| GETLOGIN(2) | System Calls Manual | GETLOGIN(2) | 
getlogin, getlogin_r,
  setlogin —
#include <unistd.h>
char *
  
  getlogin(void);
int
  
  getlogin_r(char
    *name, size_t
  len);
int
  
  setlogin(const
    char *name);
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.)
The getlogin_r() function provides the
    same service as getlogin(), however 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. The ONLY way to do this is via the
    setsid() function. The
    daemon() function calls
    setsid() which is an ideal way of detaching from a
    controlling terminal and forking into the background.
In particular, neither
    ioctl(ttyfd,
    TIOCNOTTY, ...) nor
    setpgid(...) is sufficient to
    create a new session.
Once a parent process has called setsid(),
    it is acceptable for some child of that process to then call
    setlogin(), even though it is not the session
    leader. Beware, however, that ALL processes in the session
    will change their login name at the same time, even the parent.
This is different from traditional UNIX privilege inheritance and as such can be counter-intuitive.
Since the setlogin() routine 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.
getlogin() succeeds, it returns a pointer
  to a null-terminated string in a static buffer. If the name has not been set,
  it returns NULL.
If a call to setlogin() succeeds, a value
    of 0 is returned. If setlogin() fails, a value of -1
    is returned and an error code is placed in the global location
    errno.
The getlogin_r() function returns zero if
    successful, or the error number upon failure.
EFAULT]EINVAL]MAXLOGNAME (from
      ⟨sys/param.h⟩) characters, currently
      16.EPERM]ERANGE]getlogin() and getlogin_r()
  functions conform to ISO/IEC 9945-1:1996
  (“POSIX.1”).
getlogin() function first appeared in
  4.4BSD.
setlogin().
  However, lower limits are placed on login names elsewhere in the system
  (UT_NAMESIZE in
  ⟨utmp.h⟩).
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.
| January 6, 2009 | NetBSD 10.0 |