guestfs-erlang(3) Virtualization Support guestfs-erlang(3)
NAME
guestfs-erlang - How to use libguestfs from Erlang
SYNOPSIS
{ok, G} = guestfs:create(),
ok = guestfs:add_drive_opts(G, Disk,
[{format, "raw"}, {readonly, true}]),
ok = guestfs:launch(G),
[Device] = guestfs:list_devices(G),
ok = guestfs:close(G).
DESCRIPTION
This manual page documents how to call libguestfs from the Erlang programming language. This page just documents the differences from the
C API and gives some examples. If you are not familiar with using libguestfs, you also need to read guestfs(3).
OPENING AND CLOSING THE HANDLE
The Erlang bindings are implemented using an external program called "erl-guestfs". This program must be on the current PATH, or else you
should specify the full path to the program:
{ok, G} = guestfs:create().
{ok, G} = guestfs:create("/path/to/erl-guestfs").
"G" is the libguestfs handle which you should pass to other functions.
To close the handle:
ok = guestfs:close(G).
FUNCTIONS WITH OPTIONAL ARGUMENTS
For functions that take optional arguments, the first arguments are the non-optional ones. The last argument is a list of tuples supplying
the remaining optional arguments.
ok = guestfs:add_drive_opts(G, Disk,
[{format, "raw"}, {readonly, true}]).
If the last argument would be an empty list, you can also omit it:
ok = guestfs:add_drive_opts(G, Disk).
RETURN VALUES AND ERRORS
On success, most functions return a "Result" term (which could be a list, string, tuple etc.). If there is nothing for the function to
return, then the atom "ok" is returned.
On error, you would see one of the following tuples:
"{error, Msg, Errno}"
This indicates an ordinary error from the function.
"Msg" is the error message (string) and "Errno" is the Unix error (integer).
"Errno" can be zero. See "guestfs_last_errno" in guestfs(3).
"{unknown, Function}"
This indicates that the function you called is not known. Generally this means you are mixing "erl-guestfs" from another version of
libguestfs, which you should not do.
"Function" is the name of the unknown function.
"{unknownarg, Arg}"
This indicates that you called a function with optional arguments, with an unknown argument name.
"Arg" is the name of the unknown argument.
EXAMPLE 1: CREATE A DISK IMAGE
#!/usr/bin/env escript
%%! -smp enable -sname create_disk debug verbose
% Example showing how to create a disk image.
main(_) ->
Output = "disk.img",
{ok, G} = guestfs:create(),
% Create a raw-format sparse disk image, 512 MB in size.
{ok, File} = file:open(Output, [raw, write, binary]),
{ok, _} = file:position(File, 512 * 1024 * 1024 - 1),
ok = file:write(File, " "),
ok = file:close(File),
% Set the trace flag so that we can see each libguestfs call.
ok = guestfs:set_trace(G, true),
% Set the autosync flag so that the disk will be synchronized
% automatically when the libguestfs handle is closed.
ok = guestfs:set_autosync(G, true),
% Attach the disk image to libguestfs.
ok = guestfs:add_drive_opts(G, Output,
[{format, "raw"}, {readonly, false}]),
% Run the libguestfs back-end.
ok = guestfs:launch(G),
% Get the list of devices. Because we only added one drive
% above, we expect that this list should contain a single
% element.
[Device] = guestfs:list_devices(G),
% Partition the disk as one single MBR partition.
ok = guestfs:part_disk(G, Device, "mbr"),
% Get the list of partitions. We expect a single element, which
% is the partition we have just created.
[Partition] = guestfs:list_partitions(G),
% Create a filesystem on the partition.
ok = guestfs:mkfs(G, "ext4", Partition),
% Now mount the filesystem so that we can add files. *)
ok = guestfs:mount_options(G, "", Partition, "/"),
% Create some files and directories. *)
ok = guestfs:touch(G, "/empty"),
Message = "Hello, world
",
ok = guestfs:write(G, "/hello", Message),
ok = guestfs:mkdir(G, "/foo"),
% This one uploads the local file /etc/resolv.conf into
% the disk image.
ok = guestfs:upload(G, "/etc/resolv.conf", "/foo/resolv.conf"),
% Because 'autosync' was set (above) we can just close the handle
% and the disk contents will be synchronized. You can also do
% this manually by calling guestfs:umount_all and guestfs:sync.
