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Full Discussion: How to diff between 2 users with uid 0?
Special Forums Cybersecurity How to diff between 2 users with uid 0? Post 302785075 by Don Cragun on Sunday 24th of March 2013 04:03:14 PM
Old 03-24-2013
When a user logs into a UNIX system, the login name used is saved in a system database and in the environment variable LOGNAME. The file(s) containing the database where it is stored varies from system to system, but is likely to be in a file named something like utmp or utmpx in a directory like /var/run, /var/adm, or /etc. The name stored there should be used by who (not the 1st name in the user database [AKA the passwd file] with a matching UID). The name stored in the login database should also be used by the logname() function and the logname utility (both of which are explicitly NOT allowed to use $LOGNAME since any user can alter the value of $LOGNAME in the current shell execution environment). None of these should care how many different login names are associated with a given user ID.

None of this makes it a good idea to allow multiple user names for any user ID with extended privileges. But, I don't understand why the who or whoami utilities should be unable to determine what login name was used as long as the login session is still active. (They might fail if file descriptors 0, 1, and 2 have been disconnected from the controlling terminal, but they shouldn't make up a login name just based on the UID of the calling process.)
These 2 Users Gave Thanks to Don Cragun For This Post:
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LEARN ABOUT FREEBSD

login

LOGIN(1)						    BSD General Commands Manual 						  LOGIN(1)

NAME

     login -- log into the computer

SYNOPSIS

     login [-fp] [-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 configurable via pam(8).	Password authentication is the default.

     The following options are available:

     -f      When a user name is specified, this option indicates 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      Specify 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.

     Login access can be controlled via login.access(5) or the login class in login.conf(5), which provides allow and deny records based on time,
     tty and remote host name.

     If the file /etc/fbtab exists, login changes the protection and ownership of certain devices specified in this file.

     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).

     The login utility 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).  Other environment variables may be set due to
     entries in the login class capabilities database, for the login class assigned in the user's system passwd record.  The login class also con-
     trols the maximum and current process resource limits granted to a login, process priorities and many other aspects of a user's login envi-
     ronment.

     Some shells may provide a builtin login command which is similar or identical to this utility.  Consult the builtin(1) manual page.

     The login utility will submit an audit record when login succeeds or fails.  Failure to determine the current auditing state will result in
     an error exit from login.

FILES

     /etc/fbtab 		  changes device protections
     /etc/login.conf		  login class capabilities database
     /etc/motd			  message-of-the-day
     /var/mail/user		  system mailboxes
     .hushlogin 		  makes login quieter
     /etc/pam.d/login		  pam(8) configuration file
     /etc/security/audit_user	  user flags for auditing
     /etc/security/audit_control  global flags for auditing

SEE ALSO

     builtin(1), chpass(1), csh(1), newgrp(1), passwd(1), rlogin(1), getpass(3), fbtab(5), login.access(5), login.conf(5), environ(7)

HISTORY

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

BSD
								September 13, 2006							       BSD
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