how does nfs know who is the user who attempting to access nfs mount?

[itai weisman]

which node (the exporter or the importer) manage the file access permission? how does it do it?
does user authentication happen in every attempt to access a file or a directory that is being nfs mounted?
does the answer apply to both nfs v2 and v3?

[Karthik S S · Accepted solution]

1. It resolves the user name to user ID from passwd file and or name service like NIS

2. NFS server (from where you export) maintains the access permissions.

3. Authentication happens only once when you the exported directory. Upon a successful mount depending on the permissions of the directory/file the user will be given/denied access.

4. Yes

-Karthik S S

[itai weisman]

thanks a lot for the quick answer :) - it helped me a lot -
what are the main diffrences between nfs v2 and v3 btw?

[Karthik S S]

http://www.faqs.org/rfcs/rfc1813.html

Refer the following section,
1.7 Changes from the NFS version 2 protocol . . . . . . . . 11

-Karthik S S

[Jim Keeble]

Regardless of protocol version 2 or 3, mount access is based on hostname or netgroup listed in the /etc/exports file of the server and IP address of the client .

File access, on the other hand, is based strictly on uid and gid numbers assigned, so it is important keep username/uid consistent between client(s) and server. (this is usually accomplished using NIS passwd and group maps. Otherwise uid 101 bob on the client has permissions to use uid 101 fred's files on the server.

One exception to this is the root user. Unless the client's root user is granted access by the "root=client1,client2,..." in the servers export file, uid 0 access will be translated to the uid and gid of the anonymous user on the server side.