User login process

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·         Unix booted.

·         Program Unix(kernel) is booted into main memory, and remains active till the computer is shut down

·         Program init runs as a background task and remains running till shutdown

·         User attempts to log in.

·         Kernel calls program ‘init’.

·         ‘init’ scans file /etc/inittab , which lists the ports with terminals and their characteristics and returns an active open terminal to ‘init’.

·         ‘init’ calls program ‘getty’, which issues a login prompt in the monitor

·         User enters login and password

·         ‘getty’ calls program ‘login’ which scans file /etc/passwd to match username and password

·         After validation, control passes to session startup program /bin/sh , session startup program

·         Program /bin/sh reads file /etc/profile and .profile and sets up system wide and user specific environment.

·         User gets a shell prompt