, at the cost of reducing administrative functions.
Refer to the security(7) and init(8) manual pages for complete details.

   -1    Permanently insecure mode - always run the system in level 0
         mode.  This is the default initial value.

   0     Insecure mode - immutable and append-only flags may be turned
         off.  All devices may be read or written subject to their
         permissions.

   1     Secure mode - the system immutable and system append-only
         flags may not be turned off; disks for mounted file systems,
         /dev/mem, /dev/kmem and /dev/io (if your platform has it)
         may not be opened for writing; kernel modules (see kld(4))
         may not be loaded or unloaded.

   2     Highly secure mode - same as secure mode, plus disks may not
         be opened for writing (except by mount(2)) whether mounted or
         not.  This level precludes tampering with file systems by
         unmounting them, but also inhibits running newfs(8) while the
         system is multi-user.

         In addition, kernel time changes are restricted to less than
         or equal to one second.  Attempts to change the time by more
         than this will log the message ``Time adjustment clamped to +1
         second''.

   3     Network secure mode - same as highly secure mode, plus IP
         packet filter rules (see ipfw(8), ipfirewall(4) and pfctl(8))
         cannot be changed and dummynet(4) or pf(4) configuration
         cannot be adjusted.

Securelevels must be used in combination with careful system design and
application of protective mechanisms to prevent system configuration
files from being modified in a way that compromises the protections of
the securelevel variable upon reboot.