29.4. 網路資訊系統 (NIS)
前一頁 | 章 29. 網路伺服器 | 下一頁

## 29.4. 網路資訊系統 (NIS)

Network Information System (NIS) is designed to centralize administration of UNIX®-like systems such as Solaris™, HP-UX, AIX®, Linux, NetBSD, OpenBSD, and FreeBSD. NIS was originally known as Yellow Pages but the name was changed due to trademark issues. This is the reason why NIS commands begin with `yp`.

NIS is a Remote Procedure Call (RPC)-based client/server system that allows a group of machines within an NIS domain to share a common set of configuration files. This permits a system administrator to set up NIS client systems with only minimal configuration data and to add, remove, or modify configuration data from a single location.

FreeBSD uses version 2 of the NIS protocol.

### 29.4.1. NIS 術語與程序

Table 28.1 summarizes the terms and important processes used by NIS:

表格 29.1. NIS 術語

術語 | 說明
--- | ---
NIS domain name | NIS servers and clients share an NIS domain name. Typically, this name does not have anything to do with DNS.
rpcbind(8) | This service enables RPC and must be running in order to run an NIS server or act as an NIS client.
ypbind(8) | This service binds an NIS client to its NIS server. It will take the NIS domain name and use RPC to connect to the server. It is the core of client/server communication in an NIS environment. If this service is not running on a client machine, it will not be able to access the NIS server.
ypserv(8) | This is the process for the NIS server. If this service stops running, the server will no longer be able to respond to NIS requests so hopefully, there is a slave server to take over. Some non-FreeBSD clients will not try to reconnect using a slave server and the ypbind process may need to be restarted on these clients.
rpc.yppasswdd(8) | This process only runs on NIS master servers. This daemon allows NIS clients to change their NIS passwords. If this daemon is not running, users will have to login to the NIS master server and change their passwords there.

### 29.4.2. 主機類型

There are three types of hosts in an NIS environment:

- NIS master server

  This server acts as a central repository for host configuration information and maintains the authoritative copy of the files used by all of the NIS clients. The `passwd`, `group`, and other various files used by NIS clients are stored on the master server. While it is possible for one machine to be an NIS master server for more than one NIS domain, this type of configuration will not be covered in this chapter as it assumes a relatively small-scale NIS environment.

- NIS slave servers

  NIS slave servers maintain copies of the NIS master's data files in order to provide redundancy. Slave servers also help to balance the load of the master server as NIS clients always attach to the NIS server which responds first.

- NIS clients

  NIS clients authenticate against the NIS server during log on.

Information in many files can be shared using NIS. The `master.passwd`, `group`, and `hosts` files are commonly shared via NIS. Whenever a process on a client needs information that would normally be found in these files locally, it makes a query to the NIS server that it is bound to instead.

### 29.4.3. 規劃注意事項

This section describes a sample NIS environment which consists of 15 FreeBSD machines with no centralized point of administration. Each machine has its own `/etc/passwd` and `/etc/master.passwd`. These files are kept in sync with each other only through manual intervention. Currently, when a user is added to the lab, the process must be repeated on all 15 machines.

The configuration of the lab will be as follows:

Machine name | IP 位址 | Machine role
--- | --- | ---
`ellington` | `10.0.0.2` | NIS master
`coltrane` | `10.0.0.3` | NIS slave
`basie` | `10.0.0.4` | Faculty workstation
`bird` | `10.0.0.5` | Client machine
`cli[1-11]` | `10.0.0.[6-17]` | Other client machines

If this is the first time an NIS scheme is being developed, it should be thoroughly planned ahead of time. Regardless of network size, several decisions need to be made as part of the planning process.

#### 29.4.3.1. 選擇 NIS 網域名稱

When a client broadcasts its requests for info, it includes the name of the NIS domain that it is part of. This is how multiple servers on one network can tell which server should answer which request. Think of the NIS domain name as the name for a group of hosts.

