xfs_db(8) - man - phpMan

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xfs_db(8) System Manager's Manual xfs_db(8)

NAME
xfs_db - debug an XFS filesystem

SYNOPSIS
xfs_db [ -c cmd ] ... [ -i|r|x|F ] [ -f ] [ -l logdev ] [ -p progname ] device
xfs_db -V

DESCRIPTION
xfs_db is used to examine an XFS filesystem. Under rare circumstances it can also be used to
modify an XFS filesystem, but that task is normally left to xfs_repair(8) or to scripts such
as xfs_admin(8) that run xfs_db.

OPTIONS
-c cmd xfs_db commands may be run interactively (the default) or as arguments on the command
line. Multiple -c arguments may be given. The commands are run in the sequence given,
then the program exits.

-f Specifies that the filesystem image to be processed is stored in a regular file at de‐
vice (see the mkfs.xfs(8) -d file option). This might happen if an image copy of a
filesystem has been made into an ordinary file with xfs_copy(8).

-F Specifies that we want to continue even if the superblock magic is not correct. For
use in xfs_metadump.

-i Allows execution on a mounted filesystem, provided it is mounted read-only. Useful
for shell scripts which must only operate on filesystems in a guaranteed consistent
state (either unmounted or mounted read-only). These semantics are slightly different
to that of the -r option.

-l logdev
Specifies the device where the filesystems external log resides. Only for those
filesystems which use an external log. See the mkfs.xfs(8) -l option, and refer to
xfs(5) for a detailed description of the XFS log.

-p progname
Set the program name to progname for prompts and some error messages, the default
value is xfs_db.

-r Open device or filename read-only. This option is required if the filesystem is
mounted. It is only necessary to omit this flag if a command that changes data
(write, blocktrash, crc) is to be used.

-x Specifies expert mode. This enables the (write, blocktrash, crc invalidate/revali‐
date) commands.

-V Prints the version number and exits.

CONCEPTS
xfs_db commands can be broken up into two classes. Most commands are for the navigation and
display of data structures in the filesystem. Other commands are for scanning the filesystem
in some way.

Commands which are used to navigate the filesystem structure take arguments which reflect the
names of filesystem structure fields. There can be multiple field names separated by dots
when the underlying structures are nested, as in C. The field names can be indexed (as an
array index) if the underlying field is an array. The array indices can be specified as a
range, two numbers separated by a dash.

xfs_db maintains a current address in the filesystem. The granularity of the address is a
filesystem structure. This can be a filesystem block, an inode or quota (smaller than a
filesystem block), or a directory block (could be larger than a filesystem block). There are
a variety of commands to set the current address. Associated with the current address is the
current data type, which is the structural type of this data. Commands which follow the
structure of the filesystem always set the type as well as the address. Commands which exam‐
ine pieces of an individual file (inode) need the current inode to be set, this is done with
the inode command.

The current address/type information is actually maintained in a stack that can be explicitly
manipulated with the push, pop, and stack commands. This allows for easy examination of a
nested filesystem structure. Also, the last several locations visited are stored in a ring
buffer which can be manipulated with the forward, back, and ring commands.

XFS filesystems are divided into a small number of allocation groups. xfs_db maintains a no‐
tion of the current allocation group which is manipulated by some commands. The initial allo‐
cation group is 0.

COMMANDS
Many commands have extensive online help. Use the help command for more details on any com‐
mand.

a See the addr command.

ablock filoff
Set current address to the offset filoff (a filesystem block number) in the attribute
area of the current inode.

addr [field-expression]
Set current address to the value of the field-expression. This is used to "follow" a
reference in one structure to the object being referred to. If no argument is given,
the current address is printed.

agf [agno]
Set current address to the AGF block for allocation group agno. If no argument is
given, use the current allocation group.

agfl [agno]
Set current address to the AGFL block for allocation group agno. If no argument is
given, use the current allocation group.

agi [agno]
Set current address to the AGI block for allocation group agno. If no argument is
given, use the current allocation group.

agresv [agno]
Displays the length, free block count, per-AG reservation size, and per-AG reservation
usage for a given AG. If no argument is given, display information for all AGs.

attr_remove [-r|-u|-s] [-n] name
Remove the specified extended attribute from the current file.

-r Sets the attribute in the root namespace. Only one namespace option can be
specified.

-u Sets the attribute in the user namespace. Only one namespace option can be
specified.

-s Sets the attribute in the secure namespace. Only one namespace option can be
specified.

-n Do not enable 'noattr2' mode on V4 filesystems.

attr_set [-r|-u|-s] [-n] [-R|-C] [-v namelen] name
Sets an extended attribute on the current file with the given name.

-r Sets the attribute in the root namespace. Only one namespace option can be
specified.

-u Sets the attribute in the user namespace. Only one namespace option can be
specified.

-s Sets the attribute in the secure namespace. Only one namespace option can be
specified.

-n Do not enable 'noattr2' mode on V4 filesystems.

-R Replace the attribute. The command will fail if the attribute does not already
exist.

-C Create the attribute. The command will fail if the attribute already exists.

-v Set the attribute value to a string of this length containing the letter 'v'.

b See the back command.

back Move to the previous location in the position ring.

blockfree
Free block usage information collected by the last execution of the blockget command.
This must be done before another blockget command can be given, presumably with dif‐
ferent arguments than the previous one.

blockget [-npvs] [-b bno] ... [-i ino] ...
Get block usage and check filesystem consistency. The information is saved for use by
a subsequent blockuse, ncheck, or blocktrash command.

