A solution that cannot be started after linux modifies Environment Variables

Linux cannot start after changing the environment variable. Because I modify the environment variable, X-window cannot start. Therefore, to force the command line to start it, use GRUB to start it. Press E at startup to edit the startup project, add linux single at the end of the line of kernel, press enter, and then press B to start the system. Then the system starts the system directly with the root permission. Enter # And then you can modify the profile environment variable. (So it is best to disable single logon for System Security) Conclusion: the rescue of CentOS. This avoids system reinstallation.