Ubuntu – Get last time timedatectl synchronized its time/force synchronization now

dateUbuntu

I have an Ubuntu server that is a little over a minute out of sync with the actual time. When I run timedatectl I get:

Local time: Tue 2018-04-24 14:47:57 MDT
Universal time: Tue 2018-04-24 20:47:57 UTC
RTC time: Tue 2018-04-24 20:47:57
Timezone: America/Denver (MDT, -0600)
NTP enabled: yes
NTP synchronized: yes
RTC in local TZ: no
DST active: yes
Last DST change: DST began at
          Sun 2018-03-11 01:59:59 MST
          Sun 2018-03-11 03:00:00 MDT
Next DST change: DST ends (the clock jumps one hour backwards) at
          Sun 2018-11-04 01:59:59 MDT
          Sun 2018-11-04 01:00:00 MST

My understanding is that it should be synchronizing using NTP. It's possible ntp isn't working quite right. If I run ntpq -p I get:

remote           refid      st t when poll reach   delay   offset  jitter
======================================================================
propjet.latt.ne .INIT.          16 u    - 1024    0    0.000    0.000   0.000
time-a-g.nist.g .INIT.          16 u    - 1024    0    0.000    0.000   0.000
linode227395.st .INIT.          16 u    - 1024    0    0.000    0.000   0.000
dev.smatwebdesi .INIT.          16 u    - 1024    0    0.000    0.000   0.000
pugot.canonical .INIT.          16 u    - 1024    0    0.000    0.000   0.000

Is there a way to tell when the last time was that it synced and from what server. Also, how do I force synchronization right now to fix the problem (I know I can manually set the date, but I won't get it quite right, and I want to actually fix the syncing).

Best Answer

Checking status

Since Ubuntu 16.04 timesyncd which is part of systemd is now responsible (out of the box) for syncing date/time. You can check its status using systemctl:

$ systemctl status systemd-timesyncd.service
● systemd-timesyncd.service - Network Time Synchronization
   Loaded: loaded (/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
  Drop-In: /lib/systemd/system/systemd-timesyncd.service.d
           └─disable-with-time-daemon.conf
   Active: active (running) since Sun 2018-08-05 10:14:44 EDT; 11min ago
     Docs: man:systemd-timesyncd.service(8)
 Main PID: 3714 (systemd-timesyn)
   Status: "Synchronized to time server 108.59.2.24:123 (0.debian.pool.ntp.org)."
   CGroup: /system.slice/systemd-timesyncd.service
           └─3714 /lib/systemd/systemd-timesyncd

Aug 05 10:14:44 pi-hole systemd[1]: Starting Network Time Synchronization...
Aug 05 10:14:44 pi-hole systemd[1]: Started Network Time Synchronization.
Aug 05 10:14:45 pi-hole systemd-timesyncd[3714]: Synchronized to time server 108.59.2.24:123 (0.debian.pool.ntp.org).

Or through journalctl:

$ journalctl -u systemd-timesyncd
-- Logs begin at Thu 2016-11-03 13:16:42 EDT, end at Sun 2018-08-05 10:20:01 EDT. --
Aug 05 10:14:44 pi-hole systemd[1]: Starting Network Time Synchronization...
Aug 05 10:14:44 pi-hole systemd[1]: Started Network Time Synchronization.
Aug 05 10:14:45 pi-hole systemd-timesyncd[3714]: Synchronized to time server 108.59.2.24:123 (0.debian.pool.ntp.org).

You can also watch systemd/clock:

$ stat /var/lib/systemd/clock
  File: /var/lib/systemd/clock
  Size: 0           Blocks: 0          IO Block: 4096   regular empty file
Device: b302h/45826d    Inode: 18750       Links: 1
Access: (0644/-rw-r--r--)  Uid: (  100/systemd-timesync)   Gid: (  103/systemd-timesync)
Access: 2018-08-05 10:22:13.838262405 -0400
Modify: 2018-08-05 10:22:13.838262405 -0400
Change: 2018-08-05 10:22:13.838262405 -0400
 Birth: -

The Access/Modify/Change times on this file show when systemd-timesynd last touched it.

