Mount .xzm Module with Write option

[noobTeus]

Hi,

I'm using Porteus 3

I want to add files into "/opt" of 001-core.xzm

So I extracted the core.xzm from porteus's iso & I tried with:

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mount -o loop,rw 001-core.xzm /mnt

But it mounted as read-only

So, How can I mount it with write option?


Thanks.

[Bogomips]

Suppose, copy it all somewhere, add files and then make new core.xzm. That's first thing that springs to mind.

[francois]

Right click on 001-core.xzm and use the contextual menu to extract xzm module into a directory. Modify it. Then use right click for contextual menu and build xzm module.

[brokenman]

squashfs is a read only file system. You can do something similar using aufs.

If you are impatient and just want the answer.

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mount -t aufs -o br=/mnt/sda8/writable=rw:/mnt/readonly=ro -o udba=reval none /tmp/aufs-work/

Your module is mounted in /mnt/readonly (it is read only) and you created /mnt/sda8/writable (real file system) and your target working folder is /tmp/aufs-work

Let me explain so you get a better understanding of what modules are and what a union file system does.
You will need a location out of the current aufs. For this example: /mnt/sda8/writable

## Create a directory with some files in it.

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modprobe aufs  ## Just for fun
mkdir -p /tmp/mymodule/{one,two}
touch /tmp/mymodule/file0.txt

## Make a module from it

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mksquashfs /tmp/mymodule /tmp/readonly.xzm
rm -r /tmp/mymodule

## Make a folder to mount your module as read only

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mkdir /mnt/readonly && mount -o loop /tmp/readonly.xzm /mnt/readonly

## Check that you files are in there and read only

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ls /mnt/readonly
touch /mnt/readonly/this.txt

Let's summarize. You have essentially mounted a module (squashfs read only) into the folder: /mnt/readonly

## Now create your writable folder outside of aufs (on a real file system)

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mkdir /mnt/sda8/writable

## Lastly create a folder where you merged file systems will be. You can work in here.

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mkdir /tmp/aufs-work

## Now overlay the two folders together using aufs.

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mount -t aufs -o br=/mnt/sda8/writable=rw:/mnt/readonly=ro -o udba=reval none /tmp/aufs-work/

## If you look in /tmp/aufs you will see the files from your module!

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ls /tmp/aufs-work

## And it is now writeable (kind of)

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touch /tmp/aufs-work/file2.txt
ls /tmp/aufs-work

Explanation:
mount -t aufs --> mount as a union file system
-o --> arguments that will be passed to the mount command
br= --> the branches you will create
br=/mnt/sda8/writable=rw:/mnt/readonly=ro --> mount the first path as a writable branch and the second path (your module) as a readonly branch.
udba=reval --> this means if a file is added outside of aufs it will re-evaluate
none --> no special device are connected to this
/tmp/aufs-work --> your destination

In fact what you have is two branches mounted overlaying each other.
Think of the /tmp/aufs-work as the tree trunk, and the other two folders as branches connected to the tree.
Because /mnt/readonly is exactly that (read only), any files that you create are sent to the /mnt/sda8/writable branch. If you add a file to this directory it will also appear in your tree.

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touch /mnt/sda8/writable/lookmum-nohands.txt
ls /tmp/aufs-work

Last thing to do is make a module from your additions to your module in /tmp/aufs-work.
If you are still reading then you just learnt something. Perhaps it was how a union file system works. Perhaps it was that bogomips solution is way easier.

[Bogomips]

Thanks for the tutorial. When I have a spare minute I intend to go over it in detail. Terribly complicated on first sight, but IMHO worth a detailed perusal. 8)

Afterthought: just what the doctor ordered, for mr_hero to be sinking teeth into.

[noobTeus]

First, thanks all for helps.

I shall do the extract/module create if I cant mount modules as writable at all.
Mounting the module as rw can be very helpful. So I tried it:

First mounted the module as readonly

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root@porteus:~# mount -o loop 001-core.xzm MNT1/
root@porteus:~# df -h | grep MNT1
/dev/loop12      45M   45M     0 100% /root/MNT1

Then tried the tutorial of "aufs"

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root@porteus:~# mount -t aufs -o br=/root/writable/=rw:/root/MNT1=ro -o udba=reval none /root/aufs-work/

It showed this message:

mount: wrong fs type, bad option, bad superblock on none,
missing codepage or helper program, or other error
(for several filesystems (e.g. nfs, cifs) you might
need a /sbin/mount.<type> helper program)
In some cases useful info is found in syslog - try
dmesg | tail or so

dmesg | tail showed:

[ 2640.624938] aufs test_add:263:mount[4255]: unsupported filesystem, /root/writable/ (aufs)

I tried to find "aufs" using usm with no luck:

root@porteus:~# usm -u slackware
root@porteus:~# usm -k aufs

Nothing found for: aufs

root@porteus:~# usm -k mount.aufs

Nothing found for: mount.aufs

What to do now?

[fanthom]

module is read only by design - just like an ISO file or any other archive. you will never be able to mount it read write.
you have to unpack it -> change it's content -> pack back.

[brokenman]

As fanthom says, the actual module branch will be read only. The first branch must be on a writable path OUTSIDE of the aufs. This means it can't be in /home /root or any of these. To test if it is aufs do: df -T /root/writable

br=/root/writable/ should be something like. /mnt/sda8/writable.

Much easier just to mount the module. Copy the files somewhere else. Make changes. Create another module.

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mloop /path/to/module.xzm
mkdir /tmp/newfolder
cp -a /mnt/loop/* /tmp/newfolder
## Make your changes in /tmp/newfolder
dir2xzm /tmp/newfolder /tmp/newmodule.xzm

[Bogomips]

Or do it the painless francois way. 8)

[noobTeus]

New files,folders were saved in /mnt/sda10/writable .. not in the .xzm module

Anyway I'm switching to the time-taking easy dir2xzm method.


Thanks all for helps.