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, int 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.

The return value from getlogin() points to static data whose content is overwritten by each call.  To avoid this, use 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.  Otherwise, it returns −1 and sets errno to indicate the error. 

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 also note that the prototype of this function will change in the next release for conformance with the new POSIX Threads standard. 

SEE ALSO

getuid(2), getgrent(3C), getpwent(3C), utmp(4). 

STANDARDS CONFORMANCE

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

Hewlett-Packard Company  —  HP-UX Release 10.20:  July 1996