GETLOGIN(P) GETLOGIN(P)
NAME
getlogin, getlogin_r - get login name
SYNOPSIS
#include
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 asso-
ciated by the login activity with the controlling terminal of the current process. If get-
login() 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 reentrant. A function that is not required to be reen-
trant is not required to 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.
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 return value from getlogin() may point to static data whose content is overwritten by
each call.
If successful, the getlogin_r() function shall return zero; otherwise, an error number
shall be returned to indicate the error.
ERRORS
The getlogin() and getlogin_r() functions may fail if:
EMFILE {OPEN_MAX} file descriptors are 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 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
The following example calls the getlogin() function to obtain the name of the user associ-
ated with the calling process, and passes this information to the getpwnam() function to
get the associated user database information.
#include
#include
#include
#include
...
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.1-1988 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
IEEE Std 1003.1-2001, ,
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
POSIX 2003 GETLOGIN(P)
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