getlogin(3posix)
NAME
getlogin, getlogin_r --- get login name
SYNOPSIS
#include <unistd.h> char *getlogin(void); int getlogin_r(char *name, size_t namesize);
DESCRIPTION
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 ID.
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 /dev/tty.
RETURN VALUE
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
These functions may fail if:
EMFILE All file descriptors available to the process are currently
open.
ENFILE The maximum allowable number of files is currently open in the
system.
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
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);
}
APPLICATION USAGE
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 process. 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
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.11988 standard and subsequently
removed, can be obtained by the following:
getpwuid(geteuid())
while the information provided by historical implementations of
cuserid() can be obtained by:
getpwuid(getuid())
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.
FUTURE DIRECTIONS
None.
SEE ALSO
getpwnam(), getpwuid(), geteuid(), getuid() The Base Definitions volume of POSIX.12008, <limits.h>, <unistd.h>
COPYRIGHT
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 http://www.unix.org/online.html . 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 https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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