Re: e2fsck

["Oliver Elphick" <olly@lfix.co.uk>]

"Jieyao" wrote:
  >
  >I had a few question regarding e2fsck.
  >
  >Can I assume e2fsck is something like Norton Disk Doctor for Linux.

e2fsck is a file system check and repair utility for ext2 file systems.
It checks the self-consistency of the file system.  It is run periodically on
reboot, and always if the filesystem was not properly unmounted last time
(for instance, after a power cut).  It may also be run by the administrator
if he has reason to suspect the integrity of a file system.

e2fsck is one of a group of utilities that can be called as fsck; there is
one for each (repairable) type of file system.
  >
  >When I run it, it gave me 
  >/dev/hda1 is mounted.  Do you really want to continue (y/n)?  
  >What is the danger of continuing?

fsck alters the disk contents directly; these changes are liable to be
overwritten by normal disk syncing, thus causing even worse damage
than was being repaired.  fsck should never be used to alter a mounted
file system, with the exception of the root file system, which cannot
be unmounted and for which special provision is made.
  >
  >When I do a forced check on bootup (using shutdown -F) I almost always get 
  >some error, like zreo dtime and wrong information or stuff like that, and it
      > auto 
  >fixes. The problem is after that those file that are so called 'fixed' will 
      >be 
  >missing.

Part of the disk damage can be that file pointers in directories can get
destroyed, leaving the inode used but not pointed to by anything.  If the
orphaned file is empty it will be removed; if it is not empty, it will be
reconnected into the directory lost+found, which should exist at the top
level of the file system - there is one of these directories for each
file system.  Since the orphaned file's name will have been lost, it is
simply given its inode number as a name.  To recover it, identify it by its
contents and mv it to its proper location.
  >
  >What is happening? What are the causes of the errors? How can I prevent 
  >them?

You should always go through a proper shutdown procedure:

  `shutdown -h -t 0 now'

to enable your machine to close running processes and sync the disks.  If
you just turn it off, you can damage your file systems; the extent of the
damage depends on how many sectors are held in memory waiting to be
written back to disk.

If you _are_ shutting down properly, you may have a faulty hard disk; change
it quick -- it can only get worse.

-- 
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
               PGP key from public servers; key ID 32B8FAA1
                 ========================================
     "Seeing then that we have a great high priest who has
      gone into the heavens, Jesus the Son of God, let us
      hold firmly to the faith we profess. For we do not
      have a high priest who is unable to sympathize with
      our weaknesses, but we have one who was tempted in
      every way, just as we are-yet was without sin."       
                             Hebrews 4:14,15 



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