returns the login name of the user associated with the current session,
as previously set by
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
provides the same service as
except the caller must provide the buffer
to hold the result.
The buffer should be at least
bytes in length.
sets the login name of the user associated with the current session to
This system 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).
There is only one login name per session.
important to ensure that
is only ever called after the process has taken adequate steps to ensure
that it is detached from its parents session.
system call is the
way to do this.
which is an ideal way of detaching from a controlling terminal and
forking into the background.
In particular, doing a
ioctl ttyfd TIOCNOTTY ...
Once a parent process does a
system call, it is acceptable for some child of that process to then do a
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
This is not the same as the traditional UNIX behavior of inheriting privilege.
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.