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Old 11-02-2015, 08:28 AM   #1
jeenuv
LQ Newbie
 
Registered: Aug 2014
Location: Cambridge, UK
Distribution: Linux Mint 20.1
Posts: 23

Rep: Reputation: Disabled
NFS time out


I've a Linux development board whose root file system is shared via. NFS from my PC (3.13.0-66-generic #108-Ubuntu SMP x86_64 GNU/Linux). The behaviour at times is that board mounts the NFS share, but then soon thereafter, while in execution, it started displaying NFS timeouts, retries, and hangs. Once this happens, the board won't re-boot again: it'll wait for the root file system to be mounted, fails, and then crashes.

For some reason, the only combination that doesn't work is my board mounting from my PC. My board can mount from other servers (I tested with colleagues'). Also, the said NFS share can be mounted from other PCs (including mine), so I'm sure both my server and board are functional.

I had restarted the server many times with 'sudo nfs-kernel-server restart', and have also re-exported all shares with 'exportfs -a', but none of that help. The NFS share is created with options "rw,insecure,no_root_squash,no_subtree_check".

I later found signs that the NFS server is probably allowing access to the said share. I found the following continuous traces in syslog, indicating retries from the board:

Quote:
Nov 2 11:48:26 e105349-lin rpc.mountd[7920]: authenticated mount request from 10.1.197.27:912 for /work/nfs (/work/nfs)
Nov 2 11:49:09 e105349-lin rpc.mountd[7920]: authenticated mount request from 10.1.197.27:899 for /work/nfs (/work/nfs)
Nov 2 11:50:02 e105349-lin rpc.mountd[7920]: authenticated mount request from 10.1.197.27:871 for /work/nfs (/work/nfs)
Nov 2 11:51:15 e105349-lin rpc.mountd[7920]: authenticated mount request from 10.1.197.27:759 for /work/nfs (/work/nfs)
Nov 2 11:52:48 e105349-lin rpc.mountd[7920]: authenticated mount request from 10.1.197.27:999 for /work/nfs (/work/nfs)
Nov 2 11:54:21 e105349-lin rpc.mountd[7920]: authenticated mount request from 10.1.197.27:792 for /work/nfs (/work/nfs)
Also, there are entries in /var/lib/nfs/rmtab for the said NFS share. For some reason the board isn't happy with all these, and gives up citing NFS timeout:

Quote:
[ 197.211808] VFS: Unable to mount root fs via NFS, trying floppy.
[ 197.214885] VFS: Cannot open root device "nfs" or unknown-block(2,0): error -6
[ 197.218459] Please append a correct "root=" boot option; here are the available partitions:
[ 197.222611] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)
[ 197.226702] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.15.0-rc8+ #2
As mentioned above, given that both the board and server are functional (as far as I could find out), I strongly suspect there's something fishy happening at the network level on my PC. I'm happy to provide any information that you require. Please advise.

Thanks.

Last edited by jeenuv; 11-02-2015 at 08:31 AM.
 
Old 11-03-2015, 03:07 AM   #2
jeenuv
LQ Newbie
 
Registered: Aug 2014
Location: Cambridge, UK
Distribution: Linux Mint 20.1
Posts: 23

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Rep: Reputation: Disabled
Looks like the cause of the problem was that I didn't specify "tcp" mount option in my nfsroot parameter. Also, if I don't additionally mention "v3", file system accesses seem to be particularly slow. With these options specified, file system is getting mounted fine.

Oddly enough, this requirement turned mandatory out of the blue. I never used to use these before!
 
  


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