[Mailinglist] pausing & resuming Wget for downloading ISOs

[Sunjith P S]

Hello Zaheer,

You can pause wget with ctrl+c and resume later with -c option. I have used this method successfully. But I have a few suggestions for you. Most distro ISOs will have md5 and/or sha checksum available on their sites. Download it and verify the checksum to make sure your download was successful and without errors after the ISO is completely downloaded. You can verify md5 sum as follows:
--------------------
md5sum -c md5sum_file
--------------------
[assuming the md5sum_file and iso_file are in the same dir]
If successful, it would display like:
=================
$ md5sum -c test.iso.md5
test.iso: OK
=================
Similarly for sha1sum:
=================
$ sha1sum -c test.iso.sha1
test.iso: OK
=================
If the ISO tested ok, you know for sure that the copy you have is identical to the one on the server. If they provide only the md5sum or sha1sum as text string instead of file on their site, just do "md5sum iso_file" or "sha1sum iso_file" and verify that the output matches the string provided on the site.
Even if checksum fails, don't panic. In most cases you won't have to redo the entire download, thanks to rsync. Most distros will have rsync servers as well. Locate one such server and rsync the file. It will only download the difference between the file on the server and the one on your machine. After rsync, do check the checksum again before burning. Example of rsync (see man pages or help for options):
=================
rsync -av --progress --stats --compress \ rsync://ftp.fi.muni.cz/pub/linux/fedora/linux/releases/7/Fedora/i386/iso/F-7-i386-DVD.iso\  F-7-i386-DVD.iso
=================
You can pause rsync with ctrl+c and resume later (no additional option for resume since it is only transfering the difference between files). But rsync is not recommended for whole download since it is a little slower for multi-session download as it has to compute the difference each time. So it is recommended for fixing corrupt files.
I would also like to recommend prozilla download accelerator in place of wget for downloading big files. It's much faster and rarely corrupts files. A download can be resumed with "-r" option. If resume is not specified it asks if you would like to overwrite or resume.

Regards,
Sunjith


On Monday 01 October 2007, Zaheer Mohamed Kozhakkaniyil wrote:
> Hello All,
>
> I am trying to download some ISOs using Wget (version 1.10.x)... I
> downloaded around 3 - 4 times, the same distro ISO (& a different
> distro) from different sites. And after downloding, burnt it (tried
> both Nautilus CD Burner & Brasero alternatively in OpenSuse 10.1 &
> Dreamlinux 2.2 respectively). The system does detect the CD and starts
> to boot from it ... but halts in the loading of the kernel /
> initializing during booting.
>
> Now, the problem could (or would) be, because I am stopping Wget, by
> Ctrl-C, when I leave every morning for office (I usually unplug the
> monitor and leave the system ON overnight for downloading) and resume
> it after I reach back home. But sadly, none of these ISO downloads have
> returned me a successful result. I also tried Ctrl-Z for stopping Wget
> (which 'seems' to be the right way to pause Wget), but even that is
> giving the same result.
>
> So... could somebody tell me the correct way to pause Wget when
> downloading big ISOs? My case is, I would have to pause the download in
> between and then resume later. Or is Wget not suitable for this sort of
> activity? I've searched & read some help / info / manuals on Wget, but
> none of them seems to give a specific reply to this issue. Even now, I
> am parallely trying to get more info on Wget.
>
> The syntax which I used is given below:
>
> wget -c http://linorg.usp.br/iso/dreamlinux/DL_2.2_070701MMGL_en.iso -O
> /mnt/hda8/Distros/DL22GL.iso
>
>
> Zaheer M K
> GNU/Linux user #351122
> Registered at http://counter.li.org

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