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E2FSCK(8)                            System Manager's Manual                            E2FSCK(8)

NAME
       e2fsck - check a Linux ext2/ext3/ext4 file system

SYNOPSIS
       e2fsck  [ -pacnyrdfkvtDFV ] [ -b superblock ] [ -B blocksize ] [ -l|-L bad_blocks_file ] [
       -C fd ] [ -j external-journal ] [ -E extended_options ] [ -z undo_file ] device

DESCRIPTION
       e2fsck is used to check the ext2/ext3/ext4 family of file  systems.   For  ext3  and  ext4
       filesystems that use a journal, if the system has been shut down uncleanly without any er-
       rors, normally, after replaying the committed transactions  in the journal, the file  sys-
       tem  should be marked as clean.   Hence, for filesystems that use journalling, e2fsck will
       normally replay the journal and exit, unless its superblock indicates that further  check-
       ing is required.

       device is a block device (e.g., /dev/sdc1) or file containing the file system.

       Note that in general it is not safe to run e2fsck on mounted filesystems.  The only excep-
       tion is if the -n option is specified, and -c, -l, or -L options are not specified.   How-
       ever,  even  if  it  is  safe to do so, the results printed by e2fsck are not valid if the
       filesystem is mounted.   If e2fsck asks whether or not you should check a filesystem which
       is mounted, the only correct answer is ``no''.  Only experts who really know what they are
       doing should consider answering this question in any other way.

       If e2fsck is run in interactive mode (meaning that none of -y, -n, or -p  are  specified),
       the  program will ask the user to fix each problem found in the filesystem.  A response of
       'y' will fix the error; 'n' will leave the error unfixed; and 'a' will fix the problem and
       all  subsequent  problems; pressing Enter will proceed with the default response, which is
       printed before the question mark.  Pressing Control-C terminates e2fsck immediately.

OPTIONS
       -a     This option does the same thing as the -p option.  It  is  provided  for  backwards
              compatibility only; it is suggested that people use -p option whenever possible.

       -b superblock
              Instead  of using the normal superblock, use an alternative superblock specified by
              superblock.  This option is normally used when the primary superblock has been cor-
              rupted.  The location of backup superblocks is dependent on the filesystem's block-
              size, the number of blocks per group, and features such as sparse_super.

              Additional backup superblocks can be determined by using the mke2fs  program  using
              the  -n  option  to print out where the superblocks exist, supposing mke2fs is sup-
              plied with arguments that are consistent with the filesystem's layout (e.g.  block-
              size, blocks per group, sparse_super, etc.).

              If  an  alternative  superblock is specified and the filesystem is not opened read-
              only, e2fsck will make sure that the primary superblock  is  updated  appropriately
              upon completion of the filesystem check.

       -B blocksize
              Normally, e2fsck will search for the superblock at various different block sizes in
              an attempt to find the appropriate block size.  This search can be fooled  in  some
              cases.  This option forces e2fsck to only try locating the superblock at a particu-
              lar blocksize.  If the superblock is not found, e2fsck will terminate with a  fatal
              error.

       -c     This option causes e2fsck to use badblocks(8) program to do a read-only scan of the
              device in order to find any bad blocks.  If any bad  blocks  are  found,  they  are
              added  to the bad block inode to prevent them from being allocated to a file or di-
              rectory.  If this option is specified twice, then the bad block scan will  be  done
              using a non-destructive read-write test.

       -C fd  This option causes e2fsck to write completion information to the specified file de-
              scriptor so that the progress of the filesystem check can be monitored.   This  op-
              tion  is typically used by programs which are running e2fsck.  If the file descrip-
              tor number is negative, then absolute value of the file descriptor  will  be  used,
              and the progress information will be suppressed initially.  It can later be enabled
              by sending the e2fsck process a SIGUSR1 signal.  If the file  descriptor  specified
              is  0,  e2fsck will print a completion bar as it goes about its business.  This re-
              quires that e2fsck is running on a video console or terminal.

       -d     Print debugging output (useless unless you are debugging e2fsck).

       -D     Optimize directories in filesystem.  This option causes e2fsck to try  to  optimize
              all directories, either by reindexing them if the filesystem supports directory in-
              dexing,  or by sorting and compressing directories for smaller directories, or  for
              filesystems using traditional linear directories.

              Even without the -D option, e2fsck may sometimes optimize a few directories --- for
              example, if directory indexing is enabled and a directory is not indexed and  would
              benefit from being indexed, or if the index structures are corrupted and need to be
              rebuilt.  The -D option forces all directories in the filesystem to  be  optimized.
              This can sometimes make them a little smaller and slightly faster to search, but in
              practice, you should rarely need to use this option.

