Using encrypted disks

[Anne Wilson]

On Thursday 10 April 2008 08:07:18 am Andrew Farris wrote:
> I do not have to enter my LUKS passphrase more than once for installations
> with one filesystem.  The default partitioning scheme, one LVM with root
> filesystem and swap combined, and one separate /boot, only asks for my
> passphrase once. Forgive the doubt but I'd like to see how your filesystems
> are configured if you're being asked for the the passphrase twice.
>
> I'm asked for it when / is mounted readonly, then it is not asked for when
> root is remounted and it is not asked for when udev starts.
>
> On the other hand, when I have a separate partition for root and for /home,
> both encrypted separately, I'm asked for the passphrase once at readonly
> root mount, then again when udev starts (when /home gets mounted).

df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                     228486436   2424584 226061852   2% /
/dev/sda1               194442     20120    164283  11% /boot
tmpfs                  1037608         0   1037608   0% /dev/shm

I definitely prefer a separate home, but I've not used LVM before, and I can't 
recall what happened when I tried to do that.

Here's what I got from fdisk -l:

Disk /dev/sda: 120.0 GB, 120034123776 bytes
255 heads, 63 sectors/track, 14593 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x0001232c

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          25      200781   83  Linux
/dev/sda2              26       14593   117017460   8e  Linux LVM

Disk /dev/sdb: 120.0 GB, 120034123776 bytes
255 heads, 63 sectors/track, 14593 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x837b837b

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1       14593   117218241   8e  Linux LVM

Disk /dev/dm-0: 120.0 GB, 120030950400 bytes
255 heads, 63 sectors/track, 14592 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Disk /dev/dm-0 doesn't contain a valid partition table

Disk /dev/dm-1: 119.8 GB, 119825350656 bytes
255 heads, 63 sectors/track, 14567 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Disk /dev/dm-1 doesn't contain a valid partition table

Disk /dev/dm-2: 237.6 GB, 237699596288 bytes
255 heads, 63 sectors/track, 28898 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Disk /dev/dm-2 doesn't contain a valid partition table

Disk /dev/dm-3: 2080 MB, 2080374784 bytes
255 heads, 63 sectors/track, 252 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x30307800

Disk /dev/dm-3 doesn't contain a valid partition table

I don't really know how to read this.  Why are there 4 dm-devices?

Anne