minecraft@.service

[Unit]
Description=Minecraft server: %i
Wants=network.target
After=local-fs.target network.target

[Service]
User=minecraft
Group=minecraft

EnvironmentFile=/etc/conf.d/mc-%i
KillMode=process
KillSignal=SIGINT
TimeoutStopSec=300

NoNewPrivileges=true
PrivateDevices=true
PrivateTmp=true
ProtectHome=true
ProtectSystem=full

WorkingDirectory=/opt/minecraft/%i
ExecStart=/opt/minecraft/.local/bin/MinecraftSystemdWrapper /usr/bin/java $ARGS -jar server.jar
#ExecStop=/usr/local/bin/mcrcon -H localhost -P ${RCON_PORT} -p ${RCON_PASSWD} stop

[Install]
WantedBy=multi-user.target

MinecraftSystemdWrapper.c

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

int fd[2];
pid_t pid;

void signal_handler(int sig) {
  fprintf(stderr, "Signal %s received, stoping the server\n", strsignal(sig));
  int againCounter = 0;
SEND_STOP:
  if (write(fd[1], "stop\n", 5) != -1) {
    return;
  }
  // if EAGAIN silently retry 5 times more
  if (errno == EAGAIN) {
    if (againCounter < 6) {
      againCounter++;
      goto SEND_STOP;
    } else {
      fprintf(
          stderr,
          "Error sending the stop command to the server: Too many retries\n");
    }
  } else {
    fprintf(stderr, "Error sending the stop command to the server: %s\n",
            strerror(errno));
  }
  if (kill(pid, SIGINT) == -1) {
    fprintf(stderr, "Error killing the server: %s\n", strerror(errno));
  }
}

int main(int argc, char *argv[]) {
  if (argc < 2) {
    fprintf(stderr, "No command provided\n");
    return 2;
  }

  // create pipes to communicate with the sever process
  if (pipe(fd) == -1) {
    fprintf(stderr, "Error creating the pipes\n");
    return 1;
  }

  pid = fork();
  if (pid == -1) {
    fprintf(stderr, "Error creating the child process\n");
    return 1;
  } else if (pid == 0) {
    // set pipe as stdin
    close(fd[1]);
    dup2(fd[0], STDIN_FILENO);

    // create own process group (more info in https://nth.sh/Z9vj)
    if (setsid() == -1) {
      fprintf(stderr, "Error creating new process group: %s\n",
              strerror(errno));
      return 22;
    }

    execvp(argv[1], &argv[1]);

    // this code should be replaced by the exec, if this coded is reached that
    // means that exec call failed
    perror("error executing the program");
    return 1;
  }
  close(fd[0]);

  // se-up signal handlers
  signal(SIGHUP, signal_handler);
  signal(SIGINT, signal_handler);
  signal(SIGQUIT, signal_handler);
  signal(SIGTERM, signal_handler);

  // wait for the sever to stop and replicate exit code
  int status;
  waitpid(pid, &status, 0);
  if ((status = WEXITSTATUS(status)) != 0) {
    return status;
  }

  return 0;
}