draft: crontab
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{"readable":true,"books":{"\/book\/esp":5,"\/book\/les-commandes-linux":4,"\/book\/linux-architecture-des-dossiers":3,"\/book\/la-domotique-chez-soi":2},"as":[{"asn":"","name":"LAN","country":"","hits":13041},{"asn":"8075","name":"Cloud","country":"US","hits":844},{"asn":"14618","name":"AWS EC2 (us-east-1)","country":"US","hits":433},{"asn":"24940","name":"Hetzner","country":"FI","hits":396},{"asn":"32934","name":"Meta Platforms Ireland Limited","country":"US","hits":254},{"asn":"16276","name":"OVH","country":"FR","hits":150},{"asn":"15169","name":"Google LLC","country":"US","hits":87},{"asn":"48230","name":"LLC MONOLITH.NET","country":"UA","hits":83},{"asn":"36352","name":"HostPapa","country":"US","hits":18},{"asn":"12322","name":"ProXad network \/ Free","country":"FR","hits":15},{"asn":"174","name":"Code 200, UAB","country":"FR","hits":12},{"asn":"18779","name":"EGIHosting","country":"US","hits":10},{"asn":"46261","name":"BraveWay","country":"US","hits":10},{"asn":"3209","name":"Vodafone Kabel Deutschland GmbH","country":"DE","hits":9},{"asn":"51207","name":"Free Mobile","country":"FR","hits":7},{"asn":"16509","name":"Anthropic, PBC","country":"US","hits":7},{"asn":"29695","name":"Lyse Tele AS","country":"NO","hits":5},{"asn":"41281","name":"KeFF Networks Ltd","country":"SE","hits":5},{"asn":"9443","name":"Vocus Retail","country":"AU","hits":5},{"asn":"45102","name":"Alibaba.com LLC","country":"SG","hits":5},{"asn":"37054","name":"Telma Madagascar","country":"MG","hits":4},{"asn":"396982","name":"Google Cloud (us-east5)","country":"US","hits":4},{"asn":"209366","name":"Crawlers","country":"US","hits":4},{"asn":"58087","name":"Datalix","country":"DE","hits":4},{"asn":"210743","name":"Babbar SAS","country":"FR","hits":4},{"asn":"132203","name":"Tencent Cloud Computing","country":"DE","hits":2},{"asn":"136907","name":"Huawei Cloud","country":"SG","hits":2},{"asn":"51167","name":"Contabo GmbH","country":"FR","hits":2}]}
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{"readable":true,"books":{"\/book\/esp":5,"\/book\/les-commandes-linux":4,"\/book\/linux-architecture-des-dossiers":3,"\/book\/la-domotique-chez-soi":2},"as":[{"asn":"","name":"LAN","country":"","hits":13070},{"asn":"8075","name":"Cloud","country":"US","hits":842},{"asn":"14618","name":"AWS EC2 (us-east-1)","country":"US","hits":433},{"asn":"24940","name":"Hetzner","country":"FI","hits":396},{"asn":"32934","name":"Meta Platforms Ireland Limited","country":"US","hits":284},{"asn":"16276","name":"OVH","country":"FR","hits":148},{"asn":"15169","name":"Google LLC","country":"US","hits":90},{"asn":"48230","name":"LLC MONOLITH.NET","country":"UA","hits":83},{"asn":"36352","name":"HostPapa","country":"US","hits":18},{"asn":"12322","name":"ProXad network \/ Free","country":"FR","hits":15},{"asn":"174","name":"Code 200, UAB","country":"FR","hits":12},{"asn":"18779","name":"EGIHosting","country":"US","hits":10},{"asn":"46261","name":"BraveWay","country":"US","hits":10},{"asn":"3209","name":"Vodafone Kabel Deutschland GmbH","country":"DE","hits":9},{"asn":"51207","name":"Free Mobile","country":"FR","hits":7},{"asn":"16509","name":"Anthropic, PBC","country":"US","hits":7},{"asn":"29695","name":"Lyse Tele AS","country":"NO","hits":5},{"asn":"41281","name":"KeFF Networks Ltd","country":"SE","hits":5},{"asn":"9443","name":"Vocus Retail","country":"AU","hits":5},{"asn":"45102","name":"Alibaba.com LLC","country":"SG","hits":5},{"asn":"37054","name":"Telma Madagascar","country":"MG","hits":4},{"asn":"396982","name":"Google Cloud (us-east5)","country":"US","hits":4},{"asn":"209366","name":"Crawlers","country":"US","hits":4},{"asn":"58087","name":"Datalix","country":"DE","hits":4},{"asn":"132203","name":"Tencent Cloud Computing","country":"DE","hits":4},{"asn":"210743","name":"Babbar SAS","country":"FR","hits":4},{"asn":"136907","name":"Huawei Cloud","country":"SG","hits":2},{"asn":"51167","name":"Contabo GmbH","country":"FR","hits":2}]}
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{
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"title": "crontab",
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"_updated_at": "2026-05-16 21:21:32"
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}
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# crontab
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**cron** est un démon Unix qui exécute, chaque minute, les tâches planifiées par les utilisateurs. La commande **crontab** (contraction de *chrono table*, « table de planification ») permet de consulter et modifier ces tâches.
