NAME

       checkpassword - check a password

SYNOPSIS

       checkpassword prog

DESCRIPTION

       checkpassword  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, checkpassword exits 1.  If checkpassword is  misused,  it
       may  instead exit 2.  If there is a temporary problem checking the password, checkpassword
       exits 111.

       If the password is acceptable, checkpassword runs prog.  prog  consists  of  one  or  more
       arguments.

COMPATIBLE TOOLS

       There  are  other tools that offer the same interface as checkpassword.  Applications that
       use checkpassword are encouraged to take the checkpassword name as an  argument,  so  that
       they can be used with different tools.

       Note  that  these  tools  do  not  follow  the getopt(3) interface.  Optional features are
       controlled through (1) the tool name and (2) environment variables.

THE PASSWORD DATABASE

       checkpassword checks the login name and password against /etc/passwd, using the  operating
       system's  getpwnam(3)  and  crypt(3)  functions,  supplemented  by  getspnam.   It rejects
       accounts with empty passwords.  It ignores the timestamp.

       Other checkpassword-compatible  tools  have  different  interpretations  of  login  names,
       passwords,  and  timestamps.   Both  the  login name and the password should be treated as
       secrets  by  the  application  calling  checkpassword;  the  only   distinction   is   for
       administrative  convenience.   The timestamp should include any other information that the
       password is based on; for example, the challenge in a challenge-response  system  such  as
       APOP.

       WARNING:  getpwnam  is  inherently  unreliable.  It fails to distinguish between temporary
       errors and nonexistent users.  Future versions of getpwnam(3)  should  return  ETXTBSY  to
       indicate temporary errors and ESRCH to indicate nonexistent users.

PROCESS-STATE CHANGES

       Before  invoking  prog,  checkpassword  sets  up  $USER,  $HOME, $SHELL, its supplementary
       groups, its gid, its uid, and its working directory.

       Other checkpassword-compatible tools may make different changes to the process state.   It
       is  crucial  for  these  effects  to  be documented; different applications have different
       requirements.

SEE ALSO

       getpwnam(3), crypt(3)

                                                                                 checkpassword(8)