nsswitch.conf 中文man页面-nsswitch.conf

NAME

nsswitch.conf - 系统数据库及名字服务开关配置文件

DESCRIPTION

C 程序库里很多函数都需要配置以便能在本地环境正常工作, 习惯上是使用文件(例如`/etc/passwd') 来完成这一任务. 但别的名字服务, 如网络信息服务NIS, 还有域名服务DNS等, 逐渐通用起来, 并且被加入了C 程序库里, 而它们使用的是固定的搜索顺序.

在有NYS 支持的Linux libc5以及GNU C Library 2.x (libc.so.6)里, 依靠一个更清晰完整的方案来解决该问题. 该方案模仿了Sun Microsystems公司在Solaris 2 的C 程序库里的方法, 也沿袭了它们的命名, 称为 "名字服务开关(NSS)". 所用 "数据库" 及其查找顺序在文件 /etc/nsswitch.conf 里指明.

NSS 中可用数据库如下:

: aliases 邮件别名, sendmail(8) 使用该文件.
: ethers 以太网号.
: group 用户组, getgrent(3) 函数使用该文件.
: hosts 主机名和主机号, gethostbyname(3) 以及类似的函数使用了该文件.
: netgroup 网络内主机及其用户的列表, 访问规则使用该文件.
: network 网络名及网络号, getnetent(3) 函数使用该文件.
: passwd 用户口令, getpwent(3) 函数使用该文件.
: protocols 网络协议, getprotoent(3) 函数使用该文件.
: publickey NIS+及NFS 所使用的secure_rpc的公开密匙.
: rpc
远程过程调用名及调用号, getrpcbyname(3) 及类似函数使用该文件.
: services 网络服务, getservent(3) 函数使用该文件.
: shadow shadow用户口令, getspnam(3) 函数使用该文件.

下面是

/etc/nsswitch.conf 文件的一个例子 (如果在系统中没有 /etc/nsswitch.conf 文件的话, 这就是缺省的设置):

: passwd:
compat
: group:
compat
: shadow:
compat
: hosts:
dns [!UNAVAIL=return] files
: networks:
nis [NOTFOUND=return] files
: ethers:
nis [NOTFOUND=return] files
: protocols:
nis [NOTFOUND=return] files
: rpc:
nis [NOTFOUND=return] files
: services:
nis [NOTFOUND=return] files

第一栏就是上面的表里所说的数据库, 每行的其余部分指明如何查找. 对每个数据库都可以分别指明其查找方法.

每个数据库的配置规范包含两个不同的项:

: * 服务规范, 如`files', `db', 或者`nis'.
: * 对查找结果的反应, 如`[NOTFOUND=return]'.

在有NYS支持的libc5里允许服务规范`files', `nis'及`nisplus',此外，还可以对hosts 指明`dns' 为额外服务, 对passwd及group 指明`compat', 但不能对shadow指明`compat'.

在GNU C Library里, 每个可用的SERVICE都必须有文件 /lib/libnss_SERVICE.so.1 与之对应. 在标准安装时, 可以使用`files',`db', `nis'以及`nisplus'. 此外, 还可以对hosts 指明`dns' 为额外服务, 对passwd, group, shadow 指明`compat', 而在有NYS 支持的libc5中, 不支持最后一项服务.

说明中的第二项使用户可以更好地控制查找过程. Action项处于两个服务名之间, 被括弧括着, 常规格式如下:

`[' ( `!'? STATUS `=' ACTION )+ `]'

这里

: STATUS => success | notfound | unavail | tryagain
: ACTION => return | continue

对关键字的大小写并不敏感. STATUS的值是调用指定服务查找函数的结果, 意义如下:

: success
没有错误发生, 得到想要的结果. 缺省action是`return'.
: notfound 查找顺利, 但是没有得到所要的结果. 缺省action是`continue'.
: unavail 服务永久不可用. 这可能意味着必要的文件不可用, 或者,DNS 服务不可用或不允许查询.缺省action是`continue'.
: tryagain 服务临时不可用. 可能是文件被锁住了或者服务器当前不接受过多的连接. 缺省action是`continue'.

使用+/-语法的交互(compat 模式)无NYS支持的linux libc5没有名字服务开关, 但允许用户做一些简单的策略控制. 在 /etc/passwd 里可以使用+user或+@netgroup条目(即包括NIS passwd映射所指定用户), 以及-user或-@netgroup条目(即不包括被指定用户), 还有 + 条目(即包括每个用户, 除了NIS passwd映射所排除的). 大多数人只放一个 + 在 /etc/passwd 末尾, 以此包括NIS 的所有东西. 对该情况, 开关提供更快捷的替代方式(`passwd: files nis'), 这使得无需再往 /etc/passwd, /etc/group 及 /etc/shadow 里添加单个 + 条目. 如果这还不够, NSS 的`compat' 服务提供了完全的+/-语法. 我们可以对伪数据库 passwd_compat, group_compat 及 shadow_compat 指明`nisplus'服务来覆盖缺省服务`nis', 但请注意只在GNU C Library里可以使用伪数据库.

