File Formats

Proxmox File Archive Format (.pxar)

digraph g { graph [ rankdir = "LR" fontname="Helvetica" ]; node [ fontsize = "16" shape = "record" ]; edge [ ]; "archive" [ label = "archive.pxar" shape = "record" ]; "rootdir" [ label = "<f0> ENTRY| \{XATTR\}\* extended attribute list\l | \{ACL_USER\}\* USER ACL entries\l | \{ACL_GROUP\}\* GROUP ACL entries\l| \[ACL_GROUP_OBJ\] the ACL_GROUP_OBJ \l| \[ACL_DEFAULT\] the various default ACL fields\l|\{ACL_DEFAULT_USER\}\* USER ACL entries\l|\{ACL_DEFAULT_GROUP\}\* GROUP ACL entries\l|\[FCAPS\] file capability in Linux disk format\l|\[QUOTA_PROJECT_ID\] the ext4/xfs quota project ID\l| { PAYLOAD | SYMLINK | DEVICE | { <de> \{DirectoryEntries\}\* | GOODBYE}}" shape = "record" ]; "entry" [ label = "<f0> size: u64 = 64\l|type: u64 = ENTRY\l|feature_flags: u64\l|mode: u64\l|flags: u64\l|uid: u64\l|gid: u64\l|mtime: u64\l" labeljust = "l" shape = "record" ]; "direntry" [ label = "<f0> FILENAME |{ENTRY | HARDLINK}" shape = "record" ]; "archive" -> "rootdir":f0 "rootdir":f0 -> "entry":f0 "rootdir":de -> "direntry":f0 }

Data Blob Format (.blob)

The data blob format is used to store small binary data. The magic number decides the exact format:

[66, 171, 56, 7, 190, 131, 112, 161] unencrypted uncompressed
[49, 185, 88, 66, 111, 182, 163, 127] unencrypted compressed
[123, 103, 133, 190, 34, 45, 76, 240] encrypted uncompressed
[230, 89, 27, 191, 11, 191, 216, 11] encrypted compressed

Compression algorithm is zstd. Encryption cipher is AES_256_GCM.

Unencrypted blobs use the following format:

MAGIC: [u8; 8]
CRC32: [u8; 4]
Data: (max 16MiB)

Encrypted blobs additionally contains a 16 byte IV, followed by a 16 byte Authenticated Encyryption (AE) tag, followed by the encrypted data:

MAGIC: [u8; 8]
CRC32: [u8; 4]
ÌV: [u8; 16]
TAG: [u8; 16]
Data: (max 16MiB)

Fixed Index Format (.fidx)

All numbers are stored as little-endian.

MAGIC: [u8; 8] [47, 127, 65, 237, 145, 253, 15, 205]
uuid: [u8; 16], Unique ID
ctime: i64, Creation Time (epoch)
index_csum: [u8; 32], Sha256 over the index (without header) SHA256(digest1||digest2||...)
size: u64, Image size
chunk_size: u64, Chunk size
reserved: [u8; 4016], overall header size is one page (4096 bytes)
digest1: [u8; 32] first chunk digest
digest2: [u8; 32] next chunk
... next chunk ...

Dynamic Index Format (.didx)

All numbers are stored as little-endian.

MAGIC: [u8; 8] [28, 145, 78, 165, 25, 186, 179, 205]
uuid: [u8; 16], Unique ID
ctime: i64, Creation Time (epoch)
index_csum: [u8; 32], Sha256 over the index (without header) SHA256(offset1||digest1||offset2||digest2||...)
reserved: [u8; 4032], Overall header size is one page (4096 bytes)
offset1: u64 End of first chunk
digest1: [u8; 32] first chunk digest
offset2: u64 End of second chunk
digest2: [u8; 32] second chunk digest
... next chunk offset/digest