Directory csum / cksum Post: 302769140

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Operating Systems AIX Directory csum / cksum Post 302769140 by MichaelFelt on Monday 11th of February 2013 10:08:24 AM

02-11-2013

Registered User

The reason it does not work on directories is because a very vital part of a directory entry is the first two bytes which is the inode number of an entry.

The first two entries of a directory are named . and ..
So, if either inode numbers are different csum and/or cksum will report generally report different values.

Code:

od -dc /some/directory

read: octalDump -decimalCharacter /some/directory
This will output two lines for each entry in the directory /some/directory
The first line: first number is the inode number; second line (ignore first two values (are inode number in character notation) - remaining bytes are the file/directory name)
Example:

Code:

michael@x054:[/]ls -lid /x /y
17424 drwxr-xr-x 2 pconsole pconsole 256 May 15  2012 /x
20576 drwxr-x--- 2 root     system   256 Feb 11 16:00 /y
michael@x054:[/]od -dc /x    
0000000   17424   11776       0       0       0       0       0       0
          D 020   .  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000020       2   11822       0       0       0       0       0       0
         \0 002   .   .  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000040
michael@x054:[/]od -dc /y    
0000000   20576   11776       0       0       0       0       0       0
          P   `   .  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000020       2   11822       0       0       0       0       0       0
         \0 002   .   .  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000040

Hope this helps/explains WHY cksum/csum does not work on directories.

MichaelFelt

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LEARN ABOUT LINUX

dir_ufs

dir_ufs(4)                                                         File Formats                                                         dir_ufs(4)

NAME

       dir_ufs, dir - format of ufs directories

SYNOPSIS

       #include <sys/param.h>

       #include <sys/types.h>

       #include <sys/fs/ufs_fsdir.h>

DESCRIPTION

       A  directory  consists of some number of blocks of DIRBLKSIZ bytes, where  DIRBLKSIZ is chosen such that it can be transferred to disk in a
       single atomic operation, for example, 512 bytes on most machines.

       Each  DIRBLKSIZ-byte block contains some number of directory entry structures, which are of variable length.  Each directory  entry  has  a
       struct  direct at the front of it, containing its inode number, the length of the entry, and the length of the name contained in the entry.
       These entries are followed by the name padded to a 4 byte boundary with null bytes.  All names are guaranteed null-terminated. The  maximum
       length of a name in a directory is  MAXNAMLEN.

       #define DIRBLKSIZ                        DEV_BSIZE
       #define MAXNAMLEN                        256
       struct direct {
               ulong_t  d_ino;                  /* inode number of entry */
               ushort_t d_reclen;               /* length of this record */
               ushort_t d_namlen;               /* length of string in d_name */
               char     d_name[MAXNAMLEN + 1];  /* maximum name length */
       };

ATTRIBUTES

       See attributes(5) for a description of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Interface Stability          |Unstable                     |
       +-----------------------------+-----------------------------+

SEE ALSO

       attributes(5), ufs(7FS)

SunOS 5.10                                                          16 Apr 2003                                                         dir_ufs(4)