.\" $FreeBSD: src/sbin/init/init.8,v 1.45 2004/07/22 10:38:13 keramida Exp $

.\" $FreeBSD:  Exp $

The kernel runs with five different levels of security.

If the kernel security level (see

Any super-user process can raise the security level, but no process

.Xr security 7 )

can lower it.

is initially nonzero, then

The security levels are:

.Bl -tag -width flag

.It Ic -1

Permanently insecure mode \- always run the system in level 0 mode.

This is the default initial value.

.It Ic 0

Insecure mode \- immutable and append-only flags may be turned off.

All devices may be read or written subject to their permissions.

.It Ic 1

Secure mode \- the system immutable and system append-only flags may not

be turned off;

disks for mounted file systems,

.Pa /dev/mem ,

.Pa /dev/kmem

and

.Pa /dev/io

(if your platform has it) may not be opened for writing;

kernel modules (see

.Xr kld 4 )

may not be loaded or unloaded.

.It Ic 2

Highly secure mode \- same as secure mode, plus disks may not be

opened for writing (except by

.Xr mount 2 )

whether mounted or not.

This level precludes tampering with file systems by unmounting them,

but also inhibits running

.Xr newfs 8

while the system is multi-user.

.Pp

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

.Dq Time adjustment clamped to +1 second .

.It Ic 3

Network secure mode \- same as highly secure mode, plus

IP packet filter rules (see

.Xr ipfw 8 ,

.Xr ipfirewall 4

and

.Xr pfctl 8 )

cannot be changed and

.Xr dummynet 4

or

.Xr pf 4

configuration cannot be adjusted.

.El

.Pp

If the security level is initially nonzero, then

is a per-jail

is a per-jail setting of the security level.

.Dq securelevel

setting.