sntp command

Synopsis

sntp [serverip]
sntp [servername]  # NET_LWIP=y && DNS=y only

Description

The sntp command gets the current time from an NTP time server and syncronizes the Real Time Clock (RTC) of the board. This command needs the server’s IP address to be given on the command line or via the ntpserverip environment variable.

The address of the NTP server does not need to be given if the DHCP server provides one. The legacy network stack (CONFIG_NET=y) can only use the first NTP server provided in the ntp-servers DHCP option.

When the network stack is lwIP (CONFIG_NET_LWIP=y) and DNS resolution is enabled (CONFIG_DNS=y), then the sntp command accepts a server name as an argument.

The network time is sent as UTC. So, if you want to set the RTC to any local time different from UTC, you need to set the timeoffset environment variable.

Round-trip delay compensation is not implemented/not enabled. In practice this should not matter much given that the RTC API does not have sub-second resolution, and round-trip times are typically 10 to 100 ms at most.

Examples

=> setenv ntpserverip 109.190.177.205
=> date
Date: 2025-06-16 (Monday)    Time: 15:19:35
=> date reset
Reset RTC...
Date: 2000-01-01 (Saturday)    Time:  0:00:00
=> date
Date: 2000-01-01 (Saturday)    Time:  0:00:03
=> sntp
Date: 2025-06-16 Time: 15:19:43
=> date
Date: 2025-06-16 (Monday)    Time: 15:19:47
=> setenv timeoffset 7200
=> sntp
Date: 2025-06-16 Time: 17:19:55
=> date
Date: 2025-06-16 (Monday)    Time: 17:19:57

With CONFIG_NET_LWIP=y and CONFIG_DNS=y:

=> date reset
Reset RTC...
Date: 2000-01-01 (Saturday)    Time:  0:00:00
=> sntp 0.us.pool.ntp.org
Date: 2025-06-16 Time: 15:10:59