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.IX Title "synos 1"
.TH synos 1 "2018-10-09" "Mail Avenger 0.8.5" "Mail Avenger 0.8.5"
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.SH "NAME"
synos \- guess operating system from TCP SYN fingerprint
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
synos [\-\-mtu \fImtu\fR] [\fI\-\-db\fR \fIpath\fR] \fIsyn-fingerprint\fR
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
synos takes a \s-1SYN\s0 fingerprint, in the format described for the
\&\fB\s-1CLIENT_SYNFP\s0\fR environment variable in the \fBavenger\fR\|(1)
man page, and outputs a guess as to the type of the client operating
system. synos makes use of the OpenBSD \s-1SYN\s0 fingerprint database
(which is also repackaged with Mail Avenger).
.SS "\s-1OPTIONS\s0"
.IX Subsection "OPTIONS"
.IP "\fB\-\-mtu\fR \fIval\fR" 4
.IX Item "--mtu val"
Certain operating systems set the initial \s-1TCP\s0 window size based on the
maximum transmission unit, or \s-1MTU,\s0 of the network. For such operating
systems, synos usually checks the window size using both the client's
\&\s-1MSS\s0 option plus 40 bytes (for \s-1TCP\s0 and \s-1IP\s0 headers), or a hard-coded
\&\s-1MTU,\s0 which defaults to 1,500 bytes. If either value works, the
fingerprint is considered to match the operating system. You can
change the value 1,500 by specifying this option. A value of 0 tells
synos to use only the value derived from the \s-1MSS\s0 option.
.IP "\fB\-\-db\fR \fIfile\fR" 4
.IX Item "--db file"
Specifies an alternate location for the \s-1SYN\s0 fingerprint database.
.SH "FILES"
.IX Header "FILES"
.IP "\fI/usr/local/share/pf.os\fR" 4
.IX Item "/usr/local/share/pf.os"
Default location of \s-1SYN\s0 fingerprint database.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBavenger\fR\|(1),
\&\fBasmtpd\fR\|(8)
.PP
The Mail Avenger home page: .
.PP
The OpenBSD home page: .
.SH "BUGS"
.IX Header "BUGS"
The operating system type is determined by heuristics that are not
always reliable. Moreover, not all operating systems can be
distinguished. The database may not even contain a client's
particular operating system and version.
.PP
It is not hard to fool synos deliberately by changing \s-1TCP\s0 socket
options or injecting raw packets onto the network.
.SH "AUTHOR"
.IX Header "AUTHOR"
David Mazie\*`res