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9. Process Credentials > Effective User ID and Effective Group ID

Effective User ID and Effective Group ID

On most UNIX implementations (Linux is a little different, as explained in File-System User ID and File-System Group ID), the effective user ID and group ID, in conjunction with the supplementary group IDs, are used to determine the permissions granted to a process when it tries to perform various operations (i.e., system calls). For example, these identifiers determine the permissions granted to a process when it accesses resources such as files and System V interprocess communication (IPC) objects, which themselves have associated user and group IDs determining to whom they belong. As we’ll see in Sending Signals: kill() , the effective user ID is also used by the kernel to determine whether one process can send a signal to another.


  

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