[SOLVED]mounting rootfs folders under btrfs subvolumes

[abdus]

hi there, how is it going.
i read this thread
https://wiki.gentoo.org/wiki/Filesystem/Security
so i thought of doing similar filesystem structure but with btrfs subvolumes instead of ext4 partitions.
i succeeded in mounting almost all the folders the way i wanted(as i guess), however i'm still facing a problem which is the apps no longer find their data that they were configured on.
please someone helps me figure out a way to move the data from the old directories to the new btrfs subvolumes. any needed information will be provided once requested.
the directories that i wasn't able to mount are

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/var/cache/distfiles 

and

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/var/cache/binpkgs

please help me mount them in btrfs subvolumes correctly
thank you

[alamahant]

Have you created btrfs subvolumes for distfiles and binpkgs?
If yes in fstab you should have an entry like

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UUID=<uuid of btrfs partition>	/var/cache/distfiles	btrfs	defaults,noatime,autodefrag,subvol=distfiles	0 0
etc

Or manually maybe

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mount -t btrfs -o subvol=distfiles UUID=<uuid of btrfs partition>  /var/cache/distfiles
etc

[abdus]

yes i forgot to mention that i want to mount them in fstab.
here is how they are:
#/dev/sda4 /var btrfs nodev,compress=lzo,subvolid=348 0 3 (commented them to be able to start the apps)
/dev/sda4 /usr/local btrfs nodev,compress=lzo,subvolid=349 0 3
/dev/sda4 /srv btrfs nodev,compress=lzo,subvolid=350 0 3
/dev/sda4 /root btrfs nodev,compress=lzo,subvolid=351 0 3
/dev/sda4 /opt btrfs nodev,compress=lzo,subvolid=355 0 3
#/dev/sda4 /nix btrfs nodev,compress=lzo.subvolid=356 0 3
#/dev/sda4 /var/log btrfs nodev,compress=lzo,subvolid=357 0 3
#/dev/sda4 /var/tmp btrfs nodev,compress=lzo,subvolid=358 0 3
#/dev/sda4 /var/cache/distfiles btrfs nodev,compress=lzo,subvolid=359 0 3
#/dev/sda4 /var/cache/binpkgs btrfs nodev,compress=lzo,subvolid=360 0 3
you answered something i was wondering about which is using the partition flags with btrfs subvolumes, thank you for that.
my problem is the subvolumes are empty so the installed apps cannot find the old configurations since they are in the old directories so they crash
i searched about the case, i found that there are 2 types of copying, first by moving the files themselves, and the second is like a virtual method. it appears like @subvolume (saw it in opensuse fstab)
how can i do that.

[alamahant]

In your fstab you omitted /

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/dev/sda4   /   btrfs defaults,noatime,compress=lzo   0 0
or
/dev/sda4   /   btrfs defaults,noatime,compress=lzo,subvol=@   0 0

 

Also plz replace your "0 3"s with "0 0"
I dont even think there is a "3".

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0 --> dont fscheck
1 --> fscheck
2  --> fscheck

A tip.
Next time you want to play with btrfs use an Arch live iso.
Create a btrfs partition, mount it on /mnt, create btrfs subvolumes on /mnt bootstrap a system on /mnt then use

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genfstab -U /mnt >> /mnt/etc/fstab

It will nicely and easilly create a nice fstab for you.
You can even try it now(with caution) with your Gentoo.

[abdus]

it's an option, but i guess you need to see this https://packages.gentoo.org/packages/sys-fs/genfstab

[abdus]

Have you created btrfs subvolumes for distfiles and binpkgs?
If yes in fstab you should have an entry like

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UUID=<uuid of btrfs partition>	/var/cache/distfiles	btrfs	defaults,noatime,autodefrag,subvol=distfiles	0 0
etc

Or manually maybe

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mount -t btrfs -o subvol=distfiles UUID=<uuid of btrfs partition>  /var/cache/distfiles
etc

what is the command i need to execute before i put it in the fstab the way you did, and does it really matter?
i just followed the wiki above and executed

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sudo btrfs subvolume create /mnt/btrfs/vol1

[alamahant]

