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The operating system uses a number of "databases" of information about hosts, users (passwd/shadow), groups and so forth. Data for these can come from a variety of sources: host-names and host-addresses, for example, may be found in /etc/hosts, NIS, NIS+ or DNS. Zero or more sources may be used for each database; the sources and their lookup order are specified in the /etc/nsswitch.conf file.
The following databases use the switch file:
- Database
- Used by
- aliases
- sendmail(1M)
- automount
- automount(1M)
- bootparams
- rpc.bootparamd(1M)
- ethers
- ethers(3N)
- group
- getgrnam(3C)
- hosts
- gethostbyname(3N)
- (See "Interaction with netconfig" below)
- netgroup
- innetgr(3N)
- netmasks
- ifconfig(1M)
- networks
- getnetbyname(3N)
- passwd
- getpwnam(3C) , getspnam(3C)
- protocols
- getprotobyname(3N)
- publickey
- getpublickey(3N) , secure_rpc(3N)
- rpc
- getrpcbyname(3N)
- sendmailvars
- sendmail(1M)
- services
- getservbyname(3N)
- (See "Interaction with netconfig" below)
The following sources may be used:
- Source
- Uses
- files
- /etc/hosts, /etc/passwd, /etc/shadow and so forth
- nis
- NIS (YP)
- nisplus
- NIS+
- dns
- Valid only for hosts; uses the Internet Domain Name Service.
- compat
- Valid only for passwd and group; implements "+" and "-".
(See "Interaction with +/- syntax" below)
There is an entry in /etc/nsswitch.conf for each database. Typically these entries will be simple, such as "protocols: files" or "networks: files nisplus". However, when multiple sources are specified it is sometimes necessary to define precisely the circumstances under which each source will be tried. A source can return one of the following codes:
- Status
- Meaning
- SUCCESS
- Requested database entry was found
- UNAVAIL
- Source is not responding or corrupted
- NOTFOUND
- Source responded "no such entry"
- TRYAGAIN
- Source is busy, might respond to retries
For each status code, two actions are possible:
- Action
- Meaning
- continue
- Try the next source in the list
- return
- Return now
The complete syntax of an entry is
<entry> ::= <database> ":" [<source> [<criteria>]]* <criteria> ::= "[" <criterion>+ "]" <criterion> ::= <status> "=" <action> <status> ::= "success" | "notfound" | "unavail" | "tryagain" <action> ::= "return" | "continue"
Each entry occupies a single line in the file. Lines that are blank, or that start with white space are ignored. Everything on a line following a # character is also ignored; the # character can begin anywhere in a line, to be used to begin comments. The <database> and <source> names are case-sensitive, but <action> and <status> names are case-insensitive.
The library functions contain compiled-in default entries that are used if the appropriate entry in nsswitch.conf is absent or syntactically incorrect.
The default criteria are to continue on anything except SUCCESS; in other words, [SUCCESS=return NOTFOUND=continue UNAVAIL=continue TRYAGAIN=continue].
The default, or explicitly specified, criteria are meaningless following the last source in an entry; and are ignored since the action is always to return to the caller irrespective of the status code the source returns.
In order
to ensure that they all return consistent results, gethostbyname(3N)
, getservbyname(3N)
,
and netdir_getbyname(3N)
functions are all implemented in terms of the
same internal library function. This function obtains the system-wide source
lookup policy for hosts and services based on the inet family entries in
netconfig(4)
and uses the switch entries only if the netconfig entries
have a "-" in the last column for nametoaddr libraries. See the NOTES section
in gethostbyname(3N)
and getservbyname(3N)
for details.
The NIS+ server can be run
in "YP-compatibility mode", where it handles NIS (YP) requests as well as
NIS+ requests. In this case, the clients get much the same results (except
for getspnam(3C)
) from the "nis" source as from "nisplus"; however, "nisplus"
is recommended instead of "nis".
Since SunOS 5.3 (Solaris 2.3), the NIS+ server in "NIS/YP-compatibility mode" can also be run in "DNS-forwarding mode" (see rpc.nisd(1M) ). Forwarding is effective only for requests originating from its YP clients; "hosts" policy on these clients should be configured appropriately.
When password aging is turned on only a limited set of possible name services are permitted for the passwd: database in the /etc/nsswitch.conf file.
