nss_wrapper(1)
==============
:revdate: 2019-05-21
:author: Samba Team

NAME
----

nss_wrapper - A wrapper for the user, group and hosts NSS API

SYNOPSIS
--------

LD_PRELOAD=libnss_wrapper.so NSS_WRAPPER_PASSWD=/path/to/passwd NSS_WRAPPER_GROUP=/path/to/group NSS_WRAPPER_HOSTS=/path/to/host *./myapplication*

DESCRIPTION
-----------

There are projects which provide daemons needing to be able to create, modify
and delete Unix users. Or just switch user ids to interact with the system e.g.
a user space file server. To be able to test that you need the privilege to
modify the passwd and groups file. With nss_wrapper it is possible to define
your own passwd and groups file which will be used by software to act correctly
while under test.

If you have a client and server under test they normally use functions to
resolve network names to addresses (dns) or vice versa. The nss_wrappers allow
you to create a hosts file to setup name resolution for the addresses you use
with socket_wrapper.

- Provides information for user and group accounts.
- Network name resolution using a hosts file.
- Loading and testing of NSS modules.

LIMITATIONS
-----------

Some calls in nss_wrapper will only work if uid_wrapper is loaded and active.
One of this functions is initgroups() which needs to run setgroups() to set
the groups for the user. setgroups() is wrapped by uid_wrapper.

ENVIRONMENT VARIABLES
---------------------

*NSS_WRAPPER_PASSWD*::
*NSS_WRAPPER_GROUP*::

For user and group accounts you need to create two files: 'passwd' and 'group'.
The format of the passwd file we support is:

name:password:UID:GID:GECOS:directory:shell

The format of the group file we support is:

group_name:password:GID:user_list

They are also described in 'man passwd.5' and 'man group.5' on Linux. You can
fill these files with made up accounts. You point
nss_wrapper to them using the two variables
NSS_WRAPPER_PASSWD=/path/to/your/passwd and
NSS_WRAPPER_GROUP=/path/to/your/group.

*NSS_WRAPPER_HOSTS*::

If you also need to emulate network name resolution in your environment,
especially with socket_wrapper, you can write a hosts file. The format is
described in 'man 5 hosts'. Then you can point nss_wrapper to your hosts
file using: NSS_WRAPPER_HOSTS=/path/to/your/hosts

*NSS_WRAPPER_HOSTNAME*::

If you need to return a hostname which is different from the one of your
machine is using you can use: NSS_WRAPPER_HOSTNAME=test.example.org

*NSS_WRAPPER_MODULE_SO_PATH*::
*NSS_WRAPPER_MODULE_FN_PREFIX*::

If you have a project which also provides user and group information out of a
database, you normally write your own nss modules. nss_wrapper is able to load
nss modules and ask them first before looking into the faked passwd and group
file. To point nss_wrapper to the module you can do that using
NSS_WRAPPER_MODULE_SO_PATH=/path/to/libnss_yourmodule.so. As each nss module
has a special prefix like _nss_winbind_getpwnam() you need to set the prefix
too so nss_wrapper can load the functions with
NSS_WRAPPER_MODULE_FN_PREFIX=<prefix>.

For _nss_winbind_getpwnam() this would be:

  NSS_WRAPPER_MODULE_FN_PREFIX=winbind

*NSS_WRAPPER_DEBUGLEVEL*::

If you need to see what is going on in nss_wrapper itself or try to find a
bug, you can enable logging support in nss_wrapper if you built it with
debug symbols.

- 0 = ERROR
- 1 = WARNING
- 2 = DEBUG
- 3 = TRACE

*NSS_WRAPPER_DISABLE_DEEPBIND*::

This allows you to disable deep binding in nss_wrapper. This is useful for
running valgrind tools or sanitizers like (address, undefined, thread).

EXAMPLE
-------

  $ echo "bob:x:1000:1000:bob gecos:/home/test/bob:/bin/false" > passwd
  $ echo "root:x:65534:65532:root gecos:/home/test/root:/bin/false" >> passwd
  $ echo "users:x:1000:" > group
  $ echo "root:x:65532:" >> group
  $ LD_PRELOAD=libnss_wrapper.so NSS_WRAPPER_PASSWD=passwd \
    NSS_WRAPPER_GROUP=group getent passwd bob
  bob:x:1000:1000:bob gecos:/home/test/bob:/bin/false
  $ LD_PRELOAD=libnss_wrapper.so NSS_WRAPPER_HOSTNAME=test.example.org hostname
  test.example.org
