netbsd

基于ntp协议的网络时间服务程序

Starting with NetBSD-1.6, it is possible to delegate the system clock 
control to a non root user. This enable running ntpd in a chroot 
jail under a non privilegied UID/GID, using ntpd -i and -u flags.

The delegation is done through the clockctl(4) pseudodevice driver. 
This driver makes privilegied system calls such as ntp_adjtime(2)
available through ioctl(2) on the /dev/clockctl device. If a user
is able to write to /dev/clockctl, then (s)he can control the system 
clock.

In order to use this feature, make sure that:

1) Your kernel is compiled with the following option:
pseudo-device	clockctl
This is true for GENERIC kernels on most ports. Please check 
http://wwW.netbsd.org/Documentation/kernel/
if you need information about building a kernel.

2) You have a ntpd user on your system. Here is the /etc/master.passwd
entry for ntpd user on NetBSD-1.6:
ntpd:*:15:15::0:0:& pseudo-user:/var/chroot/ntpd:/sbin/nologin
And here is the /etc/group entry for group 15:
ntpd:*:15:

3) /dev/clockctl exists and is writtable by user ntpd. Default 
NetBSD-1.6 setting is:
crw-rw----  1 root  ntpd  61, 0 Apr 1  2002 /dev/clockctl
Major device number and date is likely to be different on your system.
If you need to create the device, issue the following command:
cd /dev && ./MAKEDEV clockctl

Here is an example of how to run ntpd chrooted in /var/chroot/ntpd, 
running with ntpd UID and ntpd GID:
ntpd -i /var/chroot/ntpd -u ntpd:ntpd
Note that -i and -u options are enabled at configure time if your 
system supports system clock control by an unprivilegied user. If this
is not the case, then the -i and -u options will not be available.