-b is used to specify filesystem block numbers about which verbose information
should be printed.

-i is used to specify inode numbers about which verbose information should be
printed.

-n is used to save pathnames for inodes visited, this is used to support the
xfs_ncheck(8) command. It also means that pathnames will be printed for inodes
that have problems. This option uses a lot of memory so is not enabled by de‐
fault.

-p causes error messages to be prefixed with the filesystem name being processed.
This is useful if several copies of xfs_db are run in parallel.

-s restricts output to severe errors only. This is useful if the output is too
long otherwise.

-v enables verbose output. Messages will be printed for every block and inode pro‐
cessed.

blocktrash [-z] [-o offset] [-n count] [-x min] [-y max] [-s seed] [-0|1|2|3] [-t type] ...
Trash randomly selected filesystem metadata blocks. Trashing occurs to randomly se‐
lected bits in the chosen blocks. This command is available only in debugging ver‐
sions of xfs_db. It is useful for testing xfs_repair(8).

-0 | -1 | -2 | -3
These are used to set the operating mode for blocktrash. Only one can be used:
-0 changed bits are cleared; -1 changed bits are set; -2 changed bits are in‐
verted; -3 changed bits are randomized.

-n supplies the count of block-trashings to perform (default 1).

-o supplies the bit offset at which to start trashing the block. If the value is
preceded by a '+', the trashing will start at a randomly chosen offset that is
larger than the value supplied. The default is to randomly choose an offset
anywhere in the block.

-s supplies a seed to the random processing.

-t gives a type of blocks to be selected for trashing. Multiple -t options may be
given. If no -t options are given then all metadata types can be trashed.

-x sets the minimum size of bit range to be trashed. The default value is 1.

-y sets the maximum size of bit range to be trashed. The default value is 1024.

-z trashes the block at the top of the stack. It is not necessary to run blockget
if this option is supplied.

blockuse [-n] [-c count]
Print usage for current filesystem block(s). For each block, the type and (if any)
inode are printed.

-c specifies a count of blocks to process. The default value is 1 (the current
block only).

-n specifies that file names should be printed. The prior blockget command must
have also specified the -n option.

bmap [-a] [-d] [block [len]]
Show the block map for the current inode. The map display can be restricted to an
area of the file with the block and len arguments. If block is given and len is omit‐
ted then 1 is assumed for len.

The -a and -d options are used to select the attribute or data area of the inode, if
neither option is given then both areas are shown.

btdump [-a] [-i]
If the cursor points to a btree node, dump the btree from that block downward. If in‐
stead the cursor points to an inode, dump the data fork block mapping btree if there
is one. If the cursor points to a directory or extended attribute btree node, dump
that. By default, only records stored in the btree are dumped.

-a If the cursor points at an inode, dump the extended attribute block mapping
btree, if present.

-i Dump all keys and pointers in intermediate btree nodes, and all records in leaf
btree nodes.

btheight [-b blksz] [-n recs] [-w max|-w min] btree types...
For a given number of btree records and a btree type, report the number of records and
blocks for each level of the btree, and the total number of blocks. The btree type
must be given after the options.

A raw btree geometry can be provided in the format
"record_bytes:key_bytes:ptr_bytes:header_type", where header_type is one of "short",
"long", "shortcrc", or "longcrc".

The supported btree types are: bnobt, cntbt, inobt, finobt, bmapbt, refcountbt, and
rmapbt.

Options are as follows:

-b is used to override the btree block size. The default is the filesystem block
size.

-n is used to specify the number of records to store. This argument is required.

-w max
shows only the best case scenario, which is when the btree blocks are maximally
loaded.

-w min
shows only the worst case scenario, which is when the btree blocks are half
full.

check See the blockget command.

convert type number [type number] ... type
Convert from one address form to another. The known types, with alternate names, are:
agblock or agbno (filesystem block within an allocation group)
agino or aginode (inode number within an allocation group)
agnumber or agno (allocation group number)
bboff or daddroff (byte offset in a daddr)
blkoff or fsboff or agboff (byte offset in a agblock or fsblock)
byte or fsbyte (byte address in filesystem)
daddr or bb (disk address, 512-byte blocks)
fsblock or fsb or fsbno (filesystem block, see the fsblock command)
ino or inode (inode number)
inoidx or offset (index of inode in filesystem block)
inooff or inodeoff (byte offset in inode)

Only conversions that "make sense" are allowed. The compound form (with more than
three arguments) is useful for conversions such as convert agno ag agbno agb fsblock.

crc [-i|-r|-v]
Invalidates, revalidates, or validates the CRC (checksum) field of the current struc‐
ture, if it has one. This command is available only on CRC-enabled filesystems. With
no argument, validation is performed. Each command will display the resulting CRC
value and state.

-i Invalidate the structure's CRC value (incrementing it by one), and write it to
disk.

-r Recalculate the current structure's correct CRC value, and write it to disk.

-v Validate and display the current value and state of the structure's CRC.

daddr [d]
Set current address to the daddr (512 byte block) given by d. If no value for d is
given, the current address is printed, expressed as a daddr. The type is set to data
(uninterpreted).

dblock filoff
Set current address to the offset filoff (a filesystem block number) in the data area
of the current inode.

debug [flagbits]
Set debug option bits. These are used for debugging xfs_db. If no value is given for
flagbits, print the current debug option bits. These are for the use of the implemen‐
tor.

dquot [-g|-p|-u] id
Set current address to a group, project or user quota block for the given ID. Defaults
to user quota.

echo [arg] ...
Echo the arguments to the output.

f See the forward command.

forward
Move forward to the next entry in the position ring.

frag [-adflqRrv]
Get file fragmentation data. This prints information about fragmentation of file data
in the filesystem (as opposed to fragmentation of freespace, for which see the freesp
command). Every file in the filesystem is examined to see how far from ideal its ex‐
tent mappings are. A summary is printed giving the totals.

