NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CONCEPTS | FILE I/O COMMANDS | MEMORY MAPPED I/O COMMANDS | OTHER COMMANDS | SEE ALSO | COLOPHON

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

NAME         top

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

SYNOPSIS         top

       xfs_io [ -adfimrRstxT ] [ -c cmd ] ... [ -C cmd ] ... [ -p prog ] [
       file ]
       xfs_io -V

DESCRIPTION         top

       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 obvious read/write/mmap
       interfaces for manipulating files, but also cover all of the XFS
       extensions (such as space preallocation, additional inode flags,
       etc).

OPTIONS         top

       xfs_io commands may be run interactively (the default) or as
       arguments on the command line.  Interactive mode always runs commands
       on the current open file, whilst commands run from the command line
       may be repeated on all open files rather than just the current open
       file.  In general, open file iteration will occur for commands that
       operate on file content or state. In contrast, commands that operate
       on filesystem or system-wide state will only be run on the current
       file regardless of how many files are currently open.  Multiple
       arguments may be given on the command line and they are run in the
       sequence given. The program exits one all commands have been run.

       -c cmd    Run the specified command on all currently open files.  To
                 maintain compatibility with historical usage, commands that
                 can not be run on all open files will still be run but only
                 execute once on the current open file.  Multiple -c
                 arguments may be given and may be interleaved on the
                 command line in any order with -C commands.

       -C cmd    Run the specified command only on the current open file.
                 Multiple -C arguments may be given and may be interleaved
                 on the command line in any order with -c commands.

       -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.

       -i        Start an idle thread. The purpose of this idle thread is to
                 test io from a multi threaded process. With single threaded
                 process, the file table is not shared and file structs are
                 not reference counted.  Spawning an idle thread can help
                 detecting file struct reference leaks.

       -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         top

       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 regular file I/O - read, write, sync, space
       preallocation, etc.

       The second set of commands exist for manipulating memory mapped
       regions of a file - mapping, 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         top

       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_TMPFILE).  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 written.
                 -d  causes direct I/O, rather than the usual buffered I/O,
                     to be used when reading 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 0xcdcdcdcd.
                 -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 [ -acdelpv ] [ -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 performed 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.

       cowextsize [ -R | -D ] [ value ]
              Display and/or modify the preferred copy-on-write extent size
              used when allocating space for the currently open file. If the
              -R option is specified, a recursive descent is performed 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 CoW extent size
              is set for that directory (new files created in that directory
              inherit that CoW 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
              arguments, the POSIX_FADV_NORMAL advice is implied (default
              readahead).
                 -d  the data will not be accessed again in the near future
                     (POSIX_FADV_DONTNEED[*]).
                 -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 readahead 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 FALLOC_FL_PUNCH_HOLE flag as described in the
              fallocate(2) manual page.

       funshare offset length
              Call fallocate with FALLOC_FL_UNSHARE_RANGE flag as described
              in the fallocate(2) manual page to unshare all shared blocks
              within the range.

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

       zero offset length
              Call xfsctl with XFS_IOC_ZERO_RANGE as described in the
              xfsctl(3) manual 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 FICLONERANGE 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 FIDEDUPERANGE 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.

       copy_range [ -s src_offset ] [ -d dst_offset ] [ -l length ] src_file
              On filesystems that support the copy_file_range(2) system
              call, copies data from the src_file into the open file.  If
              src_offset, dst_offset, and length are omitted the contents of
              src_file will be copied to the beginning of the open file,
              overwriting any data already there.
                 -s  Copy data from src_file beginning from src_offset.
                 -d  Copy data into the open file beginning at dst_offset.
                 -l  Copy up to length bytes of data.

       utimes atime_sec atime_nsec mtime_sec mtime_nsec
              The utimes command changes the atime and mtime of the current
              file.  sec uses UNIX timestamp notation and is the seconds
              elapsed since 1970-01-01 00:00:00 UTC.  nsec is the
              nanoseconds since the sec. This value needs to be in the range
              0-999999999 with UTIME_NOW and UTIME_OMIT being exceptions.
              Each (sec, nsec) pair constitutes a single timestamp value.

