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some aditions to processes md

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waldek 2021-07-05 14:43:47 +02:00
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@ -307,12 +307,77 @@ I'm asking you to look for an answer online but the solution can be found the re
## Zombie processes
Yes, there are such things as zombie processes.
Learning how to create them is a bit out of our scope but I highly advise you to read up a bit on [what](https://en.wikipedia.org/wiki/Zombie_process) they are and [how](https://www.howtogeek.com/701971/how-to-kill-zombie-processes-on-linux/) to deal with them.
## Process priorities
Life is all about setting priorities and while Linux is very good at managing it's CPU time all by itself, sometimes we know better.
We've seen the priorities before in `htop` in the `NI` column but we can view them as well via `ps o nice`.
A more detailed command would be `ps o nice,pid,ppid,args` which for my laptop returns the following:
```
➜ ~ git:(master) ✗ ps o nice,pid,args
NI PID COMMAND
0 2220 zsh
0 2283 -zsh
0 2323 /bin/sh /usr/bin/startx
0 2345 xinit /etc/X11/xinit/xinitrc -- /etc/X11/xinit/xserverrc :0 vt1 -keeptty -auth /tmp/serverauth.8jVsAiU2KQ
0 2346 /usr/lib/xorg/Xorg -nolisten tcp :0 vt1 -keeptty -auth /tmp/serverauth.8jVsAiU2KQ
0 2354 x-window-manager -a --restart /run/user/1000/i3/restart-state.2354
0 5848 zsh
0 8365 zsh
0 9036 zsh
0 9065 newsboat
0 10478 ssh waldek@86thumbs.net
0 13113 vim learning_processes.md
0 13860 ps o nice,pid,args
0 28084 zsh
➜ ~ git:(master) ✗
```
All my processes are neutral on a scale from *nice* to *not-very-nice*.
You can tell because they are at `0`.
The **nice** scale goes from `-20` being not-at-all-nice to `20` being super friendly towards other processes.
The nicer a process the less aggressive it will be when demanding CPU time.
### Nice
Depending on your system a new process will get a specific nice value.
On my Debian laptop by default processes get `5` as nice value.
We can inspect this as follows where the `ping` command is the new process:
```
➜ ~ git:(master) ✗ ping 8.8.8.8 > /dev/null &
[1] 15428
➜ ~ git:(master) ✗ ps o nice,pid,args -p 15428
NI PID COMMAND
5 15428 ping 8.8.8.8
➜ ~ git:(master) ✗
```
Let's be nice to start with and set the process to be not aggressive at all.
You can launch a command with a specific nice value by prepending `nice -n 15` before the command.
The value you set will be **added** to the default value as seen below (but tops out at 19 and -19).
```
➜ ~ git:(master) ✗ nice -n 15 ping 8.8.8.8 > /dev/null &
[1] 15632
➜ ~ git:(master) ✗ ps o nice,pid,args -p 15632
NI PID COMMAND
19 15632 ping 8.8.8.8
➜ ~ git:(master) ✗
```
Now what about *aggressive* processes?
I would like you to try and set a very *not-nice* value for a `ping` or `sleep` process?
You can probably guess but it won't work.
Why do you think this is?
### Renice
## Exercises
Download the following files: