NSS(5) manual page
Table of Contents
nss - Name Service Switch configuration file
Each
call to a function which retrieves data from a system database like the
password or group database is handled by the Name Service Switch implementation
in the GNU C library. The various services provided are implemented by independent
modules, each of which naturally varies widely from the other.
The default
implementations coming with the GNU C library are by default conservative
and do not use unsafe data. This might be very costly in some situations,
especially when the databases are large. Some modules allow the system administrator
to request taking shortcuts if these are known to be safe. It is then the
system administrator’s responsibility to ensure the assumption is correct.
There are other modules where the implementation changed over time. If an
implementation used to sacrifice speed for memory consumption, it might
create problems if the preference is switched.
The /etc/default/nss file
contains a number of variable assignments. Each variable controls the behavior
of one or more NSS modules. White spaces are ignored. Lines beginning with
aq#aq are treated as comments.
The variables currently recognized are:
- NETID_AUTHORITATIVE
= TRUE|FALSE
- If set to TRUE, the NIS backend for the initgroups(3)
function
will accept the information from the netid.byname NIS map as authoritative.
This can speed up the function significantly if the group.byname map is
large. The content of the netid.byname map is used as is. The system administrator
has to make sure it is correctly generated.
- SERVICES_AUTHORITATIVE = TRUE|FALSE
- If set to TRUE, the NIS backend for the getservbyname(3)
and getservbyname_r(3)
functions will assume that the services.byservicename NIS map exists and
is authoritative, particularly that it contains both keys with /proto and
without /proto for both primary service names and service aliases. The system
administrator has to make sure it is correctly generated.
- SETENT_BATCH_READ
= TRUE|FALSE
- If set to TRUE, the NIS backend for the setpwent(3)
and setgrent(3)
functions will read the entire database at once and then hand out the requests
one by one from memory with every corresponding getpwent(3)
or getgrent(3)
call respectively. Otherwise, each getpwent(3)
or getgrent(3)
call might
result in a network communication with the server to get the next entry.
/etc/default/nss
The default configuration corresponds to the
following configuration file:
NETID_AUTHORITATIVE=FALSE
SERVICES_AUTHORITATIVE=FALSE
SETENT_BATCH_READ=FALSE
See Alsonsswitch.conf ColophonThis page is part of release 3.78 of the Linux
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