Why Is My Cron Job Not Running? Step-by-Step Diagnosis

✨ Quick Answer

The most common failure with automated Cron tasks is that the script or command runs perfectly when you execute it manually in your terminal, but fails silently when invoked by the system daemon (cron). This occurs due to critical differences between your user session and the isolated environment of Cron.

Quick Diagnostics

Cause

Cron daemon service disabled or stopped

Solution

Start cron daemon: systemctl enable --now cron (or crond)

Cause

Missing trailing newline in crontab file or relative paths used

Solution

Use absolute paths for all commands and executables in crontab

The most common failure with automated Cron tasks is that the script or command runs perfectly when you execute it manually in your terminal, but fails silently when invoked by the system daemon (cron). This occurs due to critical differences between your user session and the isolated environment of Cron.

Step-by-Step Solution

1. 1

   Step 1: Forzar el uso de rutas absolutas en comandos y scripts

   Cron does not load the environment variables from your .bashrc file or inherit the PATH variable from your interactive session. Therefore, it will not know where binaries like python3, node, or git are unless you use full paths:

   BASH Copy

   # INCORRECTO:
   * * * * * python3 /home/usuario/script.py
   
   # CORRECTO (Usa "which python3" para verificar la ruta en tu sistema):
   * * * * * /usr/bin/python3 /home/usuario/script.py
   

2. 2

   Step 2: Redirigir errores y logs de ejecución a un archivo físico

   Since background tasks do not have a physical terminal to display error messages, you must force the system to write them to a log file in order to audit the exact reason for the failure:

   BASH Copy

   # Redirigir la salida estándar (1) y el canal de errores (2) a un log
   0 5 * * * /usr/bin/bash /home/usuario/backup.sh >> /home/usuario/backup.log 2>&1
   

3. 3

   Step 3: Verificar que el demonio de Cron esté activo

   Make sure that the service responsible for coordinating the scheduled task queue is running on your server:

   BASH Copy

   sudo systemctl status cron   # En Debian/Ubuntu
   sudo systemctl status crond  # En Arch/RHEL/CentOS