Tip: find out when filesystems get full with virt-df

Another easy tip for the day: Want to receive a warning when one of your virtual machines’ filesystems is filling up? Use virt-df, awk, and cron like this.

Note: I’ve set this up so I can do it as non-root, but that meant I had to add myself to the ‘disk’ group first, so that virt-df can read out the contents of the disks of the virtual machines. There’s one extra thing needed which is to set the LIBVIRT_DEFAULT_URI environment variable to access the global libvirtd socket.

$ export LIBVIRT_DEFAULT_URI='qemu+unix:///system?socket=/var/run/libvirt/libvirt-sock-ro'
$ virt-df | awk 'strtonum(substr($5,0,length($5)-1))>=60 {print}'
Debian5x64:/dev/debian5x64/root         329233     200395     111840   61%
Windows7x32:/dev/vda2                 10381308    7740852    2640456   75%
Windows7x64:/dev/vda2                 10381308    9417676     963632   91%

You can set the threshold to whatever you want. In the above awk code it’s set to 60%, you’d probably want it higher.

Now put those two commands into a script file somewhere, and create a cronjob. The following one runs daily:

MAILTO=you@example.com
0 1 * * * /usr/local/etc/diskcheck.sh

What do you do when a VM is running out of space? Why, you run virt-resize of course.

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Ob-geekiness: The full virt-df output from one of my test hosts. This one is used for a lot of interop testing:

$ virt-df
Filesystem                           1K-blocks       Used  Available  Use%
RHEL6200910210x32:/dev/vda1             198337      36582     151515   19%
RHEL6200910210x32:/dev/vg_rhel6200910210x32/lv_root
                                       9147776    5305876    3377212   59%
RHEL6201002033x64:/dev/vda1             495844      32396     437848    7%
RHEL6201002033x64:/dev/vg_rhel6201002033x64/lv_root
                                      18102140    4097800   13084788   23%
Debian5x64:/dev/debian5x64/home        3555936    1264800    2110504   36%
Debian5x64:/dev/debian5x64/root         329233     200395     111840   61%
Debian5x64:/dev/debian5x64/tmp          309401      10294     283133    4%
Debian5x64:/dev/debian5x64/usr         3539776    1434740    1925224   41%
Debian5x64:/dev/debian5x64/var         1741648     264632    1388544   16%
Debian5x64:/dev/vda1                    233335      47272     173615   21%
Ubuntu910x64:/dev/vda1                 9827520    4180524    5147780   43%
RHEL6Alpha3x64:/dev/vda1                198337      22879     165218   12%
RHEL6Alpha3x64:/dev/vg_rhel6alpha3x64/lv_root
                                       8180152    4174904    3589712   52%
RHEL54Betax64:/dev/VolGroup00/LogVol00
                                      15109112    8695548    5633688   58%
RHEL54Betax64:/dev/vda1                 101086      12449      83418   13%
F10x32:/dev/VolGroup00/LogVol00        9191640    3083532    5642856   34%
F10x32:/dev/vda1                        194442      20706     163697   11%
F12x64:/dev/vda1                        198337      22782     165315   12%
F12x64:/dev/vg_f12x64/lv_root          9115576    4396520    4256004   49%
F13Rawhidex64:/dev/vda1                 198337      60031     128066   31%
F13Rawhidex64:/dev/vg_f13rawhide/lv_root
                                       9115576    6018664    2633860   67%
F12x64preview:/dev/vda1                 198337      22782     165315   12%
F12x64preview:/dev/vg_f12x64/lv_root   9115576    4781384    3871140   53%
Win2003x32:/dev/vda1                  20956760    3053092   17903668   15%
VSphere:/dev/vda1                     31447204    8159028   23288176   26%
Windows7x32:/dev/vda1                   102396      24712      77684   25%
Windows7x32:/dev/vda2                 10381308    7740852    2640456   75%
Windows7x64:/dev/vda1                   102396      24704      77692   25%
Windows7x64:/dev/vda2                 10381308    9417676     963632   91%
CentOS5x32:/dev/VolGroup00/LogVol00    9014656    4069840    4479512   46%
CentOS5x32:/dev/vda1                    101086      36210      59657   36%

Update There is a small but important bug in this code. Please see the fixed version.

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