How login process work in Linux? An overview of login process Init creates the getty process getty process initiates login command login command try to check user credentials getty creates user shell process getty read shell property files getty provides you with PS1 prompt Let us learn above things in detail by breaking them in to steps: Step0: Once init process completes run-level execution and executing commands in /etc/rc.local, it will start a process called getty. Getty is the process which will take care of complete login process. Step1: The getty process initiates login command and gives users with login: prompt display on the terminal screen and waits for user to enter username. Once user enter his login name, this in-turn will prompt for user password. The password what user typed will be hidden and will not be shown on screen. Step2: Now getty will check user credentials by verifying it with /etc/passwd and /etc/shadow file, if password matches it will initiates user properties gathering else getty will terminate login process and re-initiates once again with new login: prompt. This is done for three times in most Linux/Unix flavors. If user failed to enter correct password for three consecutive times, getty disable terminal for 10 seconds by using PAM module to control unauthorised logins. Step3: Now the getty process read the user properties like username, UID, GID, home directory, user shell from /etc/passwd file to respective system variables $USER, $UID, $GID, $HOME and $SHELL. Step4: Once it gathers all the properties and before the start of user shell it read /etc/motd file and display its content as banner message to user. Step5: Now getty process reads /etc/profile file for shell related settings and for importing any alias or some sort of variables which we have to set for user shell. Step6: Once it completes reading /etc/profile file, it will read user home directory content and change user shell properties according to .bashrc, .bash_profile if his default shell is bash. The getty process get shell details from /etc/passwd file. Step7: Getty now starts a software, which is called as user shell for interacting with user directly. The getty process get this information from $SHELL variable which it already parsed from /etc/passwd file. Now it presents PS1 prompt for user to execute their commands.
Posted on: Tue, 24 Sep 2013 01:15:24 +0000
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