NFS cache : file content not updated on client when modified on server

nfs

Here's my set up: One NFS Server machine (v4), several NFS client machines.

When a client machine write files to the NFS mount, the other clients see the new content instantly : no problem.

But, when the server machine modify the content of the file, this new content is not shown on the client until I do a ls of the directory from the client.

I'm absolutely stumped on this inconsistency…any help would be greatly appreciated!

Infos :

nfs 1.2.3-r1 on both client and server
acregmin, acregmax, acdirmin, acdirmax, lookupcache : default values

Best Answer

Adding as an answer based on your comment.
The solution is to add lookupcache=none to your nfs mount options.

What happens is that the first time your client reads the file it does a NFS lookup to get the NFS fileid. It then caches the NFS fileid, and when you go back to open the file, it uses the cache. Normally this isnt a problem as when the file is updated its fileid stays the same. But for some reason the old file is being removed, and a new one is created (or renamed, or something to where its not the same file).
Now normally this isnt a problem either as when your client tries to open a fileid which isnt there, it will get an error from the server and do another lookup to get the new fileid. But for some reason the NFS server is letting the client open that old fileid. Perhaps another client has the file open and so its not being deleted yet, I dont know.

In any case the way to solve it is to tell the client to always do an nfslookup before opening a file by using the nfs mount option lookupcache=none. The downside to this is that it can be expensive if you are frequently opening files since it adds more traffic to the NFS server.

Related Solutions

Linux – NFS – Files on client are not appearing on server

Don't immediately appear or don't appear for some time?

NFS will by default perform a level of caching of directory and file contents at the kernel level of the system. If machine one updates a file and machine two has still got a copy of the file in cache, then if machine two attempts to access the file then it may not see the newer version of the file until its cache expires.

Check the man page for nfs for the following parameters:

   acregmin=n     The minimum time in seconds that attributes of a  regu-
                  lar  file  should  be  cached  before  requesting fresh
                  information from a server.  The default is 3 seconds.

   acregmax=n     The maximum time in seconds that attributes of a  regu-
                  lar file can be cached before requesting fresh informa-
                  tion from a server.  The default is 60 seconds.

   acdirmin=n     The minimum time in seconds that attributes of a direc-
                  tory  should be cached before requesting fresh informa-
                  tion from a server.  The default is 30 seconds.

   acdirmax=n     The maximum time in seconds that attributes of a direc-
                  tory  can be cached before requesting fresh information
                  from a server.  The default is 60 seconds.

   actimeo=n      Using actimeo sets all of acregmin, acregmax, acdirmin,
                  and  acdirmax  to  the same value.  There is no default
                  value.

   noac           Disable all forms of attribute caching entirely.   This
                  extracts  a  significant  performance  penalty  but  it
                  allows two different  NFS  clients  to  get  reasonable
                  results  when  both  clients  are actively writing to a
                  common export on the server.

Debian – NFS: Server says “authenticated mount request”, but client sees “access denied”

I've seen this if your /etc/hosts.allow and /etc/hosts.deny are not correct; check those files for a line with portmap in it and either comment it out (unsecure if you're not behind a firewall) or set the line on the client/server to be your specific subnet.

So for instance, in /etc/hosts.allow:

portmap: 192.168.0.0/16

...and comment out whatever is in /etc/hosts.deny to make only hosts.allow active. NFS uses tcpwrappers and these files to control access along with what's in /etc/exports.