57 lines
1.8 KiB
Markdown
57 lines
1.8 KiB
Markdown
---
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id: t70u
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title: Processes
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tags: [operating-systems]
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created: Friday, June 21, 2024
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---
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# Processes
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Programs are sequences of machine instructions stored in a file. However they do
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not work by themselves. Something needs to load the file's intructions into
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memory, direct the CPU to run the program and manage it during runtime. The OS
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does this via processes.
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A process **is a running instance of a given program**. It can be thought of as
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a container in which a program runs. This container includes:
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- a copy of the program code loaded into memory
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- a memory address
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- other information about the state of the process
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Other than the `init` process started by the kernel (PID1) (see
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), every process has a parent process that started it.
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This parent-child relationship creates a tree of processes.
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It is possible that a parent process will terminate before one of its child
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processes. In this instance the child becomes an orphan. When this occurs in
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#Linux, the orphan process is adopted by `init`.
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Below, I have used the `pstree` utility to list all the running processes on my
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machine hierarchically.
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Children are represented vertically and horizontally.
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```
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├─terminator─┬─zsh───tmux: client
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│ ├─zsh───pstree
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│ └─6*[{terminator}]
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```
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For instance here, `terminator` is a child of `init`, as are `zsh` and `tmux`
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but they are also children of `terminator`.`pstree` is a child of `zsh` and
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therefore also a child (grandchild) of `terminator`.
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Each process has a unique identifier called a _process identifier_, a
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_processID_ or just _PID_.
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## Related notes
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