NFSCBD(8)

💅 NFSCBD(8) — the NFSv4 client side callback daemon, explained by your fave

okay so bestie, you found nfscbd — short for, literally, the NFSv4 client side callback daemon. Yes the name is a mouthful, no we're not changing it. Grab a strawberry drink 🍓 and let's get into it.

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✨ NAME ✨

nfscbd — NFSv4 client side callback daemon. That's the whole vibe. 🦋

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🌸 SYNOPSIS 🌸

nfscbd [-p port_number] [-P client_principal]

Two flags, both optional, both cute. Look at her go ✨

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💖 DESCRIPTION 💖

So here's the tea: nfscbd runs on a client that's using NFSv4, and its whole job is handling callback requests from the NFSv4 server. It's giving personal assistant energy — the server knocks, nfscbd answers. 🎀

Now the important part, no cap: if no nfscbd is running, your NFSv4 mounts will still work. Like, they're fine. It's fine. BUT — and this is the plot twist — the server will never issue Open Delegations to the client. So you're living half a life, honestly. 😭

One callback server and one master server are always started. Always. Both of them. Non-negotiable. 👑

The following options are available:

• -p port_number — specifies what port# the callback server should use. You pick the port, she uses the port. Slay.
• -P client_principal — specifies the host based principal name to be used as the target for callbacks over RPCSEC_GSS. For KerberosV, it must be in the client's default keytab file. This client_principal should be the same one specified by the gssname argument being used by nfsv4 mounts. And if you don't specify this argument? Callbacks will still work over AUTH_SYS, which is what many extant servers use even for RPCSEC_GSS mounts, as of 2009. So like… chill, it's handled. 🫶

Heads up bestie: that KerberosV keytab requirement is a must, not a maybe. Fr fr. 🙈

For example, "nfscbd -p 7654 -P root" starts the daemon to handle callbacks on port# 7654 and is using the host based principal root@<client-host>.<dns-domain> as the callback target. Iconic little one-liner, honestly. ⭐

And how does she know where to listen? nfscbd listens for service requests at the port defined by NFSV4_CBPORT in /usr/include/fs/nfs/nfs.h — unless -p has been specified, in which case your flag wins, obviously. 💅

For more information on what callbacks and Open Delegations actually do, see Network File System (NFS) Version 4 Protocol, RFC3530. Yes, RFC3530. Not 3531, not 3532. Write it down. 📝

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🔥 EXIT STATUS 🔥

The nfscbd utility exits 0 on success, and >0 if an error occurs.

Zero means we ate. Greater-than-zero means something's giving "call tech support." 💀

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🌈 SEE ALSO 🌈

• nfsv4(4)
• mount_nfs(8)

Go read them, iykyk 👑

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🎀 HISTORY 🎀

First introduced with the experimental nfs client for NFSv4 support in 2009. A true 2009 icon. The way that she's been serving callbacks since then… obsessed. 🦋✨

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mwah, that's the page 💜 — brought to you by Debian, dated April 25, 2009, and typed up with love by your fave manpage bestie. now go run nfscbd and let her cook 🍓👑