I would like to authenticate a squashfs image, using a public-key signature. For an elegant implementation, it would be ideal if such a signature could simply be appended to the end of the squashfs image file.

Can squashfs tools, including kernel mount code, handle a squashfs image with some extra data appended to the end of the file, without any ill effect?

1 Answer 1


As squashfs can reside on block devices, which have no relation in size to the filesystem size, apart from being at least as big, I would estimate that appending random data to a squashfs is unlikely to cause problems.

A quick browse through the kernel super.c driver function squashfs_fill_super() which seems to mount a squashfs, does not show it being concerned with data beyond the end of the bytes_used size given in the superblock, which is at the start of the filesystem, and no error messages seem relevant either.

Note, however, that a squashfs file is usually padded at the end to be a multiple of 4Kibytes, so that it can be used with loopback block devices. Make sure whatever you add is also a multiple of 4096 bytes.

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