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Chris
Asked: 2011-09-25 12:31:58 +0800 CST

df says disk is full, but it is not

  • 772

On a virtualized server running Ubuntu 10.04, df reports the following:

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             7.4G  7.0G     0 100% /
none                  498M  160K  498M   1% /dev
none                  500M     0  500M   0% /dev/shm
none                  500M   92K  500M   1% /var/run
none                  500M     0  500M   0% /var/lock
none                  500M     0  500M   0% /lib/init/rw
/dev/sda3             917G  305G  566G  36% /home

This is puzzling me for two reasons: 1.) df says that /dev/sda1, mounted at /, has a 7.4 gigabyte capacity, of which only 7.0 gigabytes are in use, yet it reports / being 100 percent full; and 2.) I can create files on / so it clearly does have space left.

Possibly relevant is that the directory /www is a symbolic link to /home/www, which is on a different partition (/dev/sda3, mounted at /home).

Can anyone offer suggestions on what might be going on here? The server appears to be working without issue, but I want to make sure there's not a problem with the partition table, file systems or something else which might result in implosion (or explosion) later.

linux ubuntu partition

12 Answers

  1. It's possible that a process has opened a large file which has since been deleted. You'll have to kill that process to free up the space. You may be able to identify the process by using lsof. On Linux deleted yet open files are known to lsof and marked as (deleted) in lsof's output.

    You can check this with sudo lsof +L1

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  2. 5% (by default) of the filesystem is reserved for cases where the filesystem fills up to prevent serious problems. Your filesystem is full. Nothing catastrophic is happening because of the 5% buffer -- root is permitted to use that safety buffer and, in your setup, non-root users have no reason to write into that filesystem.

    If you have daemons that run as a non-root user but that need to manage files in that filesystem, things will break. One common such daemon is named. Another is ntpd.

    • 57

  3. You may be out of inodes. Check inode usage with this command:

    df -i
    • 43

  4. Most Linux filesystems (ext3, ext4) reserve 5% space for use only the root user.

    You can see this with e.g

    dumpe2fs /dev/sda1 | grep -i reserved

    You can change the reserved amount using :

    tune2fs -m 0 /dev/sda1

    0 in this command stands for percent of disk size so maybe you would want to leave at least 1%.

    In most cases the server will appear to continue working fine - assuming all processes are being run as 'root'.

    • 24

  5. In addition to already suggested causes, in some cases it could be also following:

    • a different disk is mounted "over" the existing folder which is full of data
    • du will calculate the size spent of mounted disk and df will show really spent
    • solution: (when possible) unmount all non-root disks and check the size with du -md 1 again. Fix situation by moving hidden folder to some other place or mount on different place.
    • 14

  6. I had this problem and was baffled by the fact deleting various large files did not improve the situation (didn't know about the 5% buffer) anyway following some clues here

    From root walked down the largest directories revealed by repetitively doing:- 

    du -sh */

    until I came a directory for webserver log files which had some absolutely massive logs

    which I truncated with 

    :>lighttpd.error.log

    suddenly df -h was down to 48% used!

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  7. df -h is rounding the values. Even the percentages are rounded. Omit the -h and you see finer grained differences.

    Oh. And ext3 and derivates reserve a percentage (default 5%) for the file-system for exactly this problematic constellation. If your root filesystem would be really full (0 byte remaining) you can't boot the system. So the reserved portion prevents this.

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  8. If you are running out of space on /dev/shm and wondering why (given that actual used space (df -shc /dev/shm) is much smaller then /dev/shm allotted size)? lsof can help:

    $ sudo lsof -s +L1 | awk '{print $7" "$2" "$3" "$10}' | grep 'dev/shm' | grep "^[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]" 
7931428864 1133806 roel /dev/shm/1600335920/subreducer/2/data/ibtmp1
12710576128 1133806 roel /dev/shm/1600335920/subreducer/2/tmp/#sql-temptable-114cee-8-e18.MAD
4173332480 1352445 roel /dev/shm/1600335920/subreducer/1/data/ibtmp1
13040484352 1352445 roel /dev/shm/1600335920/subreducer/1/tmp/#sql-temptable-14a2fd-8-eb3.MAD
9670602752 2298724 roel /dev/shm/1600338626/subreducer/2/tmp/#sql-temptable-231364-8-d2e.MAD

    First file is consuming ~7.9GB, second about 12.7GB etc. The regex picks up on anything 1GB and over. You can tune the regex as needed. The cause could be that an otherwise dead process is holding on to a file. df -h will not show the issue;

    Filesystem      Size  Used Avail Use% Mounted on
tmpfs            90G   90G  508K 100% /dev/shm

    508K, yet...

    $ du -shc | grep total
46G total

    You can see the 90G <> 46G offset. It's in the files above.

    Then, just kill the PID (kill -9 PID) listed in the second column of the output above.

    $ kill -9 1133806

    Result:

    Filesystem      Size  Used Avail Use% Mounted on
tmpfs            90G   72G   19G  80% /dev/shm

    Great, space cleared.

    The reason for doing things this way and not just something like sudo lsof +L1 | grep '(deleted)' | grep 'dev/shm' | awk '{print $2}' | sudo xargs kill -9 is that the underlaying process(es) may still be working. If you're confident it/they is/are not, that command is a potential alternative depending on your scenario. It will kill all processes which have 'deleted' files open.

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  9. I did a big update of several libraries and there was a lot of unnecessary libraries and temporal files so I free space in the "/" folder using:

    apt-get install -f
sudo apt-get clean

    And empty your trash

    • 2

  10. check the /lost+found, I had a system (centos 7) and some of file in the /lost+found ate up all the space

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