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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.\" 30.Dd September 9, 2020 31.Dt GETLOGIN 2 32.Os 33.Sh NAME 34.Nm getlogin , 35.Nm getlogin_r , 36.Nm setlogin 37.Nd get/set login name 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In unistd.h 42.Ft char * 43.Fn getlogin void 44.In sys/param.h 45.Ft int 46.Fn getlogin_r "char *name" "size_t len" 47.Ft int 48.Fn setlogin "const char *name" 49.Sh DESCRIPTION 50The 51.Fn getlogin 52routine 53returns the login name of the user associated with the current session, 54as previously set by 55.Fn setlogin . 56The name is normally associated with a login shell 57at the time a session is created, 58and is inherited by all processes descended from the login shell. 59(This is true even if some of those processes assume another user ID, 60for example when 61.Xr su 1 62is used). 63.Pp 64The 65.Fn getlogin_r 66function 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. 75The buffer should be at least 76.Dv MAXLOGNAME 77bytes in length. 78.Pp 79The 80.Fn setlogin 81system call 82sets the login name of the user associated with the current session to 83.Fa name . 84This system call is restricted to the super-user, and 85is normally used only when a new session is being created on behalf 86of the named user 87(for example, at login time, or when a remote shell is invoked). 88.Pp 89.Em NOTE : 90There is only one login name per session. 91.Pp 92It is 93.Em CRITICALLY 94important to ensure that 95.Fn setlogin 96is only ever called after the process has taken adequate steps to ensure 97that it is detached from its parent's session. 98Making a 99.Fn setsid 100system call is the 101.Em ONLY 102way to do this. 103The 104.Xr daemon 3 105function 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 120system call, 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 UNIX behavior of inheriting privilege. 127.Pp 128Since the 129.Fn setlogin 130system call is restricted to the super-user, it is assumed that (like 131all other privileged programs) the programmer has taken adequate 132precautions to prevent security violations. 133.Sh RETURN VALUES 134If a call to 135.Fn getlogin 136succeeds, it returns a pointer to a null-terminated string in a static buffer, 137or 138.Dv NULL 139if the name has not been set. 140The 141.Fn getlogin_r 142function 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 152argument gave an 153invalid address. 154.It Bq Er EINVAL 155The 156.Fa name 157argument 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 33 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 173The 174.Fn getlogin 175system call 176and 177the 178.Fn getlogin_r 179function 180conform to 181.St -p1003.1-96 . 182.Sh HISTORY 183The 184.Fn getlogin 185system call first appeared in 186.Bx 4.4 . 187The return value of 188.Fn getlogin_r 189was changed from earlier versions of 190.Fx 191to be conformant with 192.St -p1003.1-96 . 193.Sh BUGS 194In earlier versions of the system, 195.Fn getlogin 196failed unless the process was associated with a login terminal. 197The current implementation (using 198.Fn setlogin ) 199allows getlogin to succeed even when the process has no controlling terminal. 200In earlier versions of the system, the value returned by 201.Fn getlogin 202could not be trusted without checking the user ID. 203Portable programs should probably still make this check. 204