Provided by:
login_4.1.4.2-1ubuntu3_i386 
CONFIGURATION
The following configuration variables in /etc/login.defs change the
behavior of this tool:
CONSOLE_GROUPS (string)
List of groups to add to the users supplementary groups set when
logging in on the console (as determined by the CONSOLE setting).
Default is none.
Use with caution - it is possible for users to gain permanent
access to these groups, even when not logged in on the console.
DEFAULT_HOME (boolean)
Indicate if login is allowed if we cant cd to the home directory.
Default in no.
If set to yes, the user will login in the root (/) directory if it
is not possible to cd to her home directory.
ENV_PATH (string)
If set, it will be used to define the PATH environment variable
when a regular user login. The value can be preceded by PATH=, or a
colon separated list of paths (for example /bin:/usr/bin). The
default value is PATH=/bin:/usr/bin.
ENV_SUPATH (string)
If set, it will be used to define the PATH environment variable
when the superuser login. The value can be preceded by PATH=, or a
colon separated list of paths (for example
/sbin:/bin:/usr/sbin:/usr/bin). The default value is
PATH=/bin:/usr/bin.
SULOG_FILE (string)
If defined, all su activity is logged to this file.
SU_NAME (string)
If defined, the command name to display when running "su -". For
example, if this is defined as "su" then a "ps" will display the
command is "-su". If not defined, then "ps" would display the name
of the shell actually being run, e.g. something like "-sh".
SYSLOG_SU_ENAB (boolean)
Enable "syslog" logging of su activity - in addition to sulog file
logging.
/etc/passwd
/etc/shadow
/etc/login.defs
login(1), login.defs(5), sg(1), sh(1).
09/03/2010 su(1)