November 1, 2005 LOGIN 1

### NAME

login - authenticate users and set up their session environment

### SYNOPSIS

login [-Ffps] [-a address] [-h hostname] [user]

### DESCRIPTION

The login utility logs users (and pseudo-users) into the computer system.

If no user is specified, or if a user is specified and authentication of the user fails, login prompts for a user name. Authentication of users is done via passwords. If the user can be authenticated via S/Key, then the S/Key challenge is incorporated in the password prompt. The user then has the option of entering their Kerberos or normal password or the S/Key response. Neither will be echoed.

The options are as follows:

-a
  The -a option specifies the address of the host from which the connection was received. It is used by various daemons such as telnetd(8). This option may only be used by the super-user.

-F
  The -F option acts like the -f option, but also indicates to login(1) that it should attempt to rewrite an existing kerberos5 credentials cache (specified by the KRB5CCNAME environment variable) after dropping permissions to the user logging in. This flag is not supported under pam(8).

-f
  The -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 super-user or when an already logged in user is logging in as themselves.

-h
  The -h option specifies the host from which the connection was received. It is used by various daemons such as telnetd(8). This option may only be used by the super-user.

-p
  By default, login discards any previous environment. The -p option disables this behavior.

-s
  Require a secure authentication mechanism like Kerberos or S/Key to be used. This flag is not supported under pam(8).

If a user other than the superuser attempts to login while the file ```/etc/nologin` exists, login displays its contents to the user and exits. This is used by shutdown(8) to prevent normal users from logging in when the system is about to go down.

Immediately after logging a user in, login displays the system copyright notice, the date and time the user last logged in, the message of the day as well as other information. If the file `````.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 uucp(1). login then records an entry in the wtmp(5) and utmp(5) files, executes site-specific login commands via the ttyaction(3) facility with an action of "login", and executes the user's command interpreter.

login enters information into the environment (see environ(7)) specifying the user's home directory (HOME), command interpreter (SHELL), search path (PATH), terminal type (TERM) and user name (both LOGNAME and USER).

The standard shells, csh(1) and sh(1), do not fork before executing the login utility.

### FILES

```/etc/motd`
  message-of-the-day
```/etc/nologin`
  disallows non-superuser logins
```/var/run/utmp`
  list of current logins
```/var/log/lastlog`
  last login account records
```/var/log/wtmp`
  login account records
```/var/mail/user`
  system mailboxes
```.hushlogin`
  makes login quieter

### SEE ALSO

chpass(1), passwd(1), rlogin(1), skey(1), getpass(3), ttyaction(3), login.conf(5), passwd.conf(5), utmp(5), environ(7), kerberos(8), pam(8)

### HISTORY

A login appeared in Version 6 `AT&T UNIX`.

### TRADEMARKS AND PATENTS

S/Key is a trademark of Bellcore.