1.\" $NetBSD: getlogin.2,v 1.15 2002/10/01 18:10:44 wiz Exp $ 2.\" 3.\" Copyright (c) 1989, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)getlogin.2 8.1 (Berkeley) 6/9/93 35.\" 36.Dd August 11, 2002 37.Dt GETLOGIN 2 38.Os 39.Sh NAME 40.Nm getlogin , 41.Nm setlogin 42.Nd get/set login name 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.Fd #include \*[Lt]unistd.h\*[Gt] 47.Ft char * 48.Fn getlogin void 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 setlogin 67sets the login name of the user associated with the current session to 68.Fa name . 69This call is restricted to the super-user, and 70is normally used only when a new session is being created on behalf 71of the named user 72(for example, at login time, or when a remote shell is invoked). 73.Pp 74.Em NOTE : 75There is only one login name per session. 76.Pp 77It is 78.Em CRITICALLY 79important to ensure that 80.Fn setlogin 81is only ever called after the process has taken adequate steps to ensure 82that it is detached from its parent's session. 83The 84.Em ONLY 85way to do this is via the 86.Fn setsid 87function. 88The 89.Fn daemon 90function calls 91.Fn setsid 92which is an ideal way of detaching from a controlling terminal and 93forking into the background. 94.Pp 95In particular, neither 96.Fn ioctl ttyfd TIOCNOTTY ... 97nor 98.Fn setpgid ... 99is sufficient to create a new session. 100.Pp 101Once a parent process has called 102.Fn setsid , 103it is acceptable for some child of that process to then call 104.Fn setlogin , 105even though it is not the session leader. 106Beware, however, that 107.Em ALL 108processes in the session will change their login name at the same time, 109even the parent. 110.Pp 111This is different from traditional 112.Ux 113privilege inheritance and as such can be counter-intuitive. 114.Pp 115Since the 116.Fn setlogin 117routine is restricted to the super-user, it is assumed that (like 118all other privileged programs) the programmer has taken adequate 119precautions to prevent security violations. 120.Sh RETURN VALUES 121If a call to 122.Fn getlogin 123succeeds, it returns a pointer to a null-terminated string in a static buffer. 124If the name has not been set, it returns 125.Dv NULL . 126If a call to 127.Fn setlogin 128succeeds, a value of 0 is returned. 129If 130.Fn setlogin 131fails, a value of -1 is returned and an error code is 132placed in the global location 133.Va errno . 134.Sh ERRORS 135The following errors may be returned by these calls: 136.Bl -tag -width Er 137.It Bq Er EFAULT 138The 139.Fa name 140parameter gave an 141invalid address. 142.It Bq Er EINVAL 143The 144.Fa name 145parameter 146pointed to a string that was too long. 147Login names are limited to 148.Dv MAXLOGNAME 149(from 150.Ao Pa sys/param.h Ac ) 151characters, currently 16. 152.It Bq Er EPERM 153The caller tried to set the login name and was not the super-user. 154.El 155.Sh SEE ALSO 156.Xr setsid 2 157.Sh STANDARDS 158The 159.Fn getlogin 160function conforms to 161.St -p1003.1-90 . 162.Sh HISTORY 163The 164.Fn getlogin 165function first appeared in 166.Bx 4.4 . 167.Sh BUGS 168Login names are limited in length by 169.Fn setlogin . 170However, lower limits are placed on login names elsewhere in the system 171.Pf ( Dv UT_NAMESIZE 172in 173.Ao Pa utmp.h Ac ) . 174.Pp 175In earlier versions of the system, 176.Fn getlogin 177failed unless the process was associated with a login terminal. 178The current implementation (using 179.Fn setlogin ) 180allows getlogin to succeed even when the process has no controlling terminal. 181In earlier versions of the system, the value returned by 182.Fn getlogin 183could not be trusted without checking the user ID. 184Portable programs should probably still make this check. 185