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

NAME
       xfs_io - debug the I/O path of an XFS filesystem

SYNOPSIS
       xfs_io [ -adfmrRstxT ] [ -c cmd ] ... [ -p prog ] file
       xfs_io -V

DESCRIPTION
       xfs_io  is a debugging tool like xfs_db(8), but is aimed at examining the regular file I/O
       paths rather than the raw XFS volume itself.  These code paths include not only the  obvi‐
       ous  read/write/mmap  interfaces  for  manipulating  files,  but also cover all of the XFS
       extensions (such as space preallocation, additional inode flags, etc).

OPTIONS
       -c cmd    xfs_io 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.

       -p prog   Set the program name for prompts and some error messages, the default  value  is
                 xfs_io.

       -f        Create file if it does not already exist.

       -r        Open file read-only, initially. This is required if file is immutable or append-
                 only.

       -x        Expert mode. Dangerous commands are only available in this mode.  These commands
                 also tend to require additional privileges.

       -V        Prints the version number and exits.

       The other open(2) options described below are also available from the command line.

CONCEPTS
       xfs_io  maintains  a  number  of  open  files and memory mappings.  Files can be initially
       opened on the command line (optionally), and additional files can also be opened later.

       xfs_io commands can be broken up into three groups.  Some commands are aimed at doing reg‐
       ular file I/O - read, write, sync, space preallocation, etc.

       The  second  set of commands exist for manipulating memory mapped regions of a file - map‐
       ping, accessing, storing, unmapping, flushing, etc.

       The remaining commands are for the navigation and display of data structures  relating  to
       the open files, mappings, and the filesystems where they reside.

       Many  commands  have  extensive  online help. Use the help command for more details on any
       command.

FILE I/O COMMANDS
       file [ N ]
              Display a list of all open files and (optionally) switch to  an  alternate  current
              open file.

       open [[ -acdfrstRT ] path ]
              Closes  the current file, and opens the file specified by path instead. Without any
              arguments, displays statistics about the current file - see the stat command.
                 -a  opens append-only (O_APPEND).
                 -d  opens for direct I/O (O_DIRECT).
                 -f  creates the file if it doesn't already exist (O_CREAT).
                 -r  opens read-only (O_RDONLY).
                 -s  opens for synchronous I/O (O_SYNC).
                 -t  truncates on open (O_TRUNC).
                 -n  opens in non-blocking mode if possible (O_NONBLOCK).
                 -T  create a temporary file not linked into  the  filesystem  namespace  (O_TMP‐
                     FILE).   The  pathname  passed must refer to a directory which is treated as
                     virtual parent for the newly  created  invisible  file.   Can  not  be  used
                     together with the -r option.
                 -R  marks the file as a realtime XFS file after opening it, if it is not already
                     marked as such.

       o      See the open command.

       close  Closes the current open file, marking  the  next  open  file  as  current  (if  one
              exists).

       c      See the close command.

       pread [ -b bsize ] [ -v ] [ -FBR [ -Z seed ] ] [ -V vectors ] offset length
              Reads a range of bytes in a specified blocksize from the given offset.
                 -b  can  be  used  to  set the blocksize into which the read(2) requests will be
                     split. The default blocksize is 4096 bytes.
                 -v  dump the contents of the buffer after reading, by default only the count  of
                     bytes actually read is dumped.
                 -F  read the buffers in a forwards sequential direction.
                 -B  read the buffers in a reserve sequential direction.
                 -R  read the buffers in the give range in a random order.
                 -Z seed
                     specify the random number seed used for random reads.
                 -V vectors
                     Use the vectored IO read syscall preadv(2) with a number of blocksize length
                     iovecs. The number of iovecs is set by the vectors parameter.

       r      See the pread command.

       pwrite [ -i file ] [ -d ] [ -s skip ] [ -b size ] [ -S seed ] [ -FBR [ -Z zeed ] ] [ -wW ]
       [ -V vectors ] offset length
              Writes  a range of bytes in a specified blocksize from the given offset.  The bytes
              written can be either a set pattern or read in from another file before writing.
                 -i  allows an input file to be specified as the source of the data to  be  writ‐
                     ten.
                 -d  causes direct I/O, rather than the usual buffered I/O, to be used when read‐
                     ing the input file.
                 -s  specifies the number of bytes to skip from  the  start  of  the  input  file
                     before starting to read.
                 -b  used  to  set  the blocksize into which the write(2) requests will be split.
                     The default blocksize is 4096 bytes.
                 -S  used to set the (repeated) fill pattern which is used when the data to write
                     is not coming from a file.  The default buffer fill pattern value is 0xcdcd‐
                     cdcd.
                 -F  write the buffers in a forwards sequential direction.
                 -B  write the buffers in a reserve sequential direction.
                 -R  write the buffers in the give range in a random order.
                 -Z seed
                     specify the random number seed used for random write
                 -w  call fdatasync(2) once all writes are complete (included in timing results)
                 -W  call fsync(2) once all writes are complete (included in timing results)
                 -V vectors
                     Use the vectored IO write syscall pwritev(2)  with  a  number  of  blocksize
                     length iovecs. The number of iovecs is set by the vectors parameter.

