xfs_db(1M)
xfs_db, xfs_db64 - debug an XFS filesystem
As shipped in IRIX 6.5.15. Last changed in IRIX 6.5.15.
NAME xfs_db, xfs_db64 - debug an XFS filesystem SYNOPSIS xfs_db [ -c cmd ] ... [ -p prog ] [ -r ] [ -x ] xfs_special xfs_db -f [ -c cmd ] ... [ -p prog ] [ -f ] [ -r ] [ -x ] file xfs_db64 [ -c cmd ] ... [ -p prog ] [ -f ] [ -r ] [ -x ] xfs_special xfs_db64 -f [ -c cmd ] ... [ -p prog ] [ -r ] [ -x ] file 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(1M) or to scripts such as xfs_chver that run xfs_db. xfs_db64 is a 64-bit version of xfs_db which is not as susceptible to running out of memory. It is available only on 64-bit capable systems. The options to xfs_db are: -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(1M). -f Specifies that the filesystem image to be processed is stored in a regular file (see the mkfs_xfs -d file option). This might happen if an image copy of a filesystem has been made into an ordinary file with xfs_copy(1M). -p prog Set the program name for prompts and some error messages, the default value is xfs_db or xfs_db64. -r Open file or xfs_special read-only. This option is required if xfs_special is a mounted filesystem. 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 command. 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 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. COMMANDS 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 [ -npsv ] [ -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(1M) for more information. The -b option is used to specify filesystem block numbers about which verbose information should be printed. The -i option is used to specify inode numbers about which verbose information should be printed. The -n option is used to save pathnames for inodes visited, this is used to support the xfs_ncheck(1M) 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. The -p option 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. The -s option restricts output to severe errors only. This is useful if the output is too long otherwise. The -v option enables verbose output. Messages will be printed for every block and inode processed. blocktrash [ -n c ] [ -x a ] [ -y b ] [ -s s ] [ -0123 ] [ -t t ] ... 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(1M) and xfs_check(1M). The -0, -1, -2, and -3 options (mutually exclusive) set the operating mode for blocktrash. In -0 mode, changed bits are cleared. In -1 mode, changed bits are set. In -2 mode, changed bits are inverted. In -3 mode, changed bits are randomized. The -n option supplies the count of block-trashings to perform (default 1). The -s option supplies a seed to the random processing. The -t option 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. The -x option sets the minimum size of bit range to be trashed. The default value is 1. The -y option sets the maximum size of bit range to be trashed. The default value is 1024. blockuse [ -n ] [ -c blockcount ] Print usage for current filesystem block(s). For each block, the type and (if any) inode are printed. The -c option specifies a count of blocks to process. The default value is 1 (the current block only). The -n option 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), and 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. The -v option 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. The -a option enables processing of attribute data. The -d option enables processing of directory data. The -f option enables processing of regular file data. The -l option enables processing of symbolic link data. The -q option enables processing of quota file data. The -R option enables processing of realtime control file data. The -r option enables processing of realtime file data. freesp [ -bcds ] [ -a a ] ... [ -e i ] [ -h h1 ] ... [ -m m ] Summarize free space for the filesystem. The free blocks are examined and totaled, and displayed in the form of a histogram, with a count of extents in each range of free extent sizes. The -a a option adds a to the list of allocation groups to be processed. If no -a options are given then all allocation groups are processed. The -b option specifies that the histogram buckets are binary- sized, with the starting sizes being the powers of 2. The -c option specifies that freesp will search the by-size (cnt) space Btree instead of the default by-block (bno) space Btree. The -d option specifies that every free extent will be displayed. The -e i option specifies that the histogram buckets are equal-sized, with the size specified as i. The -h h1 option specifies a starting block number for a histogram bucket as h1. Multiple -h options are given to specify the complete set of buckets. The -m m option specifies that the histogram starting block numbers are powers of m. This is the general case of -b. The -s option 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. log [ stop | start filename ] Start logging output to filename, stop logging, or print the current logging status. ncheck [ -s ] [ -i ino ] ... Print name-inode pairs. A blockget -n command must be run first to gather the information. The -i option specifies an inode number to be printed. If no -i options are given then all inodes are printed. The -s option 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, and symlink. See the TYPES section below for more information on these data types. uuid [ new-uuid | generate | rewrite ] Display or write the filesystem UUID. If no argument is given, show the current UUID. If a UUID is specified, write the new UUID to all superbolocks. If generate is specified, a new UUID is generated. If rewrite is specified, the UUID in the first superblock is copied to all other superblocks. write [ field or 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. 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 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 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 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: [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 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: [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 nonleaf (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 32GB (with either a single leaf block or the root node block). Freespace blocks start at offset 64GB. 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 4KB 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 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 journalling 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: 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: owner's project id (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, used only for realtime 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(1M) 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(1M) 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(1M) 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. DIAGNOSTICS Many messages can come from the check (blockget) command; these are documented in xfs_check(1M). SEE ALSO mkfs_xfs(1M), xfs_check(1M), xfs_copy(1M), xfs_logprint(1M), xfs_ncheck(1M), xfs_repair(1M), chmod(2), mknod(2), stat(2), xfs(4).