Docker-compose volumes mode options

Question

In the short syntax source:target:mode the official documentation only mentions ro and rw but in the cookiecutter template for django they are using other two modes: z and Z, I didn't find any reference for them anywhere, What are they?

Answer 1

The Docker run reference documents:

-v, --volume=[host-src:]container-dest[:<options>]: Bind mount a volume.
The comma-delimited `options` are [rw|ro], [z|Z],
[[r]shared|[r]slave|[r]private], and [nocopy].
The 'host-src' is an absolute path or a name value.

If neither 'rw' or 'ro' is specified then the volume is mounted in
read-write mode.

The `nocopy` mode is used to disable automatically copying the requested volume
path in the container to the volume storage location.
For named volumes, `copy` is the default mode. Copy modes are not supported
for bind-mounted volumes.

These options are further documented in the (named) volume documentation (specifically ro) and bind mount documentation.

In practice I never need any of these options, except if I happen to be deploying to a system with SELinux enabled, then z is useful.