> > Well, this is silly. If you use dd to truncate a file this way you
> > lose the trailing byte :)
dd if=/dev/zero of=x seek=newsize bs=1 count=0
I just noticed you can use count=0 to avoid the extra byte.
So, this seems to be the easiest way to truncate a file in Linux.
> I use trivial programs written in some other language to do the
> truncating. For example, python:
>
> file('xxx').truncate(10*1024*1024*1024)
>
> But do note that files created this way are sparse - and we have had
> *drastic* performance problems with files that are sparse.
I just learned about sparse files[1]! Thanks.
I guess those languages (perl/python) just make a truncate system call.
But I also guess it's not an issue truncating a root_fs because the
whole file actually exists. Usually,people create the ext3
filesystem over an existing file full of zeros created with dd.
Which also means you can create a filesystem over a
sparse file. I didn't know that.
[EMAIL PROTECTED]:~$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda6 15G 3.5G 10G 26% /
[EMAIL PROTECTED]:~$ dd if=/dev/zero of=x bs=1 count=0 seek=10485760000
[EMAIL PROTECTED]:~$ ls -lha x
-rw-r--r-- 1 n n 9.8G Mar 15 16:03 x
[EMAIL PROTECTED]:~$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda6 15G 3.5G 10G 26% /
[EMAIL PROTECTED]:~$ mkfs.ext3 x
/dev/sda6 15G 3.7G 9.8G 28% /
Thanks.
Regards,
Nelson.-
[1]http://mldonkey.berlios.de/modules.php?name=Wiki&pagename=sparse%20files
--
Homepage : http://geocities.com/arhuaco
The first principle is that you must not fool yourself
and you are the easiest person to fool.
-- Richard Feynman.
-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click
_______________________________________________
User-mode-linux-user mailing list
User-mode-linux-user@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-user
