rpcb_register(9)

💅 rpcb_register — the kernel API manual, bestie edition ✨

okay so we're in the <pink>Kernel API Manual</pink> today and the star of the show is rpcb_register(9) — yes, the (9) means it's a kernel function, we love a section-nine king 👑

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🌸 NAME 🌸

rpcb_register — sets or unsets a port registration with the local rpcbind svc 🎀

like, it's the "hey rpcbind, remember me?" function, and also the "hey rpcbind, forget me" function. dual threat. main character energy fr fr.

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✨ SYNOPSIS ✨

int rpcb_register (struct net *net , u32 prog , u32 vers , int prot ,
unsigned short port );

that's the whole signature, copy it exactly bestie, don't get creative with it 🙈

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🦋 ARGUMENTS 🦋

• net — the target network namespace. which little world are we registering in, y'know? 🌍
• prog — the RPC program number to bind. the big ID. 👑
• vers — the RPC version number to bind. the sequel number, lowkey. 💫
• prot — the transport protocol to register. which vibe of transport we're on. 🚗
• port — the port value to register. literally the port. and plot twist: if you pass zero, it unregisters — more on that below 👀

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💖 DESCRIPTION 💖

so here's the tea ☕ — this function returns zero if the registration request was dispatched successfully and the rpcbind daemon returned success. that's the slay scenario 💅✨

otherwise? it returns an errno value that reflects the nature of the error. and the errors are giving: the request could not be dispatched, it timed out, or rpcbind returned an error. pick your poison bestie 😭💀

RPC services invoke this function to advertise their contact information via the system's rpcbind daemon. it's literally them posting their @ everywhere so people can reach them 🫶

and here's the detail nobody skips in this house: RPC services invoke this function once for each [program, version, transport] tuple they wish to advertise. one call per tuple. no bundling. that's the rule 📋

okay now the iconic part. callers may also unregister RPC services that are no longer available by setting the passed-in port to zero. yes, zero. zap. ⚡ and what that does is remove all registered transports for [program, version] from the local rpcbind database. all of them. the whole group chat. gone 🙈

also important: this function uses rpcbind protocol version 2 to contact the local rpcbind daemon. version 2. not 3, not 4 — that's a whole other function, see SEE ALSO 👇

Registration works over both AF_INET and AF_INET6, and services registered via this function are advertised as available for any address. universal availability, we stan 🌈

and if the local rpcbind daemon is listening on AF_INET6, services registered via this function will be advertised on IN6ADDR_ANY (ie available for all AF_INET and AF_INET6 addresses). so it's not just v6 — it's everything. the reach is unmatched 🔥

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🧚 SEE ALSO 🧚

• Kernel file ./net/sunrpc/rpcb_clnt.c
• rpcb_v4_register(9) — the protocol-v4 sibling, go say hi 👋
• rpcb_getport_async(9)

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aaaand that's the page! 💜 source is in ./net/sunrpc, dated October 2026 — so it's fresh, it's current, it ate and left no crumbs. go register something, bestie 🍓✨