mount.nbt - Mount a Named Binary Tag File System
mount.nbt [-o <fs-option>[,...]] [-fnrvwh] <nbt-file> <mount-point>
This tool is a FUSE-based file system implementation for accessing NBT formatted
data, which is used by Minecraft to store various data about the game. Running
this tool mounts a file system from the file specified by
<nbt-file>; both standalone NBT file (usually have suffix
.dat) and Minecraft Region file (usually have suffix .mcr or
.mca) are supported.
- -f
- Operate in foreground. Useful for debugging.
- -h
- Print a brief usage message.
- -n
- Ignored.
- -o <fs-option>[,...]
- Pass gereric mount options, FUSE-specific options, and/or NBT-specific
options, in a comma-separated list. See mount(8) and fuse(8)
for gereric mount options and FUSE-specific options.
NBT-specific options are:
- ro
- Mount the file system read-only, useful to mount from a file that can't be
written to, or to prevent accidentally changing it; but see
writefile option below.
- rw
- Revert any ro option that may be specified early.
- region
- Specify the <nbt-file> is a Minecraft Region file instead of
a standalone NBT file.
- typeprefix
- Use node type prefix for node names when listing compound nodes as a
directory. This option affects directory listing only, existing nodes can
always be accessed either with or without the type prefix.
- umask=<mask>
- Set file mode mask using an octal number for NBT nodes, default 0.
- writefile=<path>
- Set an alternative path for writing NBT data; the original
<nbt-file> won't be written to if this is specified. Will
have no effect when file system is mounted read-only.
- compression={gzip|zlib}
- Set compression format for writing NBT data; default gzip for
standalone NBT file, zlib for Minecraft Region file. Will have no
effect when file system is mounted read-only.
- -r
- Mount the file system read-only. Same as specifying -o ro.
- -v
- Be Verbose during mounting.
- -V
- Display version, copyright and licensing information of this tool. The
program will exit afterward.
- -w
- Mount the file system read-write. Same as specifying -o rw.
NBT specification defined several types for a tag, they are mapped into file
types as followings:
| NBT Tag Type |
File Type |
Type Prefix Name |
| TAG_Byte |
Regular |
int8, byte |
| TAG_Short |
Regular |
int16 |
| TAG_Int |
Regular |
int32 |
| TAG_Long |
Regular |
int64 |
| TAG_Float |
Regular |
float32, float, single |
| TAG_Double |
Regular |
float64, double |
| TAG_Byte_Array |
Regular |
int8array, bytearray |
| TAG_String |
Regular |
string |
| TAG_List |
Directory |
list |
| TAG_Compound |
Directory |
compound |
| TAG_Int_Array |
Directory |
int32array |
| TAG_Long_Array |
Directory |
int64array |
For nodes directly under a compound, they can be accessed using their
name; a type prefix can also be prepended to an name to reference a
node, as typeprefix:name. For example an int64 node named
RandomSeed under a compound named Data, the following 2
pathes would referencing the exactly same node:
Data/int64:RandomSeed
compound:Data/RandomSeed
Turning on mount option typeprefix will having this type prefix be
automatically prepended to node names, when listing a compound using
readdir(3); this could be useful to preserve the type information when
copying a compound node recursively (such as using tar(1)), so
it is possible for the copied nodes be restored into another NBT later.
Nodes under a list are accessed using index numbers starting with 0; they
will also have same type, a pseudo file .type is available under any
list to indicate node type the list contains.
Any node which the file type is regular file can be read and written directly
using read(2) and write(2); they can also be
truncate(2)ed to empty, but number typed ( int8 , int16 ,
int32 , int64 , float32 and float64 ) nodes will
turn its value into 0 after that. Nodes with type int8array or
string support lseek(2) and unlimited truncate(2)
operations. Reading from a string node will have an additional line
feed character (\n) appended to the end automatically; similarly, writing to a
string node will have the ending line feed character stripped if exist.
list and compound nodes can contain other nodes,
accessing them according to above rules.
int32array and int64array nodes are represented as
directories, the array elements are accessed using an index number starting
with 0, as regular files under the directory. Creating a new regular file
with appreciate index number under the directory extends the array, and any
element between the old tail index and new index will appear automatically
as well; newly added elements will initialized to 0. An array can also be
shrunk by removing (unlink(2)) the tail element, one element at a
time; as a design limitation, only the tail element can be removed. On
supported platforms, the array nodes may also be read directly (using
read(2)); in this case seeking is supported only when aligned to
element size, which is 4 or 8 for int32array or int64array
respectively. The data stream read directly from an array will be the binary
representation of the array elements in host byte order.
Nodes under a compound can be removed by using unlink(2) or
rmdir(2), according to their represented file type; usual file system
restrictions on directory apply, meaning they can not be removed unless empty.
Unlike referencing an existing node, creating a new node under a
compound must use a type prefixed name.
Like compound, nodes under a list may be removed by using either
unlink(2) or rmdir(2); if a non-tail node was removed, the index
number of later nodes will be shifted backward by 1, which could be surprising
when trying to remove multiple nodes.
New node may be added only to the tail of a list, there is
currently not possible to insert a node in middle of a list. Newly created
node will have the type specified by the list type, indicated by the
.type pseude file.
The list type may also be changed by writing a type prefix
name into .type, but only when the list is empty.
A list node may be created under either compound or list
using mkdir(2) according to rules above, but please note newly created
list will have an invalid list type; no node can be created under such list,
and if a file system is unmounted with it, writing NBT data will fail, causing
all modifications to be lost! Any newly created list must be initiailized with
a supported list type, by writing the type prefix name to its .type
pseude file.
Data is commited to underlying <nbt-file> only upon unmounting; if
anything went wrong during this process, the error message will be sent to
syslog(3), and the file system will be unmounted without saving some or
all data.
When modifying a Minecraft Region file, it is currently not
possible to extend a modified chunk beyond the space available for the chunk
in that Region file; although this rarely happen unless a considerable
amount of additional data was copied into a chunk. If this happens, such
chunk will not be saved.
The following examples took place in an Unix shell (sh(1)).
Mount a standalone NBT file /tmp/level.dat at
/mnt/nbt, prepare to write a new NBT file at
/tmp/new-level.dat:
mount -o writefile=/tmp/new-level.dat /tmp/level.dat /mnt/nbt
Mount a Minecraft Region file /tmp/r.0.-1.mcr at
/mnt/region, with type prefix turned on for node name
listing:
mount -o region,typeprefix /tmp/r.0.-1.mcr /mnt/region
Working in a compound, create and write a new string
node named id:
echo Villager > string:id
Working in a compound, create a new list node
Pos with list type set to float64, then create and write first
node in the list:
mkdir list:Pos
echo float64 > Pos/.type
echo 31.5 > Pos/0
fuse(8), fusermount(8), mount(8)
Named Binary Tag specification by Mojang