Configurar Serial Console TTY en Proxmox

systemctl enable serial-getty@ttyS0.service
systemctl start serial-getty@ttyS0.service

##############################################################################
# Licensed under the GNU GPL v3 (https://www.gnu.org/licenses/gpl-3.0.html)
# Filename: configure_serial_console.py
# Version: 1.0
# Author: Jordi Fàbregas
# Contributors:
##############################################################################

'''
**WARNING:**  
Use at your own risk. Always back up and verify system restore before running.

Configure serial console access on Linux virtual machines running on Proxmox Virtual Environment (Proxmox VE).

Compatible only with Debian-based Linux systems that use Systemd or Upstart as the init systems.

Only tested with Debian and Ubuntu.

This script detects the init system in use (Systemd or Upstart),
creates a backup of the GRUB configuration file, updates the serial console parameters in grub,
and configures the appropriate service to enable a serial getty on ttyS0.

Proxmox Node Configuration:
From the Proxmox node shell, with the virtual machine powered off, execute:
    qm set <VMID> -serial0 socket
Then, start the virtual machine.

Usage (inside the virtual machine):
Run this script as root or with sudo:
    sudo python3 configure_serial_console.py
'''

import subprocess
import sys
import os

GRUB_CONF_FILE = '/etc/default/grub'
UPSTART_PATH = '/etc/init/'
UPSTART_TTY_FILE = 'ttyS0.conf'
BACKUP_PATH = 'backup/'
BACKUP_SUFIX = '.backup'
GRUB_CMDLINE_LINUX = 'quiet console=tty0 console=ttyS0,115200'

def check_root():
    '''
    Check if the script is executed with superuser (root) privileges.
    Input: None
    Output: Boolean
    '''
    if os.geteuid() == 0:
        return True
    else:
        return False

def check_systemd():
    '''
    Check if init system is systemd
    Input: None
    Output: Boolean
    '''
    if os.path.exists('/run/systemd/system'):
        return True
    else:
        return False

def check_upstart():
    '''
    Check if init systems is upstart
    Input: None
    Output: Boolean
    '''
    if os.path.exists('/var/log/upstart'):
        return True
    else:
        return False

def backup_grub():
    '''
    Create a backup of the GRUB configuration file.
    Saves a copy of grub file to BACKUP_PATH
    Input: None
    Output: Boolean (True if successful, False on error)
    '''
    os.makedirs(BACKUP_PATH, exist_ok=True)

    try:
        with open(GRUB_CONF_FILE, 'r') as grub_file:
            grub_content = grub_file.read()

        with open(BACKUP_PATH + 'grub' + BACKUP_SUFIX, 'w') as grub_backup:
            grub_backup.write(grub_content)

        print(f"Backup created successfully at {BACKUP_PATH}grub{BACKUP_SUFIX}", file=sys.stdout)
        return True
    except Exception as e:
        print(f"Error creating backup: {e}", file=sys.stderr)
        return False

def configure_grub():
    '''
    Configure GRUB to set serial console parameters.
    Updates GRUB_CMDLINE_LINUX with console settings for tty0 and ttyS0.
    Then runs 'update-grub' to apply changes.
    Input: None
    Output: Boolean (True if successful, False on error)
    '''
    try:
        with open (GRUB_CONF_FILE, 'r') as f:
            lines = f.readlines()

        new_file = ''

        for line in lines:
            if line.startswith('GRUB_CMDLINE_LINUX='):
                new_file += f'GRUB_CMDLINE_LINUX="{GRUB_CMDLINE_LINUX}"\n'
            else:
                new_file += line

        with open (GRUB_CONF_FILE, 'w') as f:
            f.write(new_file)

        subprocess.run(['update-grub'], check=True)

        print("GRUB configuration updated successfully", file=sys.stdout)
        return True

    except subprocess.CalledProcessError as e:
        print(f"Error executing command: {e}", file=sys.stderr)
        return False
    except Exception as e:
        print(f"Unexpected error: {e}", file=sys.stderr)
        return False    


def configure_tty_systemd():
    '''
    Enable and start the serial console service for ttyS0 using systemd.
    Runs 'systemctl enable' and 'systemctl start' for serial-getty@ttyS0.service.
    Input: None
    Output: Boolean (True if successful, False on error)
    '''
    try:

        # 2. Habilitar servicio serial
        subprocess.run(['systemctl', 'enable', 'serial-getty@ttyS0.service'], check=True)
        subprocess.run(['systemctl', 'start', 'serial-getty@ttyS0.service'], check=True)

        print('Serial console service configured successfully (Systemd)', file=sys.stdout)
        return True
    except subprocess.CalledProcessError as e:
        print(f'Error executing command: {e}', file=sys.stderr)
        return False
    except Exception as e:
        print(f'Unexpected error: {e}', file=sys.stderr)
        return False

def configure_tty_upstart():
    '''
    Create an Upstart configuration file for ttyS0 serial console.
    Writes a job configuration under /etc/init/ to manage getty on ttyS0.
    Input: None
    Output: Boolean (True after file creation)
    '''
    try:
        os.makedirs(UPSTART_PATH, exist_ok=True)

        with open (UPSTART_PATH + UPSTART_TTY_FILE, 'w') as f:
            f.write(
                '# ttyS0 - getty \n'\
                '# \n '\
                '# This service maintains a getty on ttyS0 from the point the system is \n' \
                '# started until it is shut down again. \n'
                'start on stopped rc RUNLEVEL=[12345]\n'
                'stop on runlevel [!12345]\n'
                'respawn\n'
                'exec /sbin/getty -L 115200 ttyS0 vt102\n'
                )

        print("Serial console configuration file created for Upstart", file=sys.stdout)
        return True

    except Exception as e:
        print(f"Error creating Upstart configuration: {e}", file=sys.stderr)
        return False

if __name__ == "__main__":

    if check_root():

        if check_systemd():
            backup_grub()
            configure_grub()
            configure_tty_systemd()

        elif check_upstart():
            backup_grub()
            configure_grub()
            configure_tty_upstart()

        else:
            print('Error: Unrecognized init system. This script is only compatible with Systemd and Upstart.', file=sys.stderr)

    else:
        print('Error: This script needs to be executed with root privileges.', file=sys.stderr)