make-ssh-known-hosts is a perl5 script that helps create the /etc/ssh/ssh_known_hosts file, which is used by ssh to contain the host keys of all publicly known hosts. Ssh does not normally permit login using rhosts or /etc/hosts.equiv authentication unless the server knows the client's host key. In addition, the host keys are used to prevent man-in-the-middle attacks.
In addition to /etc/ssh/ssh_known_hosts, ssh also uses the $HOME/.ssh/known_hosts file. This file, however, is intended to contain only those hosts that the particular user needs but are not in the global file. It is intended that the /etc/ssh/ssh_known_hosts file be maintained by the system administration, and periodically updated to contain the host keys for any new hosts.
The make-ssh-known-hosts program finds all the hosts in a domain by making a DNS query to the master domain name server of the domain. The master domain name server is located by searching for the SOA record of the domain from the initial domain name server (which can be specified with the --initialdns option). The master domain name server can also be given directly with the --server option.
After getting the hostname list make-ssh-known-hosts tries to get the public key from every host in the domain. It first tries to connect ssh port to check check if the host is alive, and if so, it tries to run the command cat /etc/ssh/ssh_host_key.pub on the remote machine using ssh. If the command succeeds, it knows the remote machine has ssh installed properly, and it then extracts the public key from the output, and prints the /etc/ssh/ssh_known_hosts entry for it to STDOUT. Because make-ssh-known-hosts is usually run before remote machines have /etc/ssh/ssh_known_hosts file you may have to use RSA-authentication to allow access to hosts.
If the command fails for some reason, it checks if the ssh client still got the public key from the remote host in the initial dialog, and if so, it will print a proper entry, and if --notrustdaemon option is given comment it out.
Domain_name is the domain name for which the file is to be generated. By default make-ssh-known-hosts extracts also all subdomains of domain. Many sites will want to include several domains in their /etc/ssh/ssh_known_hosts file. The entries for each domain should be extracted separately by running make-ssh-known-hosts once for each domain. The results should then be combined to create the final file.
Take_regexp is a perl regular expression that matches the hosts to be taken from the domain. The data matched contains all the DNS records in the form "fieldname=value". The fields are separated with newline, and the perl match is made in multiline mode and it is case insensetive. The multiline mode means that you can use a regexp like "^wks=.*telnet.*$" to match all hosts that have WKS (well known services) field that contains value "telnet".
Remove_regexp is similar but those hosts that match the regexp are not added (it can be used for example to filter out PCs and Macs using the hinfo field: "^hinfo=.*(mac|pc)").
The following command:
finds all public keys of the hosts in cs.hut.fi domain and put them to /etc/ssh/ssh_known_hosts file splitting domain names on a per host basis.
finds all hosts in hut.fi domain, and its subdomains having own name server (cs.hut.fi, tf.hut.fi, tky.hut.fi) that have ssh service and puts their public key to hut-hosts file. This would require that the domain name server of hut.fi would define all hosts running ssh to have entry ssh in their WKS record. Because nobody yet adds ssh to WKS, it would be better to use command
that would take those host having telnet service. This uses default subdomain list.
finds all hosts in hut.fi domain that are in dipoli.hut.fi subdomain (note dipoli.hut.fi does not have own name server so its entries are in hut.fi-server) and that are not Mac or PC.
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