NAME¶
ntpd - Network Time Protocol (NTP) daemon
SYNOPSIS¶
ntpd [ -46aAbgLmnNqx ] [ -c
conffile ] [ -f
driftfile ] [
-i
jaildir ] [ -k
keyfile ] [ -l
logfile ] [ -p
pidfile ] [ -P
priority ] [ -r
broadcastdelay ] [ -s
statsdir ] [ -t
key ] [ -u
user[:
group] ] [ -U
interface_update_interval ] [ -v
variable ] [ -V
variable
]
DESCRIPTION¶
The
ntpd program is an operating system daemon which sets and maintains
the system time of day in synchronism with Internet standard time servers. It
is a complete implementation of the Network Time Protocol (NTP) version 4, but
also retains compatibility with version 3, as defined by RFC-1305, and version
1 and 2, as defined by RFC-1059 and RFC-1119, respectively.
ntpd does
most computations in 64-bit floating-point arithmetic and does relatively
clumsy 64-bit fixed-point operations only when necessary to preserve the
ultimate precision, about 232 picoseconds. While the ultimate precision is not
achievable with ordinary workstations and networks of today, it may be
required with future gigahertz CPU clocks and gigabit LANs.
The daemon can operate in any of several modes, including symmetric
active/passive, client/server broadcast/multicast and manycast. A
broadcast/multicast or manycast client can discover remote servers, compute
server-client propagation delay correction factors and configure itself
automatically. This makes it possible to deploy a fleet of workstations
without specifying configuration details specific to the local environment.
Ordinarily,
ntpd reads the
ntp.conf configuration file at startup
time in order to determine the synchronization sources and operating modes. It
is also possible to specify a working, although limited configuration entirely
on the command line, obviating the need for a configuration file. This may be
particularly appropriate when the local host is to be configured as a
broadcast/multicast client or manycast client, with all peers being determined
by listening to broadcasts at run time.
Various internal
ntpd variables can be displayed and configuration
options altered while the daemon is running using the
ntpq and
ntpd utility programs.
When
ntpd starts it looks at the value of umask, and if it is zero
ntpd will set the umask to 0222.
OPTIONS¶
- -a
- Require cryptographic authentication for broadcast client,
multicast client and symmetric passive associations. This is the
default.
- -A
- Do not require cryptographic authentication for broadcast
client, multicast client and symmetric passive associations. This is
almost never a good idea.
- -b
- Enable the client to synchronize to broadcast servers.
- -c conffile
- Specify the name and path of the configuration file,
default /etc/ntp.conf.
- -f driftfile
- Specify the name and path of the frequency file, default
/etc/ntp.drift. This is the same operation as the driftfile
driftfile configuration command.
- -g
- Normally, ntpd exits with a message to the system
log if the offset exceeds the panic threshold, which is 1000 s by default.
This option allows the time to be set to any value without restriction;
however, this can happen only once. If the threshold is exceeded after
that, ntpd will exit with a message to the system log. This option
can be used with the -q and -x options.
- -i jaildir
- Chroot the server to the directory jaildir. This
option also implies that the server attempts to drop root privileges at
startup (otherwise, chroot gives very little additional security). You may
need to also specify a -u option.
- -I [address | interface name]
- Open the network address given, or all the addresses
associated with the given interface name. This option may appear multiple
times. This option also implies not opening other addresses, except
wildcard and localhost. This option is deprecated. Please consider using
the configuration file interface command, which is more
versatile.
- -k keyfile
- Specify the name and path of the symmetric key file,
default /etc/ntp.keys. This is the same operation as the keys
keyfile configuration command.
- -l logfile
- Specify the name and path of the log file. The default is
the system log file. This is the same operation as the logfile
logfile configuration command.
- -L
- Do not listen to virtual IPs. The default is to
listen.
- -n
- Don't fork.
- -N
- To the extent permitted by the operating system, run the
ntpd at the highest priority.
- -p pidfile
- Specify the name and path of the file used to record the
ntpd process ID. This is the same operation as the pidfile
pidfile configuration command.
- -P priority
- To the extent permitted by the operating system, run the
ntpd at the specified priority.
- -q
- Exit the ntpd just after the first time the clock is
set. This behavior mimics that of the ntpdate program, which is to
be retired. The -g and -x options can be used with this
option. Note: The kernel time discipline is disabled with this
option.
- -r broadcastdelay
- Specify the default propagation delay from the
broadcast/multicast server to this client. This is necessary only if the
delay cannot be computed automatically by the protocol.
- -s statsdir
- Specify the directory path for files created by the
statistics facility. This is the same operation as the statsdir
statsdir configuration command.
- -t key
- Add a key number to the trusted key list. This option can
occur more than once.
- -u user[:group]
- Specify a user, and optionally a group, to switch to.
- -U interface_update_interval
- Number of seconds to wait between interface list scans to
pick up new and delete network interface. Set to 0 to disable dynamic
interface list updating. The default is to scan every 5 minutes.
- -v variable, -V variable
- Add a system variable listed by default.
- -x
- Normally, the time is slewed if the offset is less than the
step threshold, which is 128 ms by default, and stepped if above the
threshold. This option sets the threshold to 600 s, which is well within
the accuracy window to set the clock manually. Note: Since the slew rate
of typical Unix kernels is limited to 0.5 ms/s, each second of adjustment
requires an amortization interval of 2000 s. Thus, an adjustment as much
as 600 s will take almost 14 days to complete. This option can be used
with the -g and -q options. Note: The kernel time discipline
is disabled with this option.
- -4
- Force IPv4 DNS name resolution.
- -6
- Force IPv6 DNS name resolution.
FILES¶
- /etc/ntp.conf
- default name of the configuration file
- /etc/ntp.drift
- default name of the drift file
SEE ALSO¶
ntp.conf(5),
ntpdate(8)
The complete documentation can be found at
/usr/share/doc/ntp-doc/html/ntpd.html in the package ntp-doc.