Hello and welcome here.
Please be a bit more descriptive (or better, show it).
You say “when I exit from the user”, but then there is no session. Then you say “and su again” but there is no session to do any “su” command in, nor was there any “su” in your description earlier, thus why the “again”?
Confusing to me.
Oh, and allow me, you being new here:
There is an important, but not easy to find feature on the forums.
Please use CODE tags around copied/pasted computer text in a post. It is the # button in the tool bar of the post editor. When applicable copy/paste complete, that is including the prompt, the command, the output and the next prompt.