What's the purpose of each of the different UIDs a process can have?

Question

Real UID, effective UID, and some systems even have a \"saved UID\". What\'s the purpose of all these, especially the last one?

Answer 1

Each Linux process has 3 UIDs associated to it.

• Real UID: The UID of the process that created THIS process.
• Effective UID: This is used to evaluate privileges of the process to perform a particular action.
• Saved UID: For the binary image file with a setuid bit on it.