1 .. SPDX-License-Identifier: GPL-2.0
7 XFS is a high performance journaling filesystem which originated
8 on the SGI IRIX platform. It is completely multi-threaded, can
9 support large files and large filesystems, extended attributes,
10 variable block sizes, is extent based, and makes extensive use of
11 Btrees (directories, extents, free space) to aid both performance
14 Refer to the documentation at https://xfs.wiki.kernel.org/
15 for further details. This implementation is on-disk compatible
16 with the IRIX version of XFS.
22 When mounting an XFS filesystem, the following options are accepted.
25 Sets the buffered I/O end-of-file preallocation size when
26 doing delayed allocation writeout (default size is 64KiB).
27 Valid values for this option are page size (typically 4KiB)
28 through to 1GiB, inclusive, in power-of-2 increments.
30 The default behaviour is for dynamic end-of-file
31 preallocation size, which uses a set of heuristics to
32 optimise the preallocation size based on the current
33 allocation patterns within the file and the access patterns
34 to the file. Specifying a fixed ``allocsize`` value turns off
35 the dynamic behaviour.
38 The options enable/disable an "opportunistic" improvement to
39 be made in the way inline extended attributes are stored
40 on-disk. When the new form is used for the first time when
41 ``attr2`` is selected (either when setting or removing extended
42 attributes) the on-disk superblock feature bit field will be
43 updated to reflect this format being in use.
45 The default behaviour is determined by the on-disk feature
46 bit indicating that ``attr2`` behaviour is active. If either
47 mount option is set, then that becomes the new default used
50 CRC enabled filesystems always use the ``attr2`` format, and so
51 will reject the ``noattr2`` mount option if it is set.
53 discard or nodiscard (default)
54 Enable/disable the issuing of commands to let the block
55 device reclaim space freed by the filesystem. This is
56 useful for SSD devices, thinly provisioned LUNs and virtual
57 machine images, but may have a performance impact.
59 Note: It is currently recommended that you use the ``fstrim``
60 application to ``discard`` unused blocks rather than the ``discard``
61 mount option because the performance impact of this option
64 grpid/bsdgroups or nogrpid/sysvgroups (default)
65 These options define what group ID a newly created file
66 gets. When ``grpid`` is set, it takes the group ID of the
67 directory in which it is created; otherwise it takes the
68 ``fsgid`` of the current process, unless the directory has the
69 ``setgid`` bit set, in which case it takes the ``gid`` from the
70 parent directory, and also gets the ``setgid`` bit set if it is
74 Make the data allocator use the filestreams allocation mode
75 across the entire filesystem rather than just on directories
78 ikeep or noikeep (default)
79 When ``ikeep`` is specified, XFS does not delete empty inode
80 clusters and keeps them around on disk. When ``noikeep`` is
81 specified, empty inode clusters are returned to the free
84 inode32 or inode64 (default)
85 When ``inode32`` is specified, it indicates that XFS limits
86 inode creation to locations which will not result in inode
87 numbers with more than 32 bits of significance.
89 When ``inode64`` is specified, it indicates that XFS is allowed
90 to create inodes at any location in the filesystem,
91 including those which will result in inode numbers occupying
92 more than 32 bits of significance.
94 ``inode32`` is provided for backwards compatibility with older
95 systems and applications, since 64 bits inode numbers might
96 cause problems for some applications that cannot handle
97 large inode numbers. If applications are in use which do
98 not handle inode numbers bigger than 32 bits, the ``inode32``
99 option should be specified.
101 largeio or nolargeio (default)
102 If ``nolargeio`` is specified, the optimal I/O reported in
103 ``st_blksize`` by **stat(2)** will be as small as possible to allow
104 user applications to avoid inefficient read/modify/write
105 I/O. This is typically the page size of the machine, as
106 this is the granularity of the page cache.
108 If ``largeio`` is specified, a filesystem that was created with a
109 ``swidth`` specified will return the ``swidth`` value (in bytes)
110 in ``st_blksize``. If the filesystem does not have a ``swidth``
111 specified but does specify an ``allocsize`` then ``allocsize``
112 (in bytes) will be returned instead. Otherwise the behaviour
113 is the same as if ``nolargeio`` was specified.
116 Set the number of in-memory log buffers. Valid numbers
117 range from 2-8 inclusive.
119 The default value is 8 buffers.
121 If the memory cost of 8 log buffers is too high on small
122 systems, then it may be reduced at some cost to performance
123 on metadata intensive workloads. The ``logbsize`` option below
124 controls the size of each buffer and so is also relevant to
128 Set the size of each in-memory log buffer. The size may be
129 specified in bytes, or in kilobytes with a "k" suffix.
