[sclug] Copy drive problem

Dickon Hood dickon-ml at fluff.org
Mon Mar 4 19:33:40 UTC 2013

On Sun, Mar 03, 2013 at 18:05:08 +0000, Neil Haughton wrote:
: On 2 March 2013 17:40, Paul Branston <apbran at rannoch.demon.co.uk> wrote:

: > Since the partitions are not the same size you would be better using
: > something like tar to do the transfer. Moving stuff using dd is very low
: > level block copying hence you have an image of the old partition with the
: > same used and free space and 'lost' a load of space.

: > > The command I used was

: > > dd iflag=nofollow if=/dev/sdb2 of=/dev/sdc2

: > > I used the iflag argument because I didn't want symlinks to my external
: > > drive to be followed. What is occupying all the extra space?

: It puzzled me too, but *man dd* has 'IFLAG=nofollow' clearly documented
: (albeit without much explanation), so I can only assume it does what it
: says on the box: "do not follow symlinks". *info coreutils* gives the same
: concise explanation. Helpful.

Well, yes, actually.  It means that if you pass the path to a symlink as
if= or of=, it won't follow that symlink to the target, and possibly
trample all over it.  I'm not sure why it exists, but I think the
behaviour is fairly obvious.

That said, it is an odd flag to have.  /dev/disk/by-*/* are all symlinks,
for example, and it's quite handy to be able to pass those as device nodes
to use, as they're consistent across reboots.  ZFS-on-Linux recommends
using by-id/* for this reason.

Dickon Hood
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