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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)getlogin.2 8.1 (Berkeley) 6/9/93 33.\" $FreeBSD: src/lib/libc/sys/getlogin.2,v 1.14.2.6 2001/12/14 18:34:00 ru Exp $ 34.\" $DragonFly: src/lib/libc/sys/getlogin.2,v 1.5 2007/07/30 22:11:33 swildner Exp $ 35.\" 36.Dd June 9, 1993 37.Dt GETLOGIN 2 38.Os 39.Sh NAME 40.Nm getlogin , 41.Nm getlogin_r , 42.Nm setlogin 43.Nd get/set login name 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In unistd.h 48.Ft char * 49.Fn getlogin void 50.In sys/param.h 51.Ft int 52.Fn getlogin_r "char *name" "int len" 53.Ft int 54.Fn setlogin "const char *name" 55.Sh DESCRIPTION 56The 57.Fn getlogin 58routine 59returns the login name of the user associated with the current session, 60as previously set by 61.Fn setlogin . 62The name is normally associated with a login shell 63at the time a session is created, 64and is inherited by all processes descended from the login shell. 65(This is true even if some of those processes assume another user ID, 66for example when 67.Xr su 1 68is used). 69.Pp 70.Fn getlogin_r 71provides the same service as 72.Fn getlogin 73except the caller must provide the buffer 74.Fa name 75with length 76.Fa len 77bytes 78to hold the result. The buffer should be at least 79.Dv MAXLOGNAME 80bytes in length. 81.Pp 82.Fn Setlogin 83sets the login name of the user associated with the current session to 84.Fa name . 85This call is restricted to the super-user, and 86is normally used only when a new session is being created on behalf 87of the named user 88(for example, at login time, or when a remote shell is invoked). 89.Pp 90.Em NOTE : 91There is only one login name per session. 92.Pp 93It is 94.Em CRITICALLY 95important to ensure that 96.Fn setlogin 97is only ever called after the process has taken adequate steps to ensure 98that it is detached from its parent's session. 99Making a 100.Fn setsid 101system call is the 102.Em ONLY 103way to do this. The 104.Fn daemon 105library call calls 106.Fn setsid 107which is an ideal way of detaching from a controlling terminal and 108forking into the background. 109.Pp 110In particular, doing a 111.Fn ioctl ttyfd TIOCNOTTY ...\& 112or 113.Fn setpgrp ...\& 114is 115.Em NOT 116sufficient. 117.Pp 118Once a parent process does a 119.Fn setsid 120call, it is acceptable for some child of that process to then do a 121.Fn setlogin 122even though it is not the session leader, but beware that ALL processes 123in the session will change their login name at the same time, even the 124parent. 125.Pp 126This is not the same as the traditional 127.Ux 128behavior of inheriting privilege. 129.Pp 130Since the 131.Fn setlogin 132system call is restricted to the super-user, it is assumed that (like 133all other privileged programs) the programmer has taken adequate 134precautions to prevent security violations. 135.Sh RETURN VALUES 136If a call to 137.Fn getlogin 138succeeds, it returns a pointer to a null-terminated string in a static buffer, 139or 140.Dv NULL 141if the name has not been set. 142.Fn getlogin_r 143returns zero if successful, or the error number upon failure. 144.Pp 145.Rv -std setlogin 146.Sh ERRORS 147The following errors may be returned by these calls: 148.Bl -tag -width Er 149.It Bq Er EFAULT 150The 151.Fa name 152parameter gave an 153invalid address. 154.It Bq Er EINVAL 155The 156.Fa name 157parameter 158pointed to a string that was too long. 159Login names are limited to 160.Dv MAXLOGNAME 161(from 162.In sys/param.h ) 163characters, currently 17 including null. 164.It Bq Er EPERM 165The caller tried to set the login name and was not the super-user. 166.It Bq Er ERANGE 167The size of the buffer is smaller than the result to be returned. 168.El 169.Sh SEE ALSO 170.Xr setsid 2 , 171.Xr daemon 3 172.Sh STANDARDS 173.Fn getlogin 174and 175.Fn getlogin_r 176conform to 177.St -p1003.1-96 . 178.Sh HISTORY 179The 180.Fn getlogin 181function first appeared in 182.Bx 4.4 . 183The return value of 184.Fn getlogin_r 185was changed from earlier versions of 186.Fx 187to be conformant with 188.St -p1003.1-96 . 189.Sh BUGS 190In earlier versions of the system, 191.Fn getlogin 192failed unless the process was associated with a login terminal. 193The current implementation (using 194.Fn setlogin ) 195allows getlogin to succeed even when the process has no controlling terminal. 196In earlier versions of the system, the value returned by 197.Fn getlogin 198could not be trusted without checking the user ID. 199Portable programs should probably still make this check. 200