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