=head1 NAME

guestfs-erlang - How to use libguestfs from Erlang

=head1 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).

=head1 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 L<guestfs(3)>.

=head2 OPENING AND CLOSING THE HANDLE

The Erlang bindings are implemented using an external program called
C<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").

C<G> is the libguestfs handle which you should pass to other
functions.

To close the handle:

 ok = guestfs:close(G).

=head2 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).

=head2 RETURN VALUES AND ERRORS

On success, most functions return a C<Result> term (which could be a
list, string, tuple etc.).  If there is nothing for the function to
return, then the atom C<ok> is returned.

On error, you would see one of the following tuples:

=over 4

=item C<{error, Msg, Errno}>

This indicates an ordinary error from the function.

C<Msg> is the error message (string) and C<Errno> is the Unix error
(integer).

C<Errno> can be zero.  See L<guestfs(3)/guestfs_last_errno>.

=item C<{unknown, Function}>

This indicates that the function you called is not known.  Generally
this means you are mixing C<erl-guestfs> from another version of
libguestfs, which you should not do.

C<Function> is the name of the unknown function.

=item C<{unknownarg, Arg}>

This indicates that you called a function with optional arguments,
with an unknown argument name.

C<Arg> is the name of the unknown argument.

=back

=head1 EXAMPLE 1: CREATE A DISK IMAGE

@EXAMPLE1@

=head1 EXAMPLE 2: INSPECT A VIRTUAL MACHINE DISK IMAGE

@EXAMPLE2@

=head1 SEE ALSO

L<guestfs(3)>,
L<guestfs-examples(3)>,
L<guestfs-golang(3)>,
L<guestfs-java(3)>,
L<guestfs-lua(3)>,
L<guestfs-ocaml(3)>,
L<guestfs-perl(3)>,
L<guestfs-python(3)>,
L<guestfs-recipes(1)>,
L<guestfs-ruby(3)>,
L<http://www.erlang.org/>.
L<http://libguestfs.org/>.

=head1 AUTHORS

Richard W.M. Jones (C<rjones at redhat dot com>)

=head1 COPYRIGHT

Copyright (C) 2011-2025 Red Hat Inc.
