login
PURPOSE
Allows you to sign on to the system.
SYNOPSIS
login (not user invokable)
DESCRIPTION
The login program logs you onto the system. Its primary
functions are:
o To validate your password.
o To make the required accounting and log entries.
o To set up your processing environment.
o To run the command interpreter that is specified in
the password file, usually the sh program.
A logger process, initially running the getty program, is
started for each enabled port. getty reads a login name
and sets work station modes (see "getty"). Then it runs
login, which may ask for a password. If you do not have
a password, press the Enter key.
Your log in attempt might fail for the following reasons:
o Your login name/password pair does not match an entry
in the password file.
o Your password has expired. This can happen if your
system requires that you change your password after a
set number of days. In this case, login runs the
passwd command instead of letting you log in. (For
more information, see "passwd.") After you change
your password, you can attempt to log in again.
o The system has reached the limit of simultaneously
logged-in users. Each AIX kernel sets a limit on the
number of concurrent log ins by nonprivileged users;
this limit may be one. A privileged user is one that
has a user ID from 0 to 20. A privileged user can
log in at any time.
In one special case, login does not ask for a user name
and password pair. When the login port is the console
and the file /etc/autolog contains a valid user name,
login creates a login session for that user automat-
ically. Other processing by login proceeds normally.
When a user logs in successfully, the login program makes
entries in /etc/utmp, the record of users logged into the
system, and in /usr/adm/wtmp (if it exists), for use in
accounting. On invalid login attempts (due to an incor-
rect login name or password), login makes entries in the
/etc/.ilog file.
Once you are logged in to the system, the login program
lists your previous login time and the system message of
the day (stored in the /etc/motd file), if it has been
modified since your last log in or if this is your first
log in of the day. If a user file size limit has been
specified in the passwd file, the limit is set with
ulimit system call. When you log in as user root or su
and the /etc/.ilog file is not empty, you see a message
advising the you to check the /etc/.ilog file for a
record of unsuccessful login attempts.
The login program sets the LOGNAME and HOME environment
variables from information in the password file. Envi-
ronment variables inherited from getty and init (such as
those specified in /etc/environment) are kept. You may
expand or modify the environment by supplying additional
parameters to login when it requests your login name.
These may take the form xxx or xxx=yyy. Parameters
without an equal sign are placed in the environment as
Lnum=xxx, where num is a number starting at 0 and incre-
mented each time a new variable name is required. Param-
eters containing an equal sign are placed into the
environment without modification. If they already exist,
the new assignment replaces the older value. There are
two exceptions: You cannot change the shell variables
PATH and SHELL. (This restriction prevents people,
logging into restricted environments, from spawning sec-
ondary shells that are not restricted.) Both login and
getty understand simple single-character quoting con-
ventions. Typing a backslash (\) in front of a character
quotes it and allows you to include such things as spaces
and tab characters.
The login command changes the current directory to your
HOME directory, changes the ownership of the port (work
station) to the user logging in, sets the user-and
group-IDs of the process, and then runs the program spec-
ified for the user in the password file, normally the
shell (/bin/sh). login calls this program with a name
consisting of - (minus) followed by the last segment of
its path name. An instance of the shell can therefore
determine from its invocation name whether it is a login
shell or a subshell.
The /etc/passwd file entry may include parameters that
are always passed to the shell program. For more
details, see the passwd file in AIX Operating System
Technical Reference.
FLAGS
-rnode Identifies the login as a remote login and speci-
fies the node requesting the login.
FILES
/etc/utmp Accounting file.
/usr/adm/wtmp Accounting file.
/etc/.ilog Accounting file.
/etc/autolog Login ID for automatic login.
/usr/motd Message of the day.
/etc/passwd Password file.
.llog Date of last login.
RELATED INFORMATION
The following commands: "users, adduser," "csh,"
"getty," "init," "passwd," and "pstart, penable,
pshare, pdelay."
Note: The csh command contains a built-in subcommand
named login. The command and subcommand do not neces-
sarily work the same way. For information on the subcom-
mand, see the csh command.
The passwd and utmp files in AIX Operating System Tech-
nical Reference.
The discussion of login sessions in Managing the AIX
Operating System.