How to know current time from internet from command line in Linux?

If you use bash the following line will do the job

$ cat </dev/tcp/time.nist.gov/13

56525 13-08-21 23:07:09 50 0 0  55.6 UTC(NIST) *

It leverages the built-in network capabilites¹ of the bash shell. If you use a POSIX shell or any other shell you can use e.g. netcat.

$ nc time.nist.gov 13

56525 13-08-21 23:07:09 50 0 0  55.6 UTC(NIST) *

Both commands query the timer server on TCP port 13 of the National Institute of Standards and Technology and output the received data on stdout.

¹EDIT: From the Bash man page: Bash handles several filenames specially when they are used in redirections, as described in the following table:

/dev/tcp/host/port
If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts to open a TCP connection to the corresponding socket.

/dev/udp/host/port
If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts to open a UDP connection to the corresponding socket.

There are several NTP services available per distro.

If you would like to do a one time clocksync:

date -s "$(curl -s --head http://google.com | grep ^Date: | sed 's/Date: //g')"

Set system time to hardware Real-Time-Clock

hwclock -r --utc
hwclock -w --utc
hwclock -r --utc

(Note: this happens to work well with Google because they have severs all over)

---

If you would like to just see what time Google's nearest server sends:

date -d "$(curl -s --head http://google.com | grep ^Date: | sed 's/Date: //g')"

The ntpdate command can do this with the -q flag:

$ ntpdate -q 1.debian.pool.ntp.org
server 88.191.120.99, stratum 3, offset -0.015076, delay 0.06604
server 88.191.235.218, stratum 2, offset -0.000676, delay 0.06592
server 188.165.240.21, stratum 3, offset 0.001191, delay 0.07005
server 91.121.34.166, stratum 2, offset 0.000565, delay 0.06998
22 Aug 00:56:21 ntpdate[31373]: adjust time server 88.191.235.218 offset -0.000676 sec

From man ntpdate:

   -q     Query only - don't set the clock.