Some organizations choose to use their Internet domain name for their NIS domain name. This is not recommended as it can cause confusion when trying to debug network problems. The NIS domain name should be unique within the network and it is helpful if it describes the group of machines it represents. For example, the Art department at Acme Inc. might be in the “acme-art” NIS domain. This example will use the domain name `test-domain`.

However, some non-FreeBSD operating systems require the NIS domain name to be the same as the Internet domain name. If one or more machines on the network have this restriction, the Internet domain name must be used as the NIS domain name.

#### 29.4.3.2. 實體伺服器需求

There are several things to keep in mind when choosing a machine to use as a NIS server. Since NIS clients depend upon the availability of the server, choose a machine that is not rebooted frequently. The NIS server should ideally be a stand alone machine whose sole purpose is to be an NIS server. If the network is not heavily used, it is acceptable to put the NIS server on a machine running other services. However, if the NIS server becomes unavailable, it will adversely affect all NIS clients.

### 29.4.4. 設定 NIS Master 伺服器

The canonical copies of all NIS files are stored on the master server. The databases used to store the information are called NIS maps. In FreeBSD, these maps are stored in `/var/yp/[domainname]` where `[domainname]` is the name of the NIS domain. Since multiple domains are supported, it is possible to have several directories, one for each domain. Each domain will have its own independent set of maps.

NIS master and slave servers handle all NIS requests through ypserv(8). This daemon is responsible for receiving incoming requests from 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.

Setting up a master NIS server can be relatively straight forward, depending on environmental needs. Since FreeBSD provides built-in NIS support, it only needs to be enabled by adding the following lines to `/etc/rc.conf`:

    nisdomainname="test-domain"
    nis_server_enable="YES"
    nis_yppasswdd_enable="YES"

| This line sets the NIS domain name to `test-domain`.
| This automates the start up of the NIS server processes when the system boots.
| This enables the rpc.yppasswdd(8) daemon so that users can change their NIS password from a client machine.

Care must be taken in a multi-server domain where the server machines are also NIS clients. It is generally a good idea to force the servers to bind to themselves rather than allowing them to broadcast bind requests and possibly become bound to each other. Strange failure modes can result if one server goes down and others are dependent upon it. Eventually, all the clients will time out and attempt to bind to other servers, but the delay involved can be considerable and the failure mode is still present since the servers might bind to each other all over again.

A server that is also a client can be forced to bind to a particular server by adding these additional lines to `/etc/rc.conf`:

    nis_client_enable="YES" # run client stuff as well
    nis_client_flags="-S NIS domain,server"

After saving the edits, type `/etc/netstart` to restart the network and apply the values defined in `/etc/rc.conf`. Before initializing the NIS maps, start ypserv(8):

    # service ypserv start

#### 29.4.4.1. 初始化 NIS 對應表

NIS maps are generated from the configuration files in `/etc` on the NIS master, with one exception: `/etc/master.passwd`. This is to prevent the propagation of passwords to all the servers in the NIS domain. Therefore, before the NIS maps are initialized, configure the primary password files:

    # cp /etc/master.passwd /var/yp/master.passwd
    # cd /var/yp
    # vi master.passwd

It is advisable to remove all entries for system accounts as well as any user accounts that do not need to be propagated to the NIS clients, such as the `root` and any other administrative accounts.

### 注意:

Ensure that the `/var/yp/master.passwd` is neither group or world readable by setting its permissions to `600`.

After completing this task, initialize the NIS maps. FreeBSD includes the ypinit(8) script to do this. When generating maps for the master server, include `-m` and specify the NIS domain name:

    ellington# ypinit -m test-domain
    Server Type: MASTER Domain: test-domain
    Creating an YP server will require that you answer a few questions.
    Questions will all be asked at the beginning of the procedure.
    Do you want this procedure to quit on non-fatal errors? [y/n: n] n
    Ok, please remember to go back and redo manually whatever fails.
    If not, something might not work.
    At this point, we have to construct a list of this domains YP servers.
    rod.darktech.org is already known as master server.
    Please continue to add any slave servers, one per line. When you are
    done with the list, type a <control D>.
    master server   :  ellington
    next host to add:  coltrane
    next host to add:  ^D
    The current list of NIS servers looks like this:
    ellington
    coltrane
    Is this correct?  [y/n: y] y

    [..output from map generation..]

