69112cca60
getlogin_r is specified by POSIX to to take a size_t len, not int. Fix our version to do the same, bump the symbol version due to ABI change and provide compat. This was reported to break compilation of Ruby 2.8. Some discussion about the necessity of the ABI compat did take place in the review. While many 64-bit platforms would likely be passing it in a 64-bit register and zero-extended and thus, not notice ABI breakage, some do sign-extend (e.g. mips). PR: 247102 Submitted by: Bertram Scharpf <software@bertram-scharpf.de> (original) Submitted by: cem (ABI compat) MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D26335
205 lines
5.5 KiB
Groff
205 lines
5.5 KiB
Groff
.\" 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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.\" $FreeBSD$
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.\"
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.Dd September 9, 2020
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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 getlogin_r ,
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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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.In sys/param.h
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.Ft int
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.Fn getlogin_r "char *name" "size_t len"
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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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The
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.Fn getlogin_r
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function
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provides the same service as
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.Fn getlogin
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except the caller must provide the buffer
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.Fa name
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with length
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.Fa len
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bytes
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to hold the result.
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The buffer should be at least
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.Dv MAXLOGNAME
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bytes in length.
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.Pp
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The
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.Fn setlogin
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system call
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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 system 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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Making a
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.Fn setsid
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system call is the
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.Em ONLY
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way to do this.
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The
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.Xr daemon 3
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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, doing a
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.Fn ioctl ttyfd TIOCNOTTY ...\&
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or
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.Fn setpgrp ...\&
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is
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.Em NOT
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sufficient.
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.Pp
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Once a parent process does a
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.Fn setsid
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system call, it is acceptable for some child of that process to then do a
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.Fn setlogin
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even though it is not the session leader, but beware that ALL processes
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in the session will change their login name at the same time, even the
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parent.
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.Pp
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This is not the same as the traditional UNIX behavior of inheriting privilege.
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.Pp
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Since the
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.Fn setlogin
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system call 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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or
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.Dv NULL
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if the name has not been set.
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The
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.Fn getlogin_r
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function
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returns zero if successful, or the error number upon failure.
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.Pp
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.Rv -std setlogin
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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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argument 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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argument
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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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.In sys/param.h )
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characters, currently 33 including null.
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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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.It Bq Er ERANGE
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The size of the buffer is smaller than the result to be returned.
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.El
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.Sh SEE ALSO
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.Xr setsid 2 ,
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.Xr daemon 3
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.Sh STANDARDS
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The
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.Fn getlogin
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system call
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and
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the
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.Fn getlogin_r
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function
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conform to
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.St -p1003.1-96 .
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.Sh HISTORY
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The
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.Fn getlogin
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system call first appeared in
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.Bx 4.4 .
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The return value of
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.Fn getlogin_r
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was changed from earlier versions of
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.Fx
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to be conformant with
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.St -p1003.1-96 .
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.Sh BUGS
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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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