Setup

Server Setup

Login to the server via SSH as root

Install sudo, create the main user, and add him to the sudoers group

# apt install sudo
# adduser <user>
# vi /etc/group (add <user> to line "sudo:x:27:<user>")

(VPS) change the machine name:

sudo edit /etc/hostname
sudo edit /etc/hosts

enable force_color_prompt=yes in file ~/.bashrc
copy /home/user/.bashrc to /root and modify PS1 prompt color (32m –> 31m)

Security

Configure SSH Access
Install UFW Firewall

Disable root login by changing file /etc/passwd from line 1 to line 2

root:x:0:0:root:/root:/bin/bash
root:x:0:0:root:/root:/sbin/nologin

Install and configure packages

Additional packages

$ sudo apt update
$ sudo apt install vim
$ sudo apt install zip
$ sudo apt install rename
$ sudo apt install rsync
$ sudo apt install openjdk-17-jre openjdk-17-jdk

Change visudo editor

$ sudo update-alternatives --config editor

Upgrade linux headers

Check remaining space on the boot partition with:
```
df -h | grep "^/dev/"
```
Remove outdated kernel packages:
```
sudo apt-get autoremove
```
First check your kernel version, so you won't delete the in-use kernel image, running:
```
uname -r
```
Delete the kernels you don't want/need anymore by running this:
```
sudo apt-get remove linux-image-VERSION
```
Update grub kernel list:
```
sudo update-grub
```

System Startup

Debian 11 uses Systemd, not SysV, that's why your commands in /etc/rc.local file would not run at system boot time. This guide explains how to enable /etc/rc.local script to run on system startup.

Create a rc.local unit file, follow Services - rc.local

Create file rc.local in /etc with the following content:

vim /etc/rc.local
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
exit 0

Add execute permissions and start daemon:

chmod +x /etc/rc.local
systemctl daemon-reload
systemctl start rc-local
systemctl status rc-local

● rc-local.service - /etc/rc.local Compatibility
   Loaded: loaded (/lib/systemd/system/rc-local.service; static; vendor preset: 
  Drop-In: /lib/systemd/system/rc-local.service.d
           └─debian.conf
   Active: active (exited) since Sun 2019-05-05 10:55:29 +07; 11min ago
  Process: 1443 ExecStart=/etc/rc.local start (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 4915)
   CGroup: /system.slice/rc-local.service

System Shutdown

Put a symbolic link to the script to be run at shutdown into /lib/systemd/system-shutdown

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