What is a file handle? for NFS troubleshooting stale issue.

UNIX for Advanced & Expert Users
1

Experts,
Can any one please explain about a "File Handle" , what it is.
Can we see it, like an inode number.

  • Also what is the significance of it in
"Stale NFS file handle"

error.

Thanks,

2

I believe it's rather talking about the unique ID it gets when an NFS is mounted... Stale can mean the remote server has rebooted and ergo doesn't remember you having mounted that filesystem, and turns down your requests. The filesystem may need remounting.

3

Corona688 , thanks for the response, yes it is taking about the unique ID.

  • Stale mean the server has rebooted: But not always necessarily true.
  • Stale error can comes with many situations, I have posted this error seeing Stale error , on SAP packages , that throws intermittently on the nfs mounted client. One stale error happening due to improper use of file handle or multiple places the same file being used. But not sure about how this is happening and doubt some SAP process causing it on the hp-ux unix side , some SAP note says so. I got one good document in the search process : link given:
15.1.2 File Handles
Each object on the NFS-mounted filesystem is referenced by a unique object called a file handle. A file handle is viewed by the client as being opaque?the client cannot interpret the contents. However, to the server, the contents have considerable meaning. The file handles uniquely identify every file and directory on the server computer.

The Unix NFS server stores three pieces of information inside each file handle.

Filesystem identifier
Refers to the partition containing the file (file identifiers such as inode numbers are usually unique only within a partition).

File identifier
Can be something as simple as an inode number, used to refer to a particular item on a partition.

Generation count
A number that is incremented each time a file is unlinked and recreated. The generation count ensures that when a client references a file on the server, that file is, in fact, the same file that the server thinks it is. Without a generation count, two clients accessing the same file on the same server could produce erroneous results if one client deleted the file and created a new file with the same inode number. The generation count prevents such situations from occurring: when the file is recreated, the generation number is incremented, and the second client gets an error message when it attempts to access the older, now nonexistent, file.

http://etutorials.org/Linux+systems/unix+internet+security/Part+III+Network+and+Internet+Security/Chapter+15.+Network+Filesystems/15.1+Understanding+NFS/

Thanks ....

4

A reboot of a sane NFS server retains the NFS file handle!
And sane clients continue without stale NFS handle!
Sporadic stale handles most likely is an internal congestion in the bad Linux NFS client, and congestions are most likely in bad SuSE kernels.