clockdiff - measure clock difference between hosts
clockdiff [-o] [-o1]
[--time-format ctime iso] [-V]
clockdiff Measures clock difference between us and
destination with 1 msec resolution using ICMP TIMESTAMP  packets
or, optionally, IP TIMESTAMP option  added to ICMP ECHO. 
Use IP TIMESTAMP with ICMP ECHO instead of ICMP TIMESTAMP
messages. It is useful with some destinations, which do not support ICMP
TIMESTAMP (f.e. Solaris <2.4).
Slightly different form of -o, namely it uses
three-term IP TIMESTAMP with prespecified hop addresses instead of four term
one. What flavor works better depends on target host. Particularly, -o
is better for Linux.
-T, --time-format ctime iso
Print time stamp in output either ISO-8601 format or
classical ctime format. The ctime format is default. The ISO time stamp
includes timezone, and is easier to parse.
Alias of --time-format iso option and argument.
Print help and exit.
Print version and exit.
• Some nodes (Cisco) use non-standard timestamps,
which is allowed by RFC, but makes timestamps mostly useless.
• Some nodes generate messed timestamps
(Solaris>2.4), when run xntpd. Seems, its IP stack uses a corrupted
clock source, which is synchronized to time-of-day clock periodically and
jumps randomly making timestamps mostly useless. Good news is that you can use
NTP in this case, which is even better.
• clockdiff shows difference in time modulo
 ICMP ECHO, RFC0792, page 14.
 ICMP TIMESTAMP, RFC0792, page 16.
 IP TIMESTAMP option, RFC0791, 3.1, page 16.
clockdiff was compiled by Alexey Kuznetsov
<firstname.lastname@example.org>. It was based on code borrowed from BSD
clockdiff requires CAP_NET_RAW capability to be executed.
It is safe to be used as set-uid root.
clockdiff is part of iputils package.