How to reset a forgotten root user password in Linux systems

🚀 Cómo solucionar el error paso a paso

Paso 1: Acceder e interceptar el cargador de arranque GRUB

1. Restart the server.
2. When the GRUB operating system selection menu screen appears, immediately press the e key on your keyboard to edit the boot variables of the selected kernel.

Paso 2: Modificar los parámetros del kernel

1. Scroll down using the arrow keys to locate the line starting with the word linux or linux16.
2. Go to the end of that line, delete the silent boot words (such as rhgb quiet) and add the following command to force the kernel to open a secure command prompt instead of the login interface:

init=/bin/bash

3. Press the Ctrl + X or F10 key combination to boot the server with this new temporary configuration.

Paso 3: Montar el disco en modo escritura y cambiar la clave

The system will boot directly as superuser without asking for a password, but with the disk configured in read-only mode. Enable write access to save changes:

# Remontar la partición raíz con privilegios de escritura
mount -o remount,rw /

# Modificar la clave del usuario administrador root
passwd root

# Forzar el reetiquetado de seguridad si usas SELinux (esencial en RHEL/Fedora/Rocky)
touch /.autorelabel

# Reiniciar el equipo
exec /sbin/init

🛡️ Consejo de Prevención

Recommended security practices:

• The ability to reset passwords in this way is a kernel feature, but it represents a major security risk if an attacker has physical access to your local servers. Protect your production system's bootloader by setting an access password for the GRUB console (grub-mkpasswd-pbkdf2), which will prevent unauthorized users from editing kernel parameters without prior authentication.