| btrfstune(8) |
| ============ |
| |
| NAME |
| ---- |
| btrfstune - tune various filesystem parameters |
| |
| SYNOPSIS |
| -------- |
| *btrfstune* [options] <dev> [<dev>...] |
| |
| DESCRIPTION |
| ----------- |
| *btrfstune* can be used to enable, disable or set various filesystem |
| parameters. The filesystem must be unmounted. |
| |
| The common usecase is to enable features that were not enabled at mkfs time. |
| Please make sure that you have kernel support for the features. You can find a |
| complete list of features and kernel version of their introduction at |
| https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature . |
| |
| OPTIONS |
| ------- |
| -S <0|1>:: |
| 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. |
| -r:: |
| Enable extended inode refs (hardlink limit per file in a directory is 65536), |
| enabled by mkfs feature 'extref'. Since kernel 3.7. |
| -x:: |
| Enable skinny metadata extent refs (more efficient representation of extents), |
| enabled by mkfs feature 'skinny-metadata'. Since kernel 3.10. |
| -n:: |
| Enable no-holes feature (more efficient representation of file holes), enabled |
| by mkfs feature 'no-holes'. Since kernel 3.14. |
| -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. |
| |
| EXIT STATUS |
| ----------- |
| *btrfstune* returns 0 if no error happened, 1 otherwise. |
| |
| COMPATIBILITY NOTE |
| ------------------ |
| This tool exists for historical reasons but is still in use today. The |
| functionality is about to be merged to the main tool someday and *btrfstune* |
| will become deprecated and removed afterwards. |
| |
| SEE ALSO |
| -------- |
| `mkfs.btrfs`(8) |