What number represents the SUID in permission settings?

The SUID (Set User ID) permission setting is represented by the number 4 in Linux file permissions. When the SUID bit is set on an executable file, it allows users to execute the file with the permissions of the file's owner rather than the user who is executing it. This can be particularly useful for programs that need elevated privileges to perform certain tasks without requiring users to have those elevated privileges themselves.

In Linux, file permissions are represented in a three-digit octal format, where the first digit specifies special attributes - including SUID, SGID (Set Group ID), and Sticky bit. Each of these special bits has an associated value: SUID has a value of 4, SGID has a value of 2, and the Sticky bit has a value of 1. Therefore, when configuring or interpreting permissions, the presence of the SUID bit can be identified with the number 4. This is crucial for managing security and ensuring that users have the appropriate level of access to execute files that may otherwise be restricted.