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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
     normally 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
     normally 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
     background.

     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
     privilege.

     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-
     terminated 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
     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 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
     controlling terminal.  In earlier versions of the system, the value
     returned by getlogin() could not be trusted without checking the user ID.
     Portable 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
     conformant with ISO/IEC 9945-1:1996 (``POSIX.1'').

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

FreeBSD 11.0-PRERELEASE          June 9, 1993          FreeBSD 11.0-PRERELEASE

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

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