How do I get the users real uid if the program is run with sudo?

Question

The program I am running needs root privledges and therefore is run with sudo, but it also needs to know what user is running it. getuid and

Answer 1

You have two good choices...

1. Trust sudo and just use its environment
2. Make your program setuid-on-execution and then geteuid, et al, will work just fine

Update:

The setuid bit is an access right flag in the file mode that causes a program to run with the capabilities of the executable file's owner. This is how sudo(1) is able to run things as root ... the sudo program itself has this mode.

$ ls -l /usr/bin/sudo
-r-s--x--x  1 root  wheel  272384 Jun 22  2009 /usr/bin/sudo*

To make a program setuid root one might:

$ chown root a.out
$ chmod +s a.out

Needless to say, setuid root programs should be written carefully. You can setuid to a less privileged user if all you need is access to a protected directory or file.