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+SSH-KEYSCAN(1) General Commands Manual SSH-KEYSCAN(1)
+
+NAME
+ ssh-keyscan M-bM-^@M-^S gather SSH public keys from servers
+
+SYNOPSIS
+ ssh-keyscan [-46cDHv] [-f file] [-p port] [-T timeout] [-t type]
+ [host | addrlist namelist]
+
+DESCRIPTION
+ ssh-keyscan is a utility for gathering the public SSH host keys of a
+ number of hosts. It was designed to aid in building and verifying
+ ssh_known_hosts files, the format of which is documented in sshd(8).
+ ssh-keyscan provides a minimal interface suitable for use by shell and
+ perl scripts.
+
+ ssh-keyscan 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 sshd(8). For scanning, one does not need
+ login access to the machines that are being scanned, nor does the
+ scanning process involve any encryption.
+
+ The options are as follows:
+
+ -4 Force ssh-keyscan to use IPv4 addresses only.
+
+ -6 Force ssh-keyscan to use IPv6 addresses only.
+
+ -c Request certificates from target hosts instead of plain keys.
+
+ -D Print keys found as SSHFP DNS records. The default is to print
+ keys in a format usable as a ssh(1) known_hosts file.
+
+ -f file
+ Read hosts or M-bM-^@M-^\addrlist namelistM-bM-^@M-^] pairs from file, one per line.
+ If M-bM-^@M-^X-M-bM-^@M-^Y is supplied instead of a filename, ssh-keyscan will read
+ from the standard input. Input is expected in the format:
+
+ 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
+
+ -H Hash all hostnames and addresses in the output. Hashed names may
+ be used normally by ssh(1) and sshd(8), but they do not reveal
+ identifying information should the file's contents be disclosed.
+
+ -p port
+ Connect to port on the remote host.
+
+ -T timeout
+ Set the timeout for connection attempts. If timeout 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 considered unavailable. The
+ default is 5 seconds.
+
+ -t type
+ Specify the type of the key to fetch from the scanned hosts. The
+ possible values are M-bM-^@M-^\dsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^], or M-bM-^@M-^\rsaM-bM-^@M-^].
+ Multiple values may be specified by separating them with commas.
+ The default is to fetch M-bM-^@M-^\rsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], and M-bM-^@M-^\ed25519M-bM-^@M-^] keys.
+
+ -v Verbose mode: print debugging messages about progress.
+
+ If an ssh_known_hosts file is constructed using ssh-keyscan without
+ verifying the keys, users will be vulnerable to man in the middle
+ attacks. On the other hand, if the security model allows such a risk,
+ ssh-keyscan can help in the detection of tampered keyfiles or man in the
+ middle attacks which have begun after the ssh_known_hosts file was
+ created.
+
+FILES
+ /etc/ssh/ssh_known_hosts
+
+EXAMPLES
+ Print the RSA host key for machine hostname:
+
+ $ ssh-keyscan -t rsa hostname
+
+ Find all hosts from the file ssh_hosts which have new or different keys
+ from those in the sorted file ssh_known_hosts:
+
+ $ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \
+ sort -u - ssh_known_hosts | diff ssh_known_hosts -
+
+SEE ALSO
+ ssh(1), sshd(8)
+
+ Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints, RFC
+ 4255, 2006.
+
+AUTHORS
+ David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne
+ Davison <wayned@users.sourceforge.net> added support for protocol version
+ 2.
+
+OpenBSD 6.8 November 30, 2019 OpenBSD 6.8