Tech Monger

Many time you want to allow other Linux users to execute your code but restrict them from reading or writing it. Below we will show you unix trick where you can make binary file non readable to users but allow execution by adding setuid to your file.

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Before we begin....

We need to note that this trick will only work with binary file and not the actual script which requires interpretation with interpreter. We have already explained how to convert python code to executable binary. You can check the guide to covert your code to corresponding binary executable based on the programming language you are using.

• Change Default Permission to Only Executable for all users except Owner. Here hello is the binary file

  $ cd /my/binaries/
  $ chmod 711 hello
  $ ls -la hello
  -rwx--x--x 1 bob bob 5.5M Apr 30 22:12 hello

• Switch to some other user and try executing file.... And user shall get error related to permission issues

  $ sudo su - alice
  $ cd /my/binaries/
  $ ./hello 
  [31868] Cannot open self /my/binaries/hello or archive 

• Make hello executable by adding setuid flag with 4711

  $ chmod 4711 hello
  $ ls -la hello
  -rws--x--x 1 bob bob 5.5M Apr 30 22:12 hello

• Now ask alice to try again

  $ sudo su - alice
  $ cd /my/binaries/
  $ ./hello 
  Hello World

Conclusion