2 virt-df - 'df'-like utility for virtualization stats
8 virt-df is a df(1)-like utility for showing the actual disk usage of
9 guests. Many command line options are the same as for ordinary *df*.
11 It uses libvirt so it is capable of showing stats across a variety of
12 different virtualization systems.
14 There are some shortcomings to the whole approach of reading disk state
15 from outside the guest. Please read SHORTCOMINGS section below for more
20 Show all domains. The default is show only running (active) domains.
23 Connect to libvirt URI. The default is to connect to the default
24 libvirt URI, normally Xen.
27 Display human-readable sizes (eg. 10GiB).
30 Display inode information.
33 Display usage summary.
36 Display version and exit.
39 virt-df spies on the guest's disk image to try to work out how much disk
40 space it is actually using. There are some shortcomings to this,
43 (1) It does not work over remote connections. The storage API does not
44 support peeking into remote disks, and libvirt has rejected a request to
47 (2) It only understands a limited set of partition types. Assuming that
48 the files and partitions that we get back from libvirt / Xen correspond
49 to block devices in the guests, we can go some way towards manually
50 parsing those partitions to find out what they contain. We can read the
51 MBR, LVM, superblocks and so on. However that's a lot of parsing work,
52 and currently there is no library which understands a wide range of
53 partition schemes and filesystem types (not even libparted which doesn't
54 support LVM yet). The Linux kernel does support that, but there's not
55 really any good way to access that work.
57 The current implementation uses a hand-coded parser which understands
58 some simple formats (MBR, LVM2, ext2/3). In future we should use
59 something like libparted.
61 (3) The statistics you get are delayed. The real state of, for example,
62 an ext2 filesystem is only stored in the memory of the guest's kernel.
63 The ext2 superblock contains some meta-information about blocks used and
64 free, but this superblock is not up to date. In fact the guest kernel
65 may not update it even on a 'sync', not until the filesystem is
66 unmounted. Some operations do appear to write the superblock, for
67 example fsync(2) [that is my reading of the ext2/3 source code at
71 The current code is probably not secure against malicious guests. In
72 particular a malicious guest can set up a disk in such a way that disk
73 structures with loops can cause virt-df to spin forever. We are
74 preparing a parsing library which can fix these sorts of problems.
76 In the meantime, do not run virt-df on untrusted guests.
79 df(1), virsh(1), xm(1), <http://www.libvirt.org/ocaml/>,
80 <http://www.libvirt.org/>, <http://et.redhat.com/~rjones/>,
81 <http://caml.inria.fr/>
84 Richard W.M. Jones <rjones @ redhat . com>
87 (C) Copyright 2007-2008 Red Hat Inc., Richard W.M. Jones
90 This program is free software; you can redistribute it and/or modify it
91 under the terms of the GNU General Public License as published by the
92 Free Software Foundation; either version 2 of the License, or (at your
93 option) any later version.
95 This program is distributed in the hope that it will be useful, but
96 WITHOUT ANY WARRANTY; without even the implied warranty of
97 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
98 Public License for more details.
100 You should have received a copy of the GNU General Public License along
101 with this program; if not, write to the Free Software Foundation, Inc.,
102 675 Mass Ave, Cambridge, MA 02139, USA.
105 Bugs can be viewed on the Red Hat Bugzilla page:
106 <https://bugzilla.redhat.com/>.
108 If you find a bug in virt-df, please follow these steps to report it:
110 1. Check for existing bug reports
111 Go to <https://bugzilla.redhat.com/> and search for similar bugs.
112 Someone may already have reported the same bug, and they may even
115 2. Capture debug and error messages
118 virt-df > virt-df.log 2>&1
120 and keep *virt-df.log*. It contains error messages which you should
121 submit with your bug report.
123 3. Get version of virt-df and version of libvirt.
128 4. Submit a bug report.
129 Go to <https://bugzilla.redhat.com/> and enter a new bug. Please
130 describe the problem in as much detail as possible.
132 Remember to include the version numbers (step 3) and the debug
133 messages file (step 2).
135 5. Assign the bug to rjones @ redhat.com
136 Assign or reassign the bug to rjones @ redhat.com (without the
137 spaces). You can also send me an email with the bug number if you
138 want a faster response.