|GETLOGIN(2)||System Calls Manual||GETLOGIN(2)|
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() routine is a reentrant
getlogin(). It is functionally identical
getlogin() except that the caller must provide a
buffer, name, in which to store the user's login name
and a corresponding length parameter, namelen, that
specifies the size of the buffer. The buffer should be large enough to store
the login name and a trailing NUL (typically
setlogin() sets the login name of the user
associated with the current session to name. This call
is restricted to the superuser, 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
TIOCNOTTY, ...) nor
setpgrp(...) is sufficient to
create a new session.
Once a parent process has called
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.
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
getlogin() succeeds, it returns a pointer to a NUL-terminated string in a static buffer. If the name has not been set, it returns
NULL. If a call to
getlogin_r() succeeds, a value of 0 is returned, else the error number is returned. 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.
setlogin() will succeed unless:
getlogin_r() may return the
setlogin() may return the following
getlogin_r() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).
getlogin() function first appeared in 4.2BSD.
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.
|September 10, 2015||OpenBSD-current|