8. FAQs

This is the FAQ section. Most of it was written by Alan Cox.

1. I get a lot of 'stale nfs handle' errors when using Linux as a nfs server.

   This is caused by a bug in some oldish nfsd versions. It is fixed in nfs-server2.2beta16 and later.

2. When I try to mount a file system I get

     can't register with portmap: system error on send
     
   

   You are probably using a Caldera system. There is a bug in the rc scripts. Please contact Caldera to obtain a fix.

3. Why can't I execute a file after copying it to the NFS server?

   The reason is that nfsd caches open file handles for performance reasons (remember, it runs in user space). While nfsd has a file open (as is the case after writing to it), the kernel won't allow you to execute it. Nfsds newer than  spring 95 release open files after a few seconds, older ones would cling to them for days.

4. My NFS files are all read only

   The Linux NFS server defaults to read only. RTFM the ``exports'' and nfsd manual pages. You will need to alter /etc/exports.

5. I mount from a linux nfs server and while ls works I can't read or write files.

   On older versions of Linux you must mount a NFS servers with rsize=1024,wsize=1024.

6. I mount from a Linux NFS server with a block size of between 3500-4000 and it crashes the Linux box regularly

   Basically don't do it then.

7. Can Linux do NFS over TCP

   No, not at present.

8. I get loads of strange errors trying to mount a machine from a Linux box.

   Make sure your users are in 8 groups or less. Older servers require this.

9. When I reboot my machine it sometimes hangs when trying to unmount a hung NFS server.

   Do not unmount NFS servers when rebooting or halting, just ignore them, it will not hurt anything if you don't unmount them. The command is umount -avt nonfs.

10. Linux NFS clients are very slow when writing to Sun and BSD systems

    NFS writes are normally synchronous (you can disable this if you don't mind risking losing data). Worse still BSD derived kernels tend to be unable to work in small blocks. Thus when you write 4K of data from a Linux box in the 1K packets it uses BSD does this

            read 4K page
            alter 1K
            write 4K back to physical disk
            read 4K page
            alter 1K
            write 4K page back to physical disk
            etc..