Provided by: xfsprogs_3.1.7_amd64
xfs_db - debug an XFS filesystem
xfs_db [ -c cmd ] ... [ -i|r|x|F ] [ -f ] [ -l logdev ] [ -p progname ] device xfs_db -V
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.
-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. This is the mechanism used to implement xfs_check(8). -f Specifies that the filesystem image to be processed is stored in a regular file at device (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_check and xfs_metadump. -i Allows execution on a mounted filesystem, provided it is mounted read-only. Useful for shell scripts such as xfs_check(8), which must only operate on filesystems in a guarenteed 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) is to be used. -x Specifies expert mode. This enables the write and blocktrash commands. -V Prints out the current version number and exits.
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 examine 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 notion of the current allocation group which is manipulated by some commands. The initial allocation group is 0.
Many commands have extensive online help. Use the help command for more details on any command. 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. 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 different 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. See xfs_check(8) for more information. -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 default. -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 processed. blocktrash [-n count] [-x min] [-y max] [-s seed] [-0|1|2|3] [-t type] ... Trash randomly selected filesystem metadata blocks. Trashing occurs to randomly selected bits in the chosen blocks. This command is available only in debugging versions of xfs_db. It is useful for testing xfs_repair(8) and xfs_check(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 inverted; -3 changed bits are randomized. -n supplies the count of block-trashings to perform (default 1). -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. 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 omitted 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. 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. 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 implementor. dquot [projectid_or_userid] Set current address to a project or user quota block. 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 extent mappings are. A summary is printed giving the totals. -v sets verbosity, every inode has information printed for it. The remaining options 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 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 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 average 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 (uninterpreted). 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. hash string Prints the hash value of string using the hash function of the XFS directory and attribute implementation. help [command] Print help for one or all commands. 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 using 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. 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 information. -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. pop Pop location from the stack. print [field-expression] ... Print field values. If no argument is given, print all fields in the current structure. 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, rtbitmap, rtsummary, sb, symlink and text. See the TYPES section below for more information on these data types. uuid [uuid | generate | rewrite] 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. rewrite copies the current UUID from the primary 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 unmounted filesystem, after mkfs.xfs(8) has created the filesystem). Support for unwritten extents can be enabled using the extflg option. Support for version 2 log format can be enabled using the log2 option. Support for extended attributes can be enabled 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 numeric values for the versionnum and features2 bits respectively, and their string equivalent reported (but no modifications are made). write [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.
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 information sorted by block number. cntroot block number of the root of the Btree holding free space information 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 entries 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 information. 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 order) 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" attribute values. Local values are stored directly in the leaf block. Remote values are stored in an independent block in the attribute fork (with no structure). Leaf blocks contain 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), namelen, and name. Fields present for local values: value (value string). Fields present for remote values: valueblk (fork block number of containing the value). bmapbt Files with many extents in their data or attribute fork will have the extents described 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 [nonleaf 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 [nonleaf 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 bnoroot field in the coresponding 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 [nonleaf blocks only] array of key records. These are the first value of each block in the level below this one. Each record contains startblock and blockcount. ptrs [nonleaf 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 cntroot field in the coresponding 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 [nonleaf blocks only] array of key records. These are the first value of each block in the level below this one. Each record contains blockcount and startblock. ptrs [nonleaf 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 display 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 contain 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 directories 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 coresponding 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 inode 0. keys [nonleaf blocks only] array of key records. These are the first value of each block in the level below this one. Each record contains startino. ptrs [nonleaf 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 considerations, 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 different 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 automatically 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 directory 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 attribute. 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 information 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 entries. 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 containing a totsize (total size in bytes) and a count of active entries, 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. 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 controlled 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 superblock 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 directories 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 filesystem. 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 quotas). 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 display purposes in xfs_db. The block data is displayed in two columns: Hexadecimal format and printable ASCII chars.
Many messages can come from the check (blockget) command; these are documented in xfs_check(8).
mkfs.xfs(8), xfs_admin(8), xfs_check(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)