Its ok you do it the way you like.
I just mentioned that in complicated fses like btrfs the Archlinux genfstab util can simplify things a bit.
Ah ah ok perfect!
I didn't know genfstab is available in Gentoo also.
Foolish me..

sudo btrfs subvolume create /mnt/btrfs/vol1

If your btrfs partition is mounted on /mnt/btrfs then yes i think its the correct command.
More like

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btrfs subvolume create /mnt/btrfs/root
btrfs subvolume create /mnt/btrfs/var
btrfs subvolume create /mnt/btrfs/usr
etc

[abdus]

what is the difference between mounting with "subvolid" and the one you mentioned "subvol"
does subvol make the files appear on the new subvolume or they both do the same? i guess it does not though (the thread below proves that)
no problem my friend, technology is always evolving and changing.
there is this thread and it tells how to make the new subvolumes with moving the data but it is not detailed enough
https://askubuntu.com/questions/100187/ ... subvolumes
please help me with it
thank you for the efforts you are doing with me

[alamahant]

what is the difference between mounting with "subvolid" and the one you mentioned "subvol"

I think both will work for you?
You mentioned consulting a suse fstab.
What do they use?

there is this thread and it tells how to make the new subvolumes with moving the data but it is not detailed enough
https://askubuntu.com/questions/100187/ ... subvolumes
please help me with it

Have you already installed gentoo on btrfs or you are working on a new install?
Plz mount your btrfs partition on /mnt and run

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btrfs subvolume list /mnt

[abdus]

here is the fstab file of opensuse leap 15.4:

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UUID=45beb54b-0ec8-4b4e-8eab-315004f078a6  /           btrfs  defaults             0  0
UUID=45beb54b-0ec8-4b4e-8eab-315004f078a6  /var        btrfs  subvol=/@/var        0  0
UUID=45beb54b-0ec8-4b4e-8eab-315004f078a6  /usr/local  btrfs  subvol=/@/usr/local  0  0
UUID=45beb54b-0ec8-4b4e-8eab-315004f078a6  /tmp        btrfs  subvol=/@/tmp        0  0
UUID=45beb54b-0ec8-4b4e-8eab-315004f078a6  /srv        btrfs  subvol=/@/srv        0  0
UUID=45beb54b-0ec8-4b4e-8eab-315004f078a6  /root       btrfs  subvol=/@/root       0  0
UUID=45beb54b-0ec8-4b4e-8eab-315004f078a6  /opt        btrfs  subvol=/@/opt        0  0
/dev/mapper/cr_home                        /home       btrfs  defaults             0  0
UUID=33d9171e-c184-4923-919d-eb84b760a861  /boot       ext3   data=ordered         0  2 

i used subvolid from a thread online.
the fstab of opensuse is generated automatically when choosing btrfs as rootfs in opensuse

[abdus]

i'm not working on a new installation, it is an old one and i am trying to make the changes on it

[alamahant]

Ok then please mount your btrfs partition on /mnt
and run

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btrfs subvolume list /mnt

at the same time please post your full fstab.
Please use code tags.
Then we will create a proper fstab and all we wil be ok.

[abdus]

i'm sorry for my late reply.
i'm sorry also to say that i deleted the subvolumes and referred back to the previous configurations.
however this is my fstab:

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/dev/sda1             /boot             ext4            defaults,noatime,noauto,ro,nouser               0 1
/dev/sda2             /boot/efi         vfat            defaults                                0 2
/dev/sda3             none              swap            sw                                      0 0
/dev/sda4             /                 btrfs           compress=lzo,noatime                    0 1
#/dev/sda4              /var            btrfs           nodev,compress=lzo,subvolid=348         0 3
#/dev/sda4              /usr/local      btrfs           nodev,compress=lzo,subvolid=349         0 3
#/dev/sda4              /srv            btrfs           nodev,compress=lzo,subvolid=350         0 3
#/dev/sda4              /root           btrfs           nodev,compress=lzo,subvolid=351         0 3
#/dev/sda4              /opt            btrfs           nodev,compress=lzo,subvolid=355         0 3
#/dev/sda4              /nix            btrfs           nodev,compress=lzo.subvolid=356         0 3
#/dev/sda4              /var/log        btrfs           nodev,compress=lzo,subvolid=357         0 3
#/dev/sda4              /var/tmp        btrfs           nodev,compress=lzo,subvolid=358         0 3
#/dev/sda4              /var/cache/distfiles    btrfs   nodev,compress=lzo,subvolid=359         0 3
#/dev/sda4              /var/cache/binpkgs      btrfs   nodev,compress=lzo,subvolid=360         0 3

