I am having trouble understanding the difference between a Process Control Block and Process Descriptor in Linux?
I have seen both of these structures referred to as a task_struct, and the terms seem to be used interchangeably - what is the difference between the two?
Many thanks for your help!
Neither of those terms ("Process Control Block" or "Process Descriptor") are considered "terms of art" in Linux kernel development. Of course, there is no official Linux kernel glossary so people are free to call things whatever makes sense to them.
In contrast, however, task_struct is a specific C structure that is used by the linux kernel to maintain state about a task. A task in Linux corresponds roughly to a thread.
Each user process has at least one thread so each process maps to one or more task_structs. More particularly, a process is one or more tasks that happen to share certain resources -- file descriptors, address space / memory map, signal handling, process and process group IDs, etc. Each thread in a process has its own individual version of certain other resources: registers/execution context, scheduling parameters, and so forth.
It's quite common for a process to have only a single thread. In that case, you could consider a process to be represented by a single task_struct.
