1.\" Copyright (c) 1995 2.\" Bill Paul <wpaul@ctr.columbia.edu>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by Bill Paul. 15.\" 4. Neither the name of the author nor the names of any co-contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY Bill Paul AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL Bill Paul OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" $FreeBSD$ 32.\" 33.Dd February 4, 1995 34.Dt YPSERV 8 35.Os 36.Sh NAME 37.Nm ypserv 38.Nd NIS database server 39.Sh SYNOPSIS 40.Nm 41.Op Fl n 42.Op Fl d 43.Op Fl p Ar path 44.Sh DESCRIPTION 45.Tn NIS 46is an RPC-based service designed to allow a number of UNIX-based 47machines to share a common set of configuration files. 48Rather than 49requiring a system administrator to update several copies of files 50such as 51.Pa /etc/hosts , 52.Pa /etc/passwd 53and 54.Pa /etc/group , 55which tend to require frequent changes in most environments, 56.Tn NIS 57allows groups of computers to share one set of data which can be 58updated from a single location. 59.Pp 60The 61.Nm 62program is the server that distributes 63.Tn NIS 64databases to client systems within an 65.Tn NIS 66.Em domain . 67Each client in an 68.Tn NIS 69domain must have its domainname set to 70one of the domains served by 71.Nm 72using the 73.Xr domainname 1 74command. 75The clients must also run 76.Xr ypbind 8 77in order to attach to a particular server, since it is possible to 78have several servers within a single 79.Tn NIS 80domain. 81.Pp 82The databases distributed by 83.Nm 84are stored in 85.Pa /var/yp/[domainname] 86where 87.Pa domainname 88is the name of the domain being served. 89There can be several 90such directories with different domainnames, and you need only one 91.Nm 92daemon to handle them all. 93.Pp 94The databases, or 95.Pa maps 96as they are often called, 97are created by 98.Pa /var/yp/Makefile 99using several system files as source. 100The database files are in 101.Xr db 3 102format to help speed retrieval when there are many records involved. 103In 104.Fx , 105the maps are always readable and writable only by root for security 106reasons. 107Technically this is only necessary for the password 108maps, but since the data in the other maps can be found in 109other world-readable files anyway, it doesn't hurt and it's considered 110good general practice. 111.Pp 112The 113.Nm 114program is started by 115.Pa /etc/rc.network 116if it has been enabled in 117.Pa /etc/rc.conf . 118.Sh SPECIAL FEATURES 119There are some problems associated with distributing a 120.Fx 121password 122database via 123.Tn NIS Ns : 124.Fx 125normally only stores encrypted passwords 126in 127.Pa /etc/master.passwd , 128which is readable and writable only by root. 129By turning this file 130into an 131.Tn NIS 132map, this security feature would be completely defeated. 133.Pp 134To make up for this, the 135.Fx 136version of 137.Nm 138handles the 139.Pa master.passwd.byname 140and 141.Pa master.passwd.byuid 142maps in a special way. 143When the server receives a request to access 144either of these two maps, it will check the TCP port from which the 145request originated and return an error if the port number is greater 146than 1023. 147Since only the superuser is allowed to bind to TCP ports 148with values less than 1024, the server can use this test to determine 149whether or not the access request came from a privileged user. 150Any requests made by non-privileged users are therefore rejected. 151.Pp 152Furthermore, the 153.Xr getpwent 3 154routines in the 155.Fx 156standard C library will only attempt to retrieve 157data from the 158.Pa master.passwd.byname 159and 160.Pa master.passwd.byuid 161maps for the superuser: if a normal user calls any of these functions, 162the standard 163.Pa passwd.byname 164and 165.Pa passwd.byuid 166maps will be accessed instead. 167The latter two maps are constructed by 168.Pa /var/yp/Makefile 169by parsing the 170.Pa master.passwd 171file and stripping out the password fields, and are therefore 172safe to pass on to unprivileged users. 173In this way, the shadow password 174aspect of the protected 175.Pa master.passwd 176database is maintained through 177.Tn NIS . 178.Sh NOTES 179.Ss Setting Up Master and Slave Servers 180.Xr ypinit 8 181is a convenient script that will help setup master and slave 182.Tn NIS 183servers. 184.Ss Limitations 185There are two problems inherent with password shadowing in 186.Tn NIS 187that users should 188be aware of: 189.Bl -enum -offset indent 190.It 191The 192.Sq TCP port less than 1024 193test is trivial to defeat for users with 194unrestricted access to machines on your network (even those machines 195which do not run UNIX-based operating systems). 196.It 197If you plan to use a 198.Fx 199system to serve 200.No non- Ns Fx 201clients that 202have no support for password shadowing (which is most of them), you 203will have to disable the password shadowing entirely by uncommenting the 204.Em UNSECURE=True 205entry in 206.Pa /var/yp/Makefile . 207This will cause the standard 208.Pa passwd.byname 209and 210.Pa passwd.byuid 211maps to be generated with valid encrypted password fields, which is 212necessary in order for 213.No non- Ns Fx 214clients to perform user 215authentication through 216.Tn NIS . 217.El 218.Pp 219.Ss Security 220In general, any remote user can issue an RPC to 221.Nm 222and retrieve the contents of your 223.Tn NIS 224maps, provided the remote user 225knows your domain name. 226To prevent such unauthorized transactions, 227.Nm 228supports a feature called 229.Pa securenets 230which can be used to restrict access to a given set of hosts. 231At startup, 232.Nm 233will attempt to load the securenets information from a file 234called 235.Pa /var/yp/securenets . 236(Note that this path varies depending on the path specified with 237the 238.Fl p 239option, which is explained below.) 