i did not change "3" because i went back to the previous configs.
i guess all i have to do is to make snapshots and for every folder i add @ in front of the original name, mount it on the root folder and add it with subvol="@(folder) in fstab.
i will try it and tell if it worked.

[abdus]

i'm wrong, there is no way to make a snapshot for a folder
this thread explains it https://unix.stackexchange.com/question ... -directory
i got the same error when i tried.
the only remaining possible way is to copy or move the files.

[alamahant]

You got me confused.Do you have a btrfs filesystem that contains a Gentoo installation or not?
Does your fstab reflect this filesystem?

[Zucca]

i'm wrong, there is no way to make a snapshot for a folder

Yes and no.
You can just btrfs sub create dir and then you can snapshot 'dir'. This assumes 'dir' didn't exist beforehand.

You can create nested subvolumes. Those subvolumes will automatically be mounted when you mount their parent.
I do this with every btrfs installation to avoid polluting my fstab.

[abdus]

You got me confused.Do you have a btrfs filesystem that contains a Gentoo installation or not?
Does your fstab reflect this filesystem?

i'm sorry for getting you confused.
i do have a system with gentoo on a btrfs filesystem. it is not a fresh install
my exact problem is finding a way to mount the system folders like /usr /var /opt etc, you know what i mean, on btrfs subvolumes like in opensuse fstab
not only that, mounting them with not having data loss as much as possible and keeping the system configs exactly the same.

[Zucca]

my exact problem is finding a way to mount the system folders like /usr /var /opt etc, you know what i mean, on btrfs subvolumes

If you plan to have your root partition also on btrfs, Then you can simply:

• Prepare your new btrfs

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  mkdir /mnt/btrfs-root
  mkfs.btrfs <list of disks and/or partitions you want to dedicate to your btrfs pool>

• mount it:

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  mount <choose a single one the disks/parttions you formatted to btrfs> /mnt/btrfs-root

• Create subvolumes inside of it (take this as an example):

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  btrfs sub create /mnt/btrfs-root/usr
  btrfs sub create /mnt/btrfs-root/var
  mkdir /mnt/btrfs-root/var/cache
  btrfs sub create /mnt/btrfs-root/var/cache/distfiles
  btrfs sub create /mnt/btrfs-root/var/cache/binpkgs
  btrfs sub create /mnt/btrfs-root/opt
  

  ... There you can see you can treat subvolumes like a special directory inside btrfs. ;)
• Copy files from your old root to the newly created btrfs root.
• Adjust your system to your new btrfs.
  • You only need to add the root btrfs line into your fstab (along with maybe /boot and EFI partition)

If you don't plan to use btrfs on your root partition, then you need to add lines for each btrfs subvolume into your fstab.

[abdus]

thank you for your answers and help guys.
i am sorry for my late reply.
after trying multiple times i was eventually able to put the system folders in btrfs subvolumes
i did not need to use live cd except for /usr folder.
mostly all i had to do was renaming the folder by executing
sudo mv /opt /opt1 for example for all the folders, afterwards execute
sudo btrfs subvolume create /opt
sudo cp -a --reflink=always /opt1/*
checking the integrity of files in the subvolume
it's optional to put it in the fstab file
then deleting the /opt1 folder using
sudo rm -fR /opt1 i did that with all the other folders without live cd for the live cd i did it with usr folder i had to mount the partition in /mnt
execute the same commands but with adding /mnt to the paths.
i will try doing the same thing with the folders under /var later.
thank you guys.
i did not succeed from the first time there was a problem with programs starting and working then i repeated again and had kernel panic
if i do not succeed i simply rename the renamed folder to the original name or remove the line of the subvolume from fstab if it is not with the same name as the folder itself and reboot