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Ed Maste
bb5c77e9d2
Full release notes are available at https://www.openssh.com/txt/release-10.4 Selected highlights from the release notes: Potentially-incompatible changes -------------------------------- * sshd(8): configuration dump mode ("sshd -G") now writes directives in mixed case (e.g. "PubkeyAuthentication") whereas previously it emitted only lower-case names. * ssh(1), sshd(8): make the transport protocol stricter by disconnecting if the peer sends non-KEX messages during a post- authentication key re-exchange. Previously a malicious peer could continue sending non-key exchange messages without penalty. These would be buffered, causing memory to be wasted up until the connection terminated or the server/client hit a memory limit. Implementations that do not restrict messages sent during key exchange as per RFC4253 section 7.1 may be disconnected. Reported by Marko Jevtic. Changes since OpenSSH 10.3 ========================== This release contains a number of security fixes as well as general bugfixes and a couple of new features. Security ======== * sftp(1): when downloading files on the command-line using "sftp host:/path .", a malicious server could cause the file to be downloaded to an unexpected location. This issue was identified by the Swival Security Scanner. * scp(1): when copying files between two remote destinations, do not allow a malicious server to write files to the parent directory of the intended target directory. This issue was identified by the Swival Security Scanner. * sshd(8): DisableForwarding=yes didn't override PermitTunnel=yes as it was documented to do. Note that PermitTunnel is not enabled by default. Reported independently by Huzaifa Sidhpurwala of Redhat and Marko Jevtic. * sshd(8): avoid a potential pre-authentication denial of service when GSSAPIAuthentication was enabled (this feature is off by default). This was not mitigated by MaxAuthTries, but would be penalised by PerSourcePenalties. This was reported by Manfred Kaiser of the milCERT AT (Austrian Ministry of Defence). * sshd(8): fix a number of cases where the minimum authentication delay was not being enforced. Reported by the Orange Cyberdefense Vulnerability Team. * ssh(1): fix a possible client-side use-after-free if the server changes its host key during a key reexchange. This was reported by Zhenpeng (Leo) Lin of Depthfirst. New features ------------ * All: add experimental support for a composite post-quantum signature scheme that combines ML-DSA 44 and Ed25519 as specified in draft-miller-sshm-mldsa44-ed25519-composite-sigs. This scheme is not enabled by default. To use it, you'll need to add it to HostKeyAlgorithms, PubkeyAcceptedAlgorithms, etc. Keys may be generated using "ssh-keygen -t mldsa44-ed25519". Bugfixes -------- * sshd(8): avoid sending observably different messages for valid vs invalid users in GSSAPIAuthentication (disabled by default). * ssh(1), sshd(8): fix several bugs that incorrectly classified bulk traffic as interactive. bz3972, bz3958 * ssh-keygen(1), ssh-add(1): skip unsupported key types when downloading resident keys from a FIDO token. Previously, downloads would abort when one was encountered. GHPR657 Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D58083
198 lines
5.1 KiB
Groff
198 lines
5.1 KiB
Groff
.\" $OpenBSD: ssh-keyscan.1,v 1.54 2026/06/26 06:17:13 djm Exp $
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.\"
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.\" Copyright 1995, 1996 by David Mazieres <[email protected]>.
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.\"
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.\" Modification and redistribution in source and binary forms is
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.\" permitted provided that due credit is given to the author and the
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.\" OpenBSD project by leaving this copyright notice intact.
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.\"
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.Dd $Mdocdate: June 26 2026 $
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.Dt SSH-KEYSCAN 1
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.Os
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.Sh NAME
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.Nm ssh-keyscan
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.Nd gather SSH public keys from servers
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.Sh SYNOPSIS
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.Nm ssh-keyscan
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.Op Fl 46cDHqv
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.Op Fl f Ar file
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.Op Fl O Ar option
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.Op Fl p Ar port
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.Op Fl T Ar timeout
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.Op Fl t Ar type
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.Op Ar host | addrlist namelist
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.Sh DESCRIPTION
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.Nm
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is a utility for gathering the public SSH host keys of a number of
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hosts.
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It was designed to aid in building and verifying
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.Pa ssh_known_hosts
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files,
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the format of which is documented in
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.Xr sshd 8 .
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.Nm
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provides a minimal interface suitable for use by shell and perl
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scripts.
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.Pp
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.Nm
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uses non-blocking socket I/O to contact as many hosts as possible in
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parallel, so it is very efficient.
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The keys from a domain of 1,000
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hosts can be collected in tens of seconds, even when some of those
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hosts are down or do not run
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.Xr sshd 8 .