130 Valid sizes for version 1 and version 2 logs are 16384 (16k)
131 and 32768 (32k). Valid sizes for version 2 logs also
132 include 65536 (64k), 131072 (128k) and 262144 (256k). The
133 logbsize must be an integer multiple of the log
134 stripe unit configured at **mkfs(8)** time.
136 The default value for version 1 logs is 32768, while the
137 default value for version 2 logs is MAX(32768, log_sunit).
139 logdev=device and rtdev=device
140 Use an external log (metadata journal) and/or real-time device.
141 An XFS filesystem has up to three parts: a data section, a log
142 section, and a real-time section. The real-time section is
143 optional, and the log section can be separate from the data
144 section or contained within it.
147 Data allocations will not be aligned at stripe unit
148 boundaries. This is only relevant to filesystems created
149 with non-zero data alignment parameters (``sunit``, ``swidth``) by
153 The filesystem will be mounted without running log recovery.
154 If the filesystem was not cleanly unmounted, it is likely to
155 be inconsistent when mounted in ``norecovery`` mode.
156 Some files or directories may not be accessible because of this.
157 Filesystems mounted ``norecovery`` must be mounted read-only or
161 Don't check for double mounted file systems using the file
162 system ``uuid``. This is useful to mount LVM snapshot volumes,
163 and often used in combination with ``norecovery`` for mounting
167 Forcibly turns off all quota accounting and enforcement
168 within the filesystem.
170 uquota/usrquota/uqnoenforce/quota
171 User disk quota accounting enabled, and limits (optionally)
172 enforced. Refer to **xfs_quota(8)** for further details.
174 gquota/grpquota/gqnoenforce
175 Group disk quota accounting enabled and limits (optionally)
176 enforced. Refer to **xfs_quota(8)** for further details.
178 pquota/prjquota/pqnoenforce
179 Project disk quota accounting enabled and limits (optionally)
180 enforced. Refer to **xfs_quota(8)** for further details.
182 sunit=value and swidth=value
183 Used to specify the stripe unit and width for a RAID device
184 or a stripe volume. "value" must be specified in 512-byte
185 block units. These options are only relevant to filesystems
186 that were created with non-zero data alignment parameters.
188 The ``sunit`` and ``swidth`` parameters specified must be compatible
189 with the existing filesystem alignment characteristics. In
190 general, that means the only valid changes to ``sunit`` are
191 increasing it by a power-of-2 multiple. Valid ``swidth`` values
192 are any integer multiple of a valid ``sunit`` value.
194 Typically the only time these mount options are necessary if
195 after an underlying RAID device has had its geometry
196 modified, such as adding a new disk to a RAID5 lun and
200 Data allocations will be rounded up to stripe width boundaries
201 when the current end of file is being extended and the file
202 size is larger than the stripe width size.
205 When specified, all filesystem namespace operations are
206 executed synchronously. This ensures that when the namespace
207 operation (create, unlink, etc) completes, the change to the
208 namespace is on stable storage. This is useful in HA setups
209 where failover must not result in clients seeing
210 inconsistent namespace presentation during or after a
213 Deprecation of V4 Format
214 ========================
216 The V4 filesystem format lacks certain features that are supported by
217 the V5 format, such as metadata checksumming, strengthened metadata
218 verification, and the ability to store timestamps past the year 2038.
219 Because of this, the V4 format is deprecated. All users should upgrade
220 by backing up their files, reformatting, and restoring from the backup.
222 Administrators and users can detect a V4 filesystem by running xfs_info
223 against a filesystem mountpoint and checking for a string containing
224 "crc=". If no such string is found, please upgrade xfsprogs to the
225 latest version and try again.
227 The deprecation will take place in two parts. Support for mounting V4
228 filesystems can now be disabled at kernel build time via Kconfig option.
229 The option will default to yes until September 2025, at which time it
230 will be changed to default to no. In September 2030, support will be
231 removed from the codebase entirely.
233 Note: Distributors may choose to withdraw V4 format support earlier than
234 the dates listed above.
236 Deprecated Mount Options
237 ========================
239 ============================ ================
240 Name Removal Schedule
241 ============================ ================
242 Mounting with V4 filesystem September 2030
243 Mounting ascii-ci filesystem September 2030
244 ikeep/noikeep September 2025
245 attr2/noattr2 September 2025
246 ============================ ================
249 Removed Mount Options
250 =====================
252 =========================== =======
254 =========================== =======
255 delaylog/nodelaylog v4.0
258 osyncisdsync/osyncisosync v4.0
261 =========================== =======
266 The following sysctls are available for the XFS filesystem:
268 fs.xfs.stats_clear (Min: 0 Default: 0 Max: 1)
269 Setting this to "1" clears accumulated XFS statistics
270 in /proc/fs/xfs/stat. It then immediately resets to "0".