-v sets verbosity, every inode has information printed for it. The remaining op‐
tions select which inodes and extents are examined. If no options are given
then all are assumed set, otherwise just those given are enabled.

-a enables processing of attribute data.

-d enables processing of directory data.

-f enables processing of regular file data.

-l enables processing of symbolic link data.

-q enables processing of quota file data.

-R enables processing of realtime control file data.

-r enables processing of realtime file data.

freesp [-bcds] [-A alignment] [-a ag] ... [-e i] [-h h1] ... [-m m]
Summarize free space for the filesystem. The free blocks are examined and totalled,
and displayed in the form of a histogram, with a count of extents in each range of
free extent sizes.

-A reports only free extents with starting blocks aligned to alignment blocks.

-a adds ag to the list of allocation groups to be processed. If no -a options are
given then all allocation groups are processed.

-b specifies that the histogram buckets are binary-sized, with the starting sizes
being the powers of 2.

-c specifies that freesp will search the by-size (cnt) space Btree instead of the
default by-block (bno) space Btree.

-d specifies that every free extent will be displayed.

-e specifies that the histogram buckets are equal-sized, with the size specified
as i.

-h specifies a starting block number for a histogram bucket as h1. Multiple -h's
are given to specify the complete set of buckets.

-m specifies that the histogram starting block numbers are powers of m. This is
the general case of -b.

-s specifies that a final summary of total free extents, free blocks, and the av‐
erage free extent size is printed.

fsb See the fsblock command.

fsblock [fsb]
Set current address to the fsblock value given by fsb. If no value for fsb is given
the current address is printed, expressed as an fsb. The type is set to data (unin‐
terpreted). XFS filesystem block numbers are computed ((agno << agshift) | agblock)
where agshift depends on the size of an allocation group. Use the convert command to
convert to and from this form. Block numbers given for file blocks (for instance from
the bmap command) are in this form.

fsmap [ start ] [ end ]
Prints the mapping of disk blocks used by an XFS filesystem. The map lists each ex‐
tent used by files, allocation group metadata, journalling logs, and static filesystem
metadata, as well as any regions that are unused. All blocks, offsets, and lengths
are specified in units of 512-byte blocks, no matter what the filesystem's block size
is. The optional start and end arguments can be used to constrain the output to a
particular range of disk blocks.

fuzz [-c] [-d] field action
Write garbage into a specific structure field on disk. Expert mode must be enabled to
use this command. The operation happens immediately; there is no buffering.

The fuzz command can take the following actions against a field:

zeroes
Clears all bits in the field.

ones
Sets all bits in the field.

firstbit
Flips the first bit in the field. For a scalar value, this is the highest bit.

middlebit
Flips the middle bit in the field.

lastbit
Flips the last bit in the field. For a scalar value, this is the lowest bit.

add Adds a small value to a scalar field.

sub Subtracts a small value from a scalar field.

random
Randomizes the contents of the field.

The following switches affect the write behavior:

-c Skip write verifiers and CRC recalculation; allows invalid data to be written
to disk.

-d Skip write verifiers but perform CRC recalculation; allows invalid data to be
written to disk to test detection of invalid data.

hash string
Prints the hash value of string using the hash function of the XFS directory and at‐
tribute implementation.

help [command]
Print help for one or all commands.

info Displays selected geometry information about the filesystem. The output will have the
same format that mkfs.xfs(8) prints when creating a filesystem or xfs_info(8) prints
when querying a filesystem.

inode [inode#]
Set the current inode number. If no inode# is given, print the current inode number.

label [label]
Set the filesystem label. The filesystem label can be used by mount(8) instead of us‐
ing a device special file. The maximum length of an XFS label is 12 characters - use
of a longer label will result in truncation and a warning will be issued. If no label
is given, the current filesystem label is printed.

log [stop | start filename]
Start logging output to filename, stop logging, or print the current logging status.

logformat [-c cycle] [-s sunit]
Reformats the log to the specified log cycle and log stripe unit. This has the effect
of clearing the log destructively. If the log cycle is not specified, the log is re‐
formatted to the current cycle. If the log stripe unit is not specified, the stripe
unit from the filesystem superblock is used.

logres Print transaction reservation size information for each transaction type. This makes
it easier to find discrepancies in the reservation calculations between xfsprogs and
the kernel, which will help when diagnosing minimum log size calculation errors.

ls [-i] [paths]...
List the contents of a directory. If a path resolves to a directory, the directory
will be listed. If no paths are supplied and the IO cursor points at a directory in‐
ode, the contents of that directory will be listed.

The output format is: directory cookie, inode number, file type, hash, name length,
name.

-i Resolve each of the given paths to an inode number and print that number. If
no paths are given and the IO cursor points to an inode, print the inode num‐
ber.

metadump [-egow] filename
Dumps metadata to a file. See xfs_metadump(8) for more information.

ncheck [-s] [-i ino] ...
Print name-inode pairs. A blockget -n command must be run first to gather the informa‐
tion.

-i specifies an inode number to be printed. If no -i options are given then all
inodes are printed.