              The -D option will detect directory entries with duplicate names in a single direc-
              tory, which e2fsck normally does not enforce for performance reasons.

       -E extended_options
              Set e2fsck extended options.  Extended options are comma separated, and may take an
              argument using the equals ('=') sign.  The following options are supported:

                   ea_ver=extended_attribute_version
                          Set the version of the extended attribute blocks which e2fsck will  re-
                          quire while checking the filesystem.  The version number may be 1 or 2.
                          The default extended attribute version format is 2.

                   journal_only
                          Only replay the journal if required, but do  not  perform  any  further
                          checks or repairs.

                   fragcheck
                          During  pass 1, print a detailed report of any discontiguous blocks for
                          files in the filesystem.

                   discard
                          Attempt to discard free blocks and unused inode blocks after  the  full
                          filesystem  check  (discarding  blocks is useful on solid state devices
                          and sparse / thin-provisioned storage). Note that discard  is  done  in
                          pass  5 AFTER the filesystem has been fully checked and only if it does
                          not contain recognizable errors. However there  might  be  cases  where
                          e2fsck  does  not fully recognize a problem and hence in this case this
                          option may prevent you from further manual data recovery.

                   nodiscard
                          Do not attempt to discard free blocks and unused inode blocks. This op-
                          tion is exactly the opposite of discard option. This is set as default.

                   no_optimize_extents
                          Do  not  offer  to  optimize the extent tree by eliminating unnecessary
                          width or depth.  This can also be enabled in  the  options  section  of
                          /etc/e2fsck.conf.

                   optimize_extents
                          Offer  to  optimize the extent tree by eliminating unnecessary width or
                          depth.   This  is   the   default   unless   otherwise   specified   in
                          /etc/e2fsck.conf.

                   inode_count_fullmap
                          Trade  off  using  memory  for speed when checking a file system with a
                          large number of hard-linked files.  The amount of  memory  required  is
                          proportional  to  the  number  of inodes in the file system.  For large
                          file systems, this can be gigabytes of memory.  (For  example,  a  40TB
                          file  system  with 2.8 billion inodes will consume an additional 5.7 GB
                          memory if this optimization is enabled.)  This optimization can also be
                          enabled in the options section of /etc/e2fsck.conf.

                   no_inode_count_fullmap
                          Disable  the inode_count_fullmap optimization.  This is the default un-
                          less otherwise specified in /etc/e2fsck.conf.

                   readahead_kb
                          Use this many KiB of memory to pre-fetch metadata in the hopes  of  re-
                          ducing  e2fsck  runtime.   By  default,  this is set to the size of two
                          block groups' inode tables (typically 4MiB on a regular  ext4  filesys-
                          tem);  if  this  amount  is  more than 1/50th of total physical memory,
                          readahead is disabled.  Set this to zero to disable readahead entirely.

                   bmap2extent
                          Convert block-mapped files to extent-mapped files.

                   fixes_only
                          Only fix damaged metadata; do not optimize htree  directories  or  com-
                          press  extent  trees.   This  option is incompatible with the -D and -E
                          bmap2extent options.

                   unshare_blocks
                          If the filesystem has shared blocks, with the shared  blocks  read-only
                          feature enabled, then this will unshare all shared blocks and unset the
                          read-only feature bit. If there is not enough free space then the oper-
                          ation will fail.  If the filesystem does not have the read-only feature
                          bit, but has shared blocks anyway, then this option will  have  no  ef-
                          fect.  Note  when using this option, if there is no free space to clone
                          blocks, there is no prompt to delete files and  instead  the  operation
                          will fail.

                          Note  that  unshare_blocks  implies  the "-f" option to ensure that all
                          passes are run. Additionally, if "-n" is also  specified,  e2fsck  will
                          simulate trying to allocate enough space to deduplicate. If this fails,
                          the exit code will be non-zero.

       -f     Force checking even if the file system seems clean.

       -F     Flush the filesystem device's buffer caches before beginning.  Only  really  useful
              for doing e2fsck time trials.

       -j external-journal
              Set the pathname where the external-journal for this filesystem can be found.

       -k     When  combined  with  the -c option, any existing bad blocks in the bad blocks list
              are preserved, and any new bad blocks found by running badblocks(8) will  be  added
              to the existing bad blocks list.

