CHRONY(1) User's Manual CHRONY(1)NAME
chrony - programs for keeping computer clocks accurate
SYNOPSIS
chronyc [OPTIONS]
chronyd [OPTIONS]
DESCRIPTION
chrony is a pair of programs for keeping computer clocks accurate. chronyd is a background (daemon) program and chronyc is a command-line
interface to it. Time reference sources for chronyd can be RFC1305 NTP servers, human (via keyboard and chronyc), or the computer's real-
time clock at boot time (Linux only). chronyd can determine the rate at which the computer gains or loses time and compensate for it while
no external reference is present. Its use of NTP servers can be switched on and off (through chronyc) to support computers with dial-
up/intermittent access to the Internet, and it can also act as an RFC1305-compatible NTP server.
USAGE
chronyc is a command-line interface program which can be used to monitor chronyd's performance and to change various operating parameters
whilst it is running.
chronyd's main function is to obtain measurements of the true (UTC) time from one of several sources, and correct the system clock accord-
ingly. It also works out the rate at which the system clock gains or loses time and uses this information to keep it accurate between mea-
surements from the reference.
The reference time can be derived from either Network Time Protocol (NTP) servers, reference clocks, or wristwatch-and-keyboard (via
chronyc). The main source of information about the Network Time Protocol is http://www.ntp.org.
It is designed so that it can work on computers which only have intermittent access to reference sources, for example computers which use a
dial-up account to access the Internet or laptops. Of course, it will work well on computers with permanent connections too.
In addition, on Linux it can monitor the system's real time clock performance, so the system can maintain accurate time even across
reboots.
Typical accuracies available between 2 machines are
On an ethernet LAN : 100-200 microseconds, often much better On a V32bis dial-up modem connection : 10's of milliseconds (from one session
to the next)
With a good reference clock the accuracy can reach one microsecond.
chronyd can also operate as an RFC1305-compatible NTP server and peer.
SEE ALSO chronyc(1), chrony(1)
http://chrony.tuxfamily.org/
AUTHOR
Richard Curnow <rc@rc0.org.uk>
This man-page was written by Jan Schaumann <jschauma@netmeister.org> as part of "The Missing Man Pages Project". Please see
http://www.netmeister.org/misc/m2p2/index.html for details.
The complete chrony documentation is supplied in texinfo format.
chrony @VERSION@ @MAN_DATE@ CHRONY(1)
Check Out this Related Man Page
TIMEDATECTL(1) timedatectl TIMEDATECTL(1)NAME
timedatectl - Control the system time and date
SYNOPSIS
timedatectl [OPTIONS...] {COMMAND}
DESCRIPTION
timedatectl may be used to query and change the system clock and its settings.
OPTIONS
The following options are understood:
-h, --help
Prints a short help text and exits.
--version
Prints a short version string and exits.
--no-pager
Do not pipe output into a pager.
--no-ask-password
Do not query the user for authentication for privileged operations.
-P, --privileged
Acquire privileges via PolicyKit before executing the operation.
-H, --host
Execute the operation remotely. Specify a hostname, or username and hostname separated by "@", to connect to. This will use SSH to talk
to a remote system.
--adjust-system-clock
If set-local-rtc is invoked and this option is passed, the system clock is synchronized from the RTC again, taking the new setting into
account. Otherwise, the RTC is synchronized from the system clock.
The following commands are understood:
status
Show current settings of the system clock and RTC.
set-time [TIME]
Set the system clock to the specified time. This will also update the RTC time accordingly. The time may be specified in the format
"2012-10-30 18:17:16".
set-timezone [TIMEZONE]
Set the system time zone to the specified value. Available timezones can be listed with list-timezones. If the RTC is configured to be
in the local time, this will also update the RTC time. This call will alter the /etc/localtime symlink. See localtime(5) for more
information.
list-timezones
List available time zones, one per line. Entries from the list can be set as the system timezone with set-timezone.
set-local-rtc [BOOL]
Takes a boolean argument. If "0", the system is configured to maintain the RTC in universal time. If "1", it will maintain the RTC in
local time instead. Note that maintaining the RTC in the local timezone is not fully supported and will create various problems with
time zone changes and daylight saving adjustments. If at all possible, keep the RTC in UTC mode. Note that invoking this will also
synchronize the RTC from the system clock, unless --adjust-system-clock is passed (see above). This command will change the 3rd line of
/etc/adjtime, as documented in hwclock(8).
set-ntp [BOOL]
Takes a boolean argument. Controls whether NTP based network time synchronization is enabled (if available).
EXIT STATUS
On success, 0 is returned, a non-zero failure code otherwise.
ENVIRONMENT
$SYSTEMD_PAGER
Pager to use when --no-pager is not given; overrides $PAGER. Setting this to an empty string or the value "cat" is equivalent to
passing --no-pager.
EXAMPLES
Show current settings:
$ timedatectl
Local time: Fri, 2012-11-02 09:26:46 CET
Universal time: Fri, 2012-11-02 08:26:46 UTC
RTC time: Fri, 2012-11-02 08:26:45
Timezone: Europe/Warsaw
UTC offset: +0100
NTP enabled: no
NTP synchronized: no
RTC in local TZ: no
DST active: no
Last DST change: CEST -> CET, DST became inactive
Sun, 2012-10-28 02:59:59 CEST
Sun, 2012-10-28 02:00:00 CET
Next DST change: CET -> CEST, DST will become active
the clock will jump one hour forward
Sun, 2013-03-31 01:59:59 CET
Sun, 2013-03-31 03:00:00 CEST
Enable an NTP daemon (chronyd):
$ timedatectl set-ntp true
==== AUTHENTICATING FOR org.freedesktop.timedate1.set-ntp ===
Authentication is required to control whether network time synchronization shall be enabled.
Authenticating as: user
Password: ********
==== AUTHENTICATION COMPLETE ===
$ systemctl status chronyd.service
chronyd.service - NTP client/server
Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled)
Active: active (running) since Fri, 2012-11-02 09:36:25 CET; 5s ago
...
SEE ALSO systemd(1), hwclock(8), date(1), localtime(5), systemctl(1), systemd-timedated.service(8)systemd 208TIMEDATECTL(1)