-s specifies that only setuid and setgid files are printed.

p See the print command.

path dir_path
Walk the directory tree to an inode using the supplied path. Absolute and relative
paths are supported.

pop Pop location from the stack.

print [field-expression] ...
Print field values. If no argument is given, print all fields in the current struc‐
ture.

push [command]
Push location to the stack. If command is supplied, set the current location to the
results of command after pushing the old location.

q See the quit command.

quit Exit xfs_db.

ring [index]
Show position ring (if no index argument is given), or move to a specific entry in the
position ring given by index.

sb [agno]
Set current address to SB header in allocation group agno. If no agno is given, use
the current allocation group number.

source source-file
Process commands from source-file. source commands can be nested.

stack View the location stack.

type [type]
Set the current data type to type. If no argument is given, show the current data
type. The possible data types are: agf, agfl, agi, attr, bmapbta, bmapbtd, bnobt,
cntbt, data, dir, dir2, dqblk, inobt, inode, log, refcntbt, rmapbt, rtbitmap, rtsum‐‐
mary, sb, symlink and text. See the TYPES section below for more information on these
data types.

timelimit [OPTIONS]
Print the minimum and maximum supported values for inode timestamps, quota expiration
timers, and quota grace periods supported by this filesystem. Options include:

--bigtime
Print the time limits of an XFS filesystem with the bigtime feature enabled.

--classic
Print the time limits of a classic XFS filesystem.

--compact
Print all limits as raw values on a single line.

--pretty
Print the timestamps in the current locale's date and time format instead of
raw seconds since the Unix epoch.

uuid [uuid | generate | rewrite | restore]
Set the filesystem universally unique identifier (UUID). The filesystem UUID can be
used by mount(8) instead of using a device special file. The uuid can be set directly
to the desired UUID, or it can be automatically generated using the generate option.
These options will both write the UUID into every copy of the superblock in the
filesystem. On a CRC-enabled filesystem, this will set an incompatible superblock
flag, and the filesystem will not be mountable with older kernels. This can be re‐
verted with the restore option, which will copy the original UUID back into place and
clear the incompatible flag as needed. rewrite copies the current UUID from the pri‐
mary superblock to all secondary copies of the superblock. If no argument is given,
the current filesystem UUID is printed.

version [feature | versionnum features2]
Enable selected features for a filesystem (certain features can be enabled on an un‐
mounted filesystem, after mkfs.xfs(8) has created the filesystem). Support for un‐
written extents can be enabled using the extflg option. Support for version 2 log for‐
mat can be enabled using the log2 option. Support for extended attributes can be en‐
abled using the attr1 or attr2 option. Once enabled, extended attributes cannot be
disabled, but the user may toggle between attr1 and attr2 at will (older kernels may
not support the newer version).

If no argument is given, the current version and feature bits are printed. With one
argument, this command will write the updated version number into every copy of the
superblock in the filesystem. If two arguments are given, they will be used as nu‐
meric values for the versionnum and features2 bits respectively, and their string
equivalent reported (but no modifications are made).

write [-c|-d] [field value] ...
Write a value to disk. Specific fields can be set in structures (struct mode), or a
block can be set to data values (data mode), or a block can be set to string values
(string mode, for symlink blocks). The operation happens immediately: there is no
buffering.

Struct mode is in effect when the current type is structural, i.e. not data. For
struct mode, the syntax is "write field value".

Data mode is in effect when the current type is data. In this case the contents of the
block can be shifted or rotated left or right, or filled with a sequence, a constant
value, or a random value. In this mode write with no arguments gives more information
on the allowed commands.

-c Skip write verifiers and CRC recalculation; allows invalid data to be written
to disk.

-d Skip write verifiers but perform CRC recalculation. This allows invalid data
to be written to disk to test detection of invalid data. (This is not possible
for some types.)

TYPES
This section gives the fields in each structure type and their meanings. Note that some
types of block cover multiple actual structures, for instance directory blocks.

agf The AGF block is the header for block allocation information; it is in the second
512-byte block of each allocation group. The following fields are defined:
magicnum AGF block magic number, 0x58414746 ('XAGF').
versionnum version number, currently 1.
seqno sequence number starting from 0.
length size in filesystem blocks of the allocation group. All allocation
groups except the last one of the filesystem have the superblock's
agblocks value here.
bnoroot block number of the root of the Btree holding free space informa‐
tion sorted by block number.
cntroot block number of the root of the Btree holding free space informa‐
tion sorted by block count.
bnolevel number of levels in the by-block-number Btree.
cntlevel number of levels in the by-block-count Btree.
flfirst index into the AGFL block of the first active entry.
fllast index into the AGFL block of the last active entry.
flcount count of active entries in the AGFL block.
freeblks count of blocks represented in the freespace Btrees.
longest longest free space represented in the freespace Btrees.
btreeblks number of blocks held in the AGF Btrees.

agfl The AGFL block contains block numbers for use of the block allocator; it is in the
fourth 512-byte block of each allocation group. Each entry in the active list is a
block number within the allocation group that can be used for any purpose if space
runs low. The AGF block fields flfirst, fllast, and flcount designate which en‐
tries are currently active. Entry space is allocated in a circular manner within
the AGFL block. Fields defined:
bno array of all block numbers. Even those which are not active are
printed.

