How
pivot_root won against a stupid RAID controller
This post is brought to you by a very stupid 3ware 9650SE RAID
controller, which doesn't understand the concept of growing a RAID
array after all disks have been replaced by bigger ones. Or, well, it
can, but the procedure, involving sending array dumps to the technical
support, then receiving a program to run under DOS (!), doesn't
inspire me with confidence. Furthermore, this stupid RAID card doesn't
allow easy reordering (if it's possible, and I just missed it, please
let me know) of the RAID arrays at runtime, only from the BIOS screen,
and I didn't have access to that (only poor man's serial console under
Linux).
So, after buying new
harddrives, and replacing the
original ones in the RAID1 array with double the capacity, I realised
I have to do a manual conversion. Basically, go into single-user mode,
remount all read-only, split the RAID1 array into its (identical)
components, change root directory to the second disk, re-partition the
first disk, copy the data from the 2nd to the 1st disk, then re-add
the 2nd disk to the 1st one (repartitioned) to re-establish the RAID1.
All this, on a headless (no keyboard, no VGA) machine, just with a
serial console. Of course, if this is just your local machine, you can
easily reboot from an external media, and do all this easily from a
full user-space. In any case, I'm writing this down, as there seem
to be no easily findable guides on how to do the resize on a 3ware
with its restrictions.
Procedure
Disclaimer: you might lose data via this, there are no
guarantees. Have up-to-date backups.
First, make sure you have power control (you can power-cycle the box
if needed) and the serial console works.
Also, make absolutely sure that the RAID array is fully
consistent, and that you don't have any bad sectors on the drives, as
you will lose redundancy during the operation.
If
/usr is not on your root file-system, then you need to copy
/usr/sbin/chroot to somewhere on it. Also, if you have tools for the
array that are not on your root file-system, you should copy them
there now. In my case, that was
tw_cli.
First reboot
Reboot into
init=/bin/sh.
Note: I've tried to simply go into single-user mode, or to reboot with
emergency, but this doesn't work, because in both modes, beside the
init process with PID 1 and your shell, there's another
init
process (the parent of the shell), and I didn't know how to tell it to
re-execute itself. To the main
init process it's easy, you just run
telinit u, but that child keeps the old root directory mounted. If
it's possible to re-exec that child too, then this step can be
skipped please let me know how!
Changing the root mount
Make sure everything is mounted read-only (should be), then split the
raid array into its component drives, using whatever tool the card
needs. For me, it was:
# tw_cli /c0/u0 migrate type=single
The second drive now should be visible e.g. as
/dev/sdc, so mount it
somewhere, and
pivot_root to it:
# mount -o ro /dev/sdcX /mnt
# cd /mnt/
# pivot_root . mnt/
# exec chroot .
At this point, the new root (on some partition on
/dev/sdc) is mount
at the root, and the
exec call replaced the current shell with
another one that has the right root directory.
So nothing should keep the old root directory (at
/dev/sdaX) in use,
and
umount /mnt (or
umount /dev/sdaX) should succeed now.
Recreate the first raid array
Now, since it's no longer in use, you can delete and recreate the
first raid array.
Once it's available, you have two choices:
- either do a bit-for-bit copy, using dd, from
/dev/sdc to
/dev/sda, then run sfdisk -R /dev/sda to re-read the changed
partition table on the target drive
- or repartition
/dev/sda if you also want to change the partition
layout
I did the latter, since I wanted to use the new alignment standards
(the initial installation was still using sector 63 for the boot
partition, etc.) as a future preparation for either SSD or 4K-sector
drives. So I used:
fdisk -cu /dev/sda, and created partitions accordingly- then re-did my physical volume for LVM, but with
--dataalignment
1024k, to have the same megabyte alignment (yes, I went a little
overboard)
In any case, either copy the entire disk, or each partition in turn,
or possibly
pvmove from the old to the new disk, etc.
Switch back the root mount
At this point,
/dev/sdc is no longer used, and you can again change
the root directory. This is similar to the first
pivot_root, but now
using
/dev/sda as a target. All the instructions are the same.
Convert back to RAID1
Now, since (in our example)
/dev/sdc is no longer in-use, you can
delete that drive and rejoin it to the first drive, recreating the
RAID1 array. In my case:
# tw_cli
/> /c0/u2 delete
blah blah [y/n] y
/> /c0/u0 migrate type=raid1 disk=X
At this point, the machine is again redundant (or will be once the
resync finishes), but it still needs one more step or it won't boot
correctly.
Reinstall the boot-loader
Now, for reinstall the boot loader, you'll probably need to mount
/boot (and mount it read-write), and do whatever you need. In my
case, I re-ran
lilo, but
grub-install /dev/sda should also work.
Final reboot
And now, you only need to reboot into the normal, resized
system. Since you can't easily use
shutdown when booted with
/bin/sh as init, just use
/proc/sysrq-trigger to
sync/unmount/reboot.
Thoughts
While I use a hardware RAID controller for the battery backup it
offers, I have never thought it cannot do such a simple operation
(compare with
mdadm --grow /dev/mdX --size=max).
