ntpdate

Synchronize and set date and time

$ sudo ntpdate [host]

$ ntpdate -q [host]

$ sudo ntpdate -u [host]

$ sudo ntpdate -b [host]

ntpdate [options] server [server...]

-4
    Force IPv4 address resolution.

-6
    Force IPv6 address resolution.

-b
    Adjust the local clock to be synchronized using the adjtime() system call, which can handle large time offsets more gracefully. However, it is often less accurate.

-d
    Enable debug mode. Display extra output about the synchronization process.

-e authdelay
    Specify the authentication delay, in seconds. This is used for authenticated NTP servers.

-o version
    Specify the NTP protocol version number (1, 2, 3, or 4). The default is 4.

-p samples
    Specify the number of samples to acquire from each server. Values are from 1 to 8 inclusive. Normally ntpdate takes a few samples from each server. Higher numbers can be usefull in high unstable environments.

-q
    Query mode. Only query the servers without setting the time. Useful for testing server availability.

-s
    Silent mode. Suppress output.

-t timeout
    Specify the timeout, in seconds, for contacting a server.

-u
    Use an unprivileged port for outgoing packets. This is useful when behind a firewall that filters outgoing traffic.

server
    The hostname or IP address of an NTP server to query.

The ntpdate command is an older utility used to set the system's date and time by querying a Network Time Protocol (NTP) server. It operates by contacting one or more NTP servers and retrieving the current time from them.
Important: It's considered obsolete and should be replaced by ntpd or chronyd for continuous time synchronization. ntpdate only performs a one-time synchronization, which can lead to jumps in time if the system clock drifts significantly. This can negatively affect applications sensitive to time changes. Using a daemon such as ntpd or chronyd is preferable because they provide continuous time adjustment and avoid abrupt changes.
While still available on some systems, its use is discouraged. Modern systems primarily rely on daemons like timedatectl or systemd-timesyncd for time synchronization, which are more robust and prevent potential issues arising from sudden time adjustments.

ntpdate can cause abrupt time changes, which can disrupt applications and system logs. It's not suitable for environments requiring continuous and smooth timekeeping. Modern systems should use ntpd, chronyd or systemd-timesyncd instead.

Using publicly available NTP servers can pose security risks. Ensure that you are using trusted NTP servers and consider authenticating to prevent man-in-the-middle attacks. However, modern NTP daemons offer more robust security features compared to the legacy ntpdate.

timedatectl is a popular systemd command that allows to control and synchronize the system clock. systemd-timesyncd is a daemon process that takes care about small adjustments with ntp protocol.

ntpdate was a common tool for one-time NTP synchronization. As system requirements evolved, the need for continuous, stable timekeeping led to the development and widespread adoption of NTP daemons like ntpd and chronyd. ntpdate is now considered legacy, and its use is generally discouraged.

ntpd(8), chronyd(8), timedatectl(1), systemd-timesyncd(8)