Linux ntp
Most these commands have been used on Ubuntu systems.
Time manipulation and troubleshooting
timedatectl - In recent Ubuntu releases timedatectl replaces ntpdate. By default timedatectl syncs the time once on boot and later on uses socket activation to recheck once network connections become active.
timesyncd - In recent Ubuntu releases timesyncd replaces the client portion of ntpd. By default timesyncd regularly checks and keeps the time in sync. It also stores time updates locally, so that after reboots monotonically advances if applicable.
Update NTP managment system
sudo update-rc.d -f ntpdate remove #remove deprecated ntpdate service sudo apt-get install ntp
Show ntp logs
cat /var/log/messages | grep ntp
Show RTC (Real Time Clock) hardware clock
hwclock --show hwclock -r hwclock --show --utc hwclock --systohc #sync system clock -> hardware clock hwclock --hctosys #sync hardware clock -> system clock
Display time details (Ubuntu 16.04)
$ timedatectl Local time: Tue 2017-08-08 09:31:14 UTC Universal time: Tue 2017-08-08 09:31:14 UTC RTC time: Tue 2017-08-08 09:31:14 Time zone: Etc/UTC (UTC, +0000) Network time on: yes NTP synchronized: no RTC in local TZ: no
- Force ntpd to sync time
Worked for Ubuntu 18.4
sudo systemctl stop ntp.service sudo ntpd -gq # -g tells the ntp daemon to correct the time regardless of the offset # -q exit immediately after setting the time; it can take 5-10 sec sudo systemctl start ntp.service #you should notice in timedatectl output NTP synchronized: yes
Troubleshooting NTP server
sudo tcpdump port 123 #capture ntp packets timedatectl status ntpdc -p #offset in seconds ntpq -p #offset in milliseconds ntpq --numeric --peers #show peers (time providers) ntpq -c lpeer #show peers (time providers) ntpq -d <time_server> #debugging mode (not sure if will update local clock) ntpdate -d <time_server> #debugging mode, in which ntpdate will go through all the steps, but doesn't adjust the local clock ntpstats ntpdate -s a_stratum_1_server_address ntpdc -c loopinfo #will display the combined offset in seconds, as seen at the last poll ntpdc -c kerninfo #will display the current remaining correction, just as ntptime does
Show difference/offset between local and remote time server
ntpdate -q <time_server> #just query NTP server and it will display time difference/offset
Set time zone
- Set timezone (Ubuntu 16.04, 20.04)
# Check the current TZ ls -l /etc/localtime lrwxrwxrwx 1 root root 27 Feb 16 08:30 /etc/localtime -> /usr/share/zoneinfo/Etc/UTC # List time zones timedatectl list-timezones | grep Europe/London Europe/London # Set a timezone sudo timedatectl set-timezone Europe/London # Verify ls -l /etc/localtime lrwxrwxrwx 1 root root 35 Mar 29 09:18 /etc/localtime -> ../usr/share/zoneinfo/Europe/London vagrant@vagrant ~ $ timedatectl Local time: Mon 2021-03-29 09:18:59 BST Universal time: Mon 2021-03-29 08:18:59 UTC RTC time: Mon 2021-03-29 08:18:58 Time zone: Europe/London (BST, +0100) System clock synchronized: no NTP service: inactive RTC in local TZ: no
- Set time zone on Amazon Linux, to UTC
cat /etc/*rel* NAME="Amazon Linux AMI" VERSION="2014.09" $ date Fri 4 Sep 15:32:12 BST 2020 # Do not change the 'UTC=true' entry to another value. This entry is for the hardware clock, # and does not need to be adjusted when you're setting a different time zone on your instance. sudo vi /etc/sysconfig/clock # edit if needed ZONE="UTC" UTC=true # List available time zones ls -l /etc/localtime # Symlink (cp) 'localtime' file with content of desired TZ sudo mv /etc/localtime /etc/localtime.original sudo ln -s /usr/share/zoneinfo/UTC /etc/localtime date # no reboot required Fri 4 Sep 14:50:26 UTC 2020
chrony
Every pre-RHEL8 uses ntpd
but recently chrony
becomes a standard time client.
# RHEL8 sudo yum -y install chrony sudo systemctl start chronyd && sudo systemctl enable chronyd sudo vi /etc/chrony.conf # add NTP server, service restart is required to apply changes
Show time sources
chronyc sources -v .-- Source mode '^' = server, '=' = peer, '#' = local clock. / .- Source state '*' = current synced, '+' = combined , '-' = not combined, | / '?' = unreachable, 'x' = time may be in error, '~' = time too variable. || .- xxxx [ yyyy ] +/- zzzz || Reachability register (octal) -. | xxxx = adjusted offset, || Log2(Polling interval) --. | | yyyy = measured offset, || \ | | zzzz = estimated error. || | | \ MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^* 169.254.169.123 3 6 17 12 +15us[ +57us] +/- 320us ^- tbag.heanet.ie 1 6 17 13 -3488us[-3446us] +/- 1779us ^- ec2-12-34-231-12.eu-west- 2 6 17 13 +893us[ +935us] +/- 7710us ^? 2a05:d018:c43:e312:ce77:6 0 6 0 10y +0ns[ +0ns] +/- 0ns ^? 2a05:d018:d34:9000:d8c6:5 0 6 0 10y +0ns[ +0ns] +/- 0ns ^? tshirt.heanet.ie 0 6 0 10y +0ns[ +0ns] +/- 0ns ^? bray.walcz.net 0 6 0 10y +0ns[ +0ns] +/- 0ns
References
Ntp Ubuntu wiki