clockdiff8
Measure clock difference between hosts
Usage
clockdiff [-o]
[-o1]
[--time-format
ctime
iso]
[-V]
destination
Overview
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,-ois 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.
Security
clockdiff requires CAP_NET_RAW and CAP_SYS_NICE capabilities to be executed. It is safe to be used as set-uid root.
Releases
9 releases since Debian 6.0 (Squeeze); the text changed 8 times.
--help since Debian 11 (Bullseye);
--version since Debian 11 (Bullseye);
-I since Debian 11 (Bullseye);
-V since Debian 11 (Bullseye);
-h since Debian 11 (Bullseye).