guestfs-ruby - Man Page

How to use libguestfs from Ruby

Synopsis

 require 'guestfs'
 g = Guestfs::Guestfs.new()
 g.add_drive_opts("disk.img",
                  :readonly => true, :format => "raw")
 g.launch()

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

Exceptions

Errors from libguestfs functions are mapped into the Error exception. This has a single parameter which is the error message (a string).

Example 1: Create a Disk Image

 # Example showing how to create a disk image.
 
 require 'guestfs'
 
 output = "disk.img"
 
 g = Guestfs::Guestfs.new()
 
 # Create a raw-format sparse disk image, 512 MB in size.
 g.disk_create (output, "raw", 512 * 1024 * 1024)
 
 # Set the trace flag so that we can see each libguestfs call.
 g.set_trace(1)
 
 # Attach the disk image to libguestfs.
 g.add_drive_opts(output, :format => "raw")
 
 # 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.
 devices = g.list_devices()
 if devices.length != 1 then
   raise "error: expected a single device from list-devices"
 end
 
 # 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.
 partitions = g.list_partitions()
 if partitions.length != 1 then
   raise "error: expected a single partition from list-partitions"
 end
 
 # 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")
 message = "Hello, world\n"
 g.write("/hello", message)
 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()

Example 2: Inspect a Virtual Machine Disk Image

 # Example showing how to inspect a virtual machine disk.
 
 require 'guestfs'
 
 if ARGV.length == 0
   puts "usage: inspect_vm disk.img"
   exit 1
 end
 disk = ARGV[0]
 
 g = Guestfs::Guestfs.new()
 
 # Attach the disk image read-only to libguestfs.
 g.add_drive_opts(disk, :readonly => true)
 
 # Run the libguestfs back-end.
 g.launch()
 
 # Ask libguestfs to inspect for operating systems.
 roots = g.inspect_os()
 if roots.length == 0
   puts "inspect_vm: no operating systems found"
   exit 1
 end
 
 for root in roots do
   printf("Root device: %s\n", root)
 
   # Print basic information about the operating system.
   printf("  Product name: %s\n", g.inspect_get_product_name(root))
   printf("  Version:      %d.%d\n",
          g.inspect_get_major_version(root),
          g.inspect_get_minor_version(root))
   printf("  Type:         %s\n", g.inspect_get_type(root))
   printf("  Distro:       %s\n", 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.
   mps = g.inspect_get_mountpoints(root)
   mps = mps.sort {|a,b| a[0].length <=> b[0].length}
   for mp in mps do
     begin
       g.mount_ro(mp[1], mp[0])
     rescue Guestfs::Error => msg
       printf("%s (ignored)\n", msg)
     end
   end
 
   # If /etc/issue.net file exists, print up to 3 lines.
   filename = "/etc/issue.net"
   if g.is_file filename then
     printf("--- %s ---\n", filename)
     lines = g.head_n(3, filename)
     for line in lines do
       puts line
     end
   end
 
   # Unmount everything.
   g.umount_all()
 end

Authors

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

Copyright

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:

The version of libguestfs.
Where you got libguestfs (eg. which Linux distro, compiled from source, etc)
Describe the bug accurately and give a way to reproduce it.
Run libguestfs-test-tool(1) and paste the complete, unedited output into the bug report.

Referenced By

guestfs(3), guestfs-examples(3), guestfs-lua(3), guestfs-ocaml(3), guestfs-perl(3), guestfs-python(3), guestfs-recipes(1), guestfs-release-notes-1.8(1).

2026-08-14 libguestfs-1.61.2 Virtualization Support