1.\" Copyright (c) 1989, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)getlogin.2 8.1 (Berkeley) 6/9/93 29.\" $FreeBSD: src/lib/libc/sys/getlogin.2,v 1.14.2.6 2001/12/14 18:34:00 ru Exp $ 30.\" $DragonFly: src/lib/libc/sys/getlogin.2,v 1.5 2007/07/30 22:11:33 swildner Exp $ 31.\" 32.Dd June 9, 1993 33.Dt GETLOGIN 2 34.Os 35.Sh NAME 36.Nm getlogin , 37.Nm getlogin_r , 38.Nm setlogin 39.Nd get/set login name 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In unistd.h 44.Ft char * 45.Fn getlogin void 46.In sys/param.h 47.Ft int 48.Fn getlogin_r "char *name" "int len" 49.Ft int 50.Fn setlogin "const char *name" 51.Sh DESCRIPTION 52The 53.Fn getlogin 54routine 55returns the login name of the user associated with the current session, 56as previously set by 57.Fn setlogin . 58The name is normally associated with a login shell 59at the time a session is created, 60and is inherited by all processes descended from the login shell. 61(This is true even if some of those processes assume another user ID, 62for example when 63.Xr su 1 64is used). 65.Pp 66.Fn getlogin_r 67provides the same service as 68.Fn getlogin 69except the caller must provide the buffer 70.Fa name 71with length 72.Fa len 73bytes 74to hold the result. The buffer should be at least 75.Dv MAXLOGNAME 76bytes in length. 77.Pp 78.Fn Setlogin 79sets the login name of the user associated with the current session to 80.Fa name . 81This call is restricted to the super-user, and 82is normally used only when a new session is being created on behalf 83of the named user 84(for example, at login time, or when a remote shell is invoked). 85.Pp 86.Em NOTE : 87There is only one login name per session. 88.Pp 89It is 90.Em CRITICALLY 91important to ensure that 92.Fn setlogin 93is only ever called after the process has taken adequate steps to ensure 94that it is detached from its parent's session. 95Making a 96.Fn setsid 97system call is the 98.Em ONLY 99way to do this. The 100.Fn daemon 101library call calls 102.Fn setsid 103which is an ideal way of detaching from a controlling terminal and 104forking into the background. 105.Pp 106In particular, doing a 107.Fn ioctl ttyfd TIOCNOTTY ...\& 108or 109.Fn setpgrp ...\& 110is 111.Em NOT 112sufficient. 113.Pp 114Once a parent process does a 115.Fn setsid 116call, it is acceptable for some child of that process to then do a 117.Fn setlogin 118even though it is not the session leader, but beware that ALL processes 119in the session will change their login name at the same time, even the 120parent. 121.Pp 122This is not the same as the traditional 123.Ux 124behavior of inheriting privilege. 125.Pp 126Since the 127.Fn setlogin 128system call is restricted to the super-user, it is assumed that (like 129all other privileged programs) the programmer has taken adequate 130precautions to prevent security violations. 131.Sh RETURN VALUES 132If a call to 133.Fn getlogin 134succeeds, it returns a pointer to a null-terminated string in a static buffer, 135or 136.Dv NULL 137if the name has not been set. 138.Fn getlogin_r 139returns zero if successful, or the error number upon failure. 140.Pp 141.Rv -std setlogin 142.Sh ERRORS 143The following errors may be returned by these calls: 144.Bl -tag -width Er 145.It Bq Er EFAULT 146The 147.Fa name 148parameter gave an 149invalid address. 150.It Bq Er EINVAL 151The 152.Fa name 153parameter 154pointed to a string that was too long. 155Login names are limited to 156.Dv MAXLOGNAME 157(from 158.In sys/param.h ) 159characters, currently 17 including null. 160.It Bq Er EPERM 161The caller tried to set the login name and was not the super-user. 162.It Bq Er ERANGE 163The size of the buffer is smaller than the result to be returned. 164.El 165.Sh SEE ALSO 166.Xr setsid 2 , 167.Xr daemon 3 168.Sh STANDARDS 169.Fn getlogin 170and 171.Fn getlogin_r 172conform to 173.St -p1003.1-96 . 174.Sh HISTORY 175The 176.Fn getlogin 177function first appeared in 178.Bx 4.4 . 179The return value of 180.Fn getlogin_r 181was changed from earlier versions of 182.Fx 183to be conformant with 184.St -p1003.1-96 . 185.Sh BUGS 186In earlier versions of the system, 187.Fn getlogin 188failed unless the process was associated with a login terminal. 189The current implementation (using 190.Fn setlogin ) 191allows getlogin to succeed even when the process has no controlling terminal. 192In earlier versions of the system, the value returned by 193.Fn getlogin 194could not be trusted without checking the user ID. 195Portable programs should probably still make this check. 196