TIMESYNCD.CONF(5) timesyncd.conf TIMESYNCD.CONF(5)

timesyncd.conf, timesyncd.conf.d - Network Time Synchronization configuration files

/etc/systemd/timesyncd.conf
/run/systemd/timesyncd.conf
/usr/local/lib/systemd/timesyncd.conf
/usr/lib/systemd/timesyncd.conf
/etc/systemd/timesyncd.conf.d/*.conf
/run/systemd/timesyncd.conf.d/*.conf
/usr/local/lib/systemd/timesyncd.conf.d/*.conf
/usr/lib/systemd/timesyncd.conf.d/*.conf

These configuration files control NTP network time synchronization. See systemd.syntax(7) for a general description of the syntax.

The default configuration is set during compilation, so configuration is only needed when it is necessary to deviate from those defaults. The main configuration file is loaded from one of the listed directories in order of priority, only the first file found is used: /etc/systemd/, /run/systemd/, /usr/local/lib/systemd/ [1], /usr/lib/systemd/. The vendor version of the file contains commented out entries showing the defaults as a guide to the administrator. Local overrides can also be created by creating drop-ins, as described below. The main configuration file can also be edited for this purpose (or a copy in /etc/ if it's shipped under /usr/), however using drop-ins for local configuration is recommended over modifications to the main configuration file.

In addition to the main configuration file, drop-in configuration snippets are read from /usr/lib/systemd/*.conf.d/, /usr/local/lib/systemd/*.conf.d/, and /etc/systemd/*.conf.d/. Those drop-ins have higher precedence and override the main configuration file. Files in the *.conf.d/ configuration subdirectories are sorted by their filename in lexicographic order, regardless of in which of the subdirectories they reside. When multiple files specify the same option, for options which accept just a single value, the entry in the file sorted last takes precedence, and for options which accept a list of values, entries are collected as they occur in the sorted files.

When packages need to customize the configuration, they can install drop-ins under /usr/. Files in /etc/ are reserved for the local administrator, who may use this logic to override the configuration files installed by vendor packages. Drop-ins have to be used to override package drop-ins, since the main configuration file has lower precedence. It is recommended to prefix all filenames in those subdirectories with a two-digit number and a dash, to simplify the ordering. This also defines a concept of drop-in priorities to allow OS vendors to ship drop-ins within a specific range lower than the range used by users. This should lower the risk of package drop-ins overriding accidentally drop-ins defined by users. It is recommended to use the range 10-40 for drop-ins in /usr/ and the range 60-90 for drop-ins in /etc/ and /run/, to make sure that local and transient drop-ins take priority over drop-ins shipped by the OS vendor.

To disable a configuration file supplied by the vendor, the recommended way is to place a symlink to /dev/null in the configuration directory in /etc/, with the same filename as the vendor configuration file.

The following settings are configured in the [Time] section:

NTP=

A space-separated list of NTP server host names or IP addresses. During runtime this list is combined with any per-interface NTP servers acquired from systemd-networkd.service(8). systemd-timesyncd will contact all configured system or per-interface servers in turn, until one responds. When the empty string is assigned, the list of NTP servers is reset, and all prior assignments will have no effect. This setting defaults to an empty list.

Added in version 216.

FallbackNTP=

A space-separated list of NTP server host names or IP addresses to be used as the fallback NTP servers. Any per-interface NTP servers obtained from systemd-networkd.service(8) take precedence over this setting, as do any servers set via NTP= above. This setting is hence only relevant if no other NTP server information is known. When the empty string is assigned, the list of NTP servers is reset, and all prior assignments will have no effect. If this option is not given, a compiled-in list of NTP servers is used.

Added in version 216.

RootDistanceMaxSec=

Maximum acceptable root distance, i.e. the maximum estimated time required for a packet to travel to the server we are connected to from the server with the reference clock. If the current server does not satisfy this limit, systemd-timesyncd will switch to a different server.

Takes a time span value. The default unit is seconds, but other units may be specified, see systemd.time(5). Defaults to 5 seconds.

Added in version 236.

PollIntervalMinSec=, PollIntervalMaxSec=

The minimum and maximum poll intervals for NTP messages. Polling starts at the minimum poll interval, and is adjusted within the specified limits in response to received packets.

Each setting takes a time span value. The default unit is seconds, but other units may be specified, see systemd.time(5). PollIntervalMinSec= defaults to 32 seconds and must not be smaller than 16 seconds. PollIntervalMaxSec= defaults to 34 min 8 s (2048 seconds) and must be larger than PollIntervalMinSec=.

Added in version 236.

ConnectionRetrySec=

Specifies the minimum delay before subsequent attempts to contact a new NTP server are made.

Takes a time span value. The default unit is seconds, but other units may be specified, see systemd.time(5). Defaults to 30 seconds and must not be smaller than 1 second.

Added in version 248.

SaveIntervalSec=

The interval at which the current time is periodically saved to disk, in the absence of any recent synchronisation from an NTP server. This is especially useful for offline systems with no local RTC, as it will guarantee that the system clock remains roughly monotonic across reboots.

Takes a time interval value. The default unit is seconds, but other units may be specified, see systemd.time(5). Defaults to 60 seconds.

Added in version 250.

systemd(1), systemd-timesyncd.service(8), systemd-networkd.service(8)

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💣💥🧨💥💥💣 Please note that those configuration files must be available at all times. If /usr/local/ is a separate partition, it may not be available during early boot, and must not be used for configuration.
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