getlogin_r(3p) — Linux manual page


GETLOGIN(3P)              POSIX Programmer's Manual             GETLOGIN(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       getlogin, getlogin_r — get login name

SYNOPSIS         top

       #include <unistd.h>

       char *getlogin(void);
       int getlogin_r(char *name, size_t namesize);

DESCRIPTION         top

       The getlogin() function shall return a pointer to a string containing
       the user name associated by the login activity with the controlling
       terminal of the current process. If getlogin() returns a non-null
       pointer, then that pointer points to the name that the user logged in
       under, even if there are several login names with the same user ID.

       The getlogin() function need not be thread-safe.

       The getlogin_r() function shall put the name associated by the login
       activity with the controlling terminal of the current process in the
       character array pointed to by name.  The array is namesize characters
       long and should have space for the name and the terminating null
       character. The maximum size of the login name is {LOGIN_NAME_MAX}.

       If getlogin_r() is successful, name points to the name the user used
       at login, even if there are several login names with the same user

       The getlogin() and getlogin_r() functions may make use of file
       descriptors 0, 1, and 2 to find the controlling terminal of the
       current process, examining each in turn until the terminal is found.
       If in this case none of these three file descriptors is open to the
       controlling terminal, these functions may fail. The method used to
       find the terminal associated with a file descriptor may depend on the
       file descriptor being open to the actual terminal device, not

RETURN VALUE         top

       Upon successful completion, getlogin() shall return a pointer to the
       login name or a null pointer if the user's login name cannot be
       found. Otherwise, it shall return a null pointer and set errno to
       indicate the error.

       The application shall not modify the string returned. The returned
       pointer might be invalidated or the string content might be
       overwritten by a subsequent call to getlogin().

       If successful, the getlogin_r() function shall return zero;
       otherwise, an error number shall be returned to indicate the error.

ERRORS         top

       These functions may fail if:

       EMFILE All file descriptors available to the process are currently

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

       ENOTTY None of the file descriptors 0, 1, or 2 is open to the
              controlling terminal of the current process.

       ENXIO  The calling process has no controlling terminal.

       The getlogin_r() function may fail if:

       ERANGE The value of namesize is smaller than the length of the string
              to be returned including the terminating null character.

       The following sections are informative.

EXAMPLES         top

   Getting the User Login Name S
       The following example calls the getlogin() function to obtain the
       name of the user associated with the calling process, and passes this
       information to the getpwnam() function to get the associated user
       database information.

           #include <unistd.h>
           #include <sys/types.h>
           #include <pwd.h>
           #include <stdio.h>
           char *lgn;
           struct passwd *pw;
           if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
               fprintf(stderr, "Get of user information failed.\n"); exit(1);


       Three names associated with the current process can be determined:
       getpwuid(geteuid()) shall return the name associated with the
       effective user ID of the process; getlogin() shall return the name
       associated with the current login activity; and getpwuid(getuid())
       shall return the name associated with the real user ID of the

       The getlogin_r() function is thread-safe and returns values in a
       user-supplied buffer instead of possibly using a static data area
       that may be overwritten by each call.

RATIONALE         top

       The getlogin() function returns a pointer to the user's login name.
       The same user ID may be shared by several login names. If it is
       desired to get the user database entry that is used during login, the
       result of getlogin() should be used to provide the argument to the
       getpwnam() function. (This might be used to determine the user's
       login shell, particularly where a single user has multiple login
       shells with distinct login names, but the same user ID.)

       The information provided by the cuserid() function, which was
       originally defined in the POSIX.1‐1988 standard and subsequently
       removed, can be obtained by the following:


       while the information provided by historical implementations of
       cuserid() can be obtained by:


       The thread-safe version of this function places the user name in a
       user-supplied buffer and returns a non-zero value if it fails. The
       non-thread-safe version may return the name in a static data area
       that may be overwritten by each call.



SEE ALSO         top

       getpwnam(3p), getpwuid(3p), geteuid(3p), getuid(3p)

       The Base Definitions volume of POSIX.1‐2008, limits.h(0p),

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see .

IEEE/The Open Group                 2013                        GETLOGIN(3P)