strage behaviour of ulimit

[Andreas Klein]

Hello.

I have found the following strange bahavoiur of ulimit.

As normal user I can increase the stack size once but not twice:

address@hidden:~$ ulimit -s
8192
address@hidden:~$ ulimit -s 20000
address@hidden:~$ ulimit -s 30000
bash: ulimit: stack size: cannot modify limit: Operation not permitted

For comparision after a new login I can do:

address@hidden:~$ ulimit -s
8192
address@hidden:~$ ulimit -s 20000

I can not imagige that this is ok. I guess a normal user should not be 
allowed to increase the stack size.

The sytem is Linux (Ubuntu).

Do you what happens and why?

Best wishes
        Andreas Klein