chrony: time synchronization over NTP

cheat sheet · Ubuntu 24.04 · chrony 4.5 https://lab.dimsanych.ru/en/wiki/chrony/

Cheat sheet

chronyc tracking is the clock in sync, and how close
chronyc sources time servers and their state
chronyc sourcestats offset and spread per server
sudo chronyc reload sources reread /etc/chrony/sources.d
sudo chronyc burst 4/4 poll the servers now
sudo chronyc makestep correct the clock in one step
chronyc waitsync 10 0.5 wait for sync (for scripts)
sudo systemctl restart chrony reread chrony.conf and conf.d

Configuration

Files and directories

The main file is /etc/chrony/chrony.conf. In Ubuntu 24.04, without comments, it is:

text

confdir /etc/chrony/conf.d
pool ntp.ubuntu.com        iburst maxsources 4
pool 0.ubuntu.pool.ntp.org iburst maxsources 1
pool 1.ubuntu.pool.ntp.org iburst maxsources 1
pool 2.ubuntu.pool.ntp.org iburst maxsources 2
sourcedir /run/chrony-dhcp
sourcedir /etc/chrony/sources.d
keyfile /etc/chrony/chrony.keys
driftfile /var/lib/chrony/chrony.drift
ntsdumpdir /var/lib/chrony
logdir /var/log/chrony
maxupdateskew 100.0
rtcsync
makestep 1 3
leapsectz right/UTC

Your own settings go into two directories:

Directory	Files	How to apply
`/etc/chrony/conf.d/`	`*.conf` — any directives	`sudo systemctl restart chrony`
`/etc/chrony/sources.d/`	`*.sources` — only `server`, `pool`, `peer`	`sudo chronyc reload sources`

reload sources rereads only sources.d: a server line in conf.d does not appear after it, a restart is needed. The lab machine has no network to the outside, the pool names do not resolve, and chronyc activity prints 16 sources with unknown address — these lines do no harm.

Directives are in the table below; the full list is man chrony.conf.