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GETLOGIN(2)

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NAME    [Toc]    [Back]

     getlogin, setlogin - get/set login name

SYNOPSIS    [Toc]    [Back]

     #include <unistd.h>

     char *
     getlogin(void);

     int
     getlogin_r(char *name, size_t namelen);

     int
     setlogin(const char *name);

DESCRIPTION    [Toc]    [Back]

     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()   routine   is  a  reentrant  version  of
getlogin().  It is
     functionally identical to 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 LOGIN_NAME_MAX bytes).

     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  ioctl(ttyfd,  TIOCNOTTY,  ...) nor
setpgrp(...) 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.

RETURN VALUES    [Toc]    [Back]

     If a call to 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 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.

ERRORS    [Toc]    [Back]

     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-1 (from
                   <sys/param.h>) characters, currently 31.

     [EPERM]       The caller tried to set the login name and was
not the superuser.


     [ERANGE]      The buffer passed to getlogin_r() is not large
enough to
                   store the user's login name.

SEE ALSO    [Toc]    [Back]

      
      
     setsid(2)

HISTORY    [Toc]    [Back]

     The getlogin() function first appeared in 4.2BSD.

BUGS    [Toc]    [Back]

     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.

OpenBSD      3.6                           June      9,      1993
[ Back ]
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