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 3, 2008 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 port 44.Op Fl p Ar path 45.Sh DESCRIPTION 46.Tn NIS 47is an RPC-based service designed to allow a number of UNIX-based 48machines to share a common set of configuration files. 49Rather than 50requiring a system administrator to update several copies of files 51such as 52.Pa /etc/hosts , 53.Pa /etc/passwd 54and 55.Pa /etc/group , 56which tend to require frequent changes in most environments, 57.Tn NIS 58allows groups of computers to share one set of data which can be 59updated from a single location. 60.Pp 61The 62.Nm 63utility is the server that distributes 64.Tn NIS 65databases to client systems within an 66.Tn NIS 67.Em domain . 68Each client in an 69.Tn NIS 70domain must have its domainname set to 71one of the domains served by 72.Nm 73using the 74.Xr domainname 1 75command. 76The clients must also run 77.Xr ypbind 8 78in order to attach to a particular server, since it is possible to 79have several servers within a single 80.Tn NIS 81domain. 82.Pp 83The databases distributed by 84.Nm 85are stored in 86.Pa /var/yp/[domainname] 87where 88.Pa domainname 89is the name of the domain being served. 90There can be several 91such directories with different domainnames, and you need only one 92.Nm 93daemon to handle them all. 94.Pp 95The databases, or 96.Pa maps 97as they are often called, 98are created by 99.Pa /var/yp/Makefile 100using several system files as source. 101The database files are in 102.Xr db 3 103format to help speed retrieval when there are many records involved. 104In 105.Fx , 106the maps are always readable and writable only by root for security 107reasons. 108Technically this is only necessary for the password 109maps, but since the data in the other maps can be found in 110other world-readable files anyway, it does not hurt and it is considered 111good general practice. 112.Pp 113The 114.Nm 115utility is started by 116.Pa /etc/rc.d/ypserv 117if it has been enabled in 118.Pa /etc/rc.conf . 119.Sh SPECIAL FEATURES 120There are some problems associated with distributing a 121.Fx 122password 123database via 124.Tn NIS : 125.Fx 126normally only stores encrypted passwords 127in 128.Pa /etc/master.passwd , 129which is readable and writable only by root. 130By turning this file 131into an 132.Tn NIS 133map, this security feature would be completely defeated. 134.Pp 135To make up for this, the 136.Fx 137version of 138.Nm 139handles the 140.Pa master.passwd.byname 141and 142.Pa master.passwd.byuid 143maps in a special way. 144When the server receives a request to access 145either of these two maps, it will check the TCP port from which the 146request originated and return an error if the port number is greater 147than 1023. 148Since only the superuser is allowed to bind to TCP ports 149with values less than 1024, the server can use this test to determine 150whether or not the access request came from a privileged user. 151Any requests made by non-privileged users are therefore rejected. 152.Pp 153Furthermore, the 154.Xr getpwent 3 155routines in the 156.Fx 157standard C library will only attempt to retrieve 158data from the 159.Pa master.passwd.byname 160and 161.Pa master.passwd.byuid 162maps for the superuser: if a normal user calls any of these functions, 163the standard 164.Pa passwd.byname 165and 166.Pa passwd.byuid 167maps will be accessed instead. 168The latter two maps are constructed by 169.Pa /var/yp/Makefile 170by parsing the 171.Pa master.passwd 172file and stripping out the password fields, and are therefore 173safe to pass on to unprivileged users. 174In this way, the shadow password 175aspect of the protected 176.Pa master.passwd 177database is maintained through 178.Tn NIS . 179.Sh NOTES 180.Ss Setting Up Master and Slave Servers 181.Xr ypinit 8 182is a convenient script that will help setup master and slave 183.Tn NIS 184servers. 185.Ss Limitations 186There are two problems inherent with password shadowing in 187.Tn NIS 188that users should 189be aware of: 190.Bl -enum -offset indent 191.It 192The 193.Sq TCP port less than 1024 194test is trivial to defeat for users with 195unrestricted access to machines on your network (even those machines 196which do not run UNIX-based operating systems). 197.It 198If you plan to use a 199.Fx 200system to serve 201.No non- Ns Fx 202clients that 203have no support for password shadowing (which is most of them), you 204will have to disable the password shadowing entirely by uncommenting the 205.Em UNSECURE=True 206entry in 207.Pa /var/yp/Makefile . 208This will cause the standard 209.Pa passwd.byname 210and 211.Pa passwd.byuid 212maps to be generated with valid encrypted password fields, which is 213necessary in order for 214.No non- Ns Fx 215clients to perform user 216authentication through 217.Tn NIS . 218.El 219.Pp 220.Ss Security 221In general, any remote user can issue an RPC to 222.Nm 223and retrieve the contents of your 224.Tn NIS 225maps, provided the remote user 226knows your domain name. 227To prevent such unauthorized transactions, 228.Nm 229supports a feature called 230.Pa securenets 231which can be used to restrict access to a given set of hosts. 232At startup, 233.Nm 234will attempt to load the securenets information from a file 235called 236.Pa /var/yp/securenets . 237(Note that this path varies depending on the path specified with 238the 239.Fl p 240option, which is explained below.) 241This file contains entries 242that consist of a network specification and a network mask separated 243by white space. 244Lines starting with 245.Dq \&# 246are considered to be comments. 