GNU Info

(libc.info)Adding another Service to NSS

---

Next: NSS Module Function Internals Prev: Extending NSS Up: Extending NSS

---

Enter node , (file) or (file)node

Adding another Service to NSS
-----------------------------

   The sources for a new service need not (and should not) be part of
the GNU C Library itself.  The developer retains complete control over
the sources and its development.  The links between the C library and
the new service module consists solely of the interface functions.

   Each module is designed following a specific interface specification.
For now the version is 2 (the interface in version 1 was not adequate)
and this manifests in the version number of the shared library object of
the NSS modules: they have the extension `.2'.  If the interface
changes again in an incompatible way, this number will be increased.
Modules using the old interface will still be usable.

   Developers of a new service will have to make sure that their module
is created using the correct interface number.  This means the file
itself must have the correct name and on ELF systems the "soname"
(Shared Object Name) must also have this number.  Building a module
from a bunch of object files on an ELF system using GNU CC could be
done like this:

     gcc -shared -o libnss_NAME.so.2 -Wl,-soname,libnss_NAME.so.2 OBJECTS

Note: Options for Linking, to learn more about this
command line.

   To use the new module the library must be able to find it.  This can
be achieved by using options for the dynamic linker so that it will
search the directory where the binary is placed.  For an ELF system
this could be done by adding the wanted directory to the value of
`LD_LIBRARY_PATH'.

   But this is not always possible since some programs (those which run
under IDs which do not belong to the user) ignore this variable.
Therefore the stable version of the module should be placed into a
directory which is searched by the dynamic linker.  Normally this should
be the directory `$prefix/lib', where `$prefix' corresponds to the
value given to configure using the `--prefix' option.  But be careful:
this should only be done if it is clear the module does not cause any
harm.  System administrators should be careful.