Score:2

Ubuntu

why `su` doesn't change $USER?

Saulo

8/15/24, 2:56 PM

I've noticed the following:

When I'm using my user, my id is 1000:

┌ sefo@tux ~
└ $ echo $EUID $USER
1000 sefo

When I run su my Id changes but my user doesn't:

┌ sefo@tux ~
└ $ echo $EUID $USER
0 sefo

And, finally, after su - my id and my user change:

┌ root@tux ~
└ $ echo $EUID $USER
0 root

What I'm struggling to understand is why su doesn't change my user. I do believe there is some rationale behind this behavior but at the moment it just seems as inconsistent to me.

Can somebody clarify this behavior?

1 + 7

command-line

bash

Saulo

8/15/24, 3:34 PM

bash as root is displayed by my prompt theme (I'm using oh-my-posh to customize the prompt). I presume it reads $EUID to evaluate when to show "as root" or not. I'm going to remove it from the post to prevent further confusion.

Luuk

8/15/24, 3:44 PM

From `man su`: "For backward compatibility, su defaults to not change the current directory and to only set the environment variables HOME and SHELL (**plus USER and LOGNAME if the target user is not root**)"

Saulo

8/15/24, 3:46 PM

I think you nailed it @Luuk. If you turn your comment into an answer I can accept it.

Saulo

8/15/24, 3:50 PM

@steeldriver the commands are those I mentioned in my question: `su` and `su -`. I'm not doing `sudo su`. After both commands (`su` and `su -`) I was asked for the root password.

Saulo

8/15/24, 3:51 PM

@Luuk sorry I didn't get what you mean. Can you clarify?

Luuk

8/15/24, 3:54 PM

@Saulo: When you need an answer, you can add one yourself, nothing wrong with that. Please do not force me into copy/paste the man-page for you.

Saulo

8/15/24, 4:01 PM

@Luuk it wasn't my intention to force you to do anything. I just tried to give you the chance to get the deserved credits for finding what seems to be right answer to my initial question. I'll create the answer. Thank you for the time you spent.

Score:1

Ubuntu

Saulo

8/15/24, 4:04 PM

As correctly pointed out by @luuk, man su states:

For backward compatibility, su defaults to not change the current directory and to only set the environment variables HOME and SHELL (plus USER and LOGNAME if the target user is not root)

Since su targets the root user, for backward compatibility ,$USER (and $LOGNAME) are preserved.

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