272 fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000)
273 The interval at which the filesystem flushes metadata
274 out to disk and runs internal cache cleanup routines.
276 fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000)
277 The interval at which the filesystem ages filestreams cache
278 references and returns timed-out AGs back to the free stream
281 fs.xfs.speculative_prealloc_lifetime
282 (Units: seconds Min: 1 Default: 300 Max: 86400)
283 The interval at which the background scanning for inodes
284 with unused speculative preallocation runs. The scan
285 removes unused preallocation from clean inodes and releases
286 the unused space back to the free pool.
288 fs.xfs.speculative_cow_prealloc_lifetime
289 This is an alias for speculative_prealloc_lifetime.
291 fs.xfs.error_level (Min: 0 Default: 3 Max: 11)
292 A volume knob for error reporting when internal errors occur.
293 This will generate detailed messages & backtraces for filesystem
294 shutdowns, for example. Current threshold values are:
300 fs.xfs.panic_mask (Min: 0 Default: 0 Max: 511)
301 Causes certain error conditions to call BUG(). Value is a bitmask;
302 OR together the tags which represent errors which should cause panics:
305 XFS_PTAG_IFLUSH 0x00000001
306 XFS_PTAG_LOGRES 0x00000002
307 XFS_PTAG_AILDELETE 0x00000004
308 XFS_PTAG_ERROR_REPORT 0x00000008
309 XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010
310 XFS_PTAG_SHUTDOWN_IOERROR 0x00000020
311 XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040
312 XFS_PTAG_FSBLOCK_ZERO 0x00000080
313 XFS_PTAG_VERIFIER_ERROR 0x00000100
315 This option is intended for debugging only.
317 fs.xfs.irix_symlink_mode (Min: 0 Default: 0 Max: 1)
318 Controls whether symlinks are created with mode 0777 (default)
319 or whether their mode is affected by the umask (irix mode).
321 fs.xfs.irix_sgid_inherit (Min: 0 Default: 0 Max: 1)
322 Controls files created in SGID directories.
323 If the group ID of the new file does not match the effective group
324 ID or one of the supplementary group IDs of the parent dir, the
325 ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl
328 fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1)
329 Setting this to "1" will cause the "sync" flag set
330 by the **xfs_io(8)** chattr command on a directory to be
331 inherited by files in that directory.
333 fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1)
334 Setting this to "1" will cause the "nodump" flag set
335 by the **xfs_io(8)** chattr command on a directory to be
336 inherited by files in that directory.
338 fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1)
339 Setting this to "1" will cause the "noatime" flag set
340 by the **xfs_io(8)** chattr command on a directory to be
341 inherited by files in that directory.
343 fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1)
344 Setting this to "1" will cause the "nosymlinks" flag set
345 by the **xfs_io(8)** chattr command on a directory to be
346 inherited by files in that directory.
348 fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1)
349 Setting this to "1" will cause the "nodefrag" flag set
350 by the **xfs_io(8)** chattr command on a directory to be
351 inherited by files in that directory.
353 fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256)
354 In "inode32" allocation mode, this option determines how many
355 files the allocator attempts to allocate in the same allocation
356 group before moving to the next allocation group. The intent
357 is to control the rate at which the allocator moves between
358 allocation groups when allocating extents for new files.
363 =========================================== ================
364 Name Removal Schedule
365 =========================================== ================
366 fs.xfs.irix_sgid_inherit September 2025
367 fs.xfs.irix_symlink_mode September 2025
368 fs.xfs.speculative_cow_prealloc_lifetime September 2025
369 =========================================== ================
375 ============================= =======
377 ============================= =======
378 fs.xfs.xfsbufd_centisec v4.0
379 fs.xfs.age_buffer_centisecs v4.0
380 ============================= =======
385 XFS can act differently according to the type of error found during its
386 operation. The implementation introduces the following concepts to the error
390 Defines how fast XFS should propagate an error upwards when a specific
391 error is found during the filesystem operation. It can propagate
392 immediately, after a defined number of retries, after a set time period,
393 or simply retry forever.
396 Specifies the subsystem the error configuration will apply to, such as
397 metadata IO or memory allocation. Different subsystems will have
398 different error handlers for which behaviour can be configured.
401 Defines the behavior for a specific error.
403 The filesystem behavior during an error can be set via ``sysfs`` files. Each
404 error handler works independently - the first condition met by an error handler
405 for a specific class will cause the error to be propagated rather than reset and
408 The action taken by the filesystem when the error is propagated is context
409 dependent - it may cause a shut down in the case of an unrecoverable error,
410 it may be reported back to userspace, or it may even be ignored because
411 there's nothing useful we can with the error or anyone we can report it to (e.g.