    NIS Map update completed.
    ellington has been setup as an YP master server without any errors.

This will create `/var/yp/Makefile` from `/var/yp/Makefile.dist`. By default, this file assumes that the environment has a single NIS server with only FreeBSD clients. Since `test-domain` has a slave server, edit this line in `/var/yp/Makefile` so that it begins with a comment (`#`):

    NOPUSH = "True"

#### 29.4.4.2. 新增使用者

Every time a new user is created, the user account must be added to the master NIS server and the NIS maps rebuilt. Until this occurs, the new user will not be able to login anywhere except on the NIS master. For example, to add the new user `jsmith` to the `test-domain` domain, run these commands on the master server:

    # pw useradd jsmith
    # cd /var/yp
    # make test-domain

The user could also be added using `adduser jsmith` instead of `pw useradd smith`.

### 29.4.5. 設定 NIS Slave 伺服器

To set up an NIS slave server, log on to the slave server and edit `/etc/rc.conf` as for the master server. Do not generate any NIS maps, as these already exist on the master server. When running `ypinit` on the slave server, use `-s` (for slave) instead of `-m` (for master). This option requires the name of the NIS master in addition to the domain name, as seen in this example:

    coltrane# ypinit -s ellington test-domain

    Server Type: SLAVE Domain: test-domain Master: ellington

    Creating an YP server will require that you answer a few questions.
    Questions will all be asked at the beginning of the procedure.

    Do you want this procedure to quit on non-fatal errors? [y/n: n]  n

    Ok, please remember to go back and redo manually whatever fails.
    If not, something might not work.
    There will be no further questions. The remainder of the procedure
    should take a few minutes, to copy the databases from ellington.
    Transferring netgroup...
    ypxfr: Exiting: Map successfully transferred
    Transferring netgroup.byuser...
    ypxfr: Exiting: Map successfully transferred
    Transferring netgroup.byhost...
    ypxfr: Exiting: Map successfully transferred
    Transferring master.passwd.byuid...
    ypxfr: Exiting: Map successfully transferred
    Transferring passwd.byuid...
    ypxfr: Exiting: Map successfully transferred
    Transferring passwd.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring group.bygid...
    ypxfr: Exiting: Map successfully transferred
    Transferring group.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring services.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring rpc.bynumber...
    ypxfr: Exiting: Map successfully transferred
    Transferring rpc.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring protocols.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring master.passwd.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring networks.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring networks.byaddr...
    ypxfr: Exiting: Map successfully transferred
    Transferring netid.byname...
    ypxfr: Exiting: Map successfully transferred
    Transferring hosts.byaddr...
    ypxfr: Exiting: Map successfully transferred
    Transferring protocols.bynumber...
    ypxfr: Exiting: Map successfully transferred
    Transferring ypservers...
    ypxfr: Exiting: Map successfully transferred
    Transferring hosts.byname...
    ypxfr: Exiting: Map successfully transferred

    coltrane has been setup as an YP slave server without any errors.
    Remember to update map ypservers on ellington.

This will generate a directory on the slave server called `/var/yp/test-domain` which contains copies of the NIS master server's maps. Adding these `/etc/crontab` entries on each slave server will force the slaves to sync their maps with the maps on the master server:

    20      *       *       *       *       root   /usr/libexec/ypxfr passwd.byname
    21      *       *       *       *       root   /usr/libexec/ypxfr passwd.byuid

These entries are not mandatory because the master server automatically attempts to push any map changes to its slaves. However, since clients may depend upon the slave server to provide correct password information, it is recommended to force frequent password map updates. This is especially important on busy networks where map updates might not always complete.

