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document -u flag and environment variables

.\"	$OpenBSD: login.1,v 1.14 2000/11/29 23:15:09 millert Exp $
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.\"	@(#)login.1	8.2 (Berkeley) 5/5/94
.\"
.Dd May 5, 1994
.Dt LOGIN 1
.Os
.Sh NAME
.Nm login
.Nd log into the computer
.Sh SYNOPSIS
.Nm login
.Op Fl fp
.Op Fl h Ar hostname
.Op Fl u Ar username
.Op Ar user
.Sh DESCRIPTION
The
.Nm
utility logs users (and pseudo-users) into the computer system.
.Pp
If no user is specified, or if a user is specified and authentication
of the user fails,
.Nm
prompts for a user name.
Authentication of users is done via passwords.
Alternately, the user can enter the password
.Qq s/key ,
in which case
S/Key authentication of users is performed, as descibed in
.Xr skey 1 .
S/Key is a Trademark of Bellcore.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl f
The
.Fl f
option is used when a user name is specified to indicate that proper
authentication has already been done and that no password need be
requested.
This option may only be used by the superuser or when an already
logged in user is logging in as themselves.
.It Fl h Ar hostname
Specifies the host from which the connection was received.
It is used by various daemons such as
.Xr telnetd 8 .
This option may only be used by the superuser.
.It Fl u Ar username
Specifies the remote user that initiated the connection.
It is used by various daemons such as
.Xr telnetd 8 .
This option may only be used by the superuser.
.It Fl p
By default,
.Nm
discards any previous environment.
The
.Fl p
option disables this behavior.
.El
.Pp
If the file
.Pa /etc/nologin
exists,
.Nm
displays its contents to the user and exits.
This is used by
.Xr shutdown 8
to prevent users from logging in when the system is about to go down.
.Pp
If the file
.Pa /etc/fbtab
exists,
.Nm
changes the protection and ownership of certain devices specified in this
file.
.Pp
If the file
.Pa /var/log/failedlogin
exists,
.Nm
will record failed login attempts in this file.
.Pp
Immediately after logging a user in,
.Nm
displays the system copyright notice, the date and time the user last
logged in, the date and time of the last unsuccessful login (if the file
.Pa /var/log/failedlogin
exists), the message of the day as well as other information.
If the file
.Dq Pa .hushlogin
exists in the user's home directory, all of these messages are suppressed.
This is to simplify logins for non-human users, such as
.Xr uucp 1 .
.Nm
then records an entry in the
.Xr wtmp 5
and
.Xr utmp 5
files and executes the user's command interpreter.
.Pp
.Nm
enters information into the environment (see
.Xr environ 7 )
specifying the user's home directory
.Pq Ev HOME ,
command interpreter
.Pq Ev SHELL ,
search path
.Pq Ev PATH ,
terminal type
.Pq Ev TERM ,
and user name
.Po both Ev LOGNAME and Ev USER
.Pc .
.Pp
The standard shells,
.Xr csh 1
and
.Xr sh 1 ,
do not fork before executing the
.Nm
utility.
.Sh ENVIRONMENT
.Nm
sets the following environment variables:
.Bl -tag -width REMOTEHOST
.It Ev HOME
The user's home directory, as specified by the password database.
.It Ev SHELL
The user's shell, as specified by the password database.
.It Ev TERM
The user's terminal type, if it can be determined.
.It Ev LOGNAME
The user's login name.
.It Ev USER
Same as
.Ev LOGNAME .
.It Ev REMOTEHOST
The name of the host from which the user logged in, if the
.Fl h
flag was specified.
.It Ev REMOTEUSER
The name of the remote user who initiated the connection, if the
.Fl u
flag was specified.
.El
.Sh FILES
.Bl -tag -width /var/log/failedlogin -compact
.It Pa /etc/fbtab
changes device protections
.It Pa /etc/motd
message-of-the-day
.It Pa /etc/nologin
disallows logins
.It Pa /var/run/utmp
current logins
.It Pa /var/log/lastlog
last login account records
.It Pa /var/log/wtmp
login account records
.It Pa /var/log/failedlogin
failed login account records
.It Pa /var/mail/user
system mailboxes
.It Pa \&.hushlogin
makes login quieter
.El
.Sh SEE ALSO
.Xr chpass 1 ,
.Xr passwd 1 ,
.Xr rlogin 1 ,
.Xr skey 1 ,
.Xr getpass 3 ,
.Xr fbtab 5 ,
.Xr utmp 5 ,
.Xr environ 7
.Sh HISTORY
A
.Nm
utility appeared in
.At v5 .