240This file contains entries 241that consist of a network specification and a network mask separated 242by white space. 243Lines starting with 244.Dq \&# 245are considered to be comments. 246A 247sample securenets file might look like this: 248.Bd -unfilled -offset indent 249# allow connections from local host -- mandatory 250127.0.0.1 255.255.255.255 251# allow connections from any host 252# on the 192.168.128.0 network 253192.168.128.0 255.255.255.0 254# allow connections from any host 255# between 10.0.0.0 to 10.0.15.255 25610.0.0.0 255.255.240.0 257.Ed 258.Pp 259If 260.Nm 261receives a request from an address that matches one of these rules, 262it will process the request normally. 263If the address fails to match 264a rule, the request will be ignored and a warning message will be 265logged. 266If the 267.Pa /var/yp/securenets 268file does not exist, 269.Nm 270will allow connections from any host. 271.Pp 272The 273.Nm 274program also has support for Wietse Venema's 275.Em tcpwrapper 276package. 277This allows the administrator to use the tcpwrapper 278configuration files 279.Pa ( /etc/hosts.allow 280and 281.Pa /etc/hosts.deny ) 282for access control instead of 283.Pa /var/yp/securenets . 284.Pp 285Note: while both of these access control mechanisms provide some 286security, they, like the privileged port test, are both vulnerable 287to 288.Dq IP spoofing 289attacks. 290.Pp 291.Ss NIS v1 compatibility 292This version of 293.Nm 294has some support for serving 295.Tn NIS 296v1 clients. 297The 298.Fx 299.Tn NIS 300implementation only uses the 301.Tn NIS 302v2 protocol, however other implementations 303include support for the v1 protocol for backwards compatibility 304with older systems. 305The 306.Xr ypbind 8 307daemons supplied with these systems will try to establish a binding 308to an 309.Tn NIS 310v1 server even though they may never actually need it (and they may 311persist in broadcasting in search of one even after they receive a 312response from a v2 server). Note that while 313support for normal client calls is provided, this version of 314.Nm 315does not handle v1 map transfer requests; consequently, it cannot 316be used as a master or slave in conjunction with older 317.Tn NIS 318servers that 319only support the v1 protocol. 320Fortunately, there probably aren't any 321such servers still in use today. 322.Ss NIS servers that are also NIS clients 323Care must be taken when running 324.Nm 325in a multi-server domain where the server machines are also 326.Tn NIS 327clients. 328It is generally a good idea to force the servers to 329bind to themselves rather than allowing them to broadcast bind 330requests and possibly become bound to each other: strange failure 331modes can result if one server goes down and 332others are dependent upon on it. 333(Eventually all the clients will 334time out and attempt to bind to other servers, but the delay 335involved can be considerable and the failure mode is still present 336since the servers might bind to each other all over again). 337.Pp 338Refer to the 339.Xr ypbind 8 340man page for details on how to force it to bind to a particular 341server. 342.Sh OPTIONS 343The following options are supported by 344.Nm : 345.Bl -tag -width flag 346.It Fl n 347This option affects the way 348.Nm 349handles yp_match requests for the 350.Pa hosts.byname 351and 352.Pa hosts.byaddress 353maps. 354By default, if 355.Nm 356can't find an entry for a given host in its hosts maps, it will 357return an error and perform no further processing. 358With the 359.Fl n 360flag, 361.Nm 362will go one step further: rather than giving up immediately, it 363will try to resolve the hostname or address using a DNS nameserver 364query. 365If the query is successful, 366.Nm 367will construct a fake database record and return it to the client, 368thereby making it seem as though the client's yp_match request 369succeeded. 370.Pp 371This feature is provided for compatiblity with SunOS 4.1.x, 372which has brain-damaged resolver functions in its standard C 373library that depend on 374.Tn NIS 375for hostname and address resolution. 376The 377.Fx 378resolver can be configured to do DNS 379queries directly, therefore it is not necessary to enable this 380option when serving only 381.Fx 382.Tn NIS 383clients. 384.It Fl d 385Cause the server to run in debugging mode. 386Normally, 387.Nm 388reports only unusual errors (access violations, file access failures) 389using the 390.Xr syslog 3 391facility. 392In debug mode, the server does not background 393itself and prints extra status messages to stderr for each 394request that it receives. 395Also, while running in debug mode, 396.Nm 397will not spawn any additional subprocesses as it normally does 398when handling yp_all requests or doing DNS lookups. 399(These actions 400often take a fair amount of time to complete and are therefore handled 401in subprocesses, allowing the parent server process to go on handling 402other requests.) 403This makes it easier to trace the server with 404a debugging tool. 405.It Fl p Ar path 406Normally, 407.Nm 408assumes that all 409.Tn NIS 410maps are stored under 411.Pa /var/yp . 412The 413.Fl p 414flag may be used to specify an alternate 415.Tn NIS 416root path, allowing 417the system administrator to move the map files to a different place 418within the filesystem. 419.El 420.Sh FILES 421.Bl -tag -width Pa -compact 422.It Pa /var/yp/[domainname]/[maps] 423the 424.Tn NIS 425maps 426.It Pa /etc/nsswitch.conf 427name switch configuration file 428.It Pa /var/yp/securenets 429host access control file 430.El 431.Sh SEE ALSO 432.Xr ypcat 1 , 433.Xr db 3 , 434.Xr hosts_access 5 , 435.Xr rpc.yppasswdd 8 , 436.Xr yp 8 , 437.Xr ypbind 8 , 438.Xr ypinit 8 , 439.Xr yppush 8 , 440.Xr ypxfr 8 441.Sh AUTHORS 442.An Bill Paul Aq wpaul@ctr.columbia.edu 443.Sh HISTORY 444This version of 445.Nm 446first appeared in 447.Fx 2.2 . 448