To finish the configuration, run `/etc/netstart` on the slave server in order to start the NIS services.

### 29.4.6. 設定 NIS 客戶端

An NIS client binds to an NIS server using ypbind(8). This daemon broadcasts RPC requests on the local network. These requests specify the domain name configured on the client. If an NIS server in the same domain receives one of the broadcasts, it will respond to ypbind, which will record the server's address. If there are several servers available, the client will use the address of the first server to respond and will direct all of its NIS requests to that server. The client will automatically ping the server on a regular basis to make sure it is still available. If it fails to receive a reply within a reasonable amount of time, ypbind will mark the domain as unbound and begin broadcasting again in the hopes of locating another server.

To configure a FreeBSD machine to be an NIS client:

1. Edit `/etc/rc.conf` and add the following lines in order to set the NIS domain name and start ypbind(8) during network startup:

       nisdomainname="test-domain"
       nis_client_enable="YES"

2. To import all possible password entries from the NIS server, use `vipw` to remove all user accounts except one from `/etc/master.passwd`. When removing the accounts, keep in mind that at least one local account should remain and this account should be a member of `wheel`. If there is a problem with NIS, this local account can be used to log in remotely, become the superuser, and fix the problem. Before saving the edits, add the following line to the end of the file:

       +:::::::::

   This line configures the client to provide anyone with a valid account in the NIS server's password maps an account on the client. There are many ways to configure the NIS client by modifying this line. One method is described in 節 29.4.8, “使用 Netgroups”. For more detailed reading, refer to the book `Managing NFS and NIS`, published by O'Reilly Media.

3. To import all possible group entries from the NIS server, add this line to `/etc/group`:

       +:*::

To start the NIS client immediately, execute the following commands as the superuser:

    # /etc/netstart
    # service ypbind start

After completing these steps, running `ypcat passwd` on the client should show the server's `passwd` map.

### 29.4.7. NIS 安全性

Since RPC is a broadcast-based service, any system running ypbind within the same domain can retrieve the contents of the NIS maps. To prevent unauthorized transactions, ypserv(8) supports a feature called “securenets” which can be used to restrict access to a given set of hosts. By default, this information is stored in `/var/yp/securenets`, unless ypserv(8) is started with `-p` and an alternate path. This file contains entries that consist of a network specification and a network mask separated by white space. Lines starting with `#` are considered to be comments. A sample `securenets` might look like this:

    # allow connections from local host -- mandatory
    127.0.0.1     255.255.255.255
    # allow connections from any host
    # on the 192.168.128.0 network
    192.168.128.0 255.255.255.0
    # allow connections from any host
    # between 10.0.0.0 to 10.0.15.255
    # this includes the machines in the testlab
    10.0.0.0      255.255.240.0

If ypserv(8) receives a request from an address that matches one of these rules, it will process the request normally. If the address fails to match a rule, the request will be ignored and a warning message will be logged. If the `securenets` does not exist, `ypserv` will allow connections from any host.

節 13.4, “TCP Wrapper” is an alternate mechanism for providing access control instead of `securenets`. While either access control mechanism adds some security, they are both vulnerable to “IP spoofing” attacks. All NIS-related traffic should be blocked at the firewall.

Servers using `securenets` may fail to serve legitimate NIS clients with archaic TCP/IP implementations. Some of these implementations set all host bits to zero when doing broadcasts or fail to observe the subnet mask when calculating the broadcast address. While some of these problems can be fixed by changing the client configuration, other problems may force the retirement of these client systems or the abandonment of `securenets`.

The use of TCP Wrapper increases the latency of the NIS server. The additional delay may be long enough to cause timeouts in client programs, especially in busy networks with slow NIS servers. If one or more clients suffer from latency, convert those clients into NIS slave servers and force them to bind to themselves.

#### 29.4.7.1. 阻擋部份使用者

In this example, the `basie` system is a faculty workstation within the NIS domain. The `passwd` map on the master NIS server contains accounts for both faculty and students. This section demonstrates how to allow faculty logins on this system while refusing student logins.

