mount.composefs - Man Page

mount a composefs filesystem image


mount.composefs [-o Options] IMAGE TARGETDIR


The composefs project uses EROFS image file to store metadata, and one or more separate directories containing content-addressed backing data for regular files.

mount.composefs mounts such an EROFS file in combination with a given set of basedir at the specified location. It can be called directly, or as a mount helper by running mount -t composefst ....


The provided IMAGE argument must be a valid composefs (EROFS) metadata image.  The TARGETDIR will be used as a mount target.

mount.composefs accepts the following colon-separated mount options when passed via the -o OPTIONS argument.


This path will be used to resolve non-empty file references stored in the composefs metadata image.  A primary use case is to have this be the same path provided to mkcomposefs --digest-store=PATH.Multiple paths can be specified, separated by :.


The image file is validated to have the specified fs-verity digest before being used. This allows a chain of trust the ensures only the expected data is ever visible in the mount.This option also implies verity.


If this is specified, all files in the IMAGE must specify an fs-verity digest, and all the files in the base dirs must have a matching fs-verity digest.Note: This needs support for the overlayfs "verity" option in the kernel, which was added in 6.6rc1.


Mounts the filesystem read-only. This is mainly useful when using upperdir as unlayered composefs images are naturally readonly.


Overrides a previous ro option


Specify an upper dir in the overlayfs mount that composefs uses. This allows a writable layer on top of the composefs image. See overlayfs docs for details.


Specifies an overlayfs workdir to go with upperdir.

See Also

composefs-info(1), mount.composefs(1)

composefs upstream ⟨

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