Change EUID of running process

Question

On Linux how can I change EUID of running process from command line (provided I have root access)?

Thanks

Answer 1

I don't think you can, I am not aware of any syscall that lets you change the effective user id of any process but the calling process.

Answer 2

There's kchuid, but that requires you to compile your own kernel modules, was last updated in 2002, and looks extremely feary.

Alternatively, you could do probably do some ptrace hacks, but a sample or direction is bit beyond me.

Answer 3

Use gdb.

# gdb -p pid

(gdb) p seteuid(userid)