       w      See the pwrite command.

       bmap [ -adlpv ] [ -n nx ]
              Prints the block mapping for the current open file. Refer to the xfs_bmap(8) manual
              page for complete documentation.

       fiemap [ -alv ] [ -n nx ]
              Prints the block mapping for the current open file using the fiemap ioctl.  Options
              behave as described in the xfs_bmap(8) manual page.

       extsize [ -R | -D ] [ value ]
              Display  and/or modify the preferred extent size used when allocating space for the
              currently open file. If the -R option is specified, a  recursive  descent  is  per‐
              formed  for  all directory entries below the currently open file (-D can be used to
              restrict the output to directories only).  If the target file is a directory,  then
              the  inherited  extent  size  is  set for that directory (new files created in that
              directory inherit that extent size).  The value should be specified  in  bytes,  or
              using  one of the usual units suffixes (k, m, g, b, etc). The extent size is always
              reported in units of bytes.

       allocsp size 0
              Sets the size of the file to size and zeroes any additional space  allocated  using
              the  XFS_IOC_ALLOCSP/XFS_IOC_FREESP  system  call described in the xfsctl(3) manual
              page.  allocsp and freesp do exactly the same thing.

       freesp size 0
              See the allocsp command.

       fadvise [ -r | -s | [[ -d | -n | -w ] offset length ]]
              On platforms which support it, allows hints be given to the  system  regarding  the
              expected I/O patterns on the file.  The range arguments are required by some advise
              commands ([*] below), and the others must have no range arguments.  With  no  argu‐
              ments, the POSIX_FADV_NORMAL advice is implied (default readahead).
                 -d  the  data  will  not  be accessed again in the near future (POSIX_FADV_DONT‐
                     NEED[*]).
                 -n  data will be accessed once and not be reused (POSIX_FADV_NOREUSE[*]).
                 -r  expect access to data in random order (POSIX_FADV_RANDOM), which sets reada‐
                     head to zero.
                 -s  expect  access  to  data  in sequential order (POSIX_FADV_SEQUENTIAL), which
                     doubles the default readahead on the file.
                 -w  advises the specified data will  be  needed  again  (POSIX_FADV_WILLNEED[*])
                     which forces the maximum readahead.

       fdatasync
              Calls fdatasync(2) to flush the file's in-core data to disk.

       fsync  Calls fsync(2) to flush all in-core file state to disk.

       s      See the fsync command.

       sync_range [ -a | -b | -w ] offset length
              On  platforms  which  support  it, allows control of syncing a range of the file to
              disk. With no options, SYNC_FILE_RANGE_WRITE is implied on the range supplied.
                 -a  wait   for   IO   in   the   given   range   to   finish    after    writing
                     (SYNC_FILE_RANGE_WAIT_AFTER).
                 -b  wait    for   IO   in   the   given   range   to   finish   before   writing
                     (SYNC_FILE_RANGE_WAIT_BEFORE).
                 -w  start writeback of dirty data in the given range (SYNC_FILE_RANGE_WRITE).

       sync   Calls sync(2) to flush all filesystems' in-core data to disk.

       syncfs Calls syncfs(2) to flush this filesystem's in-core data to disk.

       resvsp offset length
              Allocates reserved, unwritten space for part of a  file  using  the  XFS_IOC_RESVSP
              system call described in the xfsctl(3) manual page.

       unresvsp offset length
              Frees  reserved  space  for  part  of a file using the XFS_IOC_UNRESVSP system call
              described in the xfsctl(3) manual page.

       falloc [ -k ] offset length
              Allocates reserved, unwritten space for part of a file using the fallocate  routine
              as described in the fallocate(2) manual page.
                 -k  will set the FALLOC_FL_KEEP_SIZE flag as described in fallocate(2).

       fcollapse offset length
              Call  fallocate with FALLOC_FL_COLLAPSE_RANGE flag as described in the fallocate(2)
              manual page to de-allocates blocks and eliminates the hole created in this  process
              by shifting data blocks into the hole.

       finsert offset length
              Call  fallocate  with  FALLOC_FL_INSERT_RANGE flag as described in the fallocate(2)
              manual page to create the hole by shifting data blocks.

       fpunch offset length
              Punches (de-allocates) blocks in the  file  by  calling  fallocate  with  the  FAL‐
              LOC_FL_PUNCH_HOLE flag as described in the fallocate(2) manual page.

