Use the cp command with the --reflink option to create lightweight copies of a file within the same subvolume of a Btrfs file system. The copy-on-write mechanism saves disk space and enables copy operations to be almost instantaneous. The Btrfs file system creates a new inode that shares the same disk blocks as the existing file, rather than creating a complete copy of the file's data or creating a link that points to the file's inode. The resulting file appears to be a copy of the original file, but the original data blocks are not duplicated. If you subsequently write to one of the files, the Btrfs file system makes copies of the blocks before they are written to, preserving the other file's content.

For example, you would create a snapshot named bar of a file named foo as follows:

cp -reflink foo bar