rpcmountd

rpcmountd is the remote mount daemon used by the Network File System (NFS) to respond to MOUNT RPC requests from NFS clients. It runs on the NFS server as a background service and, together with the RPC bind (portmapper) service, registers itself as the MOUNT program, typically under a specific program number and version set depending on the implementation. Its primary role is to handle the initial mounting step that clients perform before accessing an exported directory.

When a client wishes to mount an exported directory, it issues a MOUNT request to rpcmountd. The daemon checks the server’s export table, usually defined in /etc/exports, and any access controls. If the requested export is permitted, rpcmountd returns a file handle that enables the client to proceed with NFS operations. After a successful mount, subsequent read and write operations are carried out by the NFS server daemon (nfsd).

Configuration and operation details vary by system. Exports are controlled by /etc/exports, with options such as rw (read-write), ro (read-only), root_squash, and others determining client permissions. rpcmountd is started at boot by the system’s service manager and may be invoked as rpc.mountd or mountd, with port requirements differing across distributions. In some setups, administrators configure fixed ports to simplify firewall rules; in others, the RPC binder assigns ports dynamically.

Security considerations include the sensitivity of the MOUNT protocol and the potential exposure of export structure. Exports should be restricted to trusted clients, and networks should be protected by firewalls and proper access controls. Keeping software up to date and monitoring mount activity are also advised.

See also: NFS, mountd, rpcbind, /etc/exports.