Manpages

NAME

guestfs-java - How to use libguestfs from Java

SYNOPSIS

import com.redhat.et.libguestfs.*;
GuestFS g = new GuestFS ();
g.add_drive ("disk.img",
new HashMap<String,Object>() {
{
put ("readonly", Boolean.TRUE);
put ("format", "raw");
}
});
g.launch ();

DESCRIPTION

This manual page documents how to call libguestfs from the Java 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).

CLOSING THE HANDLE
The handle is closed when it is reaped by the garbage collector. Because libguestfs handles include a lot of state, it is also possible to close (and hence free) them explicitly by calling the "close" method.

EXCEPTIONS
Errors from libguestfs functions are mapped into the "LibGuestFSException" exception. This has a single parameter which is the error message (a "String").

Calling any method on a closed handle raises the same exception.

If malloc(3) or some other allocation fails inside the bindings, the "LibGuestFSOutOfMemory" exception is thrown.

EVENTS
The libguestfs event API is fully supported from Java. Create a class which implements the "EventCallback" interface, create an instance of this class, and then call the "GuestFS#set_event_callback" method to register this instance. The "event" method of the class is called when libguestfs generates an event.

For example, this will print all trace events:

GuestFS g = new GuestFS ();
g.set_trace (true);
g.set_event_callback (
new EventCallback () {
public void event (long event, int eh,
String buffer, long[] array) {
System.out.println (GuestFS.eventToString (event) +
": " + buffer);
}
},
GuestFS.EVENT_TRACE);
g.add_drive_ro ("disk.img");
// etc.

The output looks similar to this:

EVENT_TRACE: add_drive_ro "disk.img"
EVENT_TRACE: add_drive_ro = 0
// etc.

OPTIONAL ARGUMENTS
Some methods take an optional map of optional parameters. An example of this is "g.add_drive" which can be called in one of two ways:

g.add_drive ("disk.img");

or with optional arguments:

Map<String, Object> optargs =
new HashMap<String, Object>() {
{
put ("readonly", Boolean.TRUE);
put ("format", "raw");
}
};
g.add_drive ("disk.img", optargs);

For more information on this topic, see "CALLS WITH OPTIONAL ARGUMENTS" in guestfs(3).

Optional handle parameters

When creating the handle you can also pass a map of optional parameters:

Map<String, Object> optargs =
new HashMap<String, Object>() {
{
put ("close_on_exit", Boolean.FALSE);
put ("environment", Boolean.TRUE);
}
};
GuestFS g = new GuestFS (optargs);

For more information, see "guestfs_create_flags" in guestfs(3).

COMPILING AND RUNNING

Libguestfs for Java is a Java Native Interface (JNI) extension, supplied in three parts:
libguestfs.jar
libguestfs-VERSION.jar

The pure Java JAR file which contains several classes, the primary one being "com.redhat.et.libguestfs.GuestFS". Upstream, the JAR file contains a version number in the filename, but some Linux distros may rename it without the version number.

libguestfs_jni.so

The JNI code (written in C). This contains private native functions that interface between Java code and the regular libguestfs C library. You should not call these directly.

libguestfs.so

The regular libguestfs C library.

To compile your Java program, you need to locate the JAR file and add it to the class path. For example:

export CLASSPATH=/usr/share/java/libguestfs.jar
javac MyProgram.java

To run your Java program, you also need to ensure that the JAR file is on the class path, as well as the path of your program. For example:

