nbdkit --filter=ext2 file fs.img ext2file=/disks/disk.raw nbdkit --filter=ext2 --filter=partition file fs.img \ partition=1 ext2file=exportname
nbdkit-ext2-filter is an nbdkit filter which can read and write files inside ext2, ext3 or ext4 filesystem images.
Suppose you have an ext2/3/4 filesystem image called fs.img which contains inside itself a file called disk.raw inside a directory on the filesystem called /disks, then you could serve that file over NBD using:
nbdkit --filter=ext2 file fs.img ext2file=/disks/disk.raw
Commonly disk images are partitioned. In that case, you must select just the partition of a disk image that contains an ext2 filesystem, by using nbdkit-partition-filter(1):
nbdkit --filter=ext2 --filter=partition file fs.img \ partition=1 ext2file=/disks/disk.raw
This filter can both read and write to the file inside the filesystem. Use the -r flag to force a readonly connection, but note this does not guarantee that no writes are made to the filesystem. In particular we may have to replay the ext3 journal in order to open a filesystem even read-only.
The filter does not support multiple parallel connections, because there is a risk of corrupting the filesystem (as if the filesystem was mounted by multiple machines). If a second connection is made to nbdkit, it will block until the first connection closes.
The filter is implemented using the ext2fs library which is provided in most Linux distros, and also available as part of the e2fsprogs project.
nbdkit-guestfs-plugin(1) is a more generic plugin which can read files from all kinds of different filesystem types, even if they are partitioned or use logical volumes. It uses libguestfs instead of e2fsprogs.
The full path of the file within the filesystem that will be exposed over NBD. The path must be absolute (starts with
The plugin will expose the path within the filesystem chosen by the exportname passed by the client. Note that this mode allows the client to deduce which files exist within the disk image, which may be a security risk in some situations.
At present, when using this mode, the server does not advertise any particular exports; however, you may use nbdkit-exportname-filter(1) to perform that task. Similarly, the underlying plugin must support the default export name,
nbdkit --dump-configto find the location of
nbdkit-ext2-filter first appeared in nbdkit 1.18, replacing
nbdkit-ext2-plugin which was added in nbdkit 1.4 and removed in nbdkit 1.22.
nbdkit(1), nbdkit-plugin(3), nbdkit-exportname-filter(1), nbdkit-partition-filter(1), nbdkit-guestfs-plugin(1), http://e2fsprogs.sourceforge.net/, fuse2fs(1).
Richard W.M. Jones
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nbdkit(1), nbdkit-exportname-filter(1), nbdkit-filter(3), nbdkit-release-notes-1.18(1), nbdkit-release-notes-1.22(1), nbdkit-release-notes-1.24(1).