%
% Note also that handles are automatically closed if they are
% reaped by the garbage collector. You only need to call close
% if you want to close the handle right away.
ok = guestfs:close(G).
EXAMPLE 2: INSPECT A VIRTUAL MACHINE DISK IMAGE
#!/usr/bin/env escript
%%! -smp enable -sname inspect_vm debug verbose
% Example showing how to inspect a virtual machine disk.
main([Disk]) ->
{ok, G} = guestfs:create(),
% Attach the disk image read-only to libguestfs.
ok = guestfs:add_drive_opts(G, Disk, [{readonly, true}]),
% Run the libguestfs back-end.
ok = guestfs:launch(G),
% Ask libguestfs to inspect for operating systems.
case guestfs:inspect_os(G) of
[] ->
io:fwrite("inspect_vm: no operating systems found~n"),
exit(no_operating_system);
Roots ->
list_os(G, Roots)
end.
list_os(_, []) ->
ok;
list_os(G, [Root|Roots]) ->
io:fwrite("Root device: ~s~n", [Root]),
% Print basic information about the operating system.
Product_name = guestfs:inspect_get_product_name(G, Root),
io:fwrite(" Product name: ~s~n", [Product_name]),
Major = guestfs:inspect_get_major_version(G, Root),
Minor = guestfs:inspect_get_minor_version(G, Root),
io:fwrite(" Version: ~w.~w~n", [Major, Minor]),
Type = guestfs:inspect_get_type(G, Root),
io:fwrite(" Type: ~s~n", [Type]),
Distro = guestfs:inspect_get_distro(G, Root),
io:fwrite(" Distro: ~s~n", [Distro]),
% Mount up the disks, like guestfish -i.
Mps = sort_mps(guestfs:inspect_get_mountpoints(G, Root)),
mount_mps(G, Mps),
% If /etc/issue.net file exists, print up to 3 lines. *)
Filename = "/etc/issue.net",
Is_file = guestfs:is_file(G, Filename),
if Is_file ->
io:fwrite("--- ~s ---~n", [Filename]),
Lines = guestfs:head_n(G, 3, Filename),
write_lines(Lines);
true -> ok
end,
% Unmount everything.
ok = guestfs:umount_all(G),
list_os(G, Roots).
% Sort keys by length, shortest first, so that we end up
% mounting the filesystems in the correct order.
sort_mps(Mps) ->
Cmp = fun ({A,_}, {B,_}) ->
length(A) =< length(B) end,
lists:sort(Cmp, Mps).
mount_mps(_, []) ->
ok;
mount_mps(G, [{Mp, Dev}|Mps]) ->
case guestfs:mount_ro(G, Dev, Mp) of
ok -> ok;
{ error, Msg, _ } ->
io:fwrite("~s (ignored)~n", [Msg])
end,
mount_mps(G, Mps).
write_lines([]) ->
ok;
write_lines([Line|Lines]) ->
io:fwrite("~s~n", [Line]),
write_lines(Lines).
SEE ALSO
guestfs(3), guestfs-examples(3), guestfs-java(3), guestfs-ocaml(3), guestfs-perl(3), guestfs-python(3), guestfs-recipes(1),
guestfs-ruby(3), <http://www.erlang.org/>. <http://libguestfs.org/>.
AUTHORS
Richard W.M. Jones ("rjones at redhat dot com")
COPYRIGHT
Copyright (C) 2011 Red Hat Inc. <http://libguestfs.org/>
The examples in this manual page may be freely copied, modified and distributed without any restrictions.
This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
libguestfs-1.18.1 2013-12-07 guestfs-erlang(3)