No possibility to set a system-wide rootless storage.conf

[Cornichon622]

Hello, I am trying to configure my home server so that each service runs under its own Linux user inside a Podman container. To maximize my drives' longevity, I want to put the graphroot in a tmpfs (/run/user/$UID/graphroot) and the imagestore in the home dir of the user (so that I don't need to pull all the images at every reboot), important data being stored in bind mounts elsewhere. Indeed some services I run keep writing unimportant data all day long, unnecessarily wearing the drives.

Ideally, I would have /etc/containers/storage.conf specify all of this in a generic fashion, for instance (this is what I would like to do, not an actual working config):

[storage]
driver = "overlay"
graphroot = "/run/user/$UID/graphroot"
imagestore = "$HOME/imagestore

However this applies mainly to the root user (only the driver parameter is used by rootless Podman here). There is a rootless_storage_path option to set a generic graphroot path for rootless users system-wide, in which I could write /run/user/$UID/graphroot, but a similar option does not seem to exist for imagestore.

Since this option does not exist, I would have to write imagestore = "$HOME/imagestore" in $HOME/.config/containers/storage.conf for every single user. However, the mere existence of this file makes rootless Podman ignore /etc/containers/storage.conf, which means I have to repeat graphroot and driver in $HOME/.config/containers/storage.conf for every single user too.

There is a last hurdle: I can't just write imagestore = "$HOME/imagestore" in $HOME/.config/containers/storage.conf because this field does not support environment variable substitution (whereas graphroot does). That means I must write imagestore = /home/username/imagestore (that is, hardcode the user's home directory) and cannot use the exact same generic file which I would copy/paste for every user.

To sum up there are three problems here:

• in the system config, there's no way to specify a default value for rootless users for all parameters, only rootless_storage_path is available to specify a rootless graphroot.
• having $HOME/.config/containers/storage.conf makes rootless Podman ignore /etc/containers/storage.conf completely, even for parameters which are specified in /etc but not in $HOME. I would expect the config in $HOME to inherit the config in /etc/, which would also solve the first problem.
• imagestore does not support environment variable substitution like graphroot or rootless_storage_path do.

Thank you for your time!

[Luap99]

This is going to get fixed as part of a larger config file rewrite for podman 6 which includes all the main files we use inclufing storage.conf. I will post a design doc soon to discus the exact implementation

https://github.com/containers/podman/blob/main/contrib/design-docs/podman6hld.md#configuration-files-configuration-files