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The term file system actually has two (2) meanings. First it refers to a software mechanism that is generally responsible for the management of all on-line files. Secondly, the way we will use the term filesystem, refers to a given subset of a physical disk drive, divided into some defined number of disk blocks.
All files are usually stored on some type of file system. Most file systems on any given machine will usually be either local (meaning the disk is physically located on that machine), or NFS (having the disk physically located elsewhere).
NFS is a network file system originally developed at Sun. With NFS, you may have a physical file on one system facilitating access to it on another. Under NFS there exists a concept of an NFS server and an NFS client. The server is the system that has the physical space and the client is the system that mounts that space (meaning that space is available). A system may act as both an NFS server and an NFS client. Moreover, any file system on a server is also available locally within that system.
From the user perspective, NFS should be transparent. Really, from the user's view, the only way to identify whether a certain file system is mounted NFS, would be to do a df. A typical df would look as follows:
Filesystem kbytes used avail capacity Mounted on /dev/sd0a 14095 11292 1393 89% / /dev/sd0e 95942 83083 3264 96% /usr /dev/sd0d 2335 319 1782 15% /tmp lynx:/src 623486 540682 20455 96% /nfs/lynx/src lynx:/usenet 582110 290034 233865 55% /nfs/lynx/usenet shale:/fog/local 189369 148562 21870 87% /nfs/shale/local shale:/u1 322658 253664 36728 87% /nfs/shale/users frisby:/spare 454838 377286 32068 92% /nfs/frisby/spare frisby:/u1 453799 375705 32714 92% /nfs/frisby/users
Here you can see this system has three (3) local file systems, and six (6) NFS mounted file systems. Consider the following line, from the above output:
lynx:/src 623486 540682 20455 96% /home/rigel/src
Here, the `lynx:/src' means the NFS server is lynx and the file system we are mounting is `/src'. The next four (4) fields show statistics about disk space over that file system. The last field, `/nfs/lynx/src', shows where on your local system the lynx:/src file system appears. So for example, if you did a cd to `src' on rigel and do an ls, you would get the same listing from ls if you did a cd to `/home/rigel/src' on this system and did an ls. This /home/rigel/src is a convention established here at PSU. On our machines all NFS file systems are mounted under /home/machine-name/file-system, so in the previous example, machine_name was rigel, and file_system was bacon.
NFS provides a means of allowing file systems form one system to appear on another. Again, this should appear transparent to the user.
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