Quickly check whether sudo permissions are available

Question

I want to be able to quickly check whether I both have sudo access and my password is already authenticated. I'm not worried about having sudo access specifically for the operation I'm about to perform, but that would be a nice bonus.

Specifically what I'm trying to use this for is a script that I want to be runnable by a range of users. Some have sudo access. All know the root password.

When they run my script, I want it to use sudo permissions without prompting for a password if that is possible, and otherwise to fall back to asking for the root password (because they might not have sudo access).

My first non-working attempt was to fork off sudo -S true with STDIN closed or reading from /dev/null. But that still prompts for the password and waits a couple of seconds.

I've tried several other things, including waiting 0.3sec to see whether it succeeded immediately, but everything I try ends up failing in some situation. (And not because my timeout is too short.) It's difficult to figure out what goes on, because I can't just strace like I normally would.

One thing I know doesn't work is to close STDIN or attach it to a pipe before running sudo -S true. I was hoping that would make the password prompt immediately fail, but it still prompts and behaves strangely. I think it might want a terminal.

Answer 1

I don't know what the ultimate reason is for needing to do this, but I think maybe you might need to rethink whatever the core reason is. Trying to do complicated, unusual things with permissions frequently leads to security holes.

More specifically, whatever it is the script is trying to do might be better done with setuid instead of sudo. (I'd also have to wonder why so many people have the root password. Sudo is there specifically to avoid giving people the root password.)

Answer 2

getent group admin | grep $particular_user

You could use whoami to get the current user.

Edit: But that doesn't help you find if you're still authed to do sudo tasks... Hmm..

Answer 3

although an old topic, i'll give it a try answering

running

sudo -S true < /dev/null &>/dev/null

seams to work, although it delays for a second before failing