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I have an ext4 volume that is 3.6T. According to df, the USED is less than SIZE with about 100GB free. However AVAIL shows 0.

If I run gparted it shows the real amount of free space (100GB).

If I try to write any files, I get the error message:

No space left on device

The only thing I can think of is that I use rsnapshot so there are lots of hardlinks to the same inode on the drive.

What is going on?

  • if you mean the root partition, that is on a separate partition. (so yes I can write there). The partition in question is the /home partition – eng3 May 1 '18 at 12:40
  • Sorry, I misunderstood your question. Yes I can write as root. I have a 5% reserve (so about 180GB). This explains whats going on – eng3 May 1 '18 at 12:51
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What you're looking at is the reserved space and the file system overhead for ext4.

Reserved space is standard 5% on any ext4 FS and is reserved for the root user only!

FS overhead consists of:

  • the inode table at format time
  • the journal ( usually 128 MB )
  • resize inodes.

So basically: the OS is still running, users cannot write to that FS any more: add more disks!

Please don't try to reduce the reserved space because that 5% also helps in keeping fragmentation to a minimum and why we never need to defragment ext2/3/4 partitions!

  • 1
    Thanks, I did not think of the reserve because I thought that was taken out of the DF reported values. – eng3 May 1 '18 at 13:04
  • No worries... ;-) Thanks for the fast acceptance. Favour returned: Q upvoted! (Couldn't find a duplicate, so answered) – Fabby May 1 '18 at 13:40
  • The reserved space doesn't cover any of the filesystem overhead actually, it's there to allow things like critical system services and logs to keep working correctly once the filesystem is mostly full. – Austin Hemmelgarn May 1 '18 at 19:27
  • @AustinHemmelgarn Please feel free to edit my answer to make that distinction more clear. (it's probably Reserved space only the OP was looking for, but I wanted the answer to be complete) ¯\_(ツ)_/¯ – Fabby May 1 '18 at 20:58

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