The essential difference
su just switch the root, but Shell is still common user environment of Shell;
su - to switch the user environment and Shell together to root identity; the only switch the environment Shell will not appear PATH environment variable error;
Difference phenomenon
1, the working directory
su working directory does not change, the average user is still working directory;
su - switch to the working directory of the root ;
2, Environment Variables
su environment has not changed, still the common user environment l;
su - to root environment ;
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