agi The AGI block is the header for inode allocation information; it is in the third
512-byte block of each allocation group. Fields defined:
magicnum AGI block magic number, 0x58414749 ('XAGI').
versionnum version number, currently 1.
seqno sequence number starting from 0.
length size in filesystem blocks of the allocation group.
count count of inodes allocated.
root block number of the root of the Btree holding inode allocation in‐
formation.
level number of levels in the inode allocation Btree.
freecount count of allocated inodes that are not in use.
newino last inode number allocated.
dirino unused.
unlinked an array of inode numbers within the allocation group. The entries
in the AGI block are the heads of lists which run through the inode
next_unlinked field. These inodes are to be unlinked the next time
the filesystem is mounted.

attr An attribute fork is organized as a Btree with the actual data embedded in the leaf
blocks. The root of the Btree is found in block 0 of the fork. The index (sort or‐
der) of the Btree is the hash value of the attribute name. All the blocks contain
a blkinfo structure at the beginning, see type dir for a description. Nonleaf
blocks are identical in format to those for version 1 and version 2 directories,
see type dir for a description. Leaf blocks can refer to "local" or "remote" attri‐
bute values. Local values are stored directly in the leaf block. Leaf blocks con‐
tain the following fields:
hdr header containing a blkinfo structure info (magic number 0xfbee), a
count of active entries, usedbytes total bytes of names and values,
the firstused byte in the name area, holes set if the block needs
compaction, and array freemap as for dir leaf blocks.
entries array of structures containing a hashval, nameidx (index into the
block of the name), and flags incomplete, root, and local.
nvlist array of structures describing the attribute names and values.
Fields always present: valuelen (length of value in bytes), name‐‐
len, and name. Fields present for local values: value (value
string). Fields present for remote values: valueblk (fork block
number of containing the value).

Remote values are stored in an independent block in the attribute fork. Prior to
v5, value blocks had no structure, but in v5 they acquired a header structure with
the following fields:
magic attr3 remote block magic number, 0x5841524d ('XARM').
offset Byte offset of this data block within the overall attribute value.
bytes Number of bytes stored in this block.
crc Checksum of the attribute block contents.
uuid Filesystem UUID.
owner Inode that owns this attribute value.
bno Block offset of this block within the inode's attribute fork.
lsn Log serial number of the last time this block was logged.
data The attribute value data.

bmapbt Files with many extents in their data or attribute fork will have the extents de‐
scribed by the contents of a Btree for that fork, instead of being stored directly
in the inode. Each bmap Btree starts with a root block contained within the inode.
The other levels of the Btree are stored in filesystem blocks. The blocks are
linked to sibling left and right blocks at each level, as well as by pointers from
parent to child blocks. Each block contains the following fields:
magic bmap Btree block magic number, 0x424d4150 ('BMAP').
level level of this block above the leaf level.
numrecs number of records or keys in the block.
leftsib left (logically lower) sibling block, 0 if none.
rightsib right (logically higher) sibling block, 0 if none.
recs [leaf blocks only] array of extent records. Each record contains
startoff, startblock, blockcount, and extentflag (1 if the extent
is unwritten).
keys [non-leaf blocks only] array of key records. These are the first
key value of each block in the level below this one. Each record
contains startoff.
ptrs [non-leaf blocks only] array of child block pointers. Each pointer
is a filesystem block number to the next level in the Btree.

bnobt There is one set of filesystem blocks forming the by-block-number allocation Btree
for each allocation group. The root block of this Btree is designated by the bno‐‐
root field in the corresponding AGF block. The blocks are linked to sibling left
and right blocks at each level, as well as by pointers from parent to child blocks.
Each block has the following fields:
magic BNOBT block magic number, 0x41425442 ('ABTB').
level level number of this block, 0 is a leaf.
numrecs number of data entries in the block.
leftsib left (logically lower) sibling block, 0 if none.
rightsib right (logically higher) sibling block, 0 if none.
recs [leaf blocks only] array of freespace records. Each record contains
startblock and blockcount.
keys [non-leaf blocks only] array of key records. These are the first
value of each block in the level below this one. Each record con‐
tains startblock and blockcount.
ptrs [non-leaf blocks only] array of child block pointers. Each pointer
is a block number within the allocation group to the next level in
the Btree.

cntbt There is one set of filesystem blocks forming the by-block-count allocation Btree
for each allocation group. The root block of this Btree is designated by the cnt‐‐
root field in the corresponding AGF block. The blocks are linked to sibling left
and right blocks at each level, as well as by pointers from parent to child blocks.
Each block has the following fields:
magic CNTBT block magic number, 0x41425443 ('ABTC').
level level number of this block, 0 is a leaf.
numrecs number of data entries in the block.
leftsib left (logically lower) sibling block, 0 if none.
rightsib right (logically higher) sibling block, 0 if none.
recs [leaf blocks only] array of freespace records. Each record contains
startblock and blockcount.
keys [non-leaf blocks only] array of key records. These are the first
value of each block in the level below this one. Each record con‐
tains blockcount and startblock.
ptrs [non-leaf blocks only] array of child block pointers. Each pointer
is a block number within the allocation group to the next level in
the Btree.

data User file blocks, and other blocks whose type is unknown, have this type for dis‐
play purposes in xfs_db. The block data is displayed in hexadecimal format.

