Crontab Cheat Sheet 2025 : 50+ Exemples d'Expressions Cron Utiles

Que vous planifiiez des sauvegardes, automatisiez des déploiements ou exécutiez des scripts de nettoyage, cron est le pilier de la planification sur Unix/Linux. Ce cheat sheet vous donne 50+ exemples d'expressions cron classés par fréquence.

1. Syntaxe des Expressions Cron

Une expression cron standard se compose de 5 champs séparés par des espaces :

┌───────────── Minute (0–59)
│ ┌─────────── Heure (0–23)
│ │ ┌───────── Jour du mois (1–31)
│ │ │ ┌─────── Mois (1–12 ou JAN–DEC)
│ │ │ │ ┌───── Jour de la semaine (0–7 ou SUN–SAT)
│ │ │ │ │
* * * * *  command_to_execute

La commande suit les cinq champs. Utilisez notre Générateur Cron pour construire des expressions visuellement.

2. Caractères Spéciaux

Cron utilise quatre caractères spéciaux pour définir les planifications :

3. 50+ Exemples d'Expressions Cron

Les tableaux ci-dessous couvrent les planifications cron les plus courantes. Chaque expression est prête à copier-coller.

Toutes les X minutes

Planifications horaires

Planifications quotidiennes

Planifications hebdomadaires

Planifications mensuelles

Planifications annuelles / trimestrielles

Planifications Business & DevOps

4. Commandes Crontab

La commande crontab gère les fichiers cron par utilisateur :

# Edit crontab
crontab -e

# List all cron jobs
crontab -l

# Backup current crontab to a file
crontab -l > my-crontab-backup.txt

# Install crontab from a file
crontab my-crontab-backup.txt

# Remove all cron jobs (careful!)
crontab -r

5. Syntaxe Cron par Plateforme

La syntaxe cron varie selon les plateformes :

# Standard 5-field crontab
*/5 * * * * /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1

# .github/workflows/scheduled.yml
on:
  schedule:
    - cron: '0 9 * * 1-5'  # Weekdays 9AM UTC

# AWS EventBridge (6 fields, note the ?)
cron(0 9 ? * MON-FRI *)  # Weekdays 9AM UTC

# Kubernetes CronJob spec
apiVersion: batch/v1
kind: CronJob
metadata:
  name: daily-backup
spec:
  schedule: "0 2 * * *"
  timeZone: "America/New_York"  # K8s 1.27+

// vercel.json
{
  "crons": [{
    "path": "/api/cron/daily-report",
    "schedule": "0 9 * * *"
  }]
}

6. Pièges Courants

Les erreurs les plus courantes avec les planifications cron :

# Gotcha: overlapping runs - use flock to prevent
*/5 * * * * /usr/bin/flock -n /tmp/myjob.lock /path/to/script.sh

# Gotcha: environment - always use full paths
0 2 * * * /usr/bin/python3 /home/user/scripts/backup.py >> /var/log/backup.log 2>&1

# Gotcha: 30-second workaround (two entries)
* * * * * /path/to/script.sh
* * * * * sleep 30 && /path/to/script.sh

# Gotcha: PATH not set - define it at the top of your crontab
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# Gotcha: percent signs (%) must be escaped in crontab
# Wrong:
0 0 * * * echo "Today is $(date +%Y-%m-%d)"
# Correct:
0 0 * * * echo "Today is $(date +\%Y-\%m-\%d)"

Sample Crontab File

Here is a complete, real-world crontab file combining several patterns discussed above:

# =============================================
# Crontab for: webserver (production)
# Last updated: 2025-01-15
# =============================================

# Environment
SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MAILTO="ops-team@example.com"

# --- BACKUPS ---
# Full database backup at 2:00 AM daily
0 2 * * * /usr/bin/flock -n /tmp/db-backup.lock /opt/scripts/db-backup.sh >> /var/log/db-backup.log 2>&1

# Incremental file backup every 6 hours
0 */6 * * * /opt/scripts/file-backup.sh >> /var/log/file-backup.log 2>&1

# --- MAINTENANCE ---
# Clear temp files older than 7 days, daily at 3 AM
0 3 * * * /usr/bin/find /tmp -type f -mtime +7 -delete

# Rotate application logs every Sunday at 4 AM
0 4 * * 0 /opt/scripts/rotate-logs.sh >> /var/log/log-rotation.log 2>&1

# --- MONITORING ---
# Health check every 5 minutes
*/5 * * * * /opt/scripts/healthcheck.sh > /dev/null 2>&1

# SSL certificate expiry check daily at 6 AM
0 6 * * * /opt/scripts/check-ssl.sh

# Disk space alert if usage > 90%, every hour
0 * * * * /opt/scripts/disk-alert.sh

# --- REPORTS ---
# Send daily summary at 8 AM on weekdays
0 8 * * 1-5 /opt/scripts/daily-report.sh

# Monthly analytics report on the 1st at 9 AM
0 9 1 * * /opt/scripts/monthly-report.sh

7. Test et Débogage

Avant de déployer un job cron en production :

# Redirect all output to a log file
0 2 * * * /path/to/backup.sh >> /var/log/cron-backup.log 2>&1

# Disable cron mail for this job
0 2 * * * /path/to/backup.sh > /dev/null 2>&1

# Set MAILTO at the top of crontab
MAILTO=""
# Or send to a real address
MAILTO="admin@example.com"

# Check cron logs on Debian/Ubuntu
grep CRON /var/log/syslog | tail -20

# Check cron logs on CentOS/RHEL
grep CRON /var/log/cron | tail -20

# On systems using journald (systemd)
journalctl -u cron --since "1 hour ago"

# Quick test: add a job that writes to a file
# Then check if the file gets updated
* * * * * echo "cron works: $(date)" >> /tmp/cron-test.log

# Verify your crontab was saved correctly
crontab -l | grep -v '^#'

# Check if cron daemon is running
systemctl status cron    # Debian/Ubuntu
systemctl status crond   # CentOS/RHEL

Common Cron Debugging Checklist

8. Questions Fréquentes