How do I tell an NFS server to use TCP?

BrianK · 12-02-2004, 06:20 PM

how do I tell my NFS server to operate over TCP instead of UDP? Does it require rebuilding NFS? Rebuilding the kernel? Is it just an option somewhere?

NFS server info:

# cat /etc/redhat-release
Red Hat Linux release 9 (Shrike)

# uname -r
2.4.20-8smp

# rpcinfo -p | grep nfs
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs

reelwylde · 12-02-2004, 07:24 PM

not entirely sure but Ithink it's an option in /etc/services

nfs 2049/tcp nfs # Sun NFS
nfs 2049/udp nfs # Sun NFS

trickykid · 12-02-2004, 07:24 PM

Its right there in the man page but its not really recommended or might not be supported:

Code:

tcp            Mount the NFS filesystem using the TCP protocol instead  of  the  default  UDP  protocol.   Many  NFS
               servers only support UDP.

I would imagine how udp and tcp work, udp is the better option when using NFS.

BrianK · 12-02-2004, 11:05 PM

Quote:

Originally posted by reelwylde
not entirely sure but Ithink it's an option in /etc/services

nfs 2049/tcp nfs # Sun NFS
nfs 2049/udp nfs # Sun NFS

hmm.. it's there for me too (both tcp and udp), but still my server is only running nfs over UDP.

Any idea why this would be?

BrianK · 12-02-2004, 11:09 PM

Quote:

Originally posted by trickykid
Its right there in the man page but its not really recommended or might not be supported:

Code:

tcp Mount the NFS filesystem using the TCP protocol instead of the default UDP protocol. Many NFS servers only support UDP.

I would imagine how udp and tcp work, udp is the better option when using NFS.

the man page is for mounting, not for serving. I know how to mount using tcp, but I'm not serving over TCP yet, so I can't mount with TCP.

UDP is sometimes a better option for NFS. It is not so good with a lossy network. With TCP, while there is a bit more back & forth, a lost packet does not force a complete retransmission - just a new packet. In that respect, it's much faster.

I am experiencing some NFS slow downs, especially on computers behind two switches. TCP sounds like it might be the solution.

Heck, lots of distros are starting to default to TCP for NFS mounts... that should tell you something, right?

mritch · 12-02-2004, 11:45 PM

trickykid is absolutely (!) right here. the client asks for tcp - the server serves tcp.

what do you think you'll find in /etc/services?

man mount. edit fstab accourdingly.

to be sure your kernel supports serving it:
$ grep NFSD_TCP config-2.4.20

sl mritch.

trickykid · 12-03-2004, 10:22 AM

Quote:

Originally posted by mritch
trickykid is absolutely (!) right here. the client asks for tcp - the server serves tcp.

what do you think you'll find in /etc/services?

man mount. edit fstab accourdingly.

to be sure your kernel supports serving it:
$ grep NFSD_TCP config-2.4.20

sl mritch.

Thanks for pointing that out mritch, like I said and like the man pages state, make sure your kernel supports serving out TCP instead of UDP, if its not working by mounting and specifying tcp, its most likely the server that doesn't support it and will default to UDP.

Read this page and you might see why UDP is by default here instead of TCP when using NFS and filesharing. http://www.informit.com/articles/article.asp?p=22081

BrianK · 12-03-2004, 05:24 PM

ahhh.. that's the answer I was looking for - it's in the kernel. (for the record, I did read the man pages & did try to mount via TCP, but it dodn't work - hence this question)

so..
# grep NFSD_TCP /boot/config-2.4.20-8
# CONFIG_NFSD_TCP is not set

Does this mean I need to recompile my kernel to get it running over TCP? Is there some way to do this without a kernel recompile?

Thanks.