dir A version 1 directory is organized as a Btree with the directory data embedded in
the leaf blocks. The root of the Btree is found in block 0 of the file. The index
(sort order) of the Btree is the hash value of the entry name. All the blocks con‐
tain a blkinfo structure at the beginning with the following fields:
forw next sibling block.
back previous sibling block.
magic magic number for this block type.
The non-leaf (node) blocks have the following fields:
hdr header containing a blkinfo structure info (magic number 0xfebe),
the count of active entries, and the level of this block above the
leaves.
btree array of entries containing hashval and before fields. The before
value is a block number within the directory file to the child
block, the hashval is the last hash value in that block.
The leaf blocks have the following fields:
hdr header containing a blkinfo structure info (magic number 0xfeeb),
the count of active entries, namebytes (total name string bytes),
holes flag (block needs compaction), and freemap (array of base,
size entries for free regions).
entries array of structures containing hashval, nameidx (byte index into
the block of the name string), and namelen.
namelist array of structures containing inumber and name.

dir2 A version 2 directory has four kinds of blocks. Data blocks start at offset 0 in
the file. There are two kinds of data blocks: single-block directories have the
leaf information embedded at the end of the block, data blocks in multi-block di‐
rectories do not. Node and leaf blocks start at offset 32GiB (with either a single
leaf block or the root node block). Freespace blocks start at offset 64GiB. The
node and leaf blocks form a Btree, with references to the data in the data blocks.
The freespace blocks form an index of longest free spaces within the data blocks.

A single-block directory block contains the following fields:
bhdr header containing magic number 0x58443242 ('XD2B') and an array
bestfree of the longest 3 free spaces in the block (offset,
length).
bu array of union structures. Each element is either an entry or a
freespace. For entries, there are the following fields: inumber,
namelen, name, and tag. For freespace, there are the following
fields: freetag (0xffff), length, and tag. The tag value is the
byte offset in the block of the start of the entry it is contained
in.
bleaf array of leaf entries containing hashval and address. The address
is a 64-bit word offset into the file.
btail tail structure containing the total count of leaf entries and stale
count of unused leaf entries.
A data block contains the following fields:
dhdr header containing magic number 0x58443244 ('XD2D') and an array
bestfree of the longest 3 free spaces in the block (offset,
length).
du array of union structures as for bu.
Leaf blocks have two possible forms. If the Btree consists of a single leaf then
the freespace information is in the leaf block, otherwise it is in separate blocks
and the root of the Btree is a node block. A leaf block contains the following
fields:
lhdr header containing a blkinfo structure info (magic number 0xd2f1 for
the single leaf case, 0xd2ff for the true Btree case), the total
count of leaf entries, and stale count of unused leaf entries.
lents leaf entries, as for bleaf.
lbests [single leaf only] array of values which represent the longest
freespace in each data block in the directory.
ltail [single leaf only] tail structure containing bestcount count of
lbests.
A node block is identical to that for types attr and dir.

A freespace block contains the following fields:
fhdr header containing magic number 0x58443246 ('XD2F'), firstdb first
data block number covered by this freespace block, nvalid number of
valid entries, and nused number of entries representing real data
blocks.
fbests array of values as for lbests.

dqblk The quota information is stored in files referred to by the superblock uquotino and
pquotino fields. Each filesystem block in a quota file contains a constant number
of quota entries. The quota entry size is currently 136 bytes, so with a 4KiB
filesystem block size there are 30 quota entries per block. The dquot command is
used to locate these entries in the filesystem. The file entries are indexed by
the user or project identifier to determine the block and offset. Each quota entry
has the following fields:
magic magic number, 0x4451 ('DQ').
version version number, currently 1.
flags flags, values include 0x01 for user quota, 0x02 for project
quota.
id user or project identifier.
blk_hardlimit absolute limit on blocks in use.
blk_softlimit preferred limit on blocks in use.
ino_hardlimit absolute limit on inodes in use.
ino_softlimit preferred limit on inodes in use.
bcount blocks actually in use.
icount inodes actually in use.
itimer time when service will be refused if soft limit is violated for
inodes.
btimer time when service will be refused if soft limit is violated for
blocks.
iwarns number of warnings issued about inode limit violations.
bwarns number of warnings issued about block limit violations.
rtb_hardlimit absolute limit on realtime blocks in use.
rtb_softlimit preferred limit on realtime blocks in use.
rtbcount realtime blocks actually in use.
rtbtimer time when service will be refused if soft limit is violated for
realtime blocks.
rtbwarns number of warnings issued about realtime block limit violations.

inobt There is one set of filesystem blocks forming the inode allocation Btree for each
allocation group. The root block of this Btree is designated by the root field in
the corresponding AGI block. The blocks are linked to sibling left and right
blocks at each level, as well as by pointers from parent to child blocks. Each
block has the following fields:
magic INOBT block magic number, 0x49414254 ('IABT').
level level number of this block, 0 is a leaf.
numrecs number of data entries in the block.
leftsib left (logically lower) sibling block, 0 if none.
rightsib right (logically higher) sibling block, 0 if none.
recs [leaf blocks only] array of inode records. Each record contains
startino allocation-group relative inode number, freecount count of
free inodes in this chunk, and free bitmap, LSB corresponds to in‐
ode 0.
keys [non-leaf blocks only] array of key records. These are the first
value of each block in the level below this one. Each record con‐
tains startino.
ptrs [non-leaf blocks only] array of child block pointers. Each pointer
is a block number within the allocation group to the next level in
the Btree.

inode Inodes are allocated in "chunks" of 64 inodes each. Usually a chunk is multiple
filesystem blocks, although there are cases with large filesystem blocks where a
chunk is less than one block. The inode Btree (see inobt above) refers to the inode
numbers per allocation group. The inode numbers directly reflect the location of
the inode block on disk. Use the inode command to point xfs_db to a specific inode.
Each inode contains four regions: core, next_unlinked, u, and a. core contains the
fixed information. next_unlinked is separated from the core due to journaling con‐
siderations, see type agi field unlinked. u is a union structure that is different
in size and format depending on the type and representation of the file data ("data
fork"). a is an optional union structure to describe attribute data, that is dif‐
ferent in size, format, and location depending on the presence and representation
of attribute data, and the size of the u data ("attribute fork"). xfs_db automati‐
cally selects the proper union members based on information in the inode.

