systemd systemd-timesyncd.service 8 systemd-timesyncd.service systemd-timesyncd Network Time Synchronization systemd-timesyncd.service /usr/lib/systemd/systemd-timesyncd systemd-timesyncd is a system service that may be used to synchronize the local system clock with a remote Network Time Protocol (NTP) server. It also saves the local time to disk every time the clock has been synchronized and uses this to possibly advance the system realtime clock on subsequent reboots to ensure it (roughly) monotonically advances even if the system lacks a battery-buffered RTC chip. The systemd-timesyncd service implements SNTP only. This minimalistic service will step the system clock for large offsets or slowly adjust it for smaller deltas. Complex use cases that require full NTP support (and where SNTP is not sufficient) are not covered by systemd-timesyncd. The NTP servers contacted are determined from the global settings in timesyncd.conf5, the per-link static settings in .network files, and the per-link dynamic settings received over DHCP. See systemd.network5 for further details. timedatectl1's set-ntp command may be used to enable and start, or disable and stop this service. timedatectl1's timesync-status or show-timesync command can be used to show the current status of this service. systemd-timesyncd initialization delays the start of units that are ordered after time-set.target (see systemd.special7 for details) until the local time has been updated from /var/lib/systemd/timesync/clock (see below) in order to make it roughly monotonic. It does not delay other units until synchronization with an accurate reference time sources has been reached. Use systemd-time-wait-sync.service8 to achieve that, which will delay start of units that are ordered after time-sync.target until synchronization to an accurate reference clock is reached. systemd and systemd-timesyncd advance the system clock to the "epoch" (the lowest date above which the system clock time is assumed to be set correctly). See "System clock epoch" section in systemd1 for details. systemd will set the clock when initializing, but /var/lib/systemd/timesync/clock might not yet be available at that point. systemd-timesyncd will advance the clock when it is started and notices that the system clock is before the modification time of /var/lib/systemd/timesync/clock. /var/lib/systemd/timesync/clock The modification time ("mtime") of this file is updated on each successful NTP synchronization or after each SaveIntervalSec= time interval, as specified in timesyncd.conf5. If present, the modification time of this file is used for the epoch by systemd1 and systemd-timesyncd.service. /run/systemd/timesync/synchronized A file that is touched on each successful synchronization to assist systemd-time-wait-sync and other applications in detecting synchronization to an accurate reference clock. systemd1 timesyncd.conf5 systemd.network5 systemd-networkd.service8 systemd-time-wait-sync.service8 systemd.special7 timedatectl1 localtime5 hwclock8