NAME¶
clockdiff - measure clock difference between hosts
SYNOPSIS¶
clockdiff [-o] [-o1]
[--time-format ctime iso] [-V]
{destination}
DESCRIPTION¶
clockdiff Measures clock difference between us and
destination with 1 msec resolution using ICMP TIMESTAMP [2] packets
or, optionally, IP TIMESTAMP option [3] added to ICMP ECHO. [1]
OPTIONS¶
-o
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).
-o1
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.
-I
Alias of --time-format iso
option and argument.
-h, --help
Print help and exit.
-V, --version
Print version and exit.
WARNINGS¶
• 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
24 days.
REFERENCES¶
[1] ICMP ECHO, RFC0792, page 14.
[2] ICMP TIMESTAMP, RFC0792, page 16.
[3] IP TIMESTAMP option, RFC0791, 3.1, page 16.
AUTHOR¶
clockdiff was compiled by Alexey Kuznetsov
<kuznet@ms2.inr.ac.ru>. It was based on code borrowed from BSD
timed daemon.
SECURITY¶
clockdiff requires CAP_NET_RAW and CAP_SYS_NICE
capabilities to be executed. It is safe to be used as set-uid root.
AVAILABILITY¶
clockdiff is part of iputils package.