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getlogin(3C)		 Standard C Library Functions		  getlogin(3C)

NAME
       getlogin, getlogin_r - get login name

SYNOPSIS
       #include <unistd.h>

       char *getlogin(void);

       char *getlogin_r(char *name, int namelen);

   Standard conforming
       cc [ flag ... ] file... -D_POSIX_PTHREAD_SEMANTICS [ library ... ]

       int getlogin_r(char *name, size_t namesize);

DESCRIPTION
       The getlogin() function returns a pointer to the login name as found in
       /var/adm/utmpx. It can be used  in  conjunction	with  getpwnam(3C)  to
       locate  the correct password file entry when the same user ID is shared
       by several login names.

       If getlogin() is called within a process that is not attached to a ter‐
       minal, it returns a null pointer. The correct procedure for determining
       the login name is to call cuserid(3C), or to call getlogin() and if  it
       fails to call getpwuid(3C).

       The  getlogin_r()  function  has	 the  same functionality as getlogin()
       except that the caller must supply a buffer name with length namelen to
       store	the    result.	  The	name   buffer	must   be   at	 least
       _POSIX_LOGIN_NAME_MAX bytes in size (defined in <limits.h>). The	 POSIX
       version	(see  standards(5)) of getlogin_r() takes a namesize parameter
       of type size_t.

RETURN VALUES
       Upon successful completion, getlogin() returns a pointer to  the	 login
       name  or a null pointer if the user's login name cannot be found.  Oth‐
       erwise it returns a null pointer and sets errno to indicate the error.

       The standard-conforming getlogin_r() returns 0 if  successful,  or  the
       error number upon failure.

ERRORS
       The getlogin_r() function will fail if:

       ERANGE	       The size of the buffer is smaller than the result to be
		       returned.

       EINVAL	       And entry for the current user was  not	found  in  the
		       /var/adm/utmpx file.

       The getlogin() and getlogin_r() functions may fail if:

       EMFILE	       There are {OPEN_MAX} file descriptors currently open in
		       the calling process.

       ENFILE	       The maximum allowable number of files is currently open
		       in the system.

       ENXIO	       The calling process has no controlling terminal.

       The getlogin_r() function may fail if:

       ERANGE	       The size of the buffer is smaller than the result to be
		       returned.

USAGE
       The return value of getlogin() points  to  thread-specific  data	 whose
       content is overwritten on each call by the same thread.

       Three names associated with the current process can be determined: get‐
       pwuid(geteuid()) returns the name associated with the effective user ID
       of the process; getlogin() returns the name associated with the current
       login activity; and getpwuid(getuid()) returns the name associated with
       the real user ID of the process.

FILES
       /var/adm/utmpx	       user access and administration information

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌─────────────────────────────┬─────────────────────────────┐
       │      ATTRIBUTE TYPE	     │	    ATTRIBUTE VALUE	   │
       ├─────────────────────────────┼─────────────────────────────┤
       │Interface Stability	     │Standard			   │
       ├─────────────────────────────┼─────────────────────────────┤
       │MT-Level		     │See below.		   │
       └─────────────────────────────┴─────────────────────────────┘

SEE ALSO
       geteuid(2),  getuid(2),	cuserid(3C), getgrnam(3C), getpwnam(3C), getp‐
       wuid(3C), utmpx(4), attributes(5), standards(5)

NOTES
       When compiling multithreaded programs, see Intro(3).

       The getlogin() function is safe to use in  multithreaded	 applications,
       but is discouraged. The getlogin_r() function should be used instead.

       Solaris	2.4  and earlier releases provided a getlogin_r() as specified
       in POSIX.1c Draft 6. The final POSIX.1c standard changed the  interface
       as  described  above. Support for the Draft 6 interface is provided for
       compatibility only and may not be supported  in	future	releases.  New
       applications  and  libraries  should use the standard-conforming inter‐
       face.

SunOS 5.10			  18 May 2004			  getlogin(3C)
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