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Richard T
Asked: 2020-08-29 19:42:09 +0800 CST

How to configure NFS to resolve symbolic links on the server side?

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My beard is solid grey now, and I long recall using NFS for all these decades and here I cite the original RFC that gives us the basis for the NFS we have today RFC1094. Of course, three decades and some have passed since then, so here's the question:

In the interim has it become possible now, via a configuration option, to have links interpreted from the server side? This would surely clear up a number of my problems of client-side interpretation of links!

Or, am I all wet, and what I'm citing is obsolete and it's really, by default, resolving on the server side and I'm just chasing rabbits down rabbit-holes in my troubleshooting?

IF IT'S STILL OLD-SCHOOL AND INTERPRETED CLIENT SIDE, and if there is NOT an option that enables server-side interpretation, does using relative links instead of absolute ones possibly help?

Thanks.

nfs symbolic-link

2 Answers

  1. The symlinks are always resolved by the client. There are several reasons for that. First of all, the NFS protocol has a concept of a file handle. Each handle points to a file system object that can be a directory, a file or a symlink (and some others). Moreover, NFSv4.1 spec is clearly says:

    Whether created by an NFS client or created locally on the server, the data in a symbolic link is not interpreted when created, but is simply stored.

    Second, by processing the symlink on the server side additional permission rules have to be taken into account, as symlink might point to outside on the exported filesystem.

    Indeed, SAMBA servers have no option to follow symlinks. This is due to (a) original MS file systems didn't have a concept of a symlinks and (b) symbolic link as file system object type are added in SMB2. The behavior, BTW, matches NFS interpretation:

    Symbolic links MUST NOT be evaluated by the server.

    There are couple of user-space NFS server that allow custom file system implementations, if needed:

    If there is a good reason to resolve symlinks on the server side, this can be added.

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  2. I have two computers on a network with the same NFS mount settings pointing to the server. On the server there are symlinks from one exported directory to another. On one client the links work just fine and on the other they are unreliable. I suspect that since the working client has a new version of NFS (same protocol use), a bug was fixed. In theory the request should go to the server and interpreted there since that is what is doing the exporting. If a client puts a symlink in the folder, then it will probably be broken on other clients. However, the server symlink should work. This general suggests that a special type of symlink for network shares is needed. Something like a server-symlink.

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