ypserv (8) - Linux Man Pages

ypserv: NIS Server


ypserv - NIS Server


/usr/sbin/ypserv [-d] [-p port] [-f|--foreground]


The Network Information Service (NIS) provides a simple network lookup service consisting of databases and processes. The databases are gdbm files in a directory tree rooted at /var/yp.

The ypserv daemon is typically activated at system startup. ypserv runs only on NIS server machines with a complete NIS database. On other machines using the NIS services, you have to run ypbind as client or under Linux you could use the libc with NYS support. ypbind must run on every machine which has NIS client processes; ypserv may or may not be running on the same node, but must be running somewhere on the network. On startup ypserv parses the file /etc/ypserv.conf. It is also possible to pass OPTIONS to ypserv using the environment variable YPSERV_ARGS and this variable can be set in /etc/sysconfig/network.


-d, --debug

Causes the server to run in debugging mode. Normally, ypserv reports only errors (access violations, dbm failures) using the syslog(3) facility. In debug mode, the server does not background itself and prints extra status messages to stderr for each request that it revceives.

-p, --port port

ypserv will bind itself to this port. This makes it possible to have a router filter packets to the NIS ports, so that access to the NIS server from hosts on the Internet can be restricted.

-v, --version

Prints the version number

-f, --foreground

will not put itself into background.


In general, any remote user can issue an RPC to ypserv and retrieve the contents of your NIS maps, if he knows your domain name. To prevent such unauthorized transactions, ypserv supports a feature called securenets which can be used to restrict access to a given set of hosts. At startup ypserv will attempt to load the securenets information from a file called /var/yp/securenets . This file contains entries that consist of a netmask and a network pair separated by white spaces. Lines starting with "#" are considered to be comments.

A sample securenets file might look like this:

# allow connections from local host -- necessary
# same as
# allow connections from any host
# on the network
# allow connections from any host
# between and

If ypserv receives a request from an address that fails to match a rule, the request will be ignored and a warning message will be logged. If the /var/yp/securenets file does not exist, ypserv will allow connections from any host.

In the /etc/ypserv.conf you could specify some access rules for special maps and hosts. But it is not very secure, it makes the life only a little bit harder for a potential hacker. If a mapname doesn't match a rule, ypserv will look for the YP_SECURE key in the map. If it exists, ypserv will only allow requests on a reserved port.

For security reasons, ypserv will only accept ypproc_xfr requests for updating maps from the same master server as the old one. This means, you have to reinstall the slave servers if you change the master server for a map.


Sending the signal SIGHUP to the server can lead to a deadlock or crash.



configuration file.


which hosts are allowed to contact ypserv.


setting additional arguments to ypserv.


ypserv was written by Peter Eriksson <pen [at] lysator.liu.se>. Thorsten Kukuk <kukuk [at] linux-nis.org> added support for master/slave server and is the new Maintainer.


domainname(1), ypcat(1), ypmatch(1), ypserv.conf(5), netgroup(5), makedbm(8), revnetgroup(8), ypinit(8), yppoll(8), yppush(8), ypset(8), ypwhich(8), ypxfr(8), rpc.ypxfrd(8)

The Network Information Service (NIS) was formerly known as Sun Yellow Pages (YP). The functionality of the two remains the same; only the name has changed. The name Yellow Pages is a registered trademark in the United Kingdom of British Telecommunications plc, and may not be used without permission.