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(libc.info)Who Logged In

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Identifying Who Logged In
=========================

   You can use the functions listed in this section to determine the
login name of the user who is running a process, and the name of the
user who logged in the current session.  See also the function `getuid'
and friends (Note: Reading Persona).  How this information is
collected by the system and how to control/add/remove information from
the background storage is described in Note: User Accounting Database.

   The `getlogin' function is declared in `unistd.h', while `cuserid'
and `L_cuserid' are declared in `stdio.h'.

 - Function: char * getlogin (void)
     The `getlogin' function returns a pointer to a string containing
     the name of the user logged in on the controlling terminal of the
     process, or a null pointer if this information cannot be
     determined.  The string is statically allocated and might be
     overwritten on subsequent calls to this function or to `cuserid'.

 - Function: char * cuserid (char *STRING)
     The `cuserid' function returns a pointer to a string containing a
     user name associated with the effective ID of the process.  If
     STRING is not a null pointer, it should be an array that can hold
     at least `L_cuserid' characters; the string is returned in this
     array.  Otherwise, a pointer to a string in a static area is
     returned.  This string is statically allocated and might be
     overwritten on subsequent calls to this function or to `getlogin'.

     The use of this function is deprecated since it is marked to be
     withdrawn in XPG4.2 and has already been removed from newer
     revisions of POSIX.1.

 - Macro: int L_cuserid
     An integer constant that indicates how long an array you might
     need to store a user name.

   These functions let your program identify positively the user who is
running or the user who logged in this session.  (These can differ when
setuid programs are involved; see Note: Process Persona.)  The user
cannot do anything to fool these functions.

   For most purposes, it is more useful to use the environment variable
`LOGNAME' to find out who the user is.  This is more flexible precisely
because the user can set `LOGNAME' arbitrarily.  Note: Standard
Environment.