sfs_hosts - Host to address mapping overriding DNS

All SFS client software uses DNS to locate server names. This is somewhat different from typical network utilities, which, often depending on a configuration file such as /etc/nsswitch.conf, can sometimes combine DNS with other techniques, such as scanning the file /etc/hosts or querying NIS (YP) servers.

SFS relies exclusively on DNS for several reasons. First, the file system is designed to provide a global namespace. Using /etc/hosts, for example, it is common for a machine to have two namesfor instance hostname, and hostname.domain.com. However, were the same file system to be available under two different self-certifying pathnames, several things would go wrong: First, bookmarks to /sfs/@hostname,.../... would only work on the local network. Even worse, it might be possible to lose a file by accidentally copying it onto itself, e.g., from /sfs/@hostname,.../... to /sfs/@hostname.domain.com,.../.... Finally, SFS allows one to specify a TCP port number other than the default (4) using DNS SRV records, while non-DNS mechanisms have no means of specifying port numbers.

Though DNS is fairly ubiquitous, there are situations in which one might like to have ``internal'' connections to SFS servers routed differently from ``external'' ones. For example, when running SFS servers behind a NAT box, external connections would need to be directed to the external IP address of the NAT box, while it would be more efficient to route internal connections directly to the internal IP address, without going through the NAT. In such situations, often the best solution is to set up a split DNS configuration. When split DNS is not an option, however, the sfs_hosts mechanism will come in handy.

sfs_hosts is a superset of the standard /etc/hosts file format, that additionally allows one to specify a port number by appending it with a % character at the end of the address. By default, the port number is 4. For example, the following two lines both specify that server.domain.com is running on port 4 of IP address 10.1.1.1:

  10.1.1.1          server.domain.com
  10.1.1.1%4        server.domain.com

If you really want /etc/hosts to override DNS with SFS, you can always run ln -s ../hosts /etc/sfs/sfs_hosts, but this is not recommended. Solutions involving DNS configuration will be much more scalable and flexible.

/etc/sfs/sfs_hosts

/usr/local/share/sfs/sfs_hosts

Host to address mapping overriding DNS

(Files in /etc/sfs supersede default versions in /usr/local/share/sfs.)

dirsearch(1), newaid(1), rex(1), sfsagent(1), sfskey(1), ssu(1), sfs_config(5), sfs_srp_params(5), sfs_users(5), sfsauthd_config(5), sfscd_config(5), sfsrosd_config(5), sfsrwsd_config(5), sfssd_config(5), sfs_environ(7), funmount(8), nfsmounter(8), sfsauthd(8), sfscd(8), sfsrosd(8), sfsrwcd(8), sfsrwsd(8), sfssd(8), vidb(8)

The full documentation for SFS is maintained as a Texinfo manual. If the info and SFS programs are properly installed at your site, the command info SFS should give you access to the complete manual.

For updates, documentation, and software distribution, please see the SFS website at http://www.fs.net/.

sfsdev@redlab.lcs.mit.edu