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GETLOGIN(2)		       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, size_t 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 normally
     associated with a login shell at the time a session is created, and is  in-
     herited  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).

     The  getlogin_r()	function  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.

     The  setlogin() system call sets the login name of the user associated with
     the current session to name.  This system call is restricted to the  super-
     user,  and is normally used only when a new session is being created on be-
     half 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(3) function calls setsid() which is an ideal way of
     detaching from a controlling terminal and forking into the background.

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

     Once  a  parent  process  does a setsid() system 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  privi-
     lege.

     Since the setlogin() system call is restricted to the super-user, it is as-
     sumed  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-terminated
     string in a static buffer, or NULL if the name has not been set.  The  get-
     login_r()	function  returns  zero  if successful, or the error number upon
     failure.

     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 argument gave an invalid address.

     [EINVAL]		The name argument pointed to a string that was too long.
			Login	names	are   limited	to   MAXLOGNAME    (from
			<sys/param.h>) characters, currently 33 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)

STANDARDS
     The getlogin() system call and the getlogin_r() function conform to ISO/IEC
     9945-1:1996 ("POSIX.1").

HISTORY
     The  getlogin()  system call first appeared in 4.4BSD.  The return value of
     getlogin_r() was changed from earlier versions of FreeBSD to be  conformant
     with ISO/IEC 9945-1:1996 ("POSIX.1").

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

FreeBSD ports 15.quarterly	September 9, 2020		     GETLOGIN(2)

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