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Chaque utilisateur dispose de sa propre table ; le démon `cron`, lancé par **root**, exécute chaque tâche sous l'identité de son propriétaire.
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## Format d'une ligne
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Chaque ligne d'une crontab suit le format suivant :
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```
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mm hh jj MMM JJJ commande
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```
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| Champ | Plage | Description |
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| ----- | ----- | ----------- |
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| `mm` | 0–59 | Minute |
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| `hh` | 0–23 | Heure |
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| `jj` | 1–31 | Jour du mois |
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| `MMM` | 1–12 | Mois |
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| `JJJ` | 0–6 | Jour de la semaine (0 = dimanche) |
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## Lister les tâches
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Afficher la table de l'utilisateur connecté :
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```
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crontab -l
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```
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## Mots-clés
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Plusieurs mots-clés peuvent remplacer le code horaire :
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| Mot-clé | Description | Équivalent |
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| ------- | ----------- | ---------- |
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| `@reboot` | Au démarrage | (aucun) |
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| `@yearly` | Tous les ans | `0 0 1 1 *` |
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| `@annually` | Tous les ans | `0 0 1 1 *` |
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| `@monthly` | Tous les mois | `0 0 1 * *` |
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| `@weekly` | Toutes les semaines | `0 0 * * 0` |
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| `@daily` | Tous les jours | `0 0 * * *` |
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| `@midnight` | Toutes les nuits | `0 0 * * *` |
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| `@hourly` | Toutes les heures | `0 * * * *` |
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## Éditer la table
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Ouvrir la crontab de l'utilisateur connecté dans l'éditeur par défaut :
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```
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crontab -e
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```
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L'éditeur utilisé peut être modifié via la variable d'environnement `EDITOR` :
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```
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$ export EDITOR=nano
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```
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## Supprimer la table
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```
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crontab -r
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```
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## Remplacer la table
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Remplacer la table courante par le contenu d'un fichier :
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```
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crontab <fichier>
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```
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## Rediriger les sorties
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Par défaut, la sortie standard d'une tâche `cron` est envoyée par mail à son propriétaire. Pour la rediriger, on utilise la syntaxe shell habituelle :
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```
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mm hh jj MMM JJJ tâche > fichier1 2> fichier2
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```
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- `fichier1` reçoit la sortie standard
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- `fichier2` reçoit l'erreur standard
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Pour ignorer toute sortie :
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```
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>/dev/null 2>&1
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```
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## Inspecter l'activité
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Afficher la date du dernier accès au script de `cron` (indicateur approximatif d'activité) :
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```
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ls -lut /etc/init.d/cron
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```
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Extraire les lignes relatives à `cron` dans le journal système :
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```
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grep -w cron /var/log/syslog
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```
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## Pour aller plus loin
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Les tables sont stockées dans un fichier propre à chaque utilisateur :
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- `/var/spool/cron/crontabs/<utilisateur>` sous Debian, MX Linux
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- `/var/spool/cron/<utilisateur>` sous Red Hat, Fedora et CentOS
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Une table système centralisée existe également dans `/etc/crontab`.
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Pour les postes qui ne restent pas allumés en permanence, l'utilitaire **anacron** prend le relais : il exécute, au démarrage, les tâches qui auraient dû tourner pendant que la machine était éteinte.
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