lpd daemon

Edit online

Although local and remote print jobs are submitted with the same commands, they are processed differently. After a print job has been transmitted to a remote host, it is no longer managed by the local print spooling subsystem.

The lpd daemon is part of the TCP/IP system group. Any host on a TCP/IP network can run the lpd daemon, and any host can send print requests to any other host on the network (if the host is currently running lpd). As a security measure, the lpd daemon forks a child process that checks each remote print request against two database files: the /etc/hosts.equiv file and the /etc/hosts.lpd file. If the name of the host submitting the print request is not in the /etc/hosts.lpd file, the print request is rejected.

Note: The /etc/hosts.equiv file defines which computers on a network are allowed to execute certain commands on a local host without supplying a password. The /etc/hosts.lpd file defines which computers on a network are allowed to execute print commands on a local host without supplying a password.

The lpd daemon on the remote print server monitors port 515 for print requests. When the lpd daemon receives a print request from a valid host, it places the request in the specified queue. The lpd daemon places files specified in print requests in the directory /var/spool/lpd. The print request is then managed by the qdaemon and the appropriate backend (usually piobe) on the remote server.

The /etc/locks/lpd file contains the process ID of the currently running instance of the lpd daemon. If a machine running the lpd daemon becomes inoperable, the ID for the lpd daemon might have to be removed before the system is restarted. The error messages lpd: lock file or duplicate daemon indicate that the ID must be removed.