MEMORY MAPPED I/O COMMANDS         top

       mmap [ N | [[ -rwx ] [-s size ] 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 specified 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).  -s size is used to
              do a mmap(size) && munmap(size) operation at first, try to
              reserve some extendible free memory space, if size is bigger
              than length parameter. But there's not guarantee that the
              memory after length ( up to size ) will stay free.  e.g.
              "mmap -rw -s 8192 1024" will mmap 0 ~ 1024 bytes memory, but
              try to reserve 1024 ~ 8192 free space(no guarantee). This free
              space will helpful for "mremap 8192" without MREMAP_MAYMOVE
              flag.

       mm     See the mmap command.

       mremap [ -f <new_address> ] [ -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).  new_length
              specifies a page-aligned address to which the mapping must be
              moved. It can be setted to 139946004389888, 4096k or 1g etc.

       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 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.  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 invalidates (-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 synchronously (-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 current memory mapping.

OTHER COMMANDS         top

       help [ command ]
              Display a brief description of one or all 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 specified, a recursive descent is performed for
              all directory entries below the currently 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 ] [ +/-riasAdtPneEfSxC ]
              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 available 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 available in expert mode and requires privileges.

       stat [ -v|-r ]
              Selected statistics from stat(2) and the XFS_IOC_GETXATTR
              system call on the current file. If the -v option is
              specified, the atime (last access), mtime (last modify), and
              ctime (last change) timestamps are also displayed.  The -r
              option dumps raw fields from the stat structure.

       statx [ -v|-r ][ -m basic | -m all | -m <mask> ][ -FD ]
              Selected statistics from stat(2) and the XFS_IOC_GETXATTR
              system call on the current file.
                 -v  Show timestamps.
                 -r  Dump raw statx structure values.
                 -m basic
                     Set the field mask for the statx call to
                     STATX_BASIC_STATS.
                 -m all
                     Set the the field mask for the statx call to STATX_ALL
                     (default).
                 -m <mask>
                     Specify a numeric field mask for the statx call.
                 -F  Force the attributes to be synced with the server.
                 -D  Don't sync attributes with the server.

       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 numbers 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.]

       inode  [ [ -n ] number ] [ -v ]
              The inode command queries physical information about an inode.
              With no arguments, it will return 1 or 0, indicating whether
              or not any inode numbers greater than 32 bits are currently in
              use in the filesystem.  If given an inode number as an
              argument, the command will return the same inode number if it
              is in use, or 0 if not. With -n number , the next used inode
              number after this number will be returned, or zero if the
              supplied inode number is the highest one in use. With -v the
              command will also report the number of bits (32 or 64) used by
              the inode number printed in the result; if no inode number was
              specified on the command line, the maximum possible inode
              number in the system will be printed along with its size.

       set_encpolicy [ -c mode ] [ -n mode ] [ -f flags ] [ -v version ] [
       keydesc ]
              On filesystems that support encryption, assign an encryption
              policy to the current file.  keydesc is a 16-byte hex string
              which identifies the encryption key to use.  If not specified,
              a "default" key descriptor of all 0's will be used.
                 -c mode
                     contents encryption mode (e.g. AES-256-XTS)
                 -n mode
                     filenames encryption mode (e.g. AES-256-CTS)
                 -f flags
                     policy flags (numeric)
                 -v version
                     version of policy structure (numeric)

       get_encpolicy
              On filesystems that support encryption, display the encryption
              policy of the current file.

SEE ALSO         top

       mkfs.xfs(8), xfsctl(3), xfs_bmap(8), xfs_db(8), xfs(5), fdatasync(2),
       fstat(2), fstatfs(2), fsync(2), ftruncate(2), futimens(3), mmap(2),
       msync(2), open(2), pread(2), pwrite(2), readdir(3).

COLOPHON         top

       This page is part of the xfsprogs (utilities for XFS filesystems)
       project.  Information about the project can be found at 
       ⟨http://xfs.org/⟩.  If you have a bug report for this manual page, see
       ⟨http://oss.sgi.com/bugzilla/buglist.cgi?product=XFS⟩.  This page was
       obtained from the project's upstream Git repository 
       ⟨git://oss.sgi.com/xfs/cmds/xfsprogs⟩ on 2017-07-05.  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

                                                                   xfs_io(8)

Pages that refer to this page: xfs_fsr(8)