ypserv

ypserv is the server daemon of the Network Information Service (NIS), originally developed by Sun Microsystems. It provides centralized access to network configuration data for clients in an NIS domain, such as user accounts, groups, hosts, and aliases. NIS allows multiple UNIX-like machines to share these databases without duplicating local files.

In an NIS setup, a domain defines a set of maps. The master server stores maps under /var/yp/<domain> and generates a published set of maps from organization-specific source files. Slave servers replicate maps from the master to provide fault tolerance. Clients install and run ypbind to locate an NIS server for their domain and fetch maps through ypserv when needed. Common maps include passwd.byname, passwd.byuid, group, hosts, and aliases.

ypserv is typically started at boot by the system’s init or systemd service scripts and is controlled by the YP-related configuration files on the server and the client, such as /etc/yp.conf and, on some distributions, /etc/ypserv.conf. Data transmission historically uses UDP; some implementations can use TCP for reliability. The protocol itself is not encrypted, which means NIS data can be vulnerable to interception or spoofing on untrusted networks unless additional security measures are employed. Because of these security limitations, NIS has seen reduced use in favor of more modern directory services and authentication mechanisms in many environments.

Historically, ypserv and NIS were widely used in UNIX networks to simplify administration before the advent of LDAP, Kerberos-based systems, and DNS-based services. Today, ypserv remains present on some systems for compatibility, but administrators often replace or shield NIS deployments with more secure alternatives.