The following are fields in the inode core:
magic inode magic number, 0x494e ('IN').
mode mode and type of file, as described in chmod(2), mknod(2), and
stat(2).
version inode version, 1 or 2.
format format of u union data (0: xfs_dev_t, 1: local file - in-inode di‐
rectory or symlink, 2: extent list, 3: Btree root, 4: unique id
[unused]).
nlinkv1 number of links to the file in a version 1 inode.
nlinkv2 number of links to the file in a version 2 inode.
projid_lo owner's project id (low word; version 2 inode only). projid_hi
owner's project id (high word; version 2 inode only).
uid owner's user id.
gid owner's group id.
atime time last accessed (seconds and nanoseconds).
mtime time last modified.
ctime time created or inode last modified.
size number of bytes in the file.
nblocks total number of blocks in the file including indirect and attri‐
bute.
extsize basic/minimum extent size for the file.
nextents number of extents in the data fork.
naextents number of extents in the attribute fork.
forkoff attribute fork offset in the inode, in 64-bit words from the start
of u.
aformat format of a data (1: local attribute data, 2: extent list, 3: Btree
root).
dmevmask DMAPI event mask.
dmstate DMAPI state information.
newrtbm file is the realtime bitmap and is "new" format.
prealloc file has preallocated data space after EOF.
realtime file data is in the realtime subvolume.
gen inode generation number.
The following fields are in the u data fork union:
bmbt bmap Btree root. This looks like a bmapbtd block with redundant in‐
formation removed.
bmx array of extent descriptors.
dev dev_t for the block or character device.
sfdir shortform (in-inode) version 1 directory. This consists of a hdr
containing the parent inode number and a count of active entries in
the directory, followed by an array list of hdr.count entries. Each
such entry contains inumber, namelen, and name string.
sfdir2 shortform (in-inode) version 2 directory. This consists of a hdr
containing a count of active entries in the directory, an i8count
of entries with inumbers that don't fit in a 32-bit value, and the
parent inode number, followed by an array list of hdr.count en‐
tries. Each such entry contains namelen, a saved offset used when
the directory is converted to a larger form, a name string, and the
inumber.
symlink symbolic link string value.
The following fields are in the a attribute fork union if it exists:
bmbt bmap Btree root, as above.
bmx array of extent descriptors.
sfattr shortform (in-inode) attribute values. This consists of a hdr con‐
taining a totsize (total size in bytes) and a count of active en‐
tries, followed by an array list of hdr.count entries. Each such
entry contains namelen, valuelen, root flag, name, and value.

log Log blocks contain the journal entries for XFS. It's not useful to examine these
with xfs_db, use xfs_logprint(8) instead.

refcntbt There is one set of filesystem blocks forming the reference count Btree for each
allocation group. The root block of this Btree is designated by the refcntroot
field in the corresponding AGF block. The blocks are linked to sibling left and
right blocks at each level, as well as by pointers from parent to child blocks.
Each block has the following fields:
magic REFC block magic number, 0x52334643 ('R3FC').
level level number of this block, 0 is a leaf.
numrecs number of data entries in the block.
leftsib left (logically lower) sibling block, 0 if none.
rightsib right (logically higher) sibling block, 0 if none.
recs [leaf blocks only] array of reference count records. Each record
contains startblock, blockcount, and refcount.
keys [non-leaf blocks only] array of key records. These are the first
value of each block in the level below this one. Each record con‐
tains startblock.
ptrs [non-leaf blocks only] array of child block pointers. Each pointer
is a block number within the allocation group to the next level in
the Btree.

rmapbt There is one set of filesystem blocks forming the reverse mapping Btree for each
allocation group. The root block of this Btree is designated by the rmaproot field
in the corresponding AGF block. The blocks are linked to sibling left and right
blocks at each level, as well as by pointers from parent to child blocks. Each
block has the following fields:
magic RMAP block magic number, 0x524d4233 ('RMB3').
level level number of this block, 0 is a leaf.
numrecs number of data entries in the block.
leftsib left (logically lower) sibling block, 0 if none.
rightsib right (logically higher) sibling block, 0 if none.
recs [leaf blocks only] array of reference count records. Each record
contains startblock, blockcount, owner, offset, attr_fork,
bmbt_block, and unwritten.
keys [non-leaf blocks only] array of double-key records. The first
("low") key contains the first value of each block in the level be‐
low this one. The second ("high") key contains the largest key that
can be used to identify any record in the subtree. Each record con‐
tains startblock, owner, offset, attr_fork, and bmbt_block.
ptrs [non-leaf blocks only] array of child block pointers. Each pointer
is a block number within the allocation group to the next level in
the Btree.

rtbitmap If the filesystem has a realtime subvolume, then the rbmino field in the superblock
refers to a file that contains the realtime bitmap. Each bit in the bitmap file
controls the allocation of a single realtime extent (set == free). The bitmap is
processed in 32-bit words, the LSB of a word is used for the first extent con‐
trolled by that bitmap word. The atime field of the realtime bitmap inode contains
a counter that is used to control where the next new realtime file will start.

