'\" te
.\" Copyright (c) 2004, 2012, Oracle and/or its affiliates. All rights reserved.
.TH ssh-keyscan 1 "20 Jun 2012" "SunOS 5.11" "User Commands"
.SH NAME
ssh-keyscan \- gather public ssh host keys of a number of hosts
.SH SYNOPSIS
.LP
.nf
\fBssh-keyscan\fR [\fB-v46\fR] [\fB-p\fR \fIport\fR] [\fB-T\fR \fItimeout\fR] [\fB-t\fR \fItype\fR] 
     [\fB-f\fR \fIfile\fR] [\fB-\fR] [\fIhost\fR... | \fIaddrlist\fR \fInamelist\fR] [...]
.fi

.SH DESCRIPTION
.sp
.LP
\fBssh-keyscan\fR is a utility for gathering the public ssh host keys of a number of hosts. It was designed to aid in building and verifying \fBssh_known_hosts\fR files. \fBssh-keyscan\fR provides a minimal interface suitable for use by shell and perl scripts. The output of \fBssh-keyscan\fR is directed to standard output.
.sp
.LP
\fBssh-keyscan\fR uses non-blocking socket I/O to contact as many hosts as possible in parallel, so it is very efficient. The keys from a domain of 1,000 hosts can be collected in tens of seconds, even when some of those hosts are down or do not run ssh. For scanning, one does not need login access to the machines that are being scanned, nor does the scanning process involve any encryption.
.SS "File Format"
.sp
.LP
Input format:
.sp
.in +2
.nf
1.2.3.4,1.2.4.4
\fIname.my.domain,name,n.my.domain,n,\fR1.2.3.4,1.2.4.4
.fi
.in -2
.sp

.sp
.LP
Output format for \fBrsa1\fR keys: 
.sp
.in +2
.nf
\fIhost-or-namelist bits exponent modulus\fR
.fi
.in -2
.sp

.sp
.LP
Output format for \fBrsa\fR and \fBdsa\fR keys, where \fIkeytype\fR is either \fBssh-rsa\fR or `\fBssh-dsa\fR: 
.sp
.in +2
.nf
\fIhost-or-namelist keytype base64-encoded-key\fR
.fi
.in -2
.sp

.SH OPTIONS
.sp
.LP
The following options are supported: 
.sp
.ne 2
.mk
.na
\fB\fB-f\fR \fIfilename\fR\fR
.ad
.sp .6
.RS 4n
Read hosts or addrlist namelist pairs from this file, one per line. If you specify - instead of a filename, \fBssh-keyscan\fR reads hosts or addrlist namelist pairs from the standard input.
.RE

.sp
.ne 2
.mk
.na
\fB\fB-p\fR \fIport\fR\fR
.ad
.sp .6
.RS 4n
Port to connect to on the remote host.
.RE

.sp
.ne 2
.mk
.na
\fB\fB-T\fR \fItimeout\fR\fR
.ad
.sp .6
.RS 4n
Set the timeout for connection attempts. If \fItimeout\fR seconds have elapsed since a connection was initiated to a host or since the last time anything was read from that host, the connection is closed and the host in question is considered unavailable. The default is for \fItimeout\fR is 5 seconds.
.RE

.sp
.ne 2
.mk
.na
\fB\fB-t\fR \fItype\fR\fR
.ad
.sp .6
.RS 4n
Specify the type of the key to fetch from the scanned hosts. The possible values for \fItype\fR are \fBrsa1\fR for protocol version 1 and \fBrsa\fR or \fBdsa\fR for protocol version 2. Specify multiple values by separating them with commas. The default is \fBrsa1\fR.
.RE

.sp
.ne 2
.mk
.na
\fB\fB-v\fR\fR
.ad
.sp .6
.RS 4n
Specify verbose mode. Print debugging messages about progress.
.RE

.sp
.ne 2
.mk
.na
\fB\fB-4\fR\fR
.ad
.sp .6
.RS 4n
Force to use IPv4 addresses only.
.RE

.sp
.ne 2
.mk
.na
\fB\fB-6\fR\fR
.ad
.sp .6
.RS 4n
Forces to use IPv6 addresses only.
.RE

.SH SECURITY
.sp
.LP
If a \fBssh_known_hosts\fR file is constructed using \fBssh-keyscan\fR without verifying the keys, users are vulnerable to man-in-the-middle attacks. If the security model allows such a risk, \fBssh-keyscan\fR can help in the detection of tampered keyfiles or man-in-the-middle attacks which have begun after the \fBssh_known_hosts\fR file was created.
.SH EXAMPLES
.LP
\fBExample 1 \fRPrinting the \fBrsa1\fR Host Key
.sp
.LP
The following example prints the \fBrsa1\fR host key for machine \fBhostname\fR:

.sp
.in +2
.nf
$ ssh-keyscan hostname
.fi
.in -2
.sp

.LP
\fBExample 2 \fRFinding All Hosts
.sp
.LP
The following commands finds all hosts from the file \fBssh_hosts\fR which have new or different keys from those in the sorted file \fBssh_known_hosts\fR:

.sp
.in +2
.nf
$ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e
     sort -u - ssh_known_hosts | diff ssh_known_hosts -
.fi
.in -2
.sp

.SH FILES
.sp
.ne 2
.mk
.na
\fB\fB/etc/ssh_known_hosts\fR\fR
.ad
.sp .6
.RS 4n
Contains list of public ssh host keys.
.RE

.SH EXIT STATUS
.sp
.LP
The following exit values are returned:
.sp
.ne 2
.mk
.na
\fB\fB0\fR\fR
.ad
.sp .6
.RS 4n
No usage errors. \fBssh-keyscan\fR might or might not have succeeded or failed to scan one, more or all of the given hosts. 
.RE

.sp
.ne 2
.mk
.na
\fB\fB1\fR\fR
.ad
.sp .6
.RS 4n
Usage error.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
Availabilitynetwork/ssh
_
Interface StabilityCommitted
.TE

.SH SEE ALSO
.sp
.LP
\fBssh\fR(1), \fBsshd\fR(1M), \fBattributes\fR(5)
.SH AUTHORS
.sp
.LP
David Mazieres wrote the initial version, and Wayne Davison added support for protocol version 2. 
.SH BUGS
.sp
.LP
\fBssh\(emkeyscan\fR generates the following messages on the consoles of all machines it scans if the server is older than version 2.9:
.sp
.in +2
.nf
Connection closed by remote host
.fi
.in -2
.sp

.sp
.LP
This is because \fBssh-keyscan\fR opens a connection to the \fBssh\fR port, reads the public key, and drops the connection as soon as it gets the key.