How to tune2fs a mount point in an LXC container?

[Colin 't Hart]

I have some containers with large disks (mount points). I'd like to reduce the number of reserved blocks on these. How can I do this?

According to mount inside the container, the filesystem is ext4:

colin@www1:/dev$ mount | grep images
/dev/mapper/pve-vm--120--disk--2 on /disks/images type ext4 (rw,noexec,noatime,stripe=2048)

Inside the container the device doesn't exist:

colin@www1:/dev$ sudo tune2fs -m 1 /dev/mapper/pve-vm--120--disk--2
tune2fs 1.45.5 (07-Jan-2020)
tune2fs: No such file or directory while trying to open /dev/mapper/pve-vm--120--disk--2
Couldn't find valid filesystem superblock.

and indeed it's not in the /dev directory:

colin@www1:/dev$ ls
console  core  fd  full  initctl  log  mqueue  null  ptmx  pts  random  shm  stderr  stdin  stdout  tty  tty1  tty2  urandom  zero

On the Proxmox host I get:

colin@vm2:~$ sudo tune2fs -m 1 /dev/mapper/pve-vm--120--disk--2
tune2fs 1.44.5 (15-Dec-2018)
tune2fs: MMP: device currently active while trying to open /dev/mapper/pve-vm--120--disk--2
MMP error info: last update: Fri Sep 16 13:14:47 2022
 node: vm2 device: dm-44

Is this not possible without shutting down the container?

I should mention that this is on an old version of Proxmox (6.4) but I'd also be curious to know whether this is possible on a newer version.

 

[leesteken]

Shutdown the container, activate the logical volume and run the command (all on the Proxmox host)?

EDIT: Apologies for not answering your actual question.

 

[Colin 't Hart]

Shutdown the container, activate the logical volume and run the command (all on the Proxmox host)?

Yes, my question was if this is possible without shutting down the container?