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LiveDVD persistence mode: suitable FS / setting aufs-rw size
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as.gentoo
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PostPosted: Mon Feb 19, 2018 3:50 pm    Post subject: LiveDVD persistence mode: suitable FS / setting aufs-rw size Reply with quote

Hello,


I tried to use ext4 (with logging turned on) for aufs-rw on a partition on an usb stick. I do this to have persistence when I use the gentoo-liveDVD-2016 … BTW: will there be a recent version soon? So I followed this https://wiki.gentoo.org/wiki/LiveDVD-Persistence-Mode with some minor (?) adaptation.

Now, it worked in general. However, after every action - like starting software or clicking a button in an app - parts of Xorg were frosen for app. 2-15 seconds. Only "partly" because the mouse pointer changed depending on the place I moved it - e.g. in a textarea or on a button. I am not completely sure but I think that it was possible to switch to other apps and work there (unless button clicket etc).

There were entries in dmesg (by ext4 I think) which said that some part of the FS (always exactly same message) is corrupt.
Unfortunately I can not supply the exact message because I forgot to save that somewhere safe. I now did format the partition with ext2 and got no problems so far - in contrast to that the setup above made problems right from the start of Xorg, maybe earlier). Interestingly those messages did not appear while I was in the "dmesg console" (STRG-&-L-ALT-&-F12).

Code:
2. Create file system. We will assume that partition is /dev/sdc4
from https://wiki.gentoo.org/wiki/LiveDVD-Persistence-Mode
Which gives ext2 as example but does not say that anything else is not suitable.



There might be an other cause. When you do use the aufs for the first time (kernel-CMDL contains aufs=/dev/…) you are asked how large the aufs-rw should be. I think I gave 8 G because I guessed that the procedure would tell me that there is only 5,125 GB space in that partition. It did not, I thought … well, maybe it uses compression. Did aufs try to access space that did not exist?


Thanks in advance!

PS: Will aufs=/dev/disk/by-label/aufs-rw in the kernel command line work? Sometimes the bios puts sdX here, sometimes there or only the UEFI devices are shown. So it is more or less trial and error to set the right device ID.
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NeddySeagoon
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PostPosted: Mon Feb 19, 2018 8:28 pm    Post subject: Reply with quote

as.gentoo,

There is a newer DVD that was made for FOSDEM 2017.
However, it uses a hardened kernel, so its not suitable for installing.
Hardened limits the functionality inside a chroot and some the the prohibited things are required.

aufs=/dev/disk/by-label/aufs-rw in the kernel command line work will fail as all the /dev/disk/by* entries are symbolic links created by udev.
As far as I know, udev is not in the initrd.

aufs=PARTUUID=<your aufs PARTUUID> may work, sice the kernel understands PARTUUID,
/sbin/blkid will tell your PARTUUIDs.
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NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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as.gentoo
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PostPosted: Mon Feb 19, 2018 10:08 pm    Post subject: Reply with quote

NeddySeagoon,

regarding the /dev/disk/by-* not being available in the kernel command line:
It's a pitty… I'll make a note for the PARTUUID on paper.

I didn't find a way to use grub for getting the device/partition information. I'd know that (hd1,3) would be sdb4 - there is no other drive w/ four partitions…
However parted says that something is wrong with the device, ignoring leads to wrong information, namely only 3 partitions (type: Apple,EFI,EFI) with wrong (too low) sizes, and a
Code:
Warning: The driver descriptor says the physical block size is 2048 bytes, but Linux says it is 512 bytes.
/sbin/fdisk works quite right except for the fact that the first partition contains the liveDVD (iso9660), instead of shown type "Empty". I think that grub has the same problem like parted.
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NeddySeagoon
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PostPosted: Mon Feb 19, 2018 11:00 pm    Post subject: Reply with quote

as.gentoo,

grub uses the BIOS to detect hard drives.
(hd1,3) is the 4th partition on the second HDD found by the BIOS,

The kernel names HDD in PCI bus:Device order. The two are not always the same.
So (hd1,3) may not be sdb4.

CDROMs have a block size of 2048 bytes and I guess that's in the iso9660 filesystem there.
The USB stick probably has 512b sectors.
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NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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