Looking for a "undo" for file with holes (GNU)

Question

Linux supports sparse files aka 'file with holes'

Note following commands

alias mystat='stat -c "%n: %B*%b blocks %s bytes"'

dd if=/dev/zero bs=1024k seek=4096 count=0 of=file-with-holes

ls -l file-with-holes
-rw-r--r-- 1 root root 4294967296 Feb 25 18:33 file-with-holes

mystat file-with-holes
file-with-holes: 512*0 blocks 4294967296 bytes

cp file-with-holes other-file

mystat other-file
other-file: 512*0 blocks 4294967296 bytes

cat file-with-holes > file-without-holes

mystat file-without-holes
file-without-holes: 512*8388608 blocks 4294967296 bytes

The cat command removed all holes from the file.

Is there a way to get the holes back?

I see you deleted you answer but check out bsdtar -S - this will create sparse files on extraction (unlike GNU tar). Not really the answer for a full fs, but maybe good if restoring a backup. Also see cpio --sparse. — Graeme, Feb 25 '14 at 18:21
Thanks, there is also a -S for rsync. I already saved a nuber of hundreds gigs. — , Feb 25 '14 at 19:14

score 4 · Accepted Answer · answered Feb 25 '14 at 17:57

4

cp --sparse=always file-without-holes another-file-with-holes

Example:

$ cp --sparse=always file-without-holes another-file-with-holes
$ du --apparent-size another
16384   another-file-with-holes
$ du another-file-with-holes
0   another-file-with-holes

answered Feb 25 '14 at 17:57

Graeme

34,027

That is a GNUism. – vonbrand Feb 25 '14 at 19:28
@vonbrand, any suggestions for commands that have POSIX options for copying sparse files like this? I can't find any. – Graeme Feb 25 '14 at 19:55
@vonbrand The question assumes Linux. I don't think there's a Busybox solution. – Gilles 'SO- stop being evil' Feb 25 '14 at 23:53

Looking for a "undo" for file with holes (GNU)

1 Answers1