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% mount.composefs 8 "" composefs "User Commands"
# NAME
mount.composefs - mount a composefs filesystem image
# SYNOPSIS
**mount.composefs** [-o OPTIONS] *IMAGE* *TARGETDIR*
# DESCRIPTION
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 composefs ...`.
# OPTIONS
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.
**basedir**=*PATH*
: 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 `:`.
**digest**=*DIGEST*
: 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**.
**idmap**=*PATH*
: Specify a path to a user namespace whose ID mapping should be used.
The typical format for this type of path is `/proc/<pid>/ns/user`
**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.
**ro**
: Mounts the filesystem read-only. This is mainly useful when using
**upperdir** as unlayered composefs images are naturally readonly.
**rw**
: Overrides a previous **ro** option
**upperdir**
: 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.
**workdir**
: Specifies an overlayfs workdir to go with **upperdir**.
# SEE ALSO
**composefs-info(1)**, **mount.composefs(1)**
[composefs upstream](https://github.com/containers/composefs)
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