My Kubuntu 12.04 system ran out of space on on the root partition and will not boot. The command df -h shows a lot of space available (with only 37% used): /dev/sda2        45G   17G   29G  37%The following page indicates that I should run the balance command:https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#I_get_.22No_space_left_on_device.22_errors.2C_but_df_says_I.27ve_got_lots_of_space$ sudo btrfs fi balance start -dusage=5 /mount/pointI'm not entirely confident that this is the best approach, but it is the only one I found. However, when I run that command, I get this error:ERROR: error during balancing '/blah/blah/blah' - No space left on deviceI get the same error with:$ sudo btrfs fi balance start -dusage=1 /mount/pointWhat is the right solution?
btrfs ERROR: error during balancing - No space left on device
filesystems;btrfs
There are ways to get balance to run in this situation.sudo btrfs fi showsudo btrfs fi df /mount/pointsudo btrfs fi balance start -dusage=10 /mount/pointIf the balance command ends with Done, had to relocate 0 out of XX chunks, then you need to increase the dusage percentage parameter till at least one chunk is relocated.if the balance command fails with:ERROR: error during balancing '/blah/blah/blah' - No space left on deviceYou might actually need to delete files from the device to make some room. Then run the balance command again.However, thanks to Marc's Blog: btrfs - Fixing Btrfs Filesystem Full Problems here is another option:One trick to get around this is to add a device (even a USB key will  do) to your btrfs filesystem. This should allow balance to start, and  then you can remove the device with btrfs device delete when the  balance is finished. It's also been said on the list that kernel 3.14  can fix some balancing issues that older kernels can't, so give that a  shot if your kernel is old.