From your own shell you run `su bob` and it succeeds. Compared with running `su - bob`, what is different about the shell you end up in?
LPIC-1 Exam 102-500, objective 110. Security medium
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The options
Correct You keep your current working directory, and bob's login files are not sourced, so you are not placed in /home/bob.
Correct. Without the dash, su starts a non-login shell: the working directory does not change and bob's ~/.bash_profile is not read. Most of your exported variables survive as well, although modern util-linux su still resets a few (HOME, SHELL, USER, LOGNAME and PATH) unless you add -m/--preserve-environment.
Not correct Nothing at all; the dash is accepted only for compatibility with older shells.
Wrong. The dash is significant. It is shorthand for -l / --login and changes the shell from a non-login to a login shell.
Not correct bob's password is not requested, whereas `su - bob` always requests it.
Wrong. Both forms prompt for the target user's password, and neither does when the caller is already root. The dash has nothing to do with authentication.
Not correct The shell runs as root rather than as bob.
Wrong. su switches to the named user in both forms. It is su with no username at all that defaults to root.
Why
`su -`, `su -l` and `su --login` all start a login shell: the environment is reset to the target user's, their login scripts run, and the working directory becomes their home. Plain `su` inherits your environment, which is a classic source of confusion because root ends up with your PATH and possibly your umask. The same distinction exists for sudo: `sudo -i` is the login-shell form and `sudo -s` runs the target user's shell while keeping the current environment and directory.
Where this comes from
- Cited
- LPI exam objective 110.1
- What it says
- Switch user identity with su and sudo and understand login versus non-login shells.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 110 and space the ones you get wrong.