FIle permission execute only

Question

How can I set file to be executable only to other users but not readable/writable, the reason for this I'm executing something with my username but I don't want to give out the password. I tried :

chmod 777 testfile
chown a=x
chown ugo+x

I still get permission denied when executing as another user.

Answer 1

You need both read and execute permissions on a script to be able to execute it. If you can't read the contents of the script, you aren't able to execute it either.

tony@matrix:~$ ./hello.world
hello world
tony@matrix:~$ ls -l hello.world
-rwxr-xr-x 1 tony tony 17 Jul 13 22:22 hello.world
tony@matrix:~$ chmod 100 hello.world
tony@matrix:~$ ls -l hello.world
---x------ 1 tony tony 17 Jul 13 22:22 hello.world
tony@matrix:~$ ./hello.world
bash: ./hello.world: Permission denied

Answer 2

If you let other users execute a program, then they can know everything the program is doing, whether the program file is readable or not. All they need to do is point a debugger (or debugger-like program such as strace). A binary executable can run if it's executable and not readable (a script can't, because the interpreter needs to be able to read the script), but this doesn't give you any security.

If you want others to be able to execute your program as a black box, without letting them see exactly what the program is doing, you need to give your script elevated privileges: make it setuid to your user. Only root can use debugging tools on setuid programs. Note that writing secure setuid programs isn't easy, and most languages aren't suitable; see Allow setuid on shell scripts for more explanations. If you're going to write a setuid program, I strongly recommend Perl, which has a mode (taint mode) that's explicitly intended to make secure setuid scripts possible.