From the command run:
sudo docker build -t myrepo/redis
there are no "arguments" passed to the docker build
command, only a single flag -t
and a value for that flag. After docker parses all of the flags for the command, there should be one argument left when you're running a build.
That argument is the build context. The standard command includes a trailing dot for the context:
sudo docker build -t myrepo/redis .
What's the build context?
Every docker build sends a directory to the build server. Docker is a client/server application, and the build runs on the server which isn't necessarily where the docker command is run. Docker uses the build context as the source for files used in COPY
and ADD
steps. When you are in the current directory to run the build, you would pass a .
for the context, aka the current directory. You could pass a completely different directory, even a git repo, and docker will perform the build using that as the context, e.g.:
docker build -t sudobmitch/base:alpine --target alpine-base \
'https://github.com/sudo-bmitch/docker-base.git#main'
For more details on these options to the build command, see the docker build documentation.
What if you included an argument?
If you are including the value for the build context (typically the .
) and still see this error message, you have likely passed more than one argument. Typically this is from failing to parse a flag, or passing a string with spaces without quotes. Possible causes for docker to see more than one argument include:
Missing quotes around a path or argument with spaces (take note using variables that may have spaces in them)
Incorrect dashes in the command: make sure to type these manually rather than copy and pasting
Incorrect quotes: smart quotes don't work on the command line, type them manually rather than copy and pasting.
Whitespace that isn't white space, or that doesn't appear to be a space.
Most all of these come from either a typo or copy and pasting from a source that modified the text to look pretty, breaking it for using as a command.
How do you figure out where the CLI error is?
The easiest way I have to debug this, run the command without any other flags:
docker build .
Once that works, add flags back in until you get the error, and then you'll know what flag is broken and needs the quotes to be fixed/added or dashes corrected, etc.