NAME

       dupemap - Creates a database of file checksums and uses it to eliminate duplicates

SYNOPSIS

       dupemap [ options ] [ -d database ] operation path...

DESCRIPTION

       dupemap recursively scans each path to find checksums of file contents.  Directories are
       searched through in no particular order.  Its actions depend on whether the -d option is
       given, and on the operation parameter, which must be a comma-seperated list of scan,
       report, delete:

   Without -d
       dupemap will take action when it sees the same checksum repeated more than once, i.e. it
       simply finds duplicates recursively.  The action depends on operation:

       report Report what files are encountered more than once, printing their names to standard
              output.

       delete[,report]
              Delete files that are encountered more than once.  Print their names if report is
              also given.

              WARNING: use the report operation first to see what will be deleted.

              WARNING: You are advised to make a backup of the target first, e.g. with "cp -al"
              (for GNU cp) to create hard links recursively.

   With -d
       The database argument to -d will denote a database file (see the "DATABASE" section in
       this manual for details) to read from or write to.  In this mode, the scan operation
       should be run on one path, followed by the report or delete operation on another (not the
       same!) path.

       scan   Add the checksum of each file to database.  This operation must be run initially to
              create the database.  To start over, you must manually delete the database file(s)
              (see the "DATABASE" section).

       report Print each file name if its checksum is found in database.

       delete[,report]
              Delete each file if its checksum is found in database.  If report is also present,
              print the name of each deleted file.

              WARNING: if you run dupemap delete on the same path you just ran dupemap scan on,
              it will delete every file! The idea of these options is to scan one path and delete
              files in a second path.

              WARNING: use the report operation first to see what will be deleted.

              WARNING: You are advised to make a backup of the target first, e.g. with "cp -al"
              (for GNU cp) to create hard links recursively.

OPTIONS

       -d database
              Use database as an on-disk database to read from or write to.  See the
              "DESCRIPTION" section above about how this influences the operation of dupemap.

       -I file
              Reads input files from file in addition to those listed on the command line.  If
              file is "-", read from standard input.  Each line will be interpreted as a file
              name.

              The paths given here will NOT be scanned recursively.  Directories will be ignored
              and symlinks will be followed.

       -m minsize
              Ignore files below this size.

       -M maxsize
              Ignore files above this size.

USAGE

   General usage
       The easiest operations to understand is when the -d option is not given.  To delete all
       duplicate files in /tmp/recovered-files, do:

           $ dupemap delete /tmp/recovered-files

       Often, dupemap scan is run to produce a checksum database of all files in a directory
       tree.  Then dupemap delete is run on another directory, possibly following dupemap report.
       For example, to delete all files in /tmp/recovered-files that already exist in $HOME, do
       this:

           $ dupemap -d homedir.map scan $HOME
           $ dupemap -d homedir.map delete,report /tmp/recovered-files

   Usage with magicrescue
       The main application for dupemap is to take some pain out of performing undelete
       operations with magicrescue(1).  The reason is that magicrescue will extract every single
       file of the specified type on the block device, so undeleting files requires you to find a
       few files out of hundreds, which can take a long time if done manually.  What we want to
       do is to only extract the documents that don't exist on the file system already.

       In the following scenario, you have accidentally deleted some important Word documents in
       Windows.  If this were a real-world scenario, then by all means use The Sleuth Kit.
       However, magicrescue will work even when the directory entries were overwritten, i.e. more
       files were stored in the same folder later.

       You boot into Linux and change to a directory with lots of space.  Mount the Windows
       partition, preferably read-only (especially with NTFS), and create the directories we will
       use.

           $ mount -o ro /dev/hda1 /mnt/windows
           $ mkdir healthy_docs rescued_docs

       Extract all the healthy Word documents with magicrescue and build a database of their
       checksums.  It may seem a little redundant to send all the documents through magicrescue
       first, but the reason is that this process may modify them (e.g. stripping trailing
       garbage), and therefore their checksum will not be the same as the original documents.
       Also, it will find documents embedded inside other files, such as uncompressed zip
       archives or files with the wrong extension.

           $ find /mnt/windows -type f \
             |magicrescue -I- -r msoffice -d healthy_docs
           $ dupemap -d healthy_docs.map scan healthy_docs
           $ rm -rf healthy_docs

       Now rescue all "msoffice" documents from the block device and get rid of everything that's
       not a *.doc.