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For scanning, one does not need
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login access to the machines that are being scanned, nor does the
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scanning process involve any encryption.
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.Pp
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Hosts to be scanned may be specified by hostname, address or by CIDR
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network range (e.g. 192.168.16/28).
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If a network range is specified, then all addresses in that range will
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be scanned.
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.Pp
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.Nm
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cannot verify the authenticity of the host keys it obtains, and an attacker
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on the network with the ability to intercept traffic could substitute their
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own host keys to enable impersonation of servers.
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Because of this,
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.Nm
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output should be verified out of band, or only used directly for host
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authentication if the network is trusted.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl 4
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Force
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.Nm
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to use IPv4 addresses only.
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.It Fl 6
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Force
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.Nm
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to use IPv6 addresses only.
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.It Fl c
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Request certificates from target hosts instead of plain keys.
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.It Fl D
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Print keys found as SSHFP DNS records.
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The default is to print keys in a format usable as an
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.Xr ssh 1
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.Pa known_hosts
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file.
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.It Fl f Ar file
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Read hosts or
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.Dq addrlist namelist
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pairs from
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.Ar file ,
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one per line.
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If
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.Sq -
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is supplied instead of a filename,
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.Nm
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will read from the standard input.
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Names read from a file must start with an address, hostname or CIDR network
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range to be scanned.
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Addresses and hostnames may optionally be followed by comma-separated name
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or address aliases that will be copied to the output.
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For example:
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.Bd -literal
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192.168.11.0/24
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10.20.1.1
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happy.example.org
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10.0.0.1,sad.example.org
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.Ed
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.It Fl H
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Hash all hostnames and addresses in the output.
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Hashed names may be used normally by
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.Xr ssh 1
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and
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.Xr sshd 8 ,
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but they do not reveal identifying information should the file's contents
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be disclosed.
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.It Fl O Ar option
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Specify a key/value option.
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At present, only a single option is supported:
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.Bl -tag -width Ds
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.It Cm hashalg Ns = Ns Ar algorithm
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Selects a hash algorithm to use when printing SSHFP records using the
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.Fl D
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flag.
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Valid algorithms are
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.Dq sha1
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and
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.Dq sha256 .
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The default is to print both.
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.El
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.It Fl p Ar port
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Connect to
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.Ar port
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on the remote host.
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.It Fl q
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Quiet mode:
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do not print server host name and banners in comments.
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.It Fl T Ar timeout
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Set the timeout for connection attempts.
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If
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.Ar timeout
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seconds have elapsed since a connection was initiated to a host or since the
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last time anything was read from that host, the connection is
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closed and the host in question considered unavailable.
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The default is 5 seconds.
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.It Fl t Ar type
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Specify the type of the key to fetch from the scanned hosts.
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The possible values are
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.Dq ecdsa ,
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.Dq ed25519 ,
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.Dq ecdsa-sk ,
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.Dq ed25519-sk ,
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or
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.Dq rsa .
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Multiple values may be specified by separating them with commas.
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The default is to fetch all the above key types.
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.It Fl v
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Verbose mode:
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print debugging messages about progress.
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.El
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.Pp
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If an ssh_known_hosts file is constructed using
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.Nm
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without verifying the keys, users will be vulnerable to
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.Em man in the middle
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attacks.
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On the other hand, if the security model allows such a risk,
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.Nm
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can help in the detection of tampered keyfiles or man in the middle
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attacks which have begun after the ssh_known_hosts file was created.
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.Sh FILES
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.Pa /etc/ssh/ssh_known_hosts
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.Sh EXAMPLES
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Print the RSA host key for machine
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.Ar hostname :
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.Pp
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.Dl $ ssh-keyscan -t rsa hostname
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.Pp
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Search a network range, printing all supported key types:
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.Pp
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.Dl $ ssh-keyscan 192.168.0.64/25
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.Pp
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Find all hosts from the file
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.Pa ssh_hosts
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which have new or different keys from those in the sorted file
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.Pa ssh_known_hosts :
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.Bd -literal -offset indent
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$ ssh-keyscan -t rsa,ecdsa,ed25519 -f ssh_hosts | \e
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sort -u - ssh_known_hosts | diff ssh_known_hosts -
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.Ed
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.Sh SEE ALSO
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.Xr ssh 1 ,
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.Xr sshd 8
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.Rs
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.%D 2006
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.%R RFC 4255
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.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
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.Re
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.Sh AUTHORS
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.An -nosplit
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.An David Mazieres Aq Mt [email protected]
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wrote the initial version, and
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.An Wayne Davison Aq Mt [email protected]
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added support for protocol version 2.
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