btrfs-send - generate a stream of changes between two subvolume snapshots
btrfs send [-ve] [-p <parent>] [-c <clone-src>] [-f <outfile>] <subvol> [<subvol>...]
This command will generate a stream of instructions that describe changes between two subvolume snapshots. The stream can be consumed by the btrfs receive command to replicate the sent snapshot on a different filesystem. The command operates in two modes: full and incremental.
All snapshots involved in one send command must be read-only, and this status cannot be changed as long as there's a running send operation that uses the snapshot. Read-only mount of the subvolume is not sufficient, there's no way to guarantee that there won't be any other writable mount of the same subvolume that would potentially write while send would be running.
In the full mode, the entire snapshot data and metadata will end up in the stream.
In the incremental mode (options -p and -c), previously sent snapshots that are available on both the sending and receiving side can be used to reduce the amount of information that has to be sent to reconstruct the sent snapshot on a different filesystem.
The -p <parent> option can be omitted when -c <clone-src> options are given, in which case btrfs send will determine a suitable parent from among the clone sources.
You must not specify clone sources unless you guarantee that these snapshots are exactly in the same state on both sides--both for the sender and the receiver. For implications of changed read-write status of a received snapshot please see section SUBVOLUME FLAGS in btrfs-subvolume(8).
- if sending multiple subvolumes at once, use the new format and omit the 'end cmd' marker in the stream separating the subvolumes
- -p <parent>
- send an incremental stream from parent to subvol
- -c <clone-src>
- use this snapshot as a clone source for an incremental send (multiple allowed)
- -f <outfile>
- output is normally written to standard output so it can be, for example, piped to btrfs receive. Use this option to write it to a file instead.
- send in NO_FILE_DATA mode
The output stream does not contain any file data and thus cannot be used to transfer changes. This mode is faster and is useful to show the differences in metadata.
- --proto <N>
- use send protocol version N
The default is 1, which was the original protocol version. Version 2 encodes file data slightly more efficiently; it is also required for sending compressed data directly (see --compressed-data). Version 2 requires at least btrfs-progs 6.0 on both the sender and receiver and at least Linux 6.0 on the sender. Passing 0 means to use the highest version supported by the running kernel.
- send data that is compressed on the filesystem directly without
If the receiver supports the BTRFS_IOC_ENCODED_WRITE ioctl (added in Linux 6.0), it can also write it directly without decompressing it. Otherwise, the receiver will fall back to decompressing it and writing it normally.
This requires protocol version 2 or higher. If --proto was not used, then --compressed-data implies --proto 2.
btrfs send returns a zero exit status if it succeeds. Non zero is returned in case of failure.
|February 28, 2023