----- Original Message -----
From: "James Polley" <s...@zhasper.com>
To: "R.G.Salisbury" <rgsalisb...@exemail.com.au>
Cc: <slug@slug.org.au>
Sent: Tuesday, December 16, 2008 4:35 PM
Subject: Re: [SLUG] Just sharing a gotcha with "rsync" that caused me big
trouble ...extra
There is nothing more worthy of contempt than a man who quotes himself
- Zhasper, 2004
On Sun, Dec 14, 2008 at 11:38 PM, R.G.Salisbury
<rgsalisb...@exemail.com.au> wrote:
Just sharing a gotcha with "rsync" that caused me big trouble ...
what's nasty about rsync ? ..
.. which may cause devastating consequences.
rsync is in my opion the best thing since sliced bread... but be careful.
CLI commands -- cp, rcp, scp, rsync, all have similarites
BUT there are some nasty gotcha's when switching from one to another.
You probably noticed some oddities , but had worked around it. (with the
help of an error message)
Without an error message you may had come to grief.
Consider ..............
Scenario:
For whatever reason -- you want to restore the /etc directory from a
local backup.
Lets just use a simple example..
"cp" should handle this.
"rsync" should also should handle this.
But "cp" is your friend if you make an error ... "rsync" is not.
OK .... There is NO source or destinantion directory "ets" but you
make a
typo "ets" instead of "etc"
"cp" will give you an error message whereas "rsync" will do what is
not
intended and you will be *unaware*
So the following commands
[r...@localhost ~]# cp -a /backup/etc/* /ets
[r...@localhost ~]# rsync -a /backup/etc/* /ets
"cp" will error out telling you that the target is not a directory
if you use cp -ar /backup/etc /etc, cp, won't give you a warning.
Thanks for reinforcing my point James
cp -ar /backup/etc /etc
will produce /etc/etc
& the data is in the wrong place ---- DISASTER again!
whereas
"rsync will SILENTLY create the dir (ets) and populate it.
so add a "-v" and you'll see some output telling you "created directory
ets".
This is not unusual. Most unix commands only bother you when there's a
problem, and there was no problem here.
Of course, you're going to ignore that output anyway, aren't you...
So if you didn't check the result .... disaster beckons.
So check it.
Note that the creation of directories occur without a trailing slash on
the source.
But in that instance directory created is the name of the source
directory.
Note that blindly using *any* command, without paying attention,
without understanding what you're doing, can lead to disaster. This is
a PEBKAC, not a fault of the tool.
I have found some other gotchas ...... But do be aware of this (nasty)
feature.
Won't go into detail .... but some are .........
No, please do!
Like the deal with the trailing slash ..... which can cause issues ---
(often put there by bashs tab completion).
I like putting a "*" after a trailing slash as i find it more intuitive.
Also ........ creating a new dir once -- but not twice..
Blah..Blah
Cheers
Roger
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