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				.\" Copyright (c) 2018 Ian Lepore <ian@FreeBSD.org>
				.\"
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				.\" $FreeBSD$
				.\"
				.Dd June 28, 2018
				.Dt MAC_NTPD 4
				.Os
				.Sh NAME
				.Nm mac_ntpd
				.Nd "policy allowing ntpd to run as non-root user"
				.Sh SYNOPSIS
				To compile the ntpd policy into your kernel, place the following lines
				in your kernel configuration file:
				.Bd -ragged -offset indent
				.Cd "options MAC"
				.Cd "options MAC_NTPD"
				.Ed
				.Pp
				Alternately, to load the ntpd policy module at boot time,
				place the following line in your kernel configuration file:
				.Bd -ragged -offset indent
				.Cd "options MAC"
				.Ed
				.Pp
				and in
				.Xr loader.conf 5 :
				.Pp
				.Dl "mac_ntpd_load=""YES"""
				.Sh DESCRIPTION
				The
				.Nm
				policy grants any process running as user
				.Sq ntpd
				(uid 123) the privileges needed to manipulate
				system time, and to (re-)bind to the privileged NTP port.
				.Pp
				When
				.Xr ntpd 8
				is started with
				.Sq -u\ <user>
				on the command line, it performs all initializations requiring root
				privileges, then drops root privileges by switching to the given user id.
				From that point on, the only privileges it requires are the ability
				to manipulate system time, and the ability to re-bind a UDP socket
				to the NTP port (port 123) after a network interface change.
				By default,
				.Fx
				starts
				.Xr ntpd 8
				with
				.Sq -u\ ntpd:ntpd
				on the command line, if the mac_ntpd policy is available to grant
				the required privileges.
				.Pp
				.Ss Privileges Granted
				The exact set of kernel privileges granted to any process running
				with the configured uid is:
				.Bl -inset -compact -offset indent
				.It PRIV_ADJTIME
				.It PRIV_CLOCK_SETTIME
				.It PRIV_NTP_ADJTIME
				.It PRIV_NETINET_RESERVEDPORT
				.It PRIV_NETINET_REUSEPORT
				.El
				.Pp
				.Ss Runtime Configuration
				The following
				.Xr sysctl 8
				MIBs are available for fine-tuning this MAC policy.
				All
				.Xr sysctl 8
				variables can also be set as
				.Xr loader 8
				tunables in
				.Xr loader.conf 5 .
				.Bl -tag -width indent
				.It Va security.mac.ntpd.enabled
				Enable the
				.Nm
				policy.
				(Default: 1).
				.It Va security.mac.ntpd.uid
				The numeric uid of the ntpd user.
				(Default: 123).
				.El
				.Sh SEE ALSO
				.Xr mac 4 ,
				.Xr ntpd 8
				.Sh HISTORY
				MAC first appeared in
				.Fx 5.0
				and
				.Nm
				first appeared in
				.Fx 12.0 .