EC2 ubuntu crob job failure

Question

Hi,

I’m trying to set up a cron job on an Ubuntu EC2 instance, but it keeps failing with a **Permission denied** error.

These are the steps I followed:

1. Edited the crontab:

```
   crontab -e
   ```

2. Added the following entry to run every minute for testing:

```
   * * * * * /usr/bin/docker system prune -af
   ```

3. Verified the entry was saved:

```
   crontab -l
   ```

The cron service is running, but when I check the logs I see:

```
Mar 10 18:06:01 remote-docker-engine-amd-01 cron[19243]: Permission denied
Mar 10 18:06:01 remote-docker-engine-amd-01 CRON[19243]: Permission denied
```

The command itself works when I run it manually as the same user:

```
/usr/bin/docker system prune -af
```

So Docker permissions seem fine when executed interactively, but the job fails when triggered by cron.

I also tried reinstalling the cron package, but the issue persists.

Am I missing something in the cron configuration or environment? Any guidance would be appreciated.

Thanks.

Riku_Kobayashi · Answer

Hello.

Even if I set "sudo" in the command set in cron, it fails to execute?  
If you run it as the root user, it should generally run successfully.  
To troubleshoot, start by enabling sudo.  
https://stackoverflow.com/questions/70099692/crontab-sudo-docker-permission-denied

Liu, George · Answer

When you run docker commands interactively, your shell session has access to the Docker socket (usually 
docker.sock) because your user is in the docker group. However, cron jobs run in a minimal environment without loading group memberships the same way.

For a quick fix, try to run the cron job as root:

sudo crontab -e

EC2 ubuntu crob job failure

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