Linux user login system

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This link: https://blog.csdn.net/qq_32067151/article/details/102745041

In general, users log in three ways:

• (1) Command Line Login
• (2) ssh login
• (3) Graphical login

For graphical user run level 5, their log in through a graphical login screen. After a successful login can go directly to KDE, Gnome and other window manager.

The paper stresses the situation or text login: When we see mingetty login screen, we can enter a user name and password to log in the system.

Linux account verification process is login, login will receive a user name mingetty came as the username parameter.

Then login user name will be analyzed: If the username is not root, and there is / etc / nologin file, login nologin will output the contents of the file, and then exit.

This prevents non-root user login time is usually used for system maintenance. The registered / securetty only / etc terminal only allow the root user login, if the file does not exist, the root user can log on any terminal.

/ Etc / usertty file is used to make additional access restrictions on users, if the file does not exist, there are no other restrictions.