#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).
The
getlogin_r ();
function
provides the same service as
getlogin ();
except the caller must provide the buffer
Fa name
with length
Fa 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
Fa name .
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).
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 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.
The
getlogin_r ();
function
returns zero if successful, or the error number upon failure.
Rv -std setlogin
ERRORS
The following errors may be returned by these calls:
Bq Er EFAULT
The
Fa name
argument gave an
invalid address.
Bq Er EINVAL
The
Fa name
argument
pointed to a string that was too long.
Login names are limited to
MAXLOGNAME
(from
In sys/param.h )
characters, currently 17 including null.
Bq Er EPERM
The caller tried to set the login name and was not the super-user.
Bq Er ERANGE
The size of the buffer is smaller than the result to be returned.
The
getlogin ();
system call
and
the
getlogin_r ();
function
conform to
St -p1003.1-96 .
HISTORY
The
getlogin ();
system call first appeared in
BSD 4.4
The return value of
getlogin_r ();
was changed from earlier versions of
Fx to be conformant with
St -p1003.1-96 .
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.
