Docker error: invalid reference format: repository name must be lowercase

Question

Ran into this Docker error with one of my projects:

invalid reference format: repository name must be lowercase

What are the various causes for

Answer 1

In my case I had a naked --env switch, i.e. one without an actual variable name or value, e.g.:

docker run \
   --env \       <----- This was the offending item
   --rm \
   --volume "/home/shared:/shared" "$(docker build . -q)"

Answer 2

Replacing image: ${DOCKER_REGISTRY}notificationsapi with image:notificationsapi or image: ${docker_registry}notificationsapi in docker-compose.yml did solves the issue

file with error

  version: '3.4'

services:
  notifications.api:
    image: ${DOCKER_REGISTRY}notificationsapi
    build:
      context: .
      dockerfile: ../Notifications.Api/Dockerfile

file without error

version: '3.4'

services:
 notifications.api:
    image: ${docker_registry}notificationsapi
    build:
      context: .
      dockerfile: ../Notifications.Api/Dockerfile

So i think error was due to non lower case letters it had

Answer 3

Try to use lower case chars in your DockerFile

For example, use:

openjdk:8

instead of

openJDK:8

Answer 4

In my case the problem was in parameters arrangement. Initially I had --name parameter after environment parameters and then volume and attach_dbs parameters, and image at the end of command like below.

docker run -p 1433:1433 -e sa_password=myComplexPwd -e ACCEPT_EULA=Y --name sql1 -v c:/temp/:c:/temp/ attach_dbs="[{'dbName':'TestDb','dbFiles':['c:\\temp\\TestDb.mdf','c:\\temp\\TestDb_log.ldf']}]" -d microsoft/mssql-server-windows-express

After rearranging the parameters like below everything worked fine (basically putting --name parameter followed by image name).

docker run -d -p 1433:1433 -e sa_password=myComplexPwd -e ACCEPT_EULA=Y --name sql1 microsoft/mssql-server-windows-express -v C:/temp/:C:/temp/ attach_dbs="[{'dbName':'TestDb','dbFiles':['C:\\temp\\TestDb.mdf','C:\\temp\\TestDb_log.ldf']}]"

Answer 5

A reference in Docker is what points to an image. This could be in a remote registry or the local registry. Let me describe the error message first and then show the solutions for this.

invalid reference format

This means that the reference we have used is not a valid format. This means, the reference (pointer) we have used to identify an image is invalid. Generally, this is followed by a description as follows. This will make the error much clearer.

invalid reference format: repository name must be lowercase

This means the reference we are using should not have uppercase letters. Try running docker run Ubuntu (wrong) vs docker run ubuntu (correct). Docker does not allow any uppercase characters as an image reference. Simple troubleshooting steps.

1) Dockerfile contains a capital letters as images.

FROM Ubuntu (wrong)
FROM ubuntu (correct)

2) Image name defined in the docker-compose.yml had uppercase letters

3) If you are using Jenkins or GoCD for deploying your docker container, please check the run command, whether the image name includes a capital letter.

Please read this document written specifically for this error.

Answer 6

In my case DockerFile contained the image name in mixed case instead of lower case.

Earlier line in my DockerFile

FROM CentOs

and when I changed above to FROM centos, it worked smoothly.