CPT 499C Lecture 17 EXTxFS

CPT 499C Lecture 17 EXTxFS - DEPARTMENT OF COMPUTER...

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EXTxFS Slide 1 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY CIT 499C Lecture 17: EXTxFX
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EXTxFS Slide 2 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY Learning Objectives The student will be able to: Identify EXTxFS components Explain the changes that take place on an EXTxFS drive when a file is saved Explain the changes that take place on an EXTxFS drive when a file is deleted Identify items of evidentiary value that can be recovered from a EXTxFS drive
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EXTxFS Slide 3 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY A Caveat: Linux file systems can be more “free- spirited” than DOS / Windows Linux family file systems are designed to be “extensible” Knowledgeable developers can “customize” some features”
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EXTxFS Slide 4 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY A Caveat: A detailed explanation of every possible EXTxFS variation is beyond the scope of this presentation
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EXTxFS Slide 5 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY EXTxFS Components EXT2FS & EXT3FS have discrete logical components that “manage” the file system, similar to the FAT System Area , or the NTFS Metadata Files
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EXTxFS Slide 6 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY EXTxFS Components Block Superblock Block Group Group Descriptor Table Block Bitmap Inode Table Inode Inode Bitmap Directory
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EXTxFS Slide 7 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY Blocks Analogous to a FAT or NTFS Cluster Block numbering starts at 0 Data blocks belong to a “ Block Group Block numbering does not restart with each group Size is defined in the “ Superblock Allocation tracked by the “ Block Bitmap
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EXTxFS Slide 8 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY Blocks In this example there are 4 sectors (2048 bytes) in each block. An EXTxFS block may be 2, 4, or 8 sectors (1024, 2048, or 4096 bytes) in length
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EXTxFS Slide 9 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY Superblock Analogous to a FAT boot record or NTFS $Boot file Normally offset 1K (1024 bytes) from the beginning of the file system 1K in size (not all bytes are used)
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EXTxFS Slide 10 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY Superblock Contains essential information: Block size Total number of blocks Number of blocks in each block group Offset to first block (number of reserved blocks) Total number of inodes Number of inodes in each block group
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EXTxFS Slide 11 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY Superblock Also contains information considered “nonessential” by the FS: Volume name Last write time Last mount time Path the volume was last mounted May be of significant forensic value If used
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EXTxFS Slide 12 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY 1024 bytes before the Superblock If the drive is bootable the first 1024 bytes will contain boot code; otherwise this area will be empty
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EXTxFS Slide 13 DEPARTMENT OF COMPUTER & INFORMATION TECHNOLOGY Superblock The superblock is located in the 1024 bytes following the first 1024 bytes of the logical drive
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