Second, I knew about
pivot_root but have not used it before. It's a
very very nice thing, and the only downside is that you can't really
use it with more than a few processes, since it's hard/impossible to
change a random process' root directory. But anyway, it works, and
it's damn handy for doing things to the root file-system or in general
to the root drive (e.g. just repartitioning it) when you can't boot
from another media (e.g. remote machine).
The Apple universe is happy to live with whatever Steve Jobs allows to get in. Numerous examples going back at least 20 years are available; most recent Apple's law action against a manufacturer offering compatible batteries and now an external harddisk for iPods.
Microsoft is obviously the traditional enemy for many (personally, I think there's not much difference between MS, Apple and Google anymore.) So no surprise that MS Exchange plays a role in the story about a remote wipe function of many smartphones. Just being connected to a MS Exchange server allows the administrator of that server to remotely factory-reset the smartphone. I'm not sure if there's a complete list of vulnerable smartphones, but at least iOS, webOS and Android based phones are affected. Personally, I'd say this is a serious security issue. But of course, according to the manufacturers, it is a function for the convenience of network adminstrators so they can wipe stolen phones remotely.
Update: Nico: If I'm somebody who is really after your data, I've got your smartphone and I'm clever enough not to connect it to the net before I got the data out. So you're only catching the Oh look what I accidentally found case, which I think is really just giving you a false sense of security.
Anonymous: Google is the company with the Do Not Be Evil company motto and the very good press and marketing team touting everywhere how much they do for the good of everybody. Except when it cuts into their earnings. Like really cooperating with the Linux kernel folks. Like living up to what they announced they'd do in China. It's also the company covertly collecting WLAN data, and only admitting to exactly as little as they can get away with when it comes into the open. And, in the end, simple greed will do the rest: it's a powerful big company with plenty of very well paid career positions, and in my experience this company tends to attract people who will use this power in any way they can to increase their income. At this level of business, a company motto like the one of Google is just a few meaningless words. The real company motto is Earn Money. In Whatever Way. Other examples are told by anybody who needed to interact with their so called customer support, either because they got their free account locked or because they had a specific request as a paying customer placing ads on Google (and I'm talking about a company with at least several CHF 10k per year in ads, not just a small nobody.)
I'm a keen amateur photographer and have been since I was at school. Of course back then it involved smelly chemicals, strange lights and dark rooms. The expense and hassle of film eventually did it in for me and in 2000 I bought my first digital camera. After a series of increasingly sophisticated devices, back in 2007 I bought a Nikon D80 and soon thereafter I discovered that you can do things with raw camera files that have some analogies to the darkroom processing of my youth.
For most of the time since then I've used UFraw for processing my raw images, combined with increasingly sophisticated batch files to harass it into shape. It has increasingly frustrated me that UFraw doesn't do several things that are essential to processing most files, since once the image leaves that programming it usually ends up in an 8-bpp processing path. It seems to me that the saving the processed image into an 8bpp format like jpeg is the last step before leaving the image alone.
Of course this can't always be the case since sometimes a judicious use of the 'Resynthesizer' plugin can make some unsightly elements just disappear, or one needs to carefully apply some censorship to the 14 year old in the background so that the 7 year-old's parents can put the photo on the mantelpiece without worrying about what Granny will say about how much better children's manners were in her day.
I'm hoping too, that when I have grandchildren I'll be able to tell them that 'in my day we only had 8 bits per pixel, and we were lucky', but The Gimp isn't there yet, no matter how much promise Gegl seems to offer.
The thing that has particularly annoyed me is sharpening. UFraw doesn't, and as a result my workflow has either involved applying some blanket sharpening, much like the camera does, or moving the image into a second tool just to apply some sharpening.
This week has been particularly demanding, as the school asked me to 'take some photographs of the production'. So of course that's a thousand-odd photos that I want to do a cull down to a hundred or so, and then I want to quickly do justice to the good ones so I can move on to other stuff.
Well this time my frustration with UFraw hit that ceiling that got me to try something else. I've done this in the past, and found myself going full circle and ending up right back at UFraw with a few extra lines added to my script, but this time I tried 
One of the things that I love about our 
In his own words:-
I'm a fan of LC_MESSAGES=de_DE and localized web pages -- almost.
Unfortunately, the wording of many translations in Debian often drives me nuts.
This applies mostly to web pages and package descriptions. Apologies to all
hard-working translators -- the percentage of good translations does not
outweigh the "wtf" cases for me. Still, I didn't want to switch to English for
all the web.
Rhonda pointed me to a Firefox ^W Iceweasel plugin:
After a few hours of hacking, I came up with 
[Nothing related to Debian here, move on if you don't care about my recurring obsession with the end of the world, 
At some point in the past my bookmarks broke in such a way that I wasn't able anymore to alter in any way the bookmarks, deletions, additions, reorganisation, nothing worked.
Peter Cox on model complexity
(update: yesterday's version was using 