       -l filename
              Add  the  block numbers listed in the file specified by filename to the list of bad
              blocks.  The format of this file is the same as  the  one  generated  by  the  bad-
              blocks(8)  program.   Note that the block numbers are based on the blocksize of the
              filesystem.  Hence, badblocks(8) must be given the blocksize of the  filesystem  in
              order  to obtain correct results.  As a result, it is much simpler and safer to use
              the -c option to e2fsck, since it will  assure  that  the  correct  parameters  are
              passed to the badblocks program.

       -L filename
              Set  the bad blocks list to be the list of blocks specified by filename.  (This op-
              tion is the same as the -l option, except the bad blocks list is cleared before the
              blocks listed in the file are added to the bad blocks list.)

       -n     Open  the filesystem read-only, and assume an answer of `no' to all questions.  Al-
              lows e2fsck to be used non-interactively.  This option may not be specified at  the
              same time as the -p or -y options.

       -p     Automatically  repair  ("preen") the file system.  This option will cause e2fsck to
              automatically fix any filesystem problems that can be safely  fixed  without  human
              intervention.   If e2fsck discovers a problem which may require the system adminis-
              trator to take additional corrective action, e2fsck will print a description of the
              problem  and  then  exit with the value 4 logically or'ed into the exit code.  (See
              the EXIT CODE section.)  This option is normally used by the system's boot scripts.
              It may not be specified at the same time as the -n or -y options.

       -r     This option does nothing at all; it is provided only for backwards compatibility.

       -t     Print  timing statistics for e2fsck.  If this option is used twice, additional tim-
              ing statistics are printed on a pass by pass basis.

       -v     Verbose mode.

       -V     Print version information and exit.

       -y     Assume an answer of `yes' to all questions; allows e2fsck to be  used  non-interac-
              tively.  This option may not be specified at the same time as the -n or -p options.

       -z undo_file
              Before  overwriting  a file system block, write the old contents of the block to an
              undo file.  This undo file can be used with e2undo(8) to restore the  old  contents
              of the file system should something go wrong.  If the empty string is passed as the
              undo_file argument, the undo file will  be  written  to  a  file  named  e2fsck-de-
              vice.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR environment vari-
              able.

              WARNING: The undo file cannot be used to recover from a power or system crash.

EXIT CODE
       The exit code returned by e2fsck is the sum of the following conditions:
            0    - No errors
            1    - File system errors corrected
            2    - File system errors corrected, system should
                   be rebooted
            4    - File system errors left uncorrected
            8    - Operational error
            16   - Usage or syntax error
            32   - E2fsck canceled by user request
            128  - Shared library error

SIGNALS
       The following signals have the following effect when sent to e2fsck.

       SIGUSR1
              This signal causes e2fsck to start displaying a completion bar or emitting progress
              information.  (See discussion of the -C option.)

       SIGUSR2
              This  signal causes e2fsck to stop displaying a completion bar or emitting progress
              information.

REPORTING BUGS
       Almost any piece of software will have bugs.  If you manage to  find  a  filesystem  which
       causes  e2fsck  to crash, or which e2fsck is unable to repair, please report it to the au-
       thor.

       Please include as much information as possible in your bug  report.   Ideally,  include  a
       complete  transcript  of the e2fsck run, so I can see exactly what error messages are dis-
       played.  (Make sure the messages printed by e2fsck are in English; if your system has been
       configured  so  that  e2fsck's messages have been translated into another language, please
       set the the LC_ALL environment variable to C so that the  transcript  of  e2fsck's  output
       will  be  useful  to  me.)   If you have a writable filesystem where the transcript can be
       stored, the script(1) program is a handy way to save the output of e2fsck to a file.

       It is also useful to send the output of dumpe2fs(8).  If a specific inode or inodes  seems
       to be giving e2fsck trouble, try running the debugfs(8) command and send the output of the
       stat(1u) command run on the relevant inode(s).  If the inode is a directory,  the  debugfs
       dump command will allow you to extract the contents of the directory inode, which can sent
       to me after being first run through uuencode(1).  The most useful data  you  can  send  to
       help  reproduce  the bug is a compressed raw image dump of the filesystem, generated using
       e2image(8).  See the e2image(8) man page for more details.

       Always include the full version string which e2fsck displays when it is  run,  so  I  know
       which version you are running.

ENVIRONMENT
       E2FSCK_CONFIG
              Determines the location of the configuration file (see e2fsck.conf(5)).

AUTHOR
       This version of e2fsck was written by Theodore Ts'o <tytso AT mit.edu>.

SEE ALSO
       e2fsck.conf(5), badblocks(8), dumpe2fs(8), debugfs(8), e2image(8), mke2fs(8), tune2fs(8)

E2fsprogs version 1.45.5                   January 2020                                 E2FSCK(8)

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