rtsummary If the filesystem has a realtime subvolume, then the rsumino field in the su‐
perblock refers to a file that contains the realtime summary data. The summary file
contains a two-dimensional array of 16-bit values. Each value counts the number of
free extent runs (consecutive free realtime extents) of a given range of sizes that
starts in a given bitmap block. The size ranges are binary buckets (low size in
the bucket is a power of 2). There are as many size ranges as are necessary given
the size of the realtime subvolume. The first dimension is the size range, the
second dimension is the starting bitmap block number (adjacent entries are for the
same size, adjacent bitmap blocks).

sb There is one sb (superblock) structure per allocation group. It is the first disk
block in the allocation group. Only the first one (block 0 of the filesystem) is
actually used; the other blocks are redundant information for xfs_repair(8) to use
if the first superblock is damaged. Fields defined:
magicnum superblock magic number, 0x58465342 ('XFSB').
blocksize filesystem block size in bytes.
dblocks number of filesystem blocks present in the data subvolume.
rblocks number of filesystem blocks present in the realtime subvolume.
rextents number of realtime extents that rblocks contain.
uuid unique identifier of the filesystem.
logstart starting filesystem block number of the log (journal). If this
value is 0 the log is "external".
rootino root inode number.
rbmino realtime bitmap inode number.
rsumino realtime summary data inode number.
rextsize realtime extent size in filesystem blocks.
agblocks size of an allocation group in filesystem blocks.
agcount number of allocation groups.
rbmblocks number of realtime bitmap blocks.
logblocks number of log blocks (filesystem blocks).
versionnum filesystem version information. This value is currently 1, 2, 3,
or 4 in the low 4 bits. If the low bits are 4 then the other bits
have additional meanings. 1 is the original value. 2 means that
attributes were used. 3 means that version 2 inodes (large link
counts) were used. 4 is the bitmask version of the version number.
In this case, the other bits are used as flags (0x0010: attributes
were used, 0x0020: version 2 inodes were used, 0x0040: quotas were
used, 0x0080: inode cluster alignment is in force, 0x0100: data
stripe alignment is in force, 0x0200: the shared_vn field is used,
0x1000: unwritten extent tracking is on, 0x2000: version 2 directo‐
ries are in use).
sectsize sector size in bytes, currently always 512. This is the size of
the superblock and the other header blocks.
inodesize inode size in bytes.
inopblock number of inodes per filesystem block.
fname obsolete, filesystem name.
fpack obsolete, filesystem pack name.
blocklog log2 of blocksize.
sectlog log2 of sectsize.
inodelog log2 of inodesize.
inopblog log2 of inopblock.
agblklog log2 of agblocks (rounded up).
rextslog log2 of rextents.
inprogress mkfs.xfs(8) or xfs_copy(8) aborted before completing this filesys‐
tem.
imax_pct maximum percentage of filesystem space used for inode blocks.
icount number of allocated inodes.
ifree number of allocated inodes that are not in use.
fdblocks number of free data blocks.
frextents number of free realtime extents.
uquotino user quota inode number.
pquotino project quota inode number; this is currently unused.
qflags quota status flags (0x01: user quota accounting is on, 0x02: user
quota limits are enforced, 0x04: quotacheck has been run on user
quotas, 0x08: project quota accounting is on, 0x10: project quota
limits are enforced, 0x20: quotacheck has been run on project quo‐
tas).
flags random flags. 0x01: only read-only mounts are allowed.
shared_vn shared version number (shared readonly filesystems).
inoalignmt inode chunk alignment in filesystem blocks.
unit stripe or RAID unit.
width stripe or RAID width.
dirblklog log2 of directory block size (filesystem blocks).

symlink Symbolic link blocks are used only when the symbolic link value does not fit inside
the inode. The block content is just the string value. Bytes past the logical end
of the symbolic link value have arbitrary values.

text User file blocks, and other blocks whose type is unknown, have this type for dis‐
play purposes in xfs_db. The block data is displayed in two columns: Hexadecimal
format and printable ASCII chars.

DIAGNOSTICS
Many messages can come from the check (blockget) command. If the filesystem is completely
corrupt, a core dump might be produced instead of the message
device is not a valid filesystem

If the filesystem is very large (has many files) then check might run out of memory. In this
case the message
out of memory
is printed.

The following is a description of the most likely problems and the associated messages. Most
of the diagnostics produced are only meaningful with an understanding of the structure of the
filesystem.

agf_freeblks n, counted m in ag a
The freeblocks count in the allocation group header for allocation group a doesn't
match the number of blocks counted free.

agf_longest n, counted m in ag a
The longest free extent in the allocation group header for allocation group a doesn't
match the longest free extent found in the allocation group.

agi_count n, counted m in ag a
The allocated inode count in the allocation group header for allocation group a
doesn't match the number of inodes counted in the allocation group.

agi_freecount n, counted m in ag a
The free inode count in the allocation group header for allocation group a doesn't
match the number of inodes counted free in the allocation group.

block a/b expected inum 0 got i
The block number is specified as a pair (allocation group number, block in the alloca‐
tion group). The block is used multiple times (shared), between multiple inodes.
This message usually follows a message of the next type.

block a/b expected type unknown got y
The block is used multiple times (shared).

block a/b type unknown not expected

SEE ALSO
mkfs.xfs(8), xfs_admin(8), xfs_copy(8), xfs_logprint(8), xfs_metadump(8), xfs_ncheck(8),
xfs_repair(8), mount(8), chmod(2), mknod(2), stat(2), xfs(5).

xfs_db(8)