181 lines
5.2 KiB
Groff
181 lines
5.2 KiB
Groff
.\" $NetBSD: getlogin.2,v 1.18 2003/08/07 16:43:58 agc Exp $
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.\"
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.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getlogin.2 8.1 (Berkeley) 6/9/93
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.\"
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.Dd August 11, 2002
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.Dt GETLOGIN 2
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.Os
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.Sh NAME
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.Nm getlogin ,
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.Nm setlogin
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.Nd get/set login name
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft char *
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.Fn getlogin void
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.Ft int
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.Fn setlogin "const char *name"
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.Sh DESCRIPTION
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The
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.Fn getlogin
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routine
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returns the login name of the user associated with the current session,
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as previously set by
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.Fn setlogin .
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The name is normally associated with a login shell
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at the time a session is created,
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and is inherited by all processes descended from the login shell.
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(This is true even if some of those processes assume another user ID,
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for example when
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.Xr su 1
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is used.)
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.Pp
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.Fn setlogin
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sets the login name of the user associated with the current session to
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.Fa name .
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This call is restricted to the super-user, and
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is normally used only when a new session is being created on behalf
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of the named user
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(for example, at login time, or when a remote shell is invoked).
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.Pp
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.Em NOTE :
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There is only one login name per session.
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.Pp
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It is
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.Em CRITICALLY
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important to ensure that
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.Fn setlogin
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is only ever called after the process has taken adequate steps to ensure
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that it is detached from its parent's session.
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The
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.Em ONLY
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way to do this is via the
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.Fn setsid
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function.
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The
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.Fn daemon
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function calls
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.Fn setsid
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which is an ideal way of detaching from a controlling terminal and
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forking into the background.
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.Pp
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In particular, neither
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.Fn ioctl ttyfd TIOCNOTTY ...
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nor
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.Fn setpgid ...
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is sufficient to create a new session.
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.Pp
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Once a parent process has called
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.Fn setsid ,
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it is acceptable for some child of that process to then call
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.Fn setlogin ,
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even though it is not the session leader.
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Beware, however, that
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.Em ALL
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processes in the session will change their login name at the same time,
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even the parent.
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.Pp
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This is different from traditional
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.Ux
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privilege inheritance and as such can be counter-intuitive.
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.Pp
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Since the
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.Fn setlogin
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routine is restricted to the super-user, it is assumed that (like
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all other privileged programs) the programmer has taken adequate
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precautions to prevent security violations.
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.Sh RETURN VALUES
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If a call to
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.Fn getlogin
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succeeds, it returns a pointer to a null-terminated string in a static buffer.
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If the name has not been set, it returns
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.Dv NULL .
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If a call to
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.Fn setlogin
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succeeds, a value of 0 is returned.
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If
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.Fn setlogin
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fails, a value of -1 is returned and an error code is
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placed in the global location
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.Va errno .
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.Sh ERRORS
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The following errors may be returned by these calls:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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The
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.Fa name
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parameter gave an
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invalid address.
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.It Bq Er EINVAL
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The
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.Fa name
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parameter
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pointed to a string that was too long.
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Login names are limited to
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.Dv MAXLOGNAME
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(from
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.Ao Pa sys/param.h Ac )
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characters, currently 16.
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.It Bq Er EPERM
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The caller tried to set the login name and was not the super-user.
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.El
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.Sh SEE ALSO
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.Xr setsid 2
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.Sh STANDARDS
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The
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.Fn getlogin
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function conforms to
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.St -p1003.1-90 .
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.Sh HISTORY
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The
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.Fn getlogin
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function first appeared in
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.Bx 4.4 .
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.Sh BUGS
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Login names are limited in length by
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.Fn setlogin .
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However, lower limits are placed on login names elsewhere in the system
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.Pf ( Dv UT_NAMESIZE
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in
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.Ao Pa utmp.h Ac ) .
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.Pp
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In earlier versions of the system,
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.Fn getlogin
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failed unless the process was associated with a login terminal.
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The current implementation (using
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.Fn setlogin )
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allows getlogin to succeed even when the process has no controlling terminal.
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In earlier versions of the system, the value returned by
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.Fn getlogin
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could not be trusted without checking the user ID.
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Portable programs should probably still make this check.
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