.\" Copyright (c) 1992/3 Theo de Raadt <email@example.com> .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. The name of the author may not be used to endorse or promote .\" products derived from this software without specific prior written .\" permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS .\" OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY .\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" from: @(#)yp.8 1.0 (deraadt) 4/26/93 .\" $FreeBSD: src/share/man/man8/yp.8,v 1.36 2005/01/21 08:36:40 ru Exp $ .\" .Dd April 5, 1993 .Dt YP 8 .Os .Sh NAME .Nm yp .Nd description of the YP/NIS system .Sh SYNOPSIS .Nm .Sh DESCRIPTION The .Nm YP subsystem allows network management of passwd, group, netgroup, hosts, services, rpc, bootparams and ethers file entries through the functions .Xr getpwent 3 , .Xr getgrent 3 , .Xr getnetgrent 3 , .Xr gethostent 3 , .Xr getnetent 3 , .Xr getrpcent 3 , and .Xr ethers 3 . The .Xr bootparamd 8 daemon makes direct .Tn NIS library calls since there are no functions in the standard C library for reading bootparams. .Tn NIS support is enabled in .Xr nsswitch.conf 5 . .Pp The .Nm YP subsystem is started automatically by .Xr launchd 8 if an .Tn NIS domain is specified in the .Pa /etc/defaultdomain configuration file, and if the directory .Pa /var/yp exists (which it does in the default distribution). .Pp .Tn NIS is an .Tn RPC Ns -based client/server system that allows a group of machines within an .Tn NIS domain to share a common set of configuration files. This permits a system administrator to set up .Tn NIS client systems with only minimal configuration data and add, remove or modify configuration data from a single location. .Pp The canonical copies of all .Tn NIS information are stored on a single machine called the .Tn NIS .Em "master server" . The databases used to store the information are called .Tn NIS .Em maps . In .Fx , these maps are stored in .Pa /var/yp/ Ns Aq Ar domainname where .Aq Ar domainname is the name of the .Tn NIS domain being served. A single .Tn NIS server can support several domains at once, therefore it is possible to have several such directories, one for each supported domain. Each domain will have its own independent set of maps. .Pp In .Fx , the .Tn NIS maps are Berkeley DB hashed database files (the same format used for the .Xr passwd 5 database files). Other operating systems that support .Tn NIS use old-style .Nm ndbm databases instead (largely because Sun Microsystems originally based their .Tn NIS implementation on .Nm ndbm , and other vendors have simply licensed Sun's code rather than design their own implementation with a different database format). On these systems, the databases are generally split into .Pa .dir and .Pa .pag files which the .Nm ndbm code uses to hold separate parts of the hash database. The Berkeley DB hash method instead uses a single file for both pieces of information. This means that while you may have .Pa passwd.byname.dir and .Pa passwd.byname.pag files on other operating systems (both of which are really parts of the same map), .Fx will have only one file called .Pa passwd.byname . The difference in format is not significant: only the .Tn NIS server, .Xr ypserv 8 , and related tools need to know the database format of the .Tn NIS maps. Client .Tn NIS systems receive all .Tn NIS data in .Tn ASCII form. .Pp There are three main types of .Tn NIS systems: .Bl -enum .It .Tn NIS clients, which query .Tn NIS servers for information. .It .Tn NIS master servers, which maintain the canonical copies of all .Tn NIS maps. .It .Tn NIS slave servers, which maintain backup copies of .Tn NIS maps that are periodically updated by the master. .El .Pp A .Tn NIS client establishes what is called a .Em binding to a particular .Tn NIS server using the .Xr ypbind 8 daemon. The .Xr ypbind 8 utility checks the system's default domain (as set by the .Xr domainname 1 command) and begins broadcasting .Tn RPC requests on the local network. These requests specify the name of the domain for which .Xr ypbind 8 is attempting to establish a binding. If a server that has been configured to serve the requested domain receives one of the broadcasts, it will respond to .Xr ypbind 8 , which will record the server's address. If there are several servers available (a master and several slaves, for example), .Xr ypbind 8 will use the address of the first one to respond. From that point on, the client system will direct all of its .Tn NIS requests to that server. The .Xr ypbind 8 utility will occasionally .Dq ping the server to make sure it is still up and running. If it fails to receive a reply to one of its pings within a reasonable amount of time, .Xr ypbind 8 will mark the domain as unbound and begin broadcasting again in the hopes of locating another server. .Pp .Tn NIS master and slave servers handle all .Tn NIS requests with the .Xr ypserv 8 daemon. The .Xr ypserv 8 utility is responsible for receiving incoming requests from .Tn NIS clients, translating the requested domain and map name to a path to the corresponding database file and transmitting data from the database back to the client. There is a specific set of requests that .Xr ypserv 8 is designed to handle, most of which are implemented as functions within the standard C library: .Bl -tag -width ".Fn yp_master" .It Fn yp_order check the creation date of a particular map .It Fn yp_master obtain the name of the .Tn NIS master server for a given map/domain .It Fn yp_match lookup the data corresponding to a given in key in a particular map/domain .It Fn yp_first obtain the first key/data pair in a particular map/domain .It Fn yp_next pass .Xr ypserv 8 a key in a particular map/domain and have it return the key/data pair immediately following it (the functions .Fn yp_first and .Fn yp_next can be used to do a sequential search of an .Tn NIS map) .It Fn yp_all retrieve the entire contents of a map .El .Pp There are a few other requests which .Xr ypserv 8 is capable of handling (i.e., acknowledge whether or not you can handle a particular domain .Pq Dv YPPROC_DOMAIN , or acknowledge only if you can handle the domain and be silent otherwise .Pq Dv YPPROC_DOMAIN_NONACK ) but these requests are usually generated only by .Xr ypbind 8 and are not meant to