[ubuntu] About Ubuntu (Server) Setting

USER

How to ADD,DELETE user

ADD

$ sudo adduser <username>
DELETE

$ sudo deluser <username>
- IF YOU WANT to remove the user files
  $ sudo deluser --remove-home <username>

To give sudo privilge

$ sudo usermod -aG sudo <username>
run a command with sudo privileges without entering the password

$ EDITOR=vim visudo
adding a line below to ~end of file~. replace username with yours

username ALL=(ALL) NOPASSWD: ALL

Connect AirPods

Enabling Airpods as earbuds and microphone

Reference 1

LVM (file system)

how to resize the default LVM volume

Reference 2

About LVM and how to manage

managing packages using apt

ls /etc/apt/sources.list.d/

sudo add-apt-repository --remove ppa:whatever/ppa

apt-key

apt-key is deprecated .. so if you got warning about it, see here

setting Firewall

with `ufw`

Reference 3

with `iptables`

If you installed AlgoVPN, you cannot use other firewall tools including ufw.
Please check this page, if you want to more.
Furthermore, if you want to save the rules, you should save the rules in /etc/iptables/rules.v4 and /etc/iptables/rules.v6 after installing the apt package iptables-persistent.

Reference

When network does not work

I’ve experienced the Internet connection wasn’t established after inserting gpu on my computer.
The reason was the settings about PCI devices. My LAN Card and GPU used PCI bus.
but when I used before, I didn’t use GPU. So my computer set LAN Card using PCI bus, named enp2s0.
However, after setting gpu, I don’t know why exactly, but LAN Card got enp3s0. I might think the gpu get second PCI device name.
Long prefaces. I solved problem using below try.

Reference 4

sudo lshw -C network
- outputs are the LAN Cards that computer can use.
- I had gotten *-network DISABLED about my mainboard LAN card.
sudo ip link set enp3s0 up

change PCI devices name on /etc/netplan/*.yaml

the exact file name is different. find your mainboard(or something you want) LAN card setting.
example

 network:
     version: 2
     renderer: NetworkManager
     ethernets:
         enp3s0:
             dhcp4: true

sudo netplan apply
sudo systemctl restart NetworkManager.service

and I don’t use this, but it could be useful maybe..

Setting the default editor for all programs

export VISUAL=vim
export EDITOR='$VISUAL'

Setting both is not necessarily needed, but some programs may be required.

How to keep turning on the laptop when it closes

Using GUI

sudo apt install gnome-tweaks
open the application Tweaks
set off Suspend when the laptop lid is closed option.

Using Terminal

sudo vim /etc/systemd/logind.conf
change #HandleLidSwitch=suspend to HandleLidSwitch=ignore

How to add swap space

Creating a swap file

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

if the fallocate failed with the error message fallocate failed: Operation not supported, try
```
  sudo dd if=/dev/zero of=/swapfile bs=1024 count=2097152
```
to make the change permanently, add the following line in /etc/fstab
```
  /swapfile swap swap defaults 0 0
```

Check and Change the Swappiness Value

check swappiness value
```
 cat /proc/sys/vm/swappiness
```
change swappiness value
```
 sudo sysctl vm.swappiness=10
```
- to make the change permanently, add the following line in /etc/sysctl.conf
```
 vm.swappiness=10
```

Removing a swap file

sudo swapoff -v /swapfile
remove the line /swapfile swap swap defaults 0 0 from the /etc/fstab file
sudo rm /swapfile