414 The configuration files are organized into the following hierarchy for each
417 /sys/fs/xfs/<dev>/error/<class>/<error>/
421 The short device name of the mounted filesystem. This is the same device
422 name that shows up in XFS kernel error messages as "XFS(<dev>): ..."
425 The subsystem the error configuration belongs to. As of 4.9, the defined
428 - "metadata": applies metadata buffer write IO
431 The individual error handler configurations.
434 Each filesystem has "global" error configuration options defined in their top
437 /sys/fs/xfs/<dev>/error/
439 fail_at_unmount (Min: 0 Default: 1 Max: 1)
440 Defines the filesystem error behavior at unmount time.
442 If set to a value of 1, XFS will override all other error configurations
443 during unmount and replace them with "immediate fail" characteristics.
444 i.e. no retries, no retry timeout. This will always allow unmount to
445 succeed when there are persistent errors present.
447 If set to 0, the configured retry behaviour will continue until all
448 retries and/or timeouts have been exhausted. This will delay unmount
449 completion when there are persistent errors, and it may prevent the
450 filesystem from ever unmounting fully in the case of "retry forever"
451 handler configurations.
453 Note: there is no guarantee that fail_at_unmount can be set while an
454 unmount is in progress. It is possible that the ``sysfs`` entries are
455 removed by the unmounting filesystem before a "retry forever" error
456 handler configuration causes unmount to hang, and hence the filesystem
457 must be configured appropriately before unmount begins to prevent
460 Each filesystem has specific error class handlers that define the error
461 propagation behaviour for specific errors. There is also a "default" error
462 handler defined, which defines the behaviour for all errors that don't have
463 specific handlers defined. Where multiple retry constraints are configured for
464 a single error, the first retry configuration that expires will cause the error
465 to be propagated. The handler configurations are found in the directory:
467 /sys/fs/xfs/<dev>/error/<class>/<error>/
469 max_retries (Min: -1 Default: Varies Max: INTMAX)
470 Defines the allowed number of retries of a specific error before
471 the filesystem will propagate the error. The retry count for a given
472 error context (e.g. a specific metadata buffer) is reset every time
473 there is a successful completion of the operation.
475 Setting the value to "-1" will cause XFS to retry forever for this
478 Setting the value to "0" will cause XFS to fail immediately when the
479 specific error is reported.
481 Setting the value to "N" (where 0 < N < Max) will make XFS retry the
482 operation "N" times before propagating the error.
484 retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day)
485 Define the amount of time (in seconds) that the filesystem is
486 allowed to retry its operations when the specific error is
489 Setting the value to "-1" will allow XFS to retry forever for this
492 Setting the value to "0" will cause XFS to fail immediately when the
493 specific error is reported.
495 Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the
496 operation for up to "N" seconds before propagating the error.
498 **Note:** The default behaviour for a specific error handler is dependent on both
499 the class and error context. For example, the default values for
500 "metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults
501 to "fail immediately" behaviour. This is done because ENODEV is a fatal,
502 unrecoverable error no matter how many times the metadata IO is retried.
504 Workqueue Concurrency
505 =====================
507 XFS uses kernel workqueues to parallelize metadata update processes. This
508 enables it to take advantage of storage hardware that can service many IO
509 operations simultaneously. This interface exposes internal implementation
510 details of XFS, and as such is explicitly not part of any userspace API/ABI
511 guarantee the kernel may give userspace. These are undocumented features of
512 the generic workqueue implementation XFS uses for concurrency, and they are
513 provided here purely for diagnostic and tuning purposes and may change at any
516 The control knobs for a filesystem's workqueues are organized by task at hand
517 and the short name of the data device. They all can be found in:
519 /sys/bus/workqueue/devices/${task}!${device}
521 ================ ===========
523 ================ ===========
524 xfs_iwalk-$pid Inode scans of the entire filesystem. Currently limited to
525 mount time quotacheck.
526 xfs-gc Background garbage collection of disk space that have been
527 speculatively allocated beyond EOF or for staging copy on
529 ================ ===========
531 For example, the knobs for the quotacheck workqueue for /dev/nvme0n1 would be
532 found in /sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/.
534 The interesting knobs for XFS workqueues are as follows:
536 ============ ===========
538 ============ ===========
539 max_active Maximum number of background threads that can be started to
541 cpumask CPUs upon which the threads are allowed to run.
542 nice Relative priority of scheduling the threads. These are the
543 same nice levels that can be applied to userspace processes.
544 ============ ===========
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