Enable seeding on a given device. Value 1 will enable seeding, 0 will disable it.

A seeding filesystem is forced to be mounted read-only. A new device can be added to the filesystem and will capture all writes keeping the seeding device intact.

(since kernel: 3.7)

Enable extended inode refs (hardlink limit per file in a directory is 65536), enabled by mkfs feature extref. -x:: (since kernel: 3.10)

Enable skinny metadata extent refs (more efficient representation of extents), enabled by mkfs feature skinny-metadata.

All newly created extents will use the new representation. To completely switch the entire filesystem, run a full balance of the metadata. Please refer to btrfs-balance(8). -n:: (since kernel: 3.14)

Enable no-holes feature (more efficient representation of file holes), enabled by mkfs feature no-holes. -f:: Allow dangerous changes, e.g. clear the seeding flag or change fsid. Make sure that you are aware of the dangers. -u:: Change fsid to a randomly generated UUID or continue previous fsid change operation in case it was interrupted. -U <UUID>:: Change fsid to UUID.

The UUID should be a 36 bytes string in printf(3) format "%08x-%04x-%04x-%04x-%012x". If there is a previous unfinished fsid change, it will continue only if the UUID matches the unfinished one or if you use the option -u.

Warning

Cancelling or interrupting a UUID change operation will make the filesystem temporarily unmountable. To fix it, rerun btrfstune -u to restore the UUID and let it complete.

Warning

Clearing the seeding flag on a device may be dangerous. If a previously-seeding device is changed, all filesystems that used that device will become unmountable. Setting the seeding flag back will not fix that. A valid usecase is seeding device as a base image. Clear the seeding flag, update the filesystem and make it seeding again, provided that it’s OK to throw away all filesystems built on top of the previous base.