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2.1 Network File System (NFS)     continued...

If you are curious about where files reside, you can use the Unix command df (disk free) to print information about the files accessible from your workstation or computer. The output of df is a set of lines that describe the capacity and amount of free space on each local disk and each remote file system currently mounted on your computer (Figure 2). Local devices typically have names that begin /dev/..., but remote systems have names that identify the network node where the file resides. The name can either be the name of a system or a symbolic name. In the example in Figure 2 fog and drizzle are the names of other Unix systems in the network, but cshost, faculty, and grads are symbolic names. The advantage of symbolic names is that if the computer where these file systems reside goes down it is relatively easy to move the disks and change the definition of the symbolic name.

Communicating with other users in a local network is also handled automatically by network system software. In Unix, programs that communicate with other users ( mail, finger, talk, etc.) are based on user login names. For a brief period as local area networks were evolving it was necessary to identify a user by the system they normally used. For example, suppose your lab had three systems, named fog, drizzle, and mist. You normally worked on fog, and your colleague named Fred worked on mist. To send mail to Fred, you had to type something like

% mail drizzle!mist!fred < msg