Ran into this Docker error with one of my projects:
invalid reference format: repository name must be lowercase
What are the various causes for this generic message?
I already figured it out after some effort, so I'm going to answer my own question in order to document it here as the solution doesn't come up right away when doing a web search and also because this error message doesn't describe the direct problem Docker encounters.
Best Answer
A "reference" in docker is a pointer to an image. It may be an image name, an image ID, include a registry server in the name, use a sha256 tag to pin the image, and anything else that can be used to point to the image you want to run.
The
invalid reference format
error message means docker cannot convert the string you've provided to an image. This may be an invalid name, or it may be from a parsing error earlier in thedocker run
command line if that's how you run the image.If the name itself is invalid, the
repository name must be lowercase
means you use upper case characters in your registry or repository name, e.g.YourImageName:latest
should beyourimagename:latest
.With the
docker run
command line, this is often the result in not quoting parameters with spaces, missing the value for an argument, and mistaking the order of the command line. The command line is ordered as:The most common error in passing args to the run is a volume mapping expanding a path name that includes a space in it, and not quoting the path or escaping the space. E.g.
Where if you're in the directory
/home/user/Some Project Dir
, that would define an anonymous volume/home/user/Some
in your container, and try to runProject:latest
with the commandDir:/data image_ref
. And the fix is to quote the argument:Other common places to miss quoting include environment variables:
which docker would interpret as trying to run the image
With:latest
and the commandSpaces image_ref
. Again, the fix is to quote the environment parameter:With a compose file, if you expand a variable in the image name, that variable may not be expanding correctly. So if you have:
Then double check that
your_image_name
is defined to an all lower case string.