文件 FILES

名为SERVICE的服务是通过位于/lib的共享对象libnss_SERVICE.so.1实现的.

: /etc/nsswitch.conf 配置文件
: /lib/libnss_compat.so.1 为GNU C Library 2.x实现`compat'
: /lib/libnss_db.so.1
为GNU C Library 2.x实现`db'
: /lib/libnss_dns.so.1 为GNU C Library 2.x实现`dns'
: /lib/libnss_files.so.1
为GNU C Library 2.x实现`files'
: /lib/libnss_hesoid.so.1 为GNU C Library 2.x实现`hesoid'
: /lib/libnss_nis.so.1 为GNU C Library 2.x实现`nis'
: /lib/libnss_nisplus.so.1 为GNU C Library 2.x实现`nisplus'

注意 NOTES

每个用到了nsswitch.conf 文件的进程只完整地读一次文件, 如果该文件后面被改变了, 进程将仍然使用原来的配置.

在Solaris 下, 不能静态连接使用了NSS Service 的程序, 但是在Linux 下, 则毫无问题.

#p#

NAME

nsswitch.conf - System Databases and Name Service Switch configuration file

DESCRIPTION

Various functions in the C Library need to be configured to work correctly in the local environment. Traditionally, this was done by using files (e.g., `/etc/passwd'), but other nameservices (like the Network Information Service (NIS) and the Domain Name Service (DNS)) became popular, and were hacked into the C library, usually with a fixed search order.

The Linux libc5 with NYS support and the GNU C Library 2.x (libc.so.6) contain a cleaner solution of this problem. It is designed after a method used by Sun Microsystems in the C library of Solaris 2. We follow their name and call this scheme "Name Service Switch" (NSS). The sources for the "databases" and their lookup order are specified in the /etc/nsswitch.conf file.

The following databases are available in the NSS:

aliases: Mail aliases, used by sendmail(8). Presently ignored.
ethers: Ethernet numbers.
group: Groups of users, used by getgrent(3) functions.
hosts: Host names and numbers, used by gethostbyname(3) and similar functions.
netgroup: Network wide list of hosts and users, used for access rules. C libraries before glibc 2.1 only support netgroups over NIS.
network: Network names and numbers, used by getnetent(3) functions.
passwd: User passwords, used by getpwent(3) functions.
protocols: Network protocols, used by getprotoent(3) functions.
publickey: Public and secret keys for Secure_RPC used by NFS and NIS+.
rpc: Remote procedure call names and numbers, used by getrpcbyname(3) and similar functions.
services: Network services, used by getservent(3) functions.
shadow: Shadow user passwords, used by getspnam(3).

An example /etc/nsswitch.conf (namely, the default used when /etc/nsswitch.conf is missing):

passwd:: compat
group:: compat
shadow:: compat
hosts:: dns [!UNAVAIL=return] files
networks:: nis [NOTFOUND=return] files
ethers:: nis [NOTFOUND=return] files
protocols:: nis [NOTFOUND=return] files
rpc:: nis [NOTFOUND=return] files
services:: nis [NOTFOUND=return] files

The first column is the database. The rest of the line specifies how the lookup process works. You can specify the way it works for each database individually.

The configuration specification for each database can contain two different items:

* The service specification like `files', `db', or `nis'.
* The reaction on lookup result like `[NOTFOUND=return]'.

For libc5 with NYS, the allowed service specifications are `files', `nis', and `nisplus'. For hosts, you could specify `dns' as extra service, for passwd and group `compat', but not for shadow.

For glibc, you must have a file called /lib/libnss_SERVICE.so.X for every SERVICE you are using. On a standard installation, you could use `files', `db', `nis', and `nisplus'. For hosts, you could specify `dns' as extra service, for passwd, group, and shadow `compat'. These services will not be used by libc5 with NYS. The version number X is 1 for glibc 2.0 and 2 for glibc 2.1.

The second item in the specification gives the user much finer control on the lookup process. Action items are placed between two service names and are written within brackets. The general form is

`[' ( `!'? STATUS `=' ACTION )+ `]'

where

STATUS => success | notfound | unavail | tryagain
ACTION => return | continue

The case of the keywords is insignificant. The STATUS values are the results of a call to a lookup function of a specific service. They mean:

success: No error occurred and the wanted entry is returned. The default action for this is `return'.
notfound: The lookup process works ok but the needed value was not found. The default action is `continue'.
unavail: The service is permanently unavailable. This can either mean the needed file is not available, or, for DNS, the server is not available or does not allow queries. The default action is `continue'.
tryagain