I am facing an issue with wrong fs space reported by df.
We are talking about bare metal Ubuntu 14.04 server, with the / partition managed by LVM.
Size reported by df is different from the size reported by fs super-block. Also calculating size from du -skh (on directories related to / partition) proves that df is showing incorrect results.
This is what reported by df:
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rootvg-lv_root 20G 16G 2.8G 86% /
This is what super-block reports (3616906*4096/1024**2=14128 MB free):
Last mounted on: /
Filesystem magic number: 0xEF53
Filesystem state: clean
Filesystem OS type: Linux
Inode count: 1290240
Block count: 5242880 << exactly 20 GB
Reserved block count: 227170
Free blocks: 3616906 << around 14 GB free
Free inodes: 1201391
First block: 0
Block size: 4096
Fragment size: 4096
I did a strace for df and found that it uses the statfs syscall to get information about a particular fs (962132*4096/1024**2=3758 MB free):
statfs("/", {f_type="EXT2_SUPER_MAGIC", f_bsize=4096, f_blocks=5129119, f_bfree=**962132**, f_bavail=730866, f_files=1290240, f_ffree=1091851, f_fsid={-456623966, 1549023591}, f_namelen=255, f_frsize=4096}) = 0
Probably the problem with statfs or with a way how it fetches fs information.
To solve it I tried to remount / partition (mount / -orw,remount), but it didn't help.
My question - how can I fix df information without rebooting or disturbing normal operation of this server?
P.S.
- there are no fd on hold by process (
lsof +L1 | grep deleted) - I aware that 883 MB is reserved for user with UID 0
- This is not a mount point masking issue (when mounted fs 'hide' files in mount point directory)