To prevent specified users from logging on to a system, even if they are present in the NIS database, use `vipw` to add `-`username`` with the correct number of colons towards the end of `/etc/master.passwd` on the client, where `username` is the username of a user to bar from logging in. The line with the blocked user must be before the `+` line that allows NIS users. In this example, `bill` is barred from logging on to `basie`:

    basie# cat /etc/master.passwd
    root:[password]:0:0::0:0:The super-user:/root:/bin/csh
    toor:[password]:0:0::0:0:The other super-user:/root:/bin/sh
    daemon:*:1:1::0:0:Owner of many system processes:/root:/sbin/nologin
    operator:*:2:5::0:0:System &:/:/sbin/nologin
    bin:*:3:7::0:0:Binaries Commands and Source,,,:/:/sbin/nologin
    tty:*:4:65533::0:0:Tty Sandbox:/:/sbin/nologin
    kmem:*:5:65533::0:0:KMem Sandbox:/:/sbin/nologin
    games:*:7:13::0:0:Games pseudo-user:/usr/games:/sbin/nologin
    news:*:8:8::0:0:News Subsystem:/:/sbin/nologin
    man:*:9:9::0:0:Mister Man Pages:/usr/share/man:/sbin/nologin
    bind:*:53:53::0:0:Bind Sandbox:/:/sbin/nologin
    uucp:*:66:66::0:0:UUCP pseudo-user:/var/spool/uucppublic:/usr/libexec/uucp/uucico
    xten:*:67:67::0:0:X-10 daemon:/usr/local/xten:/sbin/nologin
    pop:*:68:6::0:0:Post Office Owner:/nonexistent:/sbin/nologin
    nobody:*:65534:65534::0:0:Unprivileged user:/nonexistent:/sbin/nologin
    -bill:::::::::
    +:::::::::

    basie#

### 29.4.8. 使用 Netgroups

Barring specified users from logging on to individual systems becomes unscaleable on larger networks and quickly loses the main benefit of NIS: centralized administration.

Netgroups were developed to handle large, complex networks with hundreds of users and machines. Their use is comparable to UNIX® groups, where the main difference is the lack of a numeric ID and the ability to define a netgroup by including both user accounts and other netgroups.

To expand on the example used in this chapter, the NIS domain will be extended to add the users and systems shown in Tables 28.2 and 28.3:

表格 29.2. 其他使用者

使用者名稱 | 說明
--- | ---
`alpha`, `beta` | IT department employees
`charlie`, `delta` | IT department apprentices
`echo`, `foxtrott`, `golf`, ... | employees
`able`, `baker`, ... | interns

表格 29.3. 其他系統

機器名稱 | 說明
--- | ---
`war`, `death`, `famine`, `pollution` | Only IT employees are allowed to log onto these servers.
`pride`, `greed`, `envy`, `wrath`, `lust`, `sloth` | All members of the IT department are allowed to login onto these servers.
`one`, `two`, `three`, `four`, ... | Ordinary workstations used by employees.
`trashcan` | A very old machine without any critical data. Even interns are allowed to use this system.

When using netgroups to configure this scenario, each user is assigned to one or more netgroups and logins are then allowed or forbidden for all members of the netgroup. When adding a new machine, login restrictions must be defined for all netgroups. When a new user is added, the account must be added to one or more netgroups. If the NIS setup is planned carefully, only one central configuration file needs modification to grant or deny access to machines.

The first step is the initialization of the NIS `netgroup` map. In FreeBSD, this map is not created by default. On the NIS master server, use an editor to create a map named `/var/yp/netgroup`.

