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Is there such a thing as a normal root and a real root in Unix/Linux?

I am doing a buffer overflow project (in Ubuntu 11.04) and I invoke /bin/zsh and /bin/bash separately. In both cases

$whoami returns root

$id returns uid=1000, euid=0, gid=1000.

But, when I try to run

$passwd username

to change some user's password, the shell returns:

passwd: You may not view or modify password information for username

Is there something that I am missing here as I believe this is root does not have low level privileges. I have searched all over the net, but I don't seem to find a comprehensive answer.

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migrated from Oct 18 '11 at 4:13

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Also, I forgot to mention, commands such as $useradd, $userdel, $chown work without any elevation – Suchit Oct 18 '11 at 4:31

Do you mean "real UID / GID" vs "effective UID / GID" ..?

real UID : this is the UID of the process that created THIS process - e.g. as who you logged in.

effective UID: This UID is used to evaluate privileges of the process to perform actions.

you should check here:


Just found this page, which has a nice description:

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Thanks for your reply I understand what real and effective UID/GID mean, but my question is why does the real UID not become zero when I invoke /bin/bash or /bin/zsh from some buffer overflow vulnerable program? Rather effective UID is made zero. I forgot to mention that my motive is to obtain real UID to be zero without running a separate shell code that sets real uid = 0 (with setuid(0)). – Suchit Oct 18 '11 at 4:29
@Suchit: If that is what your question is, you could either update your question or ask a new one. – RedGrittyBrick Oct 18 '11 at 9:40

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