path: root/Documentation
diff options
authorDavid Sterba <>2015-09-15 00:40:00 +0200
committerDavid Sterba <>2015-09-15 00:40:00 +0200
commit1e6f19407593828baf61dc13e12ca589caa8ad95 (patch)
tree722499f5d2495b860544a48f9e9ac9ad164f81a7 /Documentation
parentc985a2b104604cede8244cd3af6e50628435dae0 (diff)
btrfs-progs: docs: add option variants, defaults and versions to mount options
Signed-off-by: David Sterba <>
Diffstat (limited to 'Documentation')
1 files changed, 48 insertions, 10 deletions
diff --git a/Documentation/btrfs-mount.asciidoc b/Documentation/btrfs-mount.asciidoc
index 8cf7a0bc..39215a8e 100644
--- a/Documentation/btrfs-mount.asciidoc
+++ b/Documentation/btrfs-mount.asciidoc
@@ -20,12 +20,17 @@ MOUNT OPTIONS
Default is 1MB.
+ (since: 3.0, default: off) +
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.
+ (since: 3.0, default: off) +
These debugging options control the behavior of the integrity checking
module (the BTRFS_FS_CHECK_INTEGRITY config option required). +
@@ -44,19 +49,25 @@ MOUNT OPTIONS
for more info.
- Set the interval of periodic commit, 30 seconds by default. Higher
+ (since: 3.12, default: 30) +
+ Set the interval of periodic commit. 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,
+ (default: off) +
+ 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.
+ NOTE: If compression is enabled, 'nodatacow' and 'nodatasum' are disabled.
+ (default: off) +
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.
@@ -67,6 +78,8 @@ MOUNT OPTIONS
setup as root. May be specified multiple times for multiple devices.
+ (default: off) +
Disable/enable discard mount option.
Discard issues frequent commands to let the block device reclaim space
freed by the filesystem.
@@ -76,14 +89,18 @@ MOUNT OPTIONS
initiate batch trims from userspace).
+ (default: off) +
Disable/enable debugging option to be more verbose in some ENOSPC conditions.
+ (since: 3.4, default: bug) +
Action to take when encountering a fatal error. +
- "bug" - BUG() on a fatal error. This is the default. +
+ "bug" - BUG() on a fatal error. +
"panic" - panic() on a fatal error.
+ (default: on) +
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
@@ -92,10 +109,13 @@ MOUNT OPTIONS
+ (since: 3.0, default: off) +
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.
+ (default: min(8192, page size) )
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
@@ -106,48 +126,64 @@ MOUNT OPTIONS
Specify that 1 metadata chunk should be allocated after every
'value' data chunks. Off by default.
+ (default: on) +
Enable/disable support for Posix Access Control Lists (ACLs). See the
`acl`(5) manual page for more information about ACLs.
+ (default: on) +
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.
+ (default: on) +
Enable/disable data copy-on-write for newly created files.
Nodatacow implies nodatasum, and disables all compression.
+ (default: on) +
Enable/disable data checksumming for newly created files.
Datasum implies datacow.
+ (default: on) +
Enable/disable the tree logging used for fsync and O_SYNC writes.
+ (since: 3.2, default: off) +
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.
+ (since: 3.12, default: off) +
Force check and rebuild procedure of the UUID tree. This should not
normally be needed.
+ (since: 3.3, default: off) +
Skip automatic resume of interrupted balance operation after mount.
May be resumed with "btrfs balance resume."
+ (since: 3.2) +
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
@@ -166,7 +202,8 @@ MOUNT OPTIONS
You can use "btrfs subvolume list" to see subvolume ID numbers.
-*subvolrootid='objectid' (deprecated)*::
+ (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
@@ -177,6 +214,7 @@ MOUNT OPTIONS
to the number of CPUs + 2, or 8, whichever is smaller.
+ (default: off) +
Allow subvolumes to be deleted by a non-root user. Use with caution.