NAME

login − sign on

SYNOPSIS

login [ name [ env-var ... ]]

DESCRIPTION

The login command is used at the beginning of each terminal session and allows you to identify yourself to the system.  It may be invoked as a command or by the system when a connection is first established.  Also, it is invoked by the system when a previous user has terminated the initial shell by typing a cntrl-d to indicate an “end-of-file.” (See How to Get Started at the beginning of this volume for instructions on how to dial up initially.) 

If login is invoked as a command it must replace the initial command interpreter.  This is accomplished by typing:

exec login

from the initial shell. 

login asks for your user name (if not supplied as an argument), and, if appropriate, your password.  Echoing is turned off (where possible) during the typing of your password, so it will not appear on the written record of the session. 

At some installations, an option may be invoked that will require you to enter a second “dialup” password.  This will occur only for dial-up connections, and will be prompted by the message “dialup password:”.  Both passwords are required for a successful login. 

If you do not complete the login successfully within a certain period of time (e.g., one minute), you are likely to be silently disconnected. 

After a successful login, accounting files are updated, the procedure /etc/profile is performed, the message-of-the-day, if any, is printed, the user-ID, the group-ID, the working directory, and the command interpreter (usually sh(1)) is initialized, and the file .profile in the working directory is executed, if it exists.  These specifications are found in the /etc/passwd file entry for the user.  The name of the command interpreter is − followed by the last component of the interpreter’s path name (i.e., −sh).  If this field in the password file is empty, then the default command interpreter, /bin/sh is used.  If this field is “∗”, then the named directory becomes the root directory, the starting point for path searches for path names beginning with a /.  At that point login is re-executed at the new level which must have its own root structure, including /etc/login and /etc/passwd. 

The basic environment is initialized to:

HOME=your-login-directory
PATH=:/bin:/usr/bin
SHELL=last-field-of-passwd-entry
MAIL=/usr/mail/your-login-name
TZ=timezone-specification

The environment may be expanded or modified by supplying additional arguments to login, either at execution time or when login requests your login name.  The arguments may take either the form xxx or xxx=yyy.  Arguments without an equal sign are placed in the environment as

Ln=xxx

where n is a number starting at 0 and is incremented each time a new variable name is required.  Variables containing an = are placed into the environment without modification.  If they already appear in the environment, then they replace the older value.  There are two exceptions.  The variables PATH and SHELL cannot be changed.  This prevents people, logging into restricted shell environments, from spawning secondary shells which are not restricted.  Both login and getty understand simple single-character quoting conventions.  Typing a backslash in front of a character quotes it and allows the inclusion of such things as spaces and tabs. 

FILES

/etc/utmpaccounting
/etc/wtmpaccounting
/usr/mail/your-namemailbox for user your-name
/etc/motdmessage-of-the-day
/etc/passwdpassword file
/etc/profilesystem profile
.profileuser’s login profile
/usr/adm/lastlogrecords last login time

SEE ALSO

mail(1), newgrp(1), sh(1), su(1M), passwd(4), profile(4), environ(5). 

DIAGNOSTICS

login incorrect if the user name or the password cannot be matched. 
No shell, cannot open password file, or no directory: consult a UNIX system programming counselor. 
No utmp entry. You must exec "login" from the lowest level "sh" if you attempted to execute login as a command without using the shell’s exec internal command or from other than the initial shell. 

NOTE

After a successful login, accounting files are updated and the user is informed of the existence of mail.  The message of the day is printed, as is the time of the last login.  Both are suppressed if the user’s home directory contains a ".hushlogin" file; this is mostly used to make life easier for non-human users, such as uucp(1C).

September 29, 2021