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GETLOGIN(2)		  FreeBSD System Calls Manual		   GETLOGIN(2)

NAME
     getlogin, getlogin_r, setlogin -- get/set login name

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <unistd.h>

     char *
     getlogin(void);

     #include <sys/param.h>

     int
     getlogin_r(char *name, int	len);

     int
     setlogin(const char *name);

DESCRIPTION
     The getlogin() routine returns the	login name of the user associated with
     the current session, as previously	set by setlogin().  The	name is	nor-
     mally associated with a login shell at the	time a session is created, and
     is	inherited by all processes descended from the login shell.  (This is
     true even if some of those	processes assume another user ID, for example
     when su(1)	is used).

     getlogin_r() provides the same service as getlogin() except the caller
     must provide the buffer name with length len bytes	to hold	the result.
     The buffer	should be at least MAXLOGNAME bytes in length.

     Setlogin()	sets the login name of the user	associated with	the current
     session to	name.  This call is restricted to the super-user, and is nor-
     mally used	only when a new	session	is being created on behalf of the
     named user	(for example, at login time, or	when a remote shell is
     invoked).

     NOTE: There is only one login name	per session.

     It	is CRITICALLY important	to ensure that setlogin() is only ever called
     after the process has taken adequate steps	to ensure that it is detached
     from its parent's session.	 Making	a setsid() system call is the ONLY way
     to	do this.  The daemon() library call calls setsid() which is an ideal
     way of detaching from a controlling terminal and forking into the back-
     ground.

     In	particular, doing a ioctl(ttyfd, TIOCNOTTY, ...) or setpgrp(...) is
     NOT sufficient.

     Once a parent process does	a setsid() call, it is acceptable for some
     child of that process to then do a	setlogin() even	though it is not the
     session leader, but beware	that ALL processes in the session will change
     their login name at the same time,	even the parent.

     This is not the same as the traditional UNIX behavior of inheriting priv-
     ilege.

     Since the setlogin() system call is restricted to the super-user, it is
     assumed that (like	all other privileged programs) the programmer has
     taken adequate precautions	to prevent security violations.

RETURN VALUES
     If	a call to getlogin() succeeds, it returns a pointer to a null-termi-
     nated string in a static buffer, or NULL if the name has not been set.
     getlogin_r() returns zero if successful, or the error number upon fail-
     ure.

     The setlogin() function returns the value 0 if successful;	otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

ERRORS
     The following errors may be returned by these calls:

     [EFAULT]		The name parameter gave	an invalid address.

     [EINVAL]		The name parameter pointed to a	string that was	too
			long.  Login names are limited to MAXLOGNAME (from
			<sys/param.h>) characters, currently 17	including
			null.

     [EPERM]		The caller tried to set	the login name and was not the
			super-user.

     [ERANGE]		The size of the	buffer is smaller than the result to
			be returned.

SEE ALSO
     setsid(2),	daemon(3)

BUGS
     In	earlier	versions of the	system,	getlogin() failed unless the process
     was associated with a login terminal.  The	current	implementation (using
     setlogin()) allows	getlogin to succeed even when the process has no con-
     trolling terminal.	 In earlier versions of	the system, the	value returned
     by	getlogin() could not be	trusted	without	checking the user ID.  Porta-
     ble programs should probably still	make this check.

HISTORY
     The getlogin() function first appeared in 4.4BSD.	The return value of
     getlogin_r() was changed from earlier versions of FreeBSD to be confor-
     mant with ISO/IEC 9945-1:1996 (``POSIX.1'').

STANDARDS
     getlogin()	and getlogin_r() conform to ISO/IEC 9945-1:1996	(``POSIX.1'').

FreeBSD	9.3			 June 9, 1993			   FreeBSD 9.3

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | BUGS | HISTORY | STANDARDS

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