           $ magicrescue -Mo -r msoffice -d rescued_docs /dev/hda1 \
             |grep -v '\.doc$'|xargs rm -f

       Remove all the rescued documents that also appear on the file system, and remove
       duplicates.

           $ dupemap -d healthy_docs.map delete,report rescued_docs
           $ dupemap delete,report rescued_docs

       The rescued_docs folder should now contain only a few files.  This will be the undeleted
       files and some documents that were not stored in contiguous blocks (use that defragger
       ;-)).

   Usage with fsck
       In this scenario (based on a true story), you have a hard disk that's gone bad.  You have
       managed to dd about 80% of the contents into the file diskimage, and you have an old
       backup from a few months ago.  The disk is using reiserfs on Linux.

       First, use fsck to make the file system usable again.  It will find many nameless files
       and put them in lost+found.  You need to make sure there is some free space on the disk
       image, so fsck has something to work with.

           $ cp diskimage diskimage.bak
           $ dd if=/dev/zero bs=1M count=2048 >> diskimage
           $ reiserfsck --rebuild-tree diskimage
           $ mount -o loop diskimage /mnt
           $ ls /mnt/lost+found
           (tons of files)

       Our strategy will be to restore the system with the old backup as a base and merge the two
       other sets of files (/mnt/lost+found and /mnt) into the backup after eliminating
       duplicates.  Therefore we create a checksum database of the directory we have unpacked the
       backup in.

           $ dupemap -d backup.map scan ~/backup

       Next, we eliminate all the files from the rescued image that are also present in the
       backup.

           $ dupemap -d backup.map delete,report /mnt

       We also want to remove duplicates from lost+found, and we want to get rid of any files
       that are also present in the other directories in /mnt.

           $ dupemap delete,report /mnt/lost+found
           $ ls /mnt|grep -v lost+found|xargs dupemap -d mnt.map scan
           $ dupemap -d mnt.map delete,report /mnt/lost+found

       This should leave only the files in /mnt that have changed since the last backup or got
       corrupted.  Particularly, the contents of /mnt/lost+found should now be reduced enough to
       manually sort through them (or perhaps use magicsort(1)).

   Primitive intrusion detection
       You can use dupemap to see what files change on your system.  This is one of the more
       exotic uses, and it's only included for inspiration.

       First, you map the whole file system.

           $ dupemap -d old.map scan /

       Then you come back a few days/weeks later and run dupemap report.  This will give you a
       view of what has not changed.  To see what has changed, you need a list of the whole file
       system.  You can get this list along with preparing a new map easily.  Both lists need to
       be sorted to be compared.

           $ dupemap -d old.map report /|sort > unchanged_files
           $ dupemap -d current.map scan /|sort > current_files

       All that's left to do is comparing these files and preparing for next week.  This assumes
       that the dbm appends the ".db" extension to database files.

           $ diff unchanged_files current_files > changed_files
           $ mv current.map.db old.map.db

DATABASE

       The actual database file(s) written by dupecheck will have some relation to the database
       argument, but most implementations append an extension.  For example, Berkeley DB names
       the files database.db, while Solaris and GDBM creates both a database.dir and database.pag
       file.

       dupecheck depends on a database library for storing the checksums.  It currently requires
       the POSIX-standardized ndbm library, which must be present on XSI-compliant UNIXes.
       Implementations are not required to handle hash key collisions, and a failure to do that
       could make dupecheck delete too many files.  I haven't heard of such an implementation,
       though.

       The current checksum algorithm is the file's CRC32 combined with its size.  Both values
       are stored in native byte order, and because of varying type sizes the database is not
       portable across architectures, compilers and operating systems.

SEE ALSO

       magicrescue(1), weeder(1)

       This tool does the same thing weeder does, except that weeder cannot seem to handle many
       files without crashing, and it has no largefile support.

BUGS

       There is a tiny chance that two different files can have the same checksum and size.  The
       probability of this happening is around 1 to 10^14, and since dupemap is part of the Magic
       Rescue package, which deals with disaster recovery, that chance becomes an insignificant
       part of the game.  You should consider this if you apply dupemap to other applications,
       especially if they are security-related (see next paragraph).

       It is possible to craft a file to have a known CRC32.  You need to keep this in mind if
       you use dupemap on untrusted data.  A solution to this could be to implement an option for
       using MD5 checksums instead.

AUTHOR

       Jonas Jensen <jbj@knef.dk>

LATEST VERSION

       This tool is part of Magic Rescue.  You can find the latest version at
       <https://github.com/jbj/magicrescue>