[mathiasgredal]

Does anyone know if there exists a tool that can convert tarballs to filesystems and back. I know you can make a loopback device, but it can be pretty hard/impossible to do inside a container, and often requires special flags and privileges.

[st_goliath]

For squashfs there is `tar2sqfs`[1] and `sqfs2tar`[2] (and now also `sqfstar`[3]) that can go from tarball to filesystem and back again.

For ext4, I recently saw a patch set on the mailing list[4].

Not sure about other filesystems tough.

[1] https://manpages.debian.org/unstable/squashfs-tools-ng/tar2s...

[2] https://manpages.debian.org/unstable/squashfs-tools-ng/sqfs2...

[3] https://manpages.debian.org/unstable/squashfs-tools/sqfstar....

[4] https://lore.kernel.org/linux-ext4/20230812150204.462962-2-j...

[cedws]

You can extract the tarball to a directory, then run mkfs.ext4 -d DIRECTORY FILENAME BLOCKS to create a filesystem[0]. You'll need to know how many blocks your filesystem needs to be in advance.

Unfortunately, mkfs.ext4 only works on Linux. There is no port for other operating systems.

[0] https://github.com/cedws/concrete-ubuntu/blob/0ae3f076c5a20d...

[guappa]

If you want to create read-only, use ext2. No point in using ext4 if you don't want journaling.

[folmar]

Extents are a useful feature even for readonly although the gain is smaller.

[cedws]

You can also use ISO9660.

[ravenstine]

I've been doing something similar recently, though it doesn't directly convert a tar to an ext4 FS. But maybe this can help you get to where you want to be.

On Alpine Linux:

```

apk add --no-cache coreutils e2fsprogs

```

```

#!/bin/sh

# Untar the tar file

mkdir -p /tmp/my_untarred_files_dir

tar -xvf my_tar_file.tar -C /tmp/my_untarred_files_dir

# Make an empty image file.

dd if=/dev/zero of="fs.raw" bs=1M count=1024

# Format the file as ext4 (with journaling) and copy untarred files into it

mke2fs -t ext4 -j -d "/tmp/my_untarred_files_dir" "fs.raw"

```

If you want to make a qcow2 image, you can then do this:

```

apk add --no-cache qemu-img

qemu-img convert -O qcow2 "fs.raw" "fs.qcow2"

```

[chociej]

7z can list and extract from ext4 images. Respectively:

$ 7z l <image>

$ 7z x <image>

[chungy]

You can use fuse2fs to mount any ext[24] file system in user space. You can even use "-o fakeroot" to get complete control over UIDs and modes.

[torcete]

Maybe you are looking for something like fsarchiver?

https://www.fsarchiver.org

[loeg]

guestfish and libarchive are sort of in this space. Neither is a canned tool for exactly this.