       fzero offset length
              Call fallocate with FALLOC_FL_ZERO_RANGE flag as described in the fallocate(2) man‐
              ual page to allocate and zero blocks within the range.

       truncate offset
              Truncates the current file at the given offset using ftruncate(2).

       sendfile -i srcfile | -f N [ offset length ]
              On platforms which support it, allows a direct  in-kernel  copy  between  two  file
              descriptors.  The  current open file is the target, the source must be specified as
              another open file (-f) or by path (-i).

       readdir [ -v ] [ -o offset ] [ -l length ]
              Read a range of directory entries from a given offset of a directory.
                 -v  verbose mode - dump dirent content as defined in readdir(3)
                 -o  specify starting offset
                 -l  specify total length to read (in bytes)

       seek  -a | -d | -h [ -r ] [ -s ] offset
              On platforms that support the lseek(2) SEEK_DATA and SEEK_HOLE options, display the
              offsets of the specified segments.
                 -a  Display both data and hole segments starting at the specified offset.
                 -d  Display the data segment starting at the specified offset.
                 -h  Display the hole segment starting at the specified offset.
                 -r  Recursively  display  all  the  specified segments starting at the specified
                     offset.
                 -s  Display the starting lseek(2) offset. This offset will be a calculated value
                     when  both  data and holes are displayed together or performing a recusively
                     display.

       reflink  [ -C ] [ -q ] src_file [src_offset dst_offset length]
              On  filesystems  that  support  the  XFS_IOC_CLONE_RANGE  or  BTRFS_IOC_CLONE_RANGE
              ioctls, map length bytes at offset dst_offset in the open file to the same physical
              blocks that are mapped at offset src_offset in the file src_file  ,  replacing  any
              contents  that  may  already have been there.  If a program writes into a reflinked
              block range of either file, the dirty  blocks  will  be  cloned,  written  to,  and
              remapped  ("copy  on  write")  in  the  affected  file,  leaving  the other file(s)
              unchanged.  If src_offset, dst_offset, and length  are  omitted,  all  contents  of
              src_file will be reflinked into the open file.
                 -C  Print timing statistics in a condensed format.
                 -q  Do not print timing statistics at all.

       dedupe  [ -C ] [ -q ] src_file src_offset dst_offset length
              On     filesystems     that     support     the     XFS_IOC_FILE_EXTENT_SAME     or
              BTRFS_IOC_FILE_EXTENT_SAME ioctls, map length bytes at  offset  dst_offset  in  the
              open  file  to the same physical blocks that are mapped at offset src_offset in the
              file src_file , but only if the contents of both ranges  are  identical.   This  is
              known  as  block-based  deduplication.   If a program writes into a reflinked block
              range of either file, the dirty blocks will be cloned,  written  to,  and  remapped
              ("copy on write") in the affected file, leaving the other file(s) unchanged.
                 -C  Print timing statistics in a condensed format.
                 -q  Do not print timing statistics at all.

MEMORY MAPPED I/O COMMANDS
       mmap [ N | [[ -rwx ] offset length ]]
              With  no  arguments,  mmap  shows the current mappings. Specifying a single numeric
              argument N sets the current mapping. If two arguments are specified (a range speci‐
              fied  by  offset  and length), a new mapping is created spanning the range, and the
              protection mode can be given as a combination of PROT_READ (-r),  PROT_WRITE  (-w),
              and PROT_EXEC (-x).
       mm     See the mmap command.
       mremap [ -f ] [ -m ] new_length
              Changes  the  current mapping size to new_length.  Whether the mapping may be moved
              is controlled by the flags passed; MREMAP_FIXED (-f), or MREMAP_MAYMOVE (-m).
       mrm    See the mremap command.
       munmap Unmaps the current memory mapping.
       mu     See the munmap command.
       mread [ -f | -v ] [ -r ] [ offset length ]
              Accesses a segment of the current memory mapping,  optionally  dumping  it  to  the
              standard output stream (with -v or -f option) for inspection. The accesses are per‐
              formed sequentially from the start offset by default, but can also be done from the
              end  backwards  through the mapping if the -r option in specified.  The two verbose
              modes differ only in the relative offsets they display, the -f option  is  relative
              to file start, whereas -v shows offsets relative to the start of the mapping.
       mr     See the mread command.
       mwrite [ -r ] [ -S seed ] [ offset length ]
              Stores  a  byte into memory for a range within a mapping.  The default stored value
              is 'X', repeated to fill the range specified, but this can be changed using the  -S
              option.   The  memory  stores  are  performed sequentially from the start offset by
              default, but can also be done from the end backwards through the mapping if the  -r
              option in specified.
       mw     See the mwrite command.
       msync [ -i ] [ -a | -s ] [ offset length ]
              Writes  all modified copies of pages over the specified range (or entire mapping if
              no range specified) to their backing storage locations.  Also,  optionally  invali‐
              dates  (-i)  so that subsequent references to the pages will be obtained from their
              backing storage locations (instead of cached copies).  The flush can be  done  syn‐
              chronously (-s) or asynchronously (-a).
       ms     See the msync command.
       madvise [ -d | -r | -s | -w ] [ offset length ]
              Modifies  page  cache  behavior  when  operating on the current mapping.  The range
              arguments are required by some advise commands ([*] below).  With no arguments, the
              POSIX_MADV_NORMAL advice is implied (default readahead).
                 -d  the pages will not be needed (POSIX_MADV_DONTNEED[*]).
                 -r  expect  random  page references (POSIX_MADV_RANDOM), which sets readahead to
                     zero.
                 -s  expect sequential page references (POSIX_MADV_SEQUENTIAL), which doubles the
                     default readahead on the file.
                 -w  advises  the  specified  pages will be needed again (POSIX_MADV_WILLNEED[*])
                     which forces the maximum readahead.

