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

Question

Problem :

Currently I am learning Docker. Recently I came across below Docker error in one of the projects:

“Invalid reference format: repository name must be lowercase”

I am trying to understand the causes of this message and way to fix above error message.

Can someone guide me in solving above error message?

Answer 1

I have enough experience in Docker to help you in fixing your error.

Your error invalid reference format clearly suggests that the docker cannot convert a string which you are providing to the image. It can be the invalid name or the from the parsing error earlier in your docker run command line if  you are running the image in that way. With your compose file if you are trying to expand your variable in your image name then I think that variable is not expanding properly.

If you are using the  docker run command line then this error will pop up for not quoting your parameters properly with spaces and also mistaking a order of your command line.

Your command line is ordered as below :

docker ${args_to_docker} run ${args_to_run} image_ref ${cmd_to_exec}

Now the most common error in passing the arguments to your run is the volume mapping while expanding the path name which includes the space in it and also not quoting your path or escaping your space.

Please find below the example:

docker run -v $(pwd):/data image_ref

And proper fix is as below:

docker run -v "$(pwd):/data" image_ref