247A 248sample securenets file might look like this: 249.Bd -unfilled -offset indent 250# allow connections from local host -- mandatory 251127.0.0.1 255.255.255.255 252# allow connections from any host 253# on the 192.168.128.0 network 254192.168.128.0 255.255.255.0 255# allow connections from any host 256# between 10.0.0.0 to 10.0.15.255 25710.0.0.0 255.255.240.0 258.Ed 259.Pp 260If 261.Nm 262receives a request from an address that matches one of these rules, 263it will process the request normally. 264If the address fails to match 265a rule, the request will be ignored and a warning message will be 266logged. 267If the 268.Pa /var/yp/securenets 269file does not exist, 270.Nm 271will allow connections from any host. 272.Pp 273The 274.Nm 275utility also has support for Wietse Venema's 276.Em tcpwrapper 277package. 278This allows the administrator to use the tcpwrapper 279configuration files 280.Pa ( /etc/hosts.allow 281and 282.Pa /etc/hosts.deny ) 283for access control instead of 284.Pa /var/yp/securenets . 285.Pp 286Note: while both of these access control mechanisms provide some 287security, they, like the privileged port test, are both vulnerable 288to 289.Dq IP spoofing 290attacks. 291.Pp 292.Ss NIS v1 compatibility 293This version of 294.Nm 295has some support for serving 296.Tn NIS 297v1 clients. 298The 299.Fx 300.Tn NIS 301implementation only uses the 302.Tn NIS 303v2 protocol, however other implementations 304include support for the v1 protocol for backwards compatibility 305with older systems. 306The 307.Xr ypbind 8 308daemons supplied with these systems will try to establish a binding 309to an 310.Tn NIS 311v1 server even though they may never actually need it (and they may 312persist in broadcasting in search of one even after they receive a 313response from a v2 server). 314Note that while 315support for normal client calls is provided, this version of 316.Nm 317does not handle v1 map transfer requests; consequently, it cannot 318be used as a master or slave in conjunction with older 319.Tn NIS 320servers that 321only support the v1 protocol. 322Fortunately, there probably are not any 323such servers still in use today. 324.Ss NIS servers that are also NIS clients 325Care must be taken when running 326.Nm 327in a multi-server domain where the server machines are also 328.Tn NIS 329clients. 330It is generally a good idea to force the servers to 331bind to themselves rather than allowing them to broadcast bind 332requests and possibly become bound to each other: strange failure 333modes can result if one server goes down and 334others are dependent upon on it. 335(Eventually all the clients will 336time out and attempt to bind to other servers, but the delay 337involved can be considerable and the failure mode is still present 338since the servers might bind to each other all over again). 339.Pp 340Refer to the 341.Xr ypbind 8 342man page for details on how to force it to bind to a particular 343server. 344.Sh OPTIONS 345The following options are supported by 346.Nm : 347.Bl -tag -width flag 348.It Fl n 349This option affects the way 350.Nm 351handles yp_match requests for the 352.Pa hosts.byname 353and 354.Pa hosts.byaddress 355maps. 356By default, if 357.Nm 358cannot find an entry for a given host in its hosts maps, it will 359return an error and perform no further processing. 360With the 361.Fl n 362flag, 363.Nm 364will go one step further: rather than giving up immediately, it 365will try to resolve the hostname or address using a DNS nameserver 366query. 367If the query is successful, 368.Nm 369will construct a fake database record and return it to the client, 370thereby making it seem as though the client's yp_match request 371succeeded. 372.Pp 373This feature is provided for compatibility with SunOS 4.1.x, 374which has brain-damaged resolver functions in its standard C 375library that depend on 376.Tn NIS 377for hostname and address resolution. 378The 379.Fx 380resolver can be configured to do DNS 381queries directly, therefore it is not necessary to enable this 382option when serving only 383.Fx 384.Tn NIS 385clients. 386.It Fl d 387Cause the server to run in debugging mode. 388Normally, 389.Nm 390reports only unusual errors (access violations, file access failures) 391using the 392.Xr syslog 3 393facility. 394In debug mode, the server does not background 395itself and prints extra status messages to stderr for each 396request that it receives. 397Also, while running in debug mode, 398.Nm 399will not spawn any additional subprocesses as it normally does 400when handling yp_all requests or doing DNS lookups. 401(These actions 402often take a fair amount of time to complete and are therefore handled 403in subprocesses, allowing the parent server process to go on handling 404other requests.) 405This makes it easier to trace the server with 406a debugging tool. 407.It Fl P Ar port 408Force ypserv to bind to a specific TCP/UDP port, rather than selecting 409its own. 410.It Fl p Ar path 411Normally, 412.Nm 413assumes that all 414.Tn NIS 415maps are stored under 416.Pa /var/yp . 417The 418.Fl p 419flag may be used to specify an alternate 420.Tn NIS 421root path, allowing 422the system administrator to move the map files to a different place 423within the file system. 424.El 425.Sh FILES 426.Bl -tag -width Pa -compact 427.It Pa /var/yp/[domainname]/[maps] 428the 429.Tn NIS 430maps 431.It Pa /etc/nsswitch.conf 432name switch configuration file 433.It Pa /var/yp/securenets 434host access control file 435.El 436.Sh SEE ALSO 437.Xr ypcat 1 , 438.Xr db 3 , 439.Xr hosts_access 5 , 440.Xr rpc.yppasswdd 8 , 441.Xr yp 8 , 442.Xr ypbind 8 , 443.Xr ypinit 8 , 444.Xr yppush 8 , 445.Xr ypxfr 8 446.Sh HISTORY 447This version of 448.Nm 449first appeared in 450.Fx 2.2 . 451.Sh AUTHORS 452.An Bill Paul Aq wpaul@ctr.columbia.edu 453