export CLASSPATH=.:/usr/share/java/libguestfs.jar
java MyProgram

EXAMPLE 1: CREATE A DISK IMAGE

// Example showing how to create a disk image.
import java.io.*;
import java.util.Map;
import java.util.HashMap;
import com.redhat.et.libguestfs.*;
public class CreateDisk
{
static String output = "disk.img";
public static void main (String[] argv)
{
try {
GuestFS g = new GuestFS ();
// Create a raw-format sparse disk image, 512 MB in size.
RandomAccessFile f = new RandomAccessFile (output, "rw");
f.setLength (512 * 1024 * 1024);
f.close ();
// Set the trace flag so that we can see each libguestfs call.
g.set_trace (true);
// Attach the disk image to libguestfs.
@SuppressWarnings("serial") Map<String, Object> optargs =
new HashMap<String, Object>() {
{
put ("format", "raw");
put ("readonly", Boolean.FALSE);
}
};
g.add_drive_opts (output, optargs);
// Run the libguestfs back-end.
g.launch ();
// Get the list of devices. Because we only added one drive
// above, we expect that this list should contain a single
// element.
String[] devices = g.list_devices ();
if (devices.length != 1)
throw new Error ("expected a single device from list-devices");
// Partition the disk as one single MBR partition.
g.part_disk (devices[0], "mbr");
// Get the list of partitions. We expect a single element, which
// is the partition we have just created.
String[] partitions = g.list_partitions ();
if (partitions.length != 1)
throw new Error ("expected a single partition from list-partitions");
// Create a filesystem on the partition.
g.mkfs ("ext4", partitions[0]);
// Now mount the filesystem so that we can add files.
g.mount (partitions[0], "/");
// Create some files and directories.
g.touch ("/empty");
String message = "Hello, world\n";
g.write ("/hello", message.getBytes());
g.mkdir ("/foo");
// This one uploads the local file /etc/resolv.conf into
// the disk image.
g.upload ("/etc/resolv.conf", "/foo/resolv.conf");
// Because we wrote to the disk and we want to detect write
// errors, call g.shutdown. You don't need to do this:
// g.close will do it implicitly.
g.shutdown ();
// 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.
g.close ();
}
catch (Exception exn) {
System.err.println (exn);
System.exit (1);
}
}
}

EXAMPLE 2: INSPECT A VIRTUAL MACHINE DISK IMAGE

// Example showing how to inspect a virtual machine disk.
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.redhat.et.libguestfs.*;
public class InspectVM
{
static final Comparator<String> COMPARE_KEYS_LEN =
new Comparator<String>() {
public int compare (String k1, String k2) {
return k1.length() - k2.length();
}
};
public static void main (String[] argv)
{
try {
if (argv.length != 1)
throw new Error ("usage: InspectVM disk.img");
String disk = argv[0];
GuestFS g = new GuestFS ();
// Attach the disk image read-only to libguestfs.
@SuppressWarnings("serial") Map<String, Object> optargs =
new HashMap<String, Object>() {
{
//put ("format", "raw");
put ("readonly", Boolean.TRUE);
}
};
g.add_drive_opts (disk, optargs);
// Run the libguestfs back-end.
g.launch ();
// Ask libguestfs to inspect for operating systems.
String roots[] = g.inspect_os ();
if (roots.length == 0)
throw new Error ("inspect_vm: no operating systems found");
for (String root : roots) {
System.out.println ("Root device: " + root);
// Print basic information about the operating system.
System.out.println (" Product name: " +
g.inspect_get_product_name (root));
System.out.println (" Version: " +
g.inspect_get_major_version (root) +
"." +
g.inspect_get_minor_version (root));
System.out.println (" Type: " +
g.inspect_get_type (root));
System.out.println (" Distro: " +
g.inspect_get_distro (root));
// Mount up the disks, like guestfish -i.
//
// Sort keys by length, shortest first, so that we end up
// mounting the filesystems in the correct order.
Map<String,String> mps = g.inspect_get_mountpoints (root);
List<String> mps_keys = new ArrayList<String> (mps.keySet ());
Collections.sort (mps_keys, COMPARE_KEYS_LEN);
for (String mp : mps_keys) {
String dev = mps.get (mp);
try {
g.mount_ro (dev, mp);
}
catch (Exception exn) {
System.err.println (exn + " (ignored)");
}
}
// If /etc/issue.net file exists, print up to 3 lines.
String filename = "/etc/issue.net";
if (g.is_file (filename)) {
System.out.println ("--- " + filename + " ---");
String[] lines = g.head_n (3, filename);
for (String line : lines)
System.out.println (line);
}
// Unmount everything.
g.umount_all ();
}
}
catch (Exception exn) {
System.err.println (exn);
System.exit (1);
}
}
}

SEE ALSO

guestfs(3), guestfs-examples(3), guestfs-erlang(3), guestfs-gobject(3), guestfs-golang(3), guestfs-lua(3), guestfs-ocaml(3), guestfs-perl(3), guestfs-python(3), guestfs-recipes(1), guestfs-ruby(3), http://libguestfs.org/, http://caml.inria.fr/.

AUTHORS

Richard W.M. Jones ("rjones at redhat dot com")

COPYRIGHT

Copyright (C) 2011-2023 Red Hat Inc.

LICENSE

This manual page contains examples which we hope you will use in your programs. The examples may be freely copied, modified and distributed for any purpose without any restrictions.

BUGS

To get a list of bugs against libguestfs, use this link: https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools

To report a new bug against libguestfs, use this link: https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools

When reporting a bug, please supply: