1.\" Copyright (c) 1980, 1990 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" %sccs.include.redist.roff% 5.\" 6.\" @(#)login.1 6.11 (Berkeley) 04/26/91 7.\" 8.Dd 9.Dt LOGIN 1 10.Os BSD 4 11.Sh NAME 12.Nm login 13.Nd log on to a system 14.Sh SYNOPSIS 15.Nm login 16.Op Fl p 17.Op Ar user 18.Nm login 19.Op Fl p 20.Op Fl h Ar hostname 21.Op Fl f 22.Op Ar user 23.Sh DESCRIPTION 24The 25.Nm login 26command 27logs the given user 28.Ar user 29onto a 30.Tn UNIX 31system. 32It has three different uses; 33logging a user on to a system, 34re-logging a user in as another 35user (without logging out), 36and logging non-human users (programs) 37onto other systems. 38In the first two instances, the 39.Nm login 40program protects the user's password 41from prying eyes by disabling the 42echoing of typed characters from terminals. 43.Pp 44Options available: 45.Bl -tag -width xxxxhostname 46.It Fl f 47The 48.Fl f 49option is used with 50a username on the command line, at initial login, 51to indicate that proper authentication has already been done 52and that no password need be requested. 53This option may be used by the superuser 54or by the user specified on the command line. 55.It Fl h Ar hostname 56The 57.Fl h 58option is used by 59.Xr telnetd 8 60(at initial login) 61and other servers to list the host from which 62the connection was received. 63.It Fl p 64Causes the remainder of the environment to be preserved, 65otherwise any previous environment is discarded. 66.El 67.Pp 68In the first usage of 69.Nm login 70it is invoked by the 71.Xr getty 8 72program which is responsible for initializing communications between 73a users terminal and 74.Tn UNIX . 75.Nm Login 76starts up 77by prompting for a user name; when it recives a valid user name and password 78the user is logged in and may proceed to work on the system. 79.Pp 80The second usage of 81.Nm login 82allows a user to log in as another user 83without having logout. 84In this case 85.Nm login 86is invoked from 87.Xr sh 1 88or 89.Xr csh 1 90as shown above in the first synopsis. 91.Pp 92The third usage is by system programs and servers like 93.Xr telnetd 94and may only be initiated by the super-user. 95.Pp 96Immediately after logging a user in, 97.Nm login 98writes the date and time the user last logged in, 99the message of the day and notifies the user 100if he/she has new mail. 101If the file 102.Dq Pa .hushlogin 103exists in the user's home directory, 104both the message of the day and mail notification are 105suppressed; this 106is usually used to simplify the logins for non-human users, such as 107.Xr uucp 1 . 108.Nm login 109then records an entry in the 110.Xr wtmp 5 111and 112.Xr utmp 5 113files and provides the user 114with the command shell found in the user's 115.Xr passwd 5 116entry. 117.Pp 118Login also modifies the 119environment (see 120.Xr environ 7 ) 121with information specifying home directory, command interpreter, terminal 122type (if available) and user name. 123.Pp 124If the file 125.Pa /etc/nologin 126exists, 127.Nm login 128prints its contents on the user's terminal and exits. This is 129used by 130.Xr shutdown 8 131to prevent users from logging in when the system is about to go down. 132.Pp 133The standard shells, 134.Xr csh 1 135and 136.Xr sh 1 137notice when login is invoked on a command line and execute 138it immediately with out calling 139.Xr fork 2 . 140.Sh FILES 141.Bl -tag -width /var/log/wtmp -compact 142.It Pa /var/run/utmp 143current logins 144.It Pa /var/log/wtmp 145login account records 146.It Pa /var/mail/* 147undelivered mail 148.It Pa /etc/motd 149message-of-the-day 150.It Pa /etc/passwd.* 151password files 152.It Pa /etc/nologin 153disallows logins 154.It Pa \&.hushlogin 155makes login quieter 156.El 157.Sh SEE ALSO 158.Xr mail 1 , 159.Xr passwd 1 , 160.Xr rlogin 1 , 161.Xr getpass 3 , 162.Xr passwd 5 , 163.Xr utmp 5 , 164.Xr environ 7 , 165.Xr init 8 , 166.Xr getty 8 , 167.Xr shutdown 8 , 168.Sh HISTORY 169A 170.Nm login 171appeared in 172.At v6 . 173.Sh DIAGNOSTICS 174Self explanatory. 175