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>.