Ciel is a tool for controlling multi-layer file systems and containers, primarily designed for building and distributing Linux distributions based on the DPKG[1] package manager. Ciel also comes with features that allow fast roll-back and merge-down functions.

Ciel uses OverlayFS, whose layering concept is similar to that of Adobe Photoshop. In Ciel, all layers but the one on top are to be locked, while the top layer could be written.

[1] The clean command contains a routine to list all files managed by a package manager, which uses the dpkg -L command.

Commands

Ciel contains the following built-in commands:

init   <tarball>

drop   [<layers>]
mount  [--read-write] [<layers>]
merge  [<upper>..]<lower> [--no-self] path
clean  [--factory-reset]

shell  [<cmdline>]
rawcmd <cmd> <arg1> <arg2> ...

Initialisation

The init command creates directory structures required by Ciel, and unpacks the specified tarball to the "bottom layer" of the current OverlayFS structure.

File System Commands

The drop command clears all files and changes made to a specific layer. When no parameter was specified, this command clears changes made to the "upper", or top layer, effectively a roll-back function.

The mount command is provided to manually mount a file system, and prints the mount point. This command should only be used where necessary. You would need to unmount and remove the mount point manually when done. File systems are mounted read-only unless --read-write is specified as a parameter.

The merge command merges file changes downwards. Its first parameter should appear similar to upperdir..cache, which specifies the "upper" and "lower" objective of this operation. The upperdir part could be omitted - where upperdir is specified by default - the first parameter could then be written as ..cache or cache, both of which equivalent to upperdir..cache. The parameter path should be used to specify the directory in which layer to be merged, where / could be specified to merge the layer specified as a whole. Additionally, --no-self could be specified to exclude files and directories themselves when merging.

The clean command could be used to clear all files not managed by dpkg, primarily designed for creating distributions. The command has a built-in whilelist to omit those files and directories not managed by the package manager, which happen to be essential for the resulting distribution to function properly. The --factory-reset parameter could be used to remove additionally automatically generated files such as system host keys (SSL) and systemd machine IDs.

Container Commands

The shell command could carry two functions: to enter a contained/jailed shell and to execute shell commands from within such environments. When no extra parameter was specified, this command would enter the container shell; when commands were appended as parameters to the shell command, this command would execute the specified command following from within the container. Do note however that this command would only accept one parameter - command-line strings containing spaces for example, should be surrounded with quotation marks.

The rawcmd command executes programmes from within the container(s). Please use shell unless necessary, as using the rawcmd for programme invokation would omit all configurations or environment variables defined in Shell configuration files. This command could take multiple parameters as needed, and is otherwise identical in usage as the shell command.

Plugins

Other commands not discussed above, for example, ciel build - would be an executable stored in the /usr/libexec/ciel-plugin directory as ciel-build - Ciel searches this directory for executables named ciel-*.

Additional Notes

Ciel exports the three standard pipes when executing Ciel shell, rawcmd or plugins, as well as the returned error code/status of that particular command(s).