---
name: "nfscbd"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/nfscbd"
---

# nfscbd(8)

NFSv4 client side callback daemon

## NAME

**nfscbd** – NFSv4 client side callback daemon

## SYNOPSIS

**nfscbd** \[**-p** *port\_number*\] \[**-P** *client\_principal*\]

## DESCRIPTION

**nfscbd** runs on a client using NFSv4 to handle callback requests from the NFSv4 server. If no **nfscbd** is running, NFSv4 mounts will still work, but the server will never issue Open Delegations to the client.

One callback server and one master server are always started.

The following options are available:

- **-p** *port\_number*

  Specifies what port# the callback server should use.

- **-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. If you do not 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.

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.

**nfscbd** listens for service requests at the port defined by NFSV4\_CBPORT in /usr/include/fs/nfs/nfs.h, unless **-p** has been specified. For more information on what callbacks and Open Delegations do, see RFC3530.

## EXIT STATUS

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

## SEE ALSO

[nfsv4(4)](/nfsv4/4.md), [mount\_nfs(8)](/mount_nfs/8.md)

## HISTORY

First introduced with the experimental nfs client for NFSv4 support in 2009.