Forcing a sync

It doesn't appear that there's any method to force a sync directly. Restarting the systemd-timesyncd service does in fact trigger a resync though:

$ systemctl restart systemd-timesyncd

You can see this in the logs:

$ journalctl -u systemd-timesyncd
-- Logs begin at Thu 2016-11-03 13:16:42 EDT, end at Sun 2018-08-05 10:44:37 EDT. --
Aug 05 10:14:44 pi-hole systemd[1]: Starting Network Time Synchronization...
Aug 05 10:14:44 pi-hole systemd[1]: Started Network Time Synchronization.
Aug 05 10:14:45 pi-hole systemd-timesyncd[3714]: Synchronized to time server 108.59.2.24:123 (0.debian.pool.ntp.org).
Aug 05 10:44:37 pi-hole systemd[1]: Stopping Network Time Synchronization...
Aug 05 10:44:37 pi-hole systemd[1]: Stopped Network Time Synchronization.
Aug 05 10:44:37 pi-hole systemd[1]: Starting Network Time Synchronization...
Aug 05 10:44:37 pi-hole systemd[1]: Started Network Time Synchronization.
Aug 05 10:44:37 pi-hole systemd-timesyncd[4157]: Synchronized to time server 208.75.88.4:123 (0.debian.pool.ntp.org).

The last line is from my restart.

Controlling interval

You can control the interval which this polls the NTP servers through these properties in the systemd-timesyncd config file /etc/systemd/timesyncd.conf:

   PollIntervalMinSec=, PollIntervalMaxSec=

   The minimum and maximum poll intervals for NTP messages. Each setting takes a time 
   value (in seconds). PollIntervalMinSec= must not be smaller than 16 seconds. 
   PollIntervalMaxSec= must be larger than PollIntervalMinSec=. PollIntervalMinSec= 
   defaults to 32 seconds, and PollIntervalMaxSec= defaults to 2048 seconds.

The above appears to have been added in late 2017 - timesync: make poll interval configurable #7268.

References

Related Solutions

Linux – How to Find Last Time a File Was Opened

This depends on exactly what you mean by "opened", but in general, yes. There are three timestamps normally recorded:

mtime — updated when the file contents change. This is the "default" file time in most cases.
ctime — updated when the file or its metadata (owner, permissions) change
atime — updated when the file is read

So, generally, what you want to see is the atime of a file. You can get that with stat or with ls. You can use ls -lu to do this, although I prefer to use ls -l --time=atime (which should be supported in almost all modern Linux distributions) because I don't use it often, and when I do I can remember it better. And to sort by time, add the -t flag to ls. So there you go.

There is a big caveat, though. Updating the atime every time a file is read causes a lot of usually-unnecessary IO, slowing everything down. So, most Linux distributions now default to the noatime filesystem mount option, which basically kills atimes, or else relatime, which only updates atimes once a limit has passed (normally once per day) or if the file was actually modified since the previous read. You can find if these options are active by running the mount command.

Also, note that access times are by inode, not by filename, so if you have hardlinks, reading from one will update all names that refer to the same file.

And, be aware that c is not "creation"; creation isn't tracked by Unix/Linux filesystems, which seems strange but actually makes sense because the filesystem has no way of knowing if it is the original — maybe the file was created forty years ago and copied here. And, in fact, many file editors work by making copies over the original. If you need that information, it's best to use a version control system like git.

Get time for system default timezone

Try unsetting the TZ variable (which is different from setting it to ""):

$ (date; export TZ=/usr/share/zoneinfo/Canada/Eastern; date; unset TZ; date)
Tue Nov 18 03:25:25 IST 2014
Mon Nov 17 16:55:25 EST 2014
Tue Nov 18 03:25:25 IST 2014

Note how I tried it in a subshell, so that my current shell remains unaffected.