be used by standard utilities. .Pp On networks with a large number of hosts, it is often a good idea to use a master server and several slaves rather than just a single master server. A slave server provides the exact same information as a master server: whenever the maps on the master server are updated, the new data should be propagated to the slave systems using the .Xr yppush 8 command. The .Tn NIS .Pa Makefile .Pq Pa /var/yp/Makefile will do this automatically if the administrator comments out the line which says .Dq Li NOPUSH=true .Va ( NOPUSH is set to true by default because the default configuration is for a small network with only one .Tn NIS server). The .Xr yppush 8 command will initiate a transaction between the master and slave during which the slave will transfer the specified maps from the master server using .Xr ypxfr 8 . (The slave server calls .Xr ypxfr 8 automatically from within .Xr ypserv 8 ; therefore it is not usually necessary for the administrator to use it directly. It can be run manually if desired, however.) Maintaining slave servers helps improve .Tn NIS performance on large networks by: .Bl -bullet .It Providing backup services in the event that the .Tn NIS master crashes or becomes unreachable .It Spreading the client load out over several machines instead of causing the master to become overloaded .It Allowing a single .Tn NIS domain to extend beyond a local network (the .Xr ypbind 8 daemon might not be able to locate a server automatically if it resides on a network outside the reach of its broadcasts. It is possible to force .Xr ypbind 8 to bind to a particular server with .Xr ypset 8 but this is sometimes inconvenient. This problem can be avoided simply by placing a slave server on the local network.) .El .Pp The .Fx .Xr ypserv 8 is specially designed to provide enhanced security (compared to other .Tn NIS implementations) when used exclusively with .Fx client systems. The .Fx password database system (which is derived directly from .Bx 4.4 ) includes support for .Em "shadow passwords" . The standard password database does not contain users' encrypted passwords: these are instead stored (along with other information) in a separate database which is accessible only by the super-user. If the encrypted password database were made available as an .Tn NIS map, this security feature would be totally disabled, since any user is allowed to retrieve .Tn NIS data. .Pp To help prevent this, .Fx Ns 's .Tn NIS server handles the shadow password maps .Pa ( master.passwd.byname and .Pa master.passwd.byuid ) in a special way: the server will only provide access to these maps in response to requests that originate on privileged ports. Since only the super-user is allowed to bind to a privileged port, the server assumes that all such requests come from privileged users. All other requests are denied: requests from non-privileged ports will receive only an error code from the server. Additionally, .Fx Ns 's .Xr ypserv 8 includes support for .An Wietse Venema Ns 's tcp wrapper package; with tcp wrapper support enabled, the administrator can configure .Xr ypserv 8 to respond only to selected client machines. .Pp While these enhancements provide better security than stock .Tn NIS , they are by no means 100% effective. It is still possible for someone with access to your network to spoof the server into disclosing the shadow password maps. .Pp On the client side, .Fx Ns 's .Xr getpwent 3 functions will automatically search for the .Pa master.passwd maps and use them if they exist. If they do, they will be used, and all fields in these special maps (class, password age and account expiration) will be decoded. If they are not found, the standard .Pa passwd maps will be used instead. .Sh COMPATIBILITY When using a .No non- Ns Fx .Tn NIS server for .Xr passwd 5 files, it is unlikely that the default MD5-based format that .Fx uses for passwords will be accepted by it. If this is the case, the value of the .Va passwd_format setting in .Xr login.conf 5 should be changed to .Qq Li des for compatibility. .Pp Some systems, such as .Tn SunOS 4.x, need .Tn NIS to be running in order for their hostname resolution functions .Fn ( gethostbyname , .Fn gethostbyaddr , etc.) to work properly. On these systems, .Xr ypserv 8 performs .Tn DNS lookups when asked to return information about a host that does not exist in its .Pa hosts.byname or .Pa hosts.byaddr maps. .Fx Ns 's resolver uses .Tn DNS by default (it can be made to use .Tn NIS , if desired), therefore its .Tn NIS server does not do .Tn DNS lookups by default. However, .Xr ypserv 8 can be made to perform .Tn DNS lookups if it is started with a special flag. It can also be made to register itself as an .Tn NIS v1 server in order to placate certain systems that insist on the presence of a v1 server .No ( Fx uses only .Tn NIS v2, but many other systems, including .Tn SunOS 4.x, search for both a v1 and v2 server when binding). .Fx Ns 's .Xr ypserv 8 does not actually handle .Tn NIS v1 requests, but this .Dq "kludge mode" is useful for silencing stubborn systems that search for both a v1 and v2 server. .Pp (Please see the .Xr ypserv 8 manual page for a detailed description of these special features and flags.) .Sh HISTORY The .Nm YP subsystem was written from the ground up by .An Theo de Raadt to be compatible to Sun's implementation. Bug fixes, improvements and .Tn NIS server support were later added by .An Bill Paul . The server-side code was originally written by .An Peter Eriksson and .An Tobias Reber and is subject to the GNU Public License. No Sun code was referenced. .Sh BUGS While .Fx now has both .Tn NIS client and server capabilities, it does not yet have support for .Xr ypupdated 8 or the .Fn yp_update function. Both of these require secure .Tn RPC , which .Fx does not support yet either. .Pp The .Xr getservent 3 and .Xr getprotoent 3 functions do not yet have .Tn NIS support. Fortunately, these files do not need to be updated that often. .Pp Many more manual pages should be written, especially .Xr ypclnt 3 . For the time being, seek out a local Sun machine and read the manuals for there. .Pp Neither Sun nor this author have found a clean way to handle the problems that occur when ypbind cannot find its server upon bootup.