MOUNTING AND EXPORTING                                                                                                             Back To Home

File System Mounting:

Mounting a file system (which is done before it can be available to processes on the system) is analogous to opening a file before it is used. If we may abuse the term "load", mounting is the process of loading a file system on to a client that has just entered the system (so that files on the network are transparent to the user).

General Mount Procedure:

• The operating system is given the name of the device, and the location within
  the file structure at which to attach the file system (called the mount point)
• Next, the OS verifies that the device contains a valid file system - i.e.
  that the directory has the expected format
• Finally, the OS notes in its directory structure that the file system has
  been mounted at the specified mount point

When an NFS client mounts a file system, the server examines the mount request to be sure that the client is authorized, then issues a magic cookie to the client for use in later accesses. The magic cookie keeps the server stateless since no record of authenticated clients needs to be kept. Unmounting and remounting an NFS filesystem changes its magic cookie. The Magic cookie persist across reboots provided that you do not boot single user or play with the file systems. Once the client has the magic cookie it uses RPC to make file requests.

File System Exporting:

Below are the rules for exporting a file system in NFS:

• Any file system or part thereof can be exported. Thus /home could be executed as well as /home/suess
• If a subdirectory of a exported filesystem is itself exported then it must reside on a seperate device.
• If a subdirectory is exported then the parent file system can only be exported if and only if it resides on a seperate device.
• Only local file systems can be exported.
• These rules force system administrators to think how they want to give access before exporting file systems. Basically, the rule is you can only export a physical device in one manner.

The format of the exports file is the following:

filesystem -options 

where options can be:
-ro                                allows only read only access
-rw=host1:host2          which hosts have write access
-access=host1:host2   which hosts can access file system
-anon=uid                    map unknown user id's to this user
-root=host1:host2       which hosts have complete access to the root

example:  /home/suess -rw=icarus.ifsm.umbc.edu,anon=suess

Next: Implications of Statelessness

Sources:

Operating System Concepts by Galvin and Silberschatz
http://dune.mcs.kent.edu/~farrell/sa96/notes/nfs/nfs_10.html
http://userpages.umbc.edu/~jack/ifsm498d/nfs.html