checkpw - checks password against the file
reads descriptor 3 through end of file
and then closes descriptor 3.
There must be at most 512 bytes of data before end of file.
The information supplied on descriptor 3
is a login name terminated by \0,
a password terminated by \0,
a timestamp terminated by \0,
and possibly more data.
There are no other restrictions
on the form of the login name, password, and timestamp.
If the password is unacceptable,
is misused, it may instead exit 2.
If there is a temporary problem checking the password,
If the password is acceptable,
consists of one or more arguments.
There are other tools that offer the same interface as
Note that these tools do not follow the
Optional features are controlled through
(1) the tool name and (2) environment variables.
The password database
checks the password
against the content of the file
in the user's home directory corresponding to the login name.
may be overidden through the environment variable
its supplementary groups,
and its working directory.