Linux can't find process started by PHP

I'm currently running an own Minecraft Server, and I wanted to build an option to restart the Minecraft server via PHP, so my friends can restart the MC server without needing access to my actual server.

Thus, first I wanted to create a script to start the server:

startup.php

<?php 

    chdir('/home/minecraft/minecraft_server/');
    exec("./start");

?>

start

screen -mdS "minecraft_up" java -Xmx4G -Xms4G -jar server.jar nogui

After a bit of permission pain etc, by calling the webadress the server can be started.
Now, my problem is that I have no access to the screen process.

When running ps -ef I get:

     UID     PID    PPID  C   TTY        TIME CMD
www-data   29642       1  0     ?    00:00:00 SCREEN -mdS minecraft_up jav
www-data   29643   29642 99 pts/5    00:02:07 java -Xmx4G -Xms4G -jar serv

When running sudo pwdx 29642 to get the process location I get:

29642: /home/minecraft/minecraft_server

But when I go into the /home/minecraft/minecraft_serverdirectory and run either screen -ls or sudo screen -ls, both times I get:

No Sockets found in /run/screen/S-minecraft.

In contrast: When executing the start file manually in the terminal, when running screen -ls I can actually see the process (or open it with screen -r):

There is a screen on:
        29025.minecraft_up      (01/24/2021 01:32:45 PM)        (Detached)
1 Socket in /run/screen/S-minecraft.

I also get the same working directory, but I cannot run the start file manually while the process started py PHP is still running.

I'm really not an expert at all at Linux, I guess theres some user permission interference or something that PHP is treated as an own user, I really don't know, which is why I'm asking.

How do I access this process started by PHP?

Solution

To create a service using systemd :

Create a file in /etc/systemd/system/ called minecraft-server.service with the following content:

[Unit]
Description=Minecraft server 
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=minecraft
Group=appmgr
ExecStart=java -Xmx4G -Xms4G -jar server.jar

[Install]
WantedBy=multi-user.target

Replace server.jar with full path.

Now lets create the new group and user.

To create new group run the following command:

sudo groupadd appmgr

Now lets create the new user and it it to a group.

sudo useradd –G appmgr minecraft

Now your service is created, we need to enable it and run it for first time.

systemctl enable minecraft-server
systemctl start minecraft-server

Last step to write php script to restart the services:

<?php 
    exec("systemctl restart minecraft-server");
?>