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Old 09-12-2007, 03:26 PM   #1
PatrickNew
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Test if two files are on the same file-system


Is there any command to test if two files reside on the same file system? I would ideally like the test to dereference sylinks, so knowing they are in the same directory may not be enough.

I see that when I 'stat' a file, I am given a device identifier, but what if two files are on the same device (hard disk) but different partitions and thus different file-systems? Or do different partitions have different "device" numbers?
 
Old 09-12-2007, 03:59 PM   #2
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You may be able to find a utility for this on Source Forge or Fresh Meat.

http://sourceforge.net

http://freshmeat.net
 
Old 09-12-2007, 06:30 PM   #3
PatrickNew
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I checked already :-( I was hoping the answer would lie in the options of a familiar command.
 
Old 09-12-2007, 06:41 PM   #4
stress_junkie
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You see these things for Windows all the time. I had expected someone to create one for Linux by now.

Well, you could write a bash script to do this. If I wanted this I would write a bash script that would generate an MD5 sum for each file on the system. The sum and the name of its file would be put into a text file. When all of the files have been summed I would sort that file based on the sum, which would be the first element in each line. Then look for duplicates. Thinking about this reminded me of my college days.
 
Old 09-12-2007, 07:45 PM   #5
PatrickNew
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I'm not sure I've been clear about what I'm trying to solve. I want to test if two files reside on the same filesystem. I shouldn't need to checksum my entire hard drive to see if a file is on the flash drive or CD.
 
Old 09-12-2007, 08:07 PM   #6
stress_junkie
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Ooops. I thought you wanted to find duplicate files. Don't ask why. I don't know. All right then.

You can use the stat command as you mentioned in your original post. The following example shows a stat for /etc/passwd and for ~/.bashrc. These files on on different partitions of the same disk.
Code:
stat  .bashrc
  File: `.bashrc'
  Size: 101             Blocks: 2          IO Block: 4096   regular file
Device: fc00h/64512d    Inode: 4712796     Links: 1
Access: (0600/-rw-------)  Uid: ( 1001/  melvin)   Gid: ( 1001/  melvin)
Access: 2007-09-12 14:55:35.000000000 -0400
Modify: 2007-05-27 17:48:36.000000000 -0400
Change: 2007-06-10 11:17:01.000000000 -0400

stat  /etc/passwd
  File: `/etc/passwd'
  Size: 1793            Blocks: 8          IO Block: 4096   regular file
Device: 303h/771d       Inode: 422733      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2007-09-12 21:08:42.000000000 -0400
Modify: 2007-08-23 20:27:32.000000000 -0400
Change: 2007-08-23 20:27:32.000000000 -0400
You can see that the device identifier is different for each file. The same thing is true for soft links on different partitions.

Hard links have got to reside on the same partition/file system. Hard links are exactly the same as all other hard links pointing to the same file so they do not need to be dereferenced. The inode number will be the same in all hard links pointing to the same file.

Last edited by stress_junkie; 09-12-2007 at 08:23 PM.
 
Old 09-12-2007, 08:25 PM   #7
syg00
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"stat -t" should work - that device number (field 7) is a combined major/minor by the looks of it. 0xMMmm - where the leading zero gets dropped. Same device (hard disk) will have same major number - each partition will have a different minor number.
Simple check for equality should suffice.
 
Old 09-12-2007, 10:24 PM   #8
PatrickNew
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Great! Thanks.
 
  


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