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+btrfs-mount - mount options and supported file attributes for the btrfs filesystem
+This document describes mount options specific to the btrfs filesystem.
+Other generic mount options are available,and are described in the
+`mount`(8) manpage.
+ Debugging option to force all block allocations above a certain
+ byte threshold on each block device. The value is specified in
+ bytes, optionally with a K, M, or G suffix, case insensitive.
+ Default is 1MB.
+ Disable/enable auto defragmentation.
+ Auto defragmentation detects small random writes into files and queue
+ them up for the defrag process. Works best for small files;
+ Not well suited for large database workloads.
+ These debugging options control the behavior of the integrity checking
+ module (the BTRFS_FS_CHECK_INTEGRITY config option required). +
+ +
+ `check_int` enables the integrity checker module, which examines all
+ block write requests to ensure on-disk consistency, at a large
+ memory and CPU cost. +
+ +
+ `check_int_data` includes extent data in the integrity checks, and
+ implies the check_int option. +
+ +
+ `check_int_print_mask` takes a bitmask of BTRFSIC_PRINT_MASK_* values
+ as defined in 'fs/btrfs/check-integrity.c', to control the integrity
+ checker module behavior. +
+ +
+ See comments at the top of 'fs/btrfs/check-integrity.c'
+ for more info.
+ Set the interval of periodic commit, 30 seconds by default. Higher
+ values defer data being synced to permanent storage with obvious
+ consequences when the system crashes. The upper bound is not forced,
+ but a warning is printed if it's more than 300 seconds (5 minutes).
+ Control BTRFS file data compression. Type may be specified as "zlib"
+ "lzo" or "no" (for no compression, used for remounting). If no type
+ is specified, zlib is used. If compress-force is specified,
+ all files will be compressed, whether or not they compress well.
+ If compression is enabled, nodatacow and nodatasum are disabled.
+ Allow mounts to continue with missing devices. A read-write mount may
+ fail with too many devices missing, for example if a stripe member
+ is completely missing.
+ Specify a device during mount so that ioctls on the control device
+ can be avoided. Especially useful when trying to mount a multi-device
+ setup as root. May be specified multiple times for multiple devices.
+ Disable/enable discard mount option.
+ Discard issues frequent commands to let the block device reclaim space
+ freed by the filesystem.
+ This is useful for SSD devices, thinly provisioned
+ LUNs and virtual machine images, but may have a significant
+ performance impact. (The fstrim command is also available to
+ initiate batch trims from userspace).
+ Disable/enable debugging option to be more verbose in some ENOSPC conditions.
+ Action to take when encountering a fatal error. +
+ "bug" - BUG() on a fatal error. This is the default. +
+ "panic" - panic() on a fatal error.
+ The `flushoncommit` mount option forces any data dirtied by a write in a
+ prior transaction to commit as part of the current commit. This makes
+ the committed state a fully consistent view of the file system from the
+ application's perspective (i.e., it includes all completed file system
+ operations). This was previously the behavior only when a snapshot is
+ created.
+ Enable free inode number caching. Defaults to off due to an overflow
+ problem when the free space crcs don't fit inside a single page.
+ Specify the maximum amount of space, in bytes, that can be inlined in
+ a metadata B-tree leaf. The value is specified in bytes, optionally
+ with a K, M, or G suffix, case insensitive. In practice, this value
+ is limited by the root sector size, with some space unavailable due
+ to leaf headers. For a 4k sectorsize, max inline data is ~3900 bytes.
+ Specify that 1 metadata chunk should be allocated after every
+ 'value' data chunks. Off by default.
+ Enable/disable support for Posix Access Control Lists (ACLs). See the
+ `acl`(5) manual page for more information about ACLs.
+ ensure that certain IOs make it through the device cache and are on
+ persistent storage. If disabled on a device with a volatile
+ (non-battery-backed) write-back cache, nobarrier option will lead to
+ filesystem corruption on a system crash or power loss.
+ Enable/disable data copy-on-write for newly created files.
+ Nodatacow implies nodatasum, and disables all compression.
+ Enable/disable data checksumming for newly created files.
+ Datasum implies datacow.
+ Enable/disable the tree logging used for fsync and O_SYNC writes.
+ Enable autorecovery attempts if a bad tree root is found at mount time.
+ Currently this scans a list of several previous tree roots and tries to
+ use the first readable.
+ Force check and rebuild procedure of the UUID tree. This should not
+ normally be needed.
+ Skip automatic resume of interrupted balance operation after mount.
+ May be resumed with "btrfs balance resume."
+ Disable freespace cache loading without clearing the cache.
+ Force clearing and rebuilding of the disk space cache if something
+ has gone wrong.
+ Options to control ssd allocation schemes. By default, BTRFS will
+ enable or disable ssd allocation heuristics depending on whether a
+ rotational or nonrotational disk is in use. The ssd and nossd options
+ can override this autodetection. +
+ The ssd_spread mount option attempts to allocate into big chunks
+ of unused space, and may perform better on low-end ssds. ssd_spread
+ implies ssd, enabling all other ssd heuristics as well.
+ Mount subvolume at 'path' rather than the root subvolume. The
+ 'path' is relative to the top level subvolume.
+ Mount subvolume specified by an ID number rather than the root subvolume.
+ This allows mounting of subvolumes which are not in the root of the mounted
+ filesystem.
+ You can use "btrfs subvolume list" to see subvolume ID numbers.
+*subvolrootid='objectid' (deprecated)*::
+ Mount subvolume specified by 'objectid' rather than the root subvolume.
+ This allows mounting of subvolumes which are not in the root of the mounted
+ filesystem.
+ You can use "btrfs subvolume show" to see the object ID for a subvolume.
+ The number of worker threads to allocate. The default number is equal
+ to the number of CPUs + 2, or 8, whichever is smaller.
+ Allow subvolumes to be deleted by a non-root user. Use with caution.
+The btrfs filesystem supports setting the following file
+attributes the `chattr`(1) utility
+*a* -- append only
+*A* -- no atime updates
+*c* -- compressed
+*C* -- no copy on write
+*d* -- no dump
+*D* -- synchronous directory updates
+*i* -- immutable
+*S* -- synchronous updates
+*X* -- no compression
+For descriptions of these attribute flags, please refer to the
+`chattr`(1) man page.