rpc-srv/tcp: nfsd: shutting down socket #linux #nfs
Let's say you for some reason have to reboot your NFS server, and after it has started up again, some of the clients can't mount the file systems they usually mount. Others can.
If you then check dmesg on the NFS server and you see messages like this:
rpc-srv/tcp: nfsd: got error -104 when sending 20 bytes - shutting down socket
rpc-srv/tcp: nfsd: got error -32 when sending 20 bytes - shutting down socket
and you start searching for those error messages without finding anything enlightening... The answer might be: DNS!
We had this with an NFS server at work, and it turned out that it came up after reboot with DNS servers - configured specifically for the network interface?! - that were not able to resolve the hostname from the IP-address of some of the clients.
Yes, the venerable "reverse DNS must match NFS client hostname"-problem.
It took us a while to hone in on as those error message did not scream rDNS to me. However, as soon as we fixed the DNS resolver configuration, everything started working again.
I dislike the meme "It's always DNS", it's in the same category as "RAID is not backup" and "The hardest problems in computer science are [software development challenges that are not computer science]" - but this time, it was DNS.
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