2.11BSD/man/cat8/ntpd.0
NTPD(8) Clockwatcher's Programming Manual NTPD(8)
NAME
ntpd - time synchronization daemon implementing NTP
SYNOPSIS
ntpd [-d] [-s] [-t]
OPTIONS
-d will bump the debug level by one. May be specified more
than once to increment debug level by one each time. Has no
effect if _n_t_p_d has not been compiled with DEBUG defined.
-s will cause _n_t_p_d to not adjust the the local clock.
-t will cause _n_t_p_d to modify the value of _t_i_c_k_a_d_j in your
kernel. This will have no effect unless _n_t_p_d was compiled
with SETTICKADJ defined.
DESCRIPTION
_N_T_P_D is the network time synchronization daemon and is nor-
mally invoked at boot time from the /_e_t_c/_r_c(8) file. It
implements a new revision of the Network Time Protocol first
described in RFC-958. It maintains the host's time syn-
chronized with a set of distributed time servers, each with
varying accurracy and reliability. Multiple time server
masters may exist, but there is no requirement for election
of a single master.
_N_t_p_d uses the _a_d_j_t_i_m_e(2) system call to slew the clock of
the host by small amount in order to keep the clock syn-
chronized. If the local clock exceeds the ``correct'' time
by some threshold, then _s_e_t_t_i_m_e_o_f_d_a_y(2) is used to make a
step adjustment of the local clock.
When _n_t_p_d(8) is started on the machine, it reads configura-
tion information from /_e_t_c/_n_t_p._c_o_n_f which contains informa-
tion about other _n_t_p time servers and host specific informa-
tion. Configuration information is listed one entry per
line, with fields separated by whitespace. Lines which
begin with a ``#'' character are treated as comments. Here
is a sample configuration file:
#
# Local clock parameters
#
# Precision of the local clock to the nearest power of 2
# ex.
# 60-HZ = 2**-6
# 100-HZ = 2**-7
# 1000-HZ = 2**-10
precision -7
#
# intrinsic drift of local clock
#
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NTPD(8) Clockwatcher's Programming Manual NTPD(8)
tickadj 1
#
# Peers Type Name
#
peer foo.umd.edu
peer 192.5.39.94
peer bar.arpa
server bogon.umd.edu
passive bozo.umd.edu
There are two major types of information specified in the
configuration file: local host information, and remote timer
server specification. The local host information is used to
describe the intrinsic properties of the local host's time-
keeping machinary. The commands in this group are preci-
sion, and tickadj.
The precision command takes a number which describes the
resolution of the local clock, as a power of two. For exam-
ple, a _V_A_X system typically has a 100 HZ clock and thus a
_p_r_e_c_i_s_i_o_n of -7. If the symbol _hz is defined in the namel-
ist of /vmunix, this value is automatically set based on the
value of hz.
The tickadj command is used to specify the granularity of
clock adjustment done by the _a_d_j_t_i_m_e(_2) system call. If the
-s option is specified when ntpd is invoked, the kernel
variable _tickadj is modified via /_d_e_v/_k_m_e_m. The preferred
method of setting tickadj is by changing the value in the
kernel file _c_o_n_f._c instead of having ntpd set in this rude
fashion. On a VAX, a value of 1 is usually used. See the
README file for typical values of tickadj on various
hardware platforms.
Currently three timer server specifications are supported.
They are peer, server and passive. Each command takes either
a dotted-quad internet address or a host name. Each host
specified in any one of the three commands is elligable to
be synchronized to, while random hosts which set up a peer
relationship are not. The peer and server commands create
an active polling situation; in the case of peer, the NTP
packets are sourced in _S_y_m_m_e_t_r_i_c-_A_c_t_i_v_e mode, while using
server causes the packets to be in _C_l_i_e_n_t mode. When
reachability is lost with a configured host in either of
these two cases, the daemon will continue to poll to re-
acquire that host. A host specified in the passive command
will not continue to be polled. If that host begins to poll
us, it will be eligable as to be synchronized but will not
be polled if reachability is lost.
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NTPD(8) Clockwatcher's Programming Manual NTPD(8)
It is recommended that the bulk of the peers configured
should be specified with the _c_l_i_e_n_t keyword; this will
minimize resource usage on the remote NTP server. If your
host will be serving as a redistribution point for a cluster
of hosts, you should set up _p_e_e_r relationships with higher
quality clocks (lower stratums) and other equal stratum
clocks. In other words, if you are not redistributing time
to others, you shouldn't need to configure any _p_e_e_r_s in your
NTP configuration; _c_l_i_e_n_t specifications are more appropri-
ate.
NOTES
Please choose your NTP peers carefully; send mail to
_n_t_p@_T_R_A_N_T_O_R._U_M_D._E_D_U for assitance.
There exists a broadcast command which will exercise com-
pletely untested code. Use at your own risk.
There is no reason to believe that the hpux code which was
added still works. In general, this code and adaptations of
the NTPD to platforms without the _a_d_j_t_i_m_e(_2) system call are
not likely to be very satisfying.
BUGS
No doubt.
FILES
/etc/ntp.conf NTP daemon configuration file
SEE ALSO
adjtime(2), settimeofday(2), RFC-958, _N_e_t_w_o_r_k _T_i_m_e _P_r_o_t_o_c_o_l
(_V_e_r_s_i_o_n _1) _S_p_e_c_i_f_i_c_a_t_i_o_n _R_e_v_i_s_e_d _1_7 _S_e_p_t_e_m_b_e_r _1_9_8_8
AUTHORS
Louis A. Mamakos, _l_o_u_i_e@_T_R_A_N_T_O_R._U_M_D._E_D_U
Michael G. Petry, _p_e_t_r_y@_T_R_A_N_T_O_R._U_M_D._E_D_U
The University of Maryland, Computer Science Center.
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