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UID/GID on Executable: Effective vs. Real UID concept

farzanj
farzanj asked
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Last Modified: 2012-05-10
I wrote a short C++ program that only receives an input value (basically cin >> a ;).  I enabled UID on it.  So ls -l shows:
-rwsr-xr-x 1 root root   6058 Sep 15 09:50 prog

Now I executed it as "test" user and checked the real vs. effective UID as under:
 ps -eo cmd,ruser,euser,ruid,euid,pid | grep prog | grep -v grep
./prog                      test     root       501     0 14251

Just as I expected, real userid is 501(test) and effective uid is 0(root).

So far so good.

Now I tried to do the same using a shell script.  A bash script called script which should do the same thing but it doesn't.  Why?  Is there a way to see it working in a shell script.

-rwsr-xr-x 1 root root      5 Sep 15 09:29 script

ps -eo cmd,ruser,euser,ruid,euid,pid | grep 14328
bash                        test     test       501   501 14328

Second, will the script work as root or as user test?
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I ran it on Red Hat Linux (RHEL5.5).
Second, please clarify if effective uid/gid the one that is checked for determining the access/permissions.  Does real uid/gid ever matter at all?
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Thank you so much for your clarification and your time.  Appreciated.
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