You are not able to download any images from a registry in the Container Manager (DSM 7.2 and above) or Docker (DSM 7.1.1 and below) package.

Identify and troubleshoot the issue

Follow the steps below to pinpoint the causes of the issue and try to download the image again.

1. DNS server setting:
   Go to Control Panel > Network > General. Select Manually configure DNS server and set the preferred and alternative DNS servers to 8.8.8.8 and 8.8.4.4 temporarily.^{1 2 3}
2. Network interface setting:
   Go to Control Panel > Network > Network Interface, select a network interface, and click Edit > IPv6. Make sure the IPv6 setup setting is Off.⁴ Also, disable the MTU setting in the IPv4 tab.⁵
3. Time setting:
   Go to Control Panel > Regional Options > Time, and select Synchronize with NTP server. Select an NTP server and click Update Now to make sure the time shown on your Synology NAS is correct.⁶
4. Storage space:
   Go to Storage Manager > Overview and make sure the volume with Container Manager or Docker installed has enough space for downloaded images.
5. Registry setting:
   Access to certain registries may be limited in some of the regions. If the current registry is inaccessible in your region, you can switch to other registries from which you want to download the images. Go to Container Manager or Docker > Registry, and click Settings > Add to set up new registries.
6. Firewall or proxy server settings:
   If you've set up firewall rules or proxy servers, make sure the URLs for Container Manager or Docker are not blocked.
7. Docker Hub rate limit:
   Due to the rate limit of Docker Hub, you might encounter issues downloading the image if the limit is exceeded. Ensure you stay within the limit, and if exceeded, retry the download after the restriction period.

Download images using a command

You can also download the images to your Synology NAS using command lines.

1. Sign in to DSM with root privilege via SSH.
2. Use the docker pull command to download an image. Refer to Docker's documentation for detailed information.

Download and import an image into your Synology NAS

If you have access to another Synology NAS that can connect to the desired registry, you may follow the instructions below.

1. On another Synology NAS that can connect to the registry, go to Container Manager or Docker > Registry and download the image.
2. Go to the Image page and export the image.
3. Send the image to the Synology NAS that cannot connect to the registry.
4. Import the image to Container Manager or Docker.