'\" t
.TH "CLOCKDIFF" "8" "" "iputils 20240117" "iputils"
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.SH "NAME"
clockdiff \- measure clock difference between hosts
.SH "SYNOPSIS"
.HP \w'\fBclockdiff\fR\ 'u
\fBclockdiff\fR [\fB\-o\fR] [\fB\-o1\fR] [\fB\-\-time\-format\ \fR\fB\fIctime\ iso\fR\fR] [\fB\-V\fR] {destination}
.SH "DESCRIPTION"
.PP
\fBclockdiff\fR
Measures clock difference between us and
\fIdestination\fR
with 1 msec resolution using ICMP TIMESTAMP [2] packets or, optionally, IP TIMESTAMP option [3] added to ICMP ECHO\&. [1]
.SH "OPTIONS"
.PP
\fB\-o\fR
.RS 4
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)\&.
.RE
.PP
\fB\-o1\fR
.RS 4
Slightly different form of
\fB\-o\fR, 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,
\fB\-o\fR
is better for Linux\&.
.RE
.PP
\fB\-T\fR, \fB\-\-time\-format \fR\fB\fIctime iso\fR\fR
.RS 4
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\&.
.RE
.PP
\fB\-I\fR
.RS 4
Alias of
\fB\-\-time\-format \fR\fB\fIiso\fR\fR\fB \fR
option and argument\&.
.RE
.PP
\fB\-h\fR, \fB\-\-help\fR
.RS 4
Print help and exit\&.
.RE
.PP
\fB\-V\fR, \fB\-\-version\fR
.RS 4
Print version and exit\&.
.RE
.SH "WARNINGS"
.PP
.RS 4
\(bu Some nodes (Cisco) use non\-standard timestamps, which is allowed by RFC, but makes timestamps mostly useless\&.
.RE
.PP
.RS 4
\(bu Some nodes generate messed timestamps (Solaris>2\&.4), when run
\fBxntpd\fR\&. 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\&.
.RE
.PP
.RS 4
\(bu
\fBclockdiff\fR
shows difference in time modulo 24 days\&.
.RE
.SH "SEE ALSO"
.PP
\fBping\fR(8),
\fBarping\fR(8),
\fBtracepath\fR(8)\&.
.SH "REFERENCES"
.PP
[1] ICMP ECHO, RFC0792, page 14\&.
.PP
[2] ICMP TIMESTAMP, RFC0792, page 16\&.
.PP
[3] IP TIMESTAMP option, RFC0791, 3\&.1, page 16\&.
.SH "AUTHOR"
.PP
\fBclockdiff\fR
was compiled by Alexey Kuznetsov <kuznet@ms2\&.inr\&.ac\&.ru>\&. It was based on code borrowed from BSD
\fBtimed\fR
daemon\&.
.SH "SECURITY"
.PP
\fBclockdiff\fR
requires CAP_NET_RAW and CAP_SYS_NICE capabilities to be executed\&. It is safe to be used as set\-uid root\&.
.SH "AVAILABILITY"
.PP
\fBclockdiff\fR
is part of
\fIiputils\fR
package\&.