Composefs achieves whole-filesystem integrity verification through image sealing: a single cryptographic digest authenticates an entire filesystem, covering both file contents and metadata (directory structure, permissions, ownership, symlinks, and xattrs). This goes further than fs-verity alone, which can only verify individual file contents, and avoids the fixed-partition requirement of dm-verity. The mechanism combines an EROFS image for metadata, a content-addressed object store for file data, and overlayfs with verity=require to enforce integrity checks on every file access at the kernel level.