getlogin(3C)

NAME

getlogin(), getlogin_r() — get name of user logged in on this terminal

SYNOPSIS

#include <unistd.h>

char *getlogin(void);

int getlogin_r(char *buf, size_t buflen);

DESCRIPTION

The getlogin() function retrieves the name of the user currently logged in on a terminal associated with the calling process, as found in /etc/utmp.

At least one of the standard input, standard output, or standard error must be a terminal. For the first of these found that is a terminal, a user must have logged in on that terminal, and that terminal must be the controlling terminal of the session leader process of the calling process's session.

The getlogin() function can be used in conjunction with getpwnam() to locate the correct password file entry when the same user ID is shared by several login names.

The recommended procedure to obtain the user name associated with the real user ID of the calling process is to call getlogin(), and if that fails, to call getpwuid(getuid()).

To get the user name associated with the effective user ID, call getpwuid(geteuid()).

getlogin_r() performs the same operations as getlogin(), but returns the login name in the buffer to which buf points, whose size in bytes should be passed in buflen. buf should have space for the name and the terminating null character. The maximum size of the login name is LOGIN_NAME_MAX.

APPLICATION USAGE

The return value from getlogin() points to static data whose content is overwritten by each call. getlogin_r() is thread-safe. getlogin_r() is not async-cancel-safe. A cancellation point may occur when a thread is executing getlogin() or getlogin_r().

RETURN VALUE

Upon successfully finding and validating the login name of the user logged in on the terminal, getlogin() returns a pointer to the name. Otherwise, it returns a null pointer, and sets errno to indicate the error.

Upon successfully finding, validating, and copying to the buffer the login name of the user logged in on the terminal, getlogin_r() returns 0 upon success and returns an error number upon failure.

ERRORS

getlogin() and getlogin_r() fail if any of the following is true:

[EACCES]: Access permission to read the /etc/utmp file, or to get the status of the terminal device file, was denied.
[EMFILE]: Too many file descriptors are in use by this process.
[ENFILE]: Too many file descriptors are in use on the system.
[ENOENT]: The /etc/utmp file or the terminal device file cannot be found.
[ENOTTY]: None of the standard input, standard output, or standard error is a terminal, or for the first of these that is a terminal, no current login is registered on that terminal, or the session leader process of the calling process has no controlling terminal.
[EPERM]: One of the standard input, standard output, or standard error is a terminal, and a current login was found on that terminal, but that terminal is not the same as the controlling terminal of the session of the calling process.
[ESRCH]: The session leader process of the calling process is no longer running.

The error condition associated with [EPERM] prevents processes that have access to some other user's terminal from believing that they are related to that other user's login session.

getlogin_r() also fails if the following is true:

[ERANGE]: The length of the name to be returned, including the terminating null byte, exceeds buflen.

FILES

/etc/utmp: Database that maps user logins to terminals.

WARNINGS

Users of getlogin_r() should note getlogin_r() now conforms with the POSIX.1c Threads standard. The old prototype of getlogin_r() is supported for compatibility with existing DCE applications only.

STANDARDS CONFORMANCE

getlogin(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1

getlogin_r(): POSIX.1c