NAME

       bup-damage - randomly destroy blocks of a file

SYNOPSIS

       bup damage [-n count][-s maxsize] [--percent pct][-S seed] [--equal] <filenames...>

DESCRIPTION

       Use  bup damage  to  deliberately destroy blocks in a .pack or .idx file (from .bup/objects/pack) to test
       the recovery features of bup-fsck(1) or other programs.

       THIS PROGRAM IS EXTREMELY DANGEROUS AND WILL DESTROY YOUR DATA

       bup damage is primarily useful for automated or manual tests of data recovery tools, to reassure yourself
       that the tools actually work.

OPTIONS

       -n, --num=numblocks
              the  number  of  separate blocks to damage in each file (default 10).  Note that it's possible for
              more than one damaged segment to fall in the same bup-fsck(1) recovery block,  so  you  might  not
              damage as many recovery blocks as you expect.  If this is a problem, use --equal.

       -s, --size=maxblocksize
              the maximum size, in bytes, of each damaged block (default 1 unless --percent is specified).  Note
              that because of the way bup-fsck(1) works, a multi-byte block could fall on the  boundary  between
              two  recovery  blocks,  and thus damaging two separate recovery blocks.  In small files, it's also
              possible for a damaged block to be larger than a recovery block.   If  these  issues  might  be  a
              problem, you should use the default damage size of one byte.

       --percent=maxblockpercent
              the  maximum  size,  in  percent  of the original file, of each damaged block.  If both --size and
              --percent are given, the maximum block size is the minimum of the two restrictions.  You  can  use
              this  to  ensure  that  a  given block will never damage more than one or two git-fsck(1) recovery
              blocks.

       -S, --seed=randomseed
              seed the random number generator with the given value.  If you use this option, your tests will be
              repeatable,  since the damaged block offsets, sizes, and contents will be the same every time.  By
              default, the random numbers are different every  time  (so  you  can  run  tests  in  a  loop  and
              repeatedly test with different damage each time).

       --equal
              instead of choosing random offsets for each damaged block, space the blocks equally throughout the
              file, starting at offset 0.  If you also choose a correct maximum block size, this  can  guarantee
              that any given damage block never damages more than one git-fsck(1) recovery block.  (This is also
              guaranteed if you use -s 1.)

EXAMPLE

              # make a backup in case things go horribly wrong
              cp -a ~/.bup/objects/pack ~/bup-packs.bak

              # generate recovery blocks for all packs
              bup fsck -g

              # deliberately damage the packs
              bup damage -n 10 -s 1 -S 0 ~/.bup/objects/pack/*.{pack,idx}

              # recover from the damage
              bup fsck -r

SEE ALSO

       bup-fsck(1), par2(1)

BUP

       Part of the bup(1) suite.

AUTHORS

       Avery Pennarun <apenwarr@gmail.com>.