The problem is your "ownership" is derived from management's ownership of that hardware and software. So if they demand access, you do not have the authority to deny it.

Yes and no.

If the the authority clause can imply full automatic access, then the boss should ask for a copy of all passwords, disks or files, too. I am not sure that this is even automatically permitted under many jurisdictions. Think of forensics and liability here.

We can understand the problem as similar one to an airplane owner and a pilot (or a shipping magnate and a captain, etc): Being the owner of the plane does not imply that you should fly it every now and then, maybe "on-the-fly", just because you own it. You surely have reserved the right to do so. BUT. The pilot should also have the right, to exit the plane safely on ground upon your demand, inform his crew on the spot of his actions and properly handing over the control. This is how business should be done.

Talking about systems, a solution could be to put all administrative passwords in an envelope, seal it, hand it to your boss on the condition that you take responsibility of the systems as long as the envelope remains sealed. If the envelope is broken, it's his job. If you are asked to hand-over the systems, you unseal together the envelope; the "agreed protocol" takes care of the rest. At any such step, it is appropriate for the sysadmin to disclaim further responsibility to his users, in some brief, formal, communication.

I refuse to co-sysadmin my systems together with my managers, unless they can also share the responsibility, solve problems etc. After all, *I* have choice in the job market and I am authoritative enough to make use of that. ;-)

In the end of the day, it's just a question of professionalism from all parties involved.

OSS advocacy and Mobile Phones don't mix. Stop writing software for it and making your phonecalls with it.