This example creates four netgroups to represent IT employees, IT apprentices, employees, and interns:

    IT_EMP  (,alpha,test-domain)    (,beta,test-domain)
    IT_APP  (,charlie,test-domain)  (,delta,test-domain)
    USERS   (,echo,test-domain)     (,foxtrott,test-domain) \
            (,golf,test-domain)
    INTERNS (,able,test-domain)     (,baker,test-domain)

Each entry configures a netgroup. The first column in an entry is the name of the netgroup. Each set of brackets represents either a group of one or more users or the name of another netgroup. When specifying a user, the three comma-delimited fields inside each group represent:

1. The name of the host(s) where the other fields representing the user are valid. If a hostname is not specified, the entry is valid on all hosts.

2. The name of the account that belongs to this netgroup.

3. The NIS domain for the account. Accounts may be imported from other NIS domains into a netgroup.

If a group contains multiple users, separate each user with whitespace. Additionally, each field may contain wildcards. See netgroup(5) for details.

Netgroup names longer than 8 characters should not be used. The names are case sensitive and using capital letters for netgroup names is an easy way to distinguish between user, machine and netgroup names.

Some non-FreeBSD NIS clients cannot handle netgroups containing more than 15 entries. This limit may be circumvented by creating several sub-netgroups with 15 users or fewer and a real netgroup consisting of the sub-netgroups, as seen in this example:

    BIGGRP1  (,joe1,domain)  (,joe2,domain)  (,joe3,domain) [...]
    BIGGRP2  (,joe16,domain)  (,joe17,domain) [...]
    BIGGRP3  (,joe31,domain)  (,joe32,domain)
    BIGGROUP  BIGGRP1 BIGGRP2 BIGGRP3

Repeat this process if more than 225 (15 times 15) users exist within a single netgroup.

To activate and distribute the new NIS map:

    ellington# cd /var/yp
    ellington# make

This will generate the three NIS maps `netgroup`, `netgroup.byhost` and `netgroup.byuser`. Use the map key option of ypcat(1) to check if the new NIS maps are available:

    ellington% ypcat -k netgroup
    ellington% ypcat -k netgroup.byhost
    ellington% ypcat -k netgroup.byuser

The output of the first command should resemble the contents of `/var/yp/netgroup`. The second command only produces output if host-specific netgroups were created. The third command is used to get the list of netgroups for a user.

To configure a client, use vipw(8) to specify the name of the netgroup. For example, on the server named `war`, replace this line:

    +:::::::::

with

    +@IT_EMP:::::::::

This specifies that only the users defined in the netgroup `IT_EMP` will be imported into this system's password database and only those users are allowed to login to this system.

This configuration also applies to the `~` function of the shell and all routines which convert between user names and numerical user IDs. In other words, `cd ~`user`` will not work, `ls -l` will show the numerical ID instead of the username, and `find . -user joe -print` will fail with the message No such user. To fix this, import all user entries without allowing them to login into the servers. This can be achieved by adding an extra line:

    +:::::::::/sbin/nologin

This line configures the client to import all entries but to replace the shell in those entries with `/sbin/nologin`.

Make sure that extra line is placed after `+@IT_EMP:::::::::`. Otherwise, all user accounts imported from NIS will have `/sbin/nologin` as their login shell and no one will be able to login to the system.

To configure the less important servers, replace the old `+:::::::::` on the servers with these lines:

    +@IT_EMP:::::::::
    +@IT_APP:::::::::
    +:::::::::/sbin/nologin

The corresponding lines for the workstations would be:

    +@IT_EMP:::::::::
    +@USERS:::::::::
    +:::::::::/sbin/nologin

NIS supports the creation of netgroups from other netgroups which can be useful if the policy regarding user access changes. One possibility is the creation of role-based netgroups. For example, one might create a netgroup called `BIGSRV` to define the login restrictions for the important servers, another netgroup called `SMALLSRV` for the less important servers, and a third netgroup called `USERBOX` for the workstations. Each of these netgroups contains the netgroups that are allowed to login onto these machines. The new entries for the NIS `netgroup` map would look like this:

    BIGSRV    IT_EMP  IT_APP
    SMALLSRV  IT_EMP  IT_APP  ITINTERN
    USERBOX   IT_EMP  ITINTERN USERS

This method of defining login restrictions works reasonably well when it is possible to define groups of machines with identical restrictions. Unfortunately, this is the exception and not the rule. Most of the time, the ability to define login restrictions on a per-machine basis is required.