       mincore
              Dumps a list of pages or ranges of pages that are currently in core, for  the  cur‐
              rent memory mapping.

OTHER COMMANDS
       print  Display  a  list of all open files and memory mapped regions.  The current file and
              current mapping are distinguishable from any others.

       p      See the print command.

       quit   Exit xfs_io.

       q      See the quit command.

       lsattr [ -R | -D | -a | -v ]
              List extended inode flags on the currently open file. If the -R  option  is  speci‐
              fied,  a  recursive  descent  is performed for all directory entries below the cur‐
              rently open file (-D can be used to restrict the output to directories only).  This
              is  a  depth  first descent, it does not follow symlinks and it also does not cross
              mount points.

       chattr [ -R | -D ] [ +/-riasAdtPneEfS ]
              Change extended inode flags on the currently open file. The -R and -D options  have
              the  same  meaning  as  above.  The mapping between each letter and the inode flags
              (refer to xfsctl(3) for the full list) is available via the help command.

       freeze Suspend all write I/O requests to the filesystem of the current file.  Only  avail‐
              able in expert mode and requires privileges.

       thaw   Undo  the  effects of a filesystem freeze operation.  Only available in expert mode
              and requires privileges.

       flink path
              Link the currently open file descriptor into the filesystem namespace.

       inject [ tag ]
              Inject errors into a filesystem to observe filesystem behavior at  specific  points
              under adverse conditions. Without the tag argument, displays the list of error tags
              available.  Only available in expert mode and requires privileges.

       resblks [ blocks ]
              Get and/or set count of reserved filesystem blocks using the XFS_IOC_GET_RESBLKS or
              XFS_IOC_SET_RESBLKS system calls.  Note -- this can be useful for exercising out of
              space behavior.  Only available in expert mode and requires privileges.

       shutdown [ -f ]
              Force the filesystem to shutdown (with or without flushing the log).   Only  avail‐
              able in expert mode and requires privileges.

       stat [ -v ]
              Selected  statistics  from stat(2) and the XFS_IOC_GETXATTR system call on the cur‐
              rent file. If the -v option is specified, the atime (last access), mtime (last mod‐
              ify), and ctime (last change) timestamps are also displayed.

       statfs Selected  statistics  from  statfs(2) and the XFS_IOC_FSGEOMETRY system call on the
              filesystem where the current file resides.

       chproj [ -R|-D ]
              Modifies the project identifier associated with the current  path.  The  -R  option
              will  recursively  descend  if  the current path is a directory. The -D option will
              also recursively descend, only setting modifying projects on  subdirectories.   See
              the xfs_quota(8) manual page for more information about project identifiers.

       lsproj [ -R|-D ]
              Displays  the  project  identifier  associated with the current path. The -R and -D
              options behave as described above, in chproj.

       parent [ -cpv ]
              By default this command prints out the parent inode numbers, inode generation  num‐
              bers  and  basenames  of  all the hardlinks which point to the inode of the current
              file.
                 -p  the output is similar to the default  output  except  pathnames  up  to  the
                     mount-point are printed out instead of the component name.
                 -c  the file's filesystem will check all the parent attributes for consistency.
                 -v  verbose output will be printed.
              [NOTE: Not currently operational on Linux.]

SEE ALSO
       mkfs.xfs(8),   xfsctl(3),   xfs_bmap(8),   xfs_db(8),   xfs(5),   fdatasync(2),  fstat(2),
       fstatfs(2), fsync(2), ftruncate(2), mmap(2), msync(2), open(2), pread(2), pwrite(2), read‐
       dir(3).

                                                                                        xfs_io(8)

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