setuid not working - Ubuntu

Ok, I am posting it here because I struggled a lot with this, sought/got lot of help and finally got this :-)

If you want to run any script as a root forever, I mean, no matter who starts the script, it should run as a root then lay back because Ubuntu wont let you do it easily.

Ideally, to run any script as root irrespective of who starts it, root should own it and the user id of script should be set to root. It goes like this -

on your root prompt i.e. sudo su - root
create your script, say foo.sh

and let root own it
chown root:root foo.sh

then set the UID
sudo chmod 4755 foo.sh

exit the root prompt and run your script as a normal user. It should run as root. BUT the sad part is that it does not.

The newer versions of ubuntu (I have tested on 9.04+) don't allow setting the uid for scripts. So even if you set it, it will automatically revert back or not work as expected.

But there is a ray of hope. You can still set the uid for binaries. So here it goes -

write a small c program which takes the name of your script as a parameter and runs it :-)

#include
int main(int argc, char* argv[])
{
system(argv[1]);
return 0;
}

compile it and set uid for its binary
gcc foo.c -o foo
sudo chown root:root foo
sudo chmod 4755 foo

Make your script executable
chmod 755 foo.sh

and you are done



execute the binary with name of your script as a parameter, something like this

./foo ./foo.sh

and the script will run under root :-)

To mention a use case - I was using Hudson CI tool which was supposed to invoke a shell script and the script required root privileges. This solution worked just perfect for me