Machine-specific netgroup definitions are another possibility to deal with the policy changes. In this scenario, the `/etc/master.passwd` of each system contains two lines starting with “+”. The first line adds a netgroup with the accounts allowed to login onto this machine and the second line adds all other accounts with `/sbin/nologin` as shell. It is recommended to use the “ALL-CAPS” version of the hostname as the name of the netgroup:

    +@BOXNAME:::::::::
    +:::::::::/sbin/nologin

Once this task is completed on all the machines, there is no longer a need to modify the local versions of `/etc/master.passwd` ever again. All further changes can be handled by modifying the NIS map. Here is an example of a possible `netgroup` map for this scenario:

    # Define groups of users first
    IT_EMP    (,alpha,test-domain)    (,beta,test-domain)
    IT_APP    (,charlie,test-domain)  (,delta,test-domain)
    DEPT1     (,echo,test-domain)     (,foxtrott,test-domain)
    DEPT2     (,golf,test-domain)     (,hotel,test-domain)
    DEPT3     (,india,test-domain)    (,juliet,test-domain)
    ITINTERN  (,kilo,test-domain)     (,lima,test-domain)
    D_INTERNS (,able,test-domain)     (,baker,test-domain)
    #
    # Now, define some groups based on roles
    USERS     DEPT1   DEPT2     DEPT3
    BIGSRV    IT_EMP  IT_APP
    SMALLSRV  IT_EMP  IT_APP    ITINTERN
    USERBOX   IT_EMP  ITINTERN  USERS
    #
    # And a groups for a special tasks
    # Allow echo and golf to access our anti-virus-machine
    SECURITY  IT_EMP  (,echo,test-domain)  (,golf,test-domain)
    #
    # machine-based netgroups
    # Our main servers
    WAR       BIGSRV
    FAMINE    BIGSRV
    # User india needs access to this server
    POLLUTION  BIGSRV  (,india,test-domain)
    #
    # This one is really important and needs more access restrictions
    DEATH     IT_EMP
    #
    # The anti-virus-machine mentioned above
    ONE       SECURITY
    #
    # Restrict a machine to a single user
    TWO       (,hotel,test-domain)
    # [...more groups to follow]

It may not always be advisable to use machine-based netgroups. When deploying a couple of dozen or hundreds of systems, role-based netgroups instead of machine-based netgroups may be used to keep the size of the NIS map within reasonable limits.

### 29.4.9. 密碼格式

NIS requires that all hosts within an NIS domain use the same format for encrypting passwords. If users have trouble authenticating on an NIS client, it may be due to a differing password format. In a heterogeneous network, the format must be supported by all operating systems, where DES is the lowest common standard.

To check which format a server or client is using, look at this section of `/etc/login.conf`:

    default:\
    	:passwd_format=des:\
    	:copyright=/etc/COPYRIGHT:\
    	[Further entries elided]

In this example, the system is using the DES format. Other possible values are `blf` for Blowfish and `md5` for MD5 encrypted passwords.

If the format on a host needs to be edited to match the one being used in the NIS domain, the login capability database must be rebuilt after saving the change:

    # cap_mkdb /etc/login.conf

### 注意:

The format of passwords for existing user accounts will not be updated until each user changes their password after the login capability database is rebuilt.

前一頁 | 上一層 | 下一頁
29.3. 網路檔案系統 (NFS) | 起始頁 | 29.5. 輕量級目錄存取協定 (LDAP)

本文及其他文件，可由此下載： ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/。

若有 FreeBSD 方面疑問，請先閱讀 FreeBSD 相關文件，如不能解決的話，再洽詢 <questions@FreeBSD.org>。
關於本文件的問題，請洽詢 <doc@FreeBSD.org>。