Knowing when a different program modifies a file Post: 302797543

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Top Forums UNIX for Dummies Questions & Answers Knowing when a different program modifies a file Post 302797543 by hanson44 on Monday 22nd of April 2013 06:54:40 PM

04-22-2013

Registered User

Quote:

The OP stated having to restart to resume logging

I can't seen the OP's machine to know what really happened. If restart was really needed, then I agree. On my test, restart was not needed. Anyway, based on our tests (see below), it all makes sense.

----------------------------

Code:

Your test:
$ echo foo > file
$ cat file
foo
$ ls -i file
472445 file
$ # vim 7.0 opens file in a different terminal, showing just one line, "foo"
$ echo bar >> file
$ cat file
foo
bar
$ ls -i file
472445 file
$ # vim :wq in the other  (after it warns that the file has changed)
$ cat file
foo
$ ls -i file
472449 file

I just saw this previous post (above). It was at the same time I posted, so got missed. I re-ran the exact sequence of operations (below), using vim 7.3.547 and linux, as a reality check, and the inode does not change:

Code:

My re-test:
$ echo foo > file
$ cat file
foo
$ ls -i file
786454 file
$ # vim 7.3 opens file in a different terminal, showing just one line, "foo"
$ cat file
foo
$ echo bar >> file
$ cat file
foo
bar
$ ls -i file
786454 file
$ # vim :wq in the other  (after it warns that the file has changed)
$ cat file
foo
$ ls -i file
786454 file

It seems you have shown that vim can be configured to create a new file with a new inode. As you explained, it has something to do with the backup file. My vim happens not to be configured that way (I don't think I would want it configured that way). The OP could well have had their vi configured in that way, so that would explain what happened. But that wasn't the question. The previous contention was that vim had to create a new file, that the inode had to change, due to something more fundamental going on. It was the believable idea Nothing to do with vi nor syslog; it's just the way the file system works that nobody else objected to, that I decided to investigate. I just wanted to know the answer. My test shows that shows vim does not have to create a new file. Your test shows vim can be configured to create a new file.

Quote:

If by "overwritten" you mean that the editor changed the
file's contents, then you are wrong. If by "overwritten" you
mean that the editor created a completely different file,
then you are correct.

If the inode does not change, isn't it still the original file? The inode does not change in my test, as shown above. Your test shows that vim can be configured to create a new file under the test conditions, not that the new file creation is inevitable or required. I appreciate that you posted the test, and helped clarify this.

hanson44

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e2image

E2IMAGE(8)						      System Manager's Manual							E2IMAGE(8)

NAME

       e2image - Save critical ext2 filesystem data to a file

SYNOPSIS

       e2image [ -r ] device image-file

DESCRIPTION

       The  e2image  program  will  save critical filesystem data on the ext2 filesystem located on device to a file specified by image-file.  The
       image file may be examined by dumpe2fs and debugfs, by using the -i option to those programs.  This can be used by an expert  in  assisting
       the  recovery  of  catastrophically corrupted filesystems.  In the future, e2fsck will be enhanced to be able to use the image file to help
       recover a badly damaged filesystem.

       If image-file is -, then the output of e2image will be sent to standard output.

       The -r option will create a raw image file instead of a normal image file.  A raw image file differs from a normal image file in two  ways.
       First,  the  filesystem	metadata  is  placed in the proper position so that e2fsck, dumpe2fs, debugfs, etc. can be run directly on the raw
       image file.  In order to minimize the amount of disk space consumed by a raw image file, the file is created as a sparse file.  (Beware	of
       copying	or  compressing/decompressing  this  file with utilities that don't understand how to create sparse files; the file will become as
       large as the filesystem itself!)  Secondly, the raw image file also includes indirect blocks and data blocks, which the current image  file
       does not have, although this may change in the future.

       It  is  a  very	good idea to periodically (at boot time and every week or so) to create image files for all of filesystems on a system, as
       well as saving the partition layout (which can be generated using the using fdisk -l command).  Ideally the image file should be stored	on
       some  filesystem  other	that the filesystem whose data it contains, to ensure that its data is accessible in the case where the filesystem
       has been badly damaged.

       To save disk space, e2image creates the image file as a sparse file.  Hence, if the image file needs to be copied to another  location,	it
       should either be compressed first or copied using the --sparse=always option to GNU version of cp.

       The  size of an ext2 image file depends primarily on the size of the filesystems and how many inodes are in use.  For a typical 10 gigabyte
       filesystem, with 200,000 inodes in use out of 1.2 million inodes, the image file be approximately 35 megabytes;	a  4  gigabyte	filesystem
       with  15,000  inodes  in  use  out of 550,000 inodes will result in a 3 megabyte image file.  Image files tend to be quite compressible; an
       image file taking up 32 megabytes of space on disk will generally compress down to 3 or 4 megabytes.

AUTHOR

       e2image was written by Theodore Ts'o (tytso@mit.edu).

AVAILABILITY

       e2image is part of the e2fsprogs package and is available from anonymous http://e2fsprogs.sourceforge.net.

SEE ALSO

       dumpe2fs(8), debugfs(8)

E2fsprogs version 1.32						   November 2002							E2IMAGE(8)

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