sntp

Simple Network Time Protocol client

TLDR

Query time from an NTP server

$ sntp [pool.ntp.org]

Step (set) the system clock from a server

$ sudo sntp -S [pool.ntp.org]

Slew (gradually adjust) the system clock

$ sudo sntp -s [pool.ntp.org]

Query using IPv4 only

$ sntp -4 [pool.ntp.org]

Query using IPv6 only

$ sntp -6 [pool.ntp.org]

Use reserved NTP port 123

$ sudo sntp -r [pool.ntp.org]

SYNOPSIS

sntp [-46dhKoSs] [-a keyid] [-b bcaddress] [-c filename] [-M threshold] [-r] [server...]

sntp is a Simple Network Time Protocol client that queries NTP servers and displays the time offset between the local system clock and the server. With appropriate privileges, it can correct the system clock.Unlike the full ntpd daemon, sntp performs one-time synchronization, making it suitable for cron jobs or scripts where continuous synchronization is unnecessary. It can either step (immediately set) or slew (gradually adjust) the clock.Output shows the time offset and error bounds in seconds, indicating how far the local clock deviates from the server.

PARAMETERS

-S, --step

Step (set) the system clock using settimeofday()

-s, --slew

Slew (gradually adjust) the clock using adjtime()

-4, --ipv4

Force IPv4 DNS resolution

-6, --ipv6

Force IPv6 DNS resolution

-r, --usereservedport

Use reserved NTP port 123 for communication

-M threshold

Slew if offset is less than threshold milliseconds, otherwise step

-t seconds

Timeout to wait for responses (default: 5)

-d, --debug-level

Increase debug verbosity (can be specified multiple times)

-K file, --kod=file

KoD (Kiss-of-Death) history file

-a keyid, --authentication=keyid

Enable authentication with the specified key number

-b address

Listen to the specified address for broadcast time sync

-l file, --logfile=file

Log status messages to the specified file

-c, --concurrent

Send concurrent queries to resolved IPs (for hostnames resolving to multiple addresses on different machines)

CAVEATS

Stepping the clock can disrupt applications depending on monotonic time. Slewing is safer but limited to small adjustments. Modern distributions often use chronyd or systemd-timesyncd instead.

HISTORY

sntp implements RFC 4330 (Simple Network Time Protocol Version 4). It is part of the NTP reference implementation but has been largely superseded by more robust alternatives like chrony and systemd-timesyncd.