- passwd:
- files
- passwd:
- files nis
- passwd:
- files nisplus
- passwd:
- compat
- passwd:
- compat
- passwd_compat:
- nisplus
Any
other settings will cause the passwd(1)
command to fail when it attempts
to change the password after expiration and will prevent the user from
logging in. These are the only permitted settings when password aging has
been turned on. Otherwise you can work around incorrect passwd: lines by
using the -r repository argument to the passwd(1)
command and using passwd
-r repository to override the nsswitch.conf settings and specify in which
name service you want to modify your password.
Releases prior to SunOS 5.0 did not have the name service switch but did allow the user some policy control. In /etc/passwd one could have entries of the form +user (include the specified user from NIS passwd.byname), -user (exclude the specified user) and + (include everything, except excluded users, from NIS passwd.byname). The desired behavior was often "everything in the file followed by everything in NIS", expressed by a solitary + at the end of /etc/passwd. The switch provides an alternative for this case ("passwd: files nis") that does not require + entries in /etc/passwd and /etc/shadow (the latter is a new addition to SunOS 5.0, see shadow(4) ).
If this is not sufficient, the NIS/YP compatibility source provides full +/- semantics. It reads /etc/passwd for getpwnam(3C) functions and /etc/shadow for getspnam(3C) functions and, if it finds +/- entries, invokes an appropriate source. By default the source is "nis", but this may be overridden by specifying "nisplus" as the source for the pseudo-database passwd_compat.
Note that for every /etc/passwd entry, there should be a corresponding entry in the /etc/shadow file.
The NIS/YP compatibility source also provides full +/- semantics for group; the relevant pseudo-database is group_compat.
The compiled-in default entries for all databases use NIS (YP) as the enterprise level name service and are identical to those in the default configuration of this file:
- passwd:
- files nis
- group:
- files nis
- hosts:
- nis [NOTFOUND=return] files
- networks:
- nis [NOTFOUND=return] files
- protocols:
- nis [NOTFOUND=return] files
- rpc:
- nis [NOTFOUND=return] files
- ethers:
- nis [NOTFOUND=return] files
- netmasks:
- nis [NOTFOUND=return] files
- bootparams:
- nis [NOTFOUND=return] files
- publickey:
- nis [NOTFOUND=return] files
- netgroup:
- nis
- automount:
- files nis
- aliases:
- files nis
- services:
- files nis
- sendmailvars:
- files
The policy "nis [NOTFOUND=return] files" implies "if nis is UNAVAIL, continue on to files, and if nis returns NOTFOUND, return to the caller; in other words, treat nis as the authoritative source of information and try files only if nis is down." This, and other policies listed in the default configuration above, are identical to the hard-wired policies in SunOS releases prior to 5.0.
If compatibility with the +/- syntax for passwd and group is required, simply modify the entries for passwd and group to:
- passwd:
- compat
- group:
- compat
If NIS+ is the enterprise level name service, the default configuration should be modified to use nisplus instead of nis for every database on client machines. The file /etc/nsswitch.nisplus contains a sample configuration that can be copied to /etc/nsswitch.conf to set this policy.
If the use of +/- syntax is desired in conjunction with nisplus, use the following four entries:
nisplus
- passwd:
- compat
- passwd_compat:
- nisplus
- group:
- compat
- group_compat:
In order to get information from the Internet Domain Name Service for hosts that are not listed in the enterprise level name service, NIS+, use the following configuration and set up the /etc/resolv.conf file (see resolv.conf(4) for more details):
files
- hosts:
- nisplus dns [NOTFOUND=return]
In general the use of the enumeration functions is deprecated. In the case of passwd, shadow and group, it may sometimes be appropriate to use fgetgrent(), fgetpwent() and fgetspent() (see getgrnam(3C) , getpwnam(3C) , and getspnam(3C) , respectively), which use only the files source.
A source named SSS is implemented by a shared object named nss_SSS.so.1 that resides in /usr/lib.
Within each process that uses nsswitch.conf, the entire file is read only once; if the file is later changed, the process will continue using the old configuration.
Programs that use the getXXbyYY() functions cannot be linked statically since the implementation of these functions requires dynamic linker functionality to access the shared objects /usr/lib/nss_SSS.so.1 at run time.
The use of both nis and nisplus as sources for the same database is strongly discouraged since both the name services are expected to store similar information and the lookups on the database may yield different results depending on which name service is operational at the time of the request.
Misspelled names of sources and databases will be treated as legitimate names of (most likely nonexistent) sources and databases.
The following functions do not use the switch: fgetgrent(3C) , fgetpwent(3C) , fgetspent(3C) , getpw(3C) , putpwent(3C) . shadow(4)