Online resizing of an LXC container on LVM volume

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Published on June 24th 2014 - Listed in Linux

In the past I already tried to dynamically resize a running LXC on a Debian Wheezy machine with LXC 0.8. Although the logical volume and its file system could be increased, the LXC itself, running on this LV, did not see the new disk size. Only after a reboot of the LXC in question, the new disk size was seen.

That has changed now and it works. On an Ubuntu 14.04 with LXC 1.0.3 I successfully increased an LXC's rootfs while running.

The disk size was first 20G, which could be seen in the LXC itself:

root@lxc1:~# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/lxc/lxc1   20G  8.2G   11G  44% /
none            4.0K     0  4.0K   0% /sys/fs/cgroup
none            3.2G   80K  3.2G   1% /run
none            5.0M     0  5.0M   0% /run/lock
none             16G     0   16G   0% /run/shm
none            100M     0  100M   0% /run/user

On the physical host I increased/extended the logical volume of this LXC with additional 100GB:

root@physical-host:~# lvextend -L +100G /dev/lxc/lxc1
  Extending logical volume lxc1 to 120.00 GiB
  Logical volume lxc1 successfully resized

... and then adjusted the file system size to the new LV size:

root@physical-host:~# resize2fs /dev/lxc/lxc1
resize2fs 1.42.9 (4-Feb-2014)
Filesystem at /dev/lxc/lxc1 is mounted on /var/lib/lxc1/rootfs; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 8
The filesystem on /dev/lxc/lxc1 is now 31457280 blocks long.

In the LXC, I ran df again:

root@lxc1:~# df -h
Filesystem     Size  Used Avail Use% Mounted on
/dev/lxc/lxc1  118G  8.2G  105G   8% /
none           4.0K     0  4.0K   0% /sys/fs/cgroup
none           3.2G   84K  3.2G   1% /run
none           5.0M     0  5.0M   0% /run/lock
none            16G     0   16G   0% /run/shm
none           100M     0  100M   0% /run/user

Fun :-).

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