system: Provide a new VM image configuration.

* gnu/system/examples/vm-image.tmpl: Rewrite.
* doc/guix.texi (Running Guix in a VM): Adjust accordingly.

doc/guix.texi

@@ -24576,13 +24576,23 @@ example graph.
 @section Running Guix in a Virtual Machine
 
 @cindex virtual machine
-To run Guix in a virtual machine (VM), one can either use the
-pre-built Guix VM image distributed at
+To run Guix in a virtual machine (VM), one can use the pre-built Guix VM image
+distributed at
 @indicateurl{https://alpha.gnu.org/gnu/guix/guix-system-vm-image-@value{VERSION}.@var{system}.xz}
-, or build their own virtual machine image using @command{guix system
-vm-image} (@pxref{Invoking guix system}).  The returned image is in
-qcow2 format, which the @uref{http://qemu.org/, QEMU emulator} can
-efficiently use.
+This image is a compressed image in QCOW format.  You will first need to
+decompress with @command{xz -d}, and then you can pass it to an emulator such
+as QEMU (see below for details).
+
+This image boots the Xfce graphical environment and it contains some
+commonly-used tools.  You can install more software in the image by running
+@command{guix package} in a terminal (@pxref{Invoking guix package}).  You can
+also reconfigure the system based on its initial configuration file available
+as @file{/etc/config.scm} (@pxref{Using the Configuration System}).
+
+Instead of using this pre-built image, one can also build their own virtual
+machine image using @command{guix system vm-image} (@pxref{Invoking guix
+system}).  The returned image is in qcow2 format, which the
+@uref{http://qemu.org/, QEMU emulator} can efficiently use.
 
 @cindex QEMU
 If you built your own image, you must copy it out of the store
@@ -24595,7 +24605,7 @@ vm-image} on x86_64 hardware:
 @example
 $ qemu-system-x86_64 \
    -net user -net nic,model=virtio \
-   -enable-kvm -m 256 /tmp/qemu-image
+   -enable-kvm -m 512 /tmp/qemu-image
 @end example
 
 Here is what each of these options means:
@@ -24621,7 +24631,7 @@ If your system has hardware virtualization extensions, enabling the
 virtual machine support (KVM) of the Linux kernel will make things run
 faster.
 
-@item -m 256
+@item -m 512
 RAM available to the guest OS, in mebibytes.  Defaults to 128@tie{}MiB,
 which may be insufficient for some operations.
 

gnu/system/examples/vm-image.tmpl

@@ -1,58 +1,85 @@
-;;; This is an operating system configuration template for a "bare-bones" setup,
-;;; suitable for booting in a virtualized environment, including virtual private
-;;; servers (VPS).
+;; This is an operating system configuration for a VM image.
+;; Modify it as you see fit and instantiate the changes by running:
+;;
+;;   guix system reconfigure /etc/config.scm
+;;
 
-(use-modules (gnu))
-(use-package-modules bootloaders disk nvi)
+(use-modules (gnu) (srfi srfi-1))
+(use-service-modules xorg desktop)
+(use-package-modules bootloaders nvi wget xorg)
 
 (define vm-image-motd (plain-file "motd" "
-This is the GNU system.  Welcome!
+\x1b[1;37mThis is the GNU system.  Welcome!\x1b[0m
 
-This instance of Guix System is a bare-bones template for virtualized environments.
+This instance of Guix is a template for virtualized environments.
+You can reconfigure the whole system by adjusting /etc/config.scm
+and running:
 
-You will probably want to do these things first if you booted in a virtual
-private server (VPS):
+  guix system reconfigure /etc/config.scm
+
+\x1b[1;33mConsider setting a password for the 'root' and 'guest' \
+accounts.\x1b[0m
+"))
+
+(define this-file
+  (local-file "./vm-image.tmpl" "config.scm"))
 
-* Set a password for 'root'.
-* Set up networking.
-* Expand the root partition to fill the space available by 0) deleting and
-recreating the partition with fdisk, 1) reloading the partition table with
-partprobe, and then 2) resizing the filesystem with resize2fs.\n"))
 
 (operating-system
   (host-name "gnu")
   (timezone "Etc/UTC")
   (locale "en_US.utf8")
+  (keyboard-layout (keyboard-layout "us" "altgr-intl"))
 
   (firmware '())
 
-  ;; Assuming /dev/sdX is the target hard disk, and "my-root" is
-  ;; the label of the target root file system.
+  ;; Below we assume /dev/vda is the VM's hard disk.
+  ;; Adjust as needed.
   (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
-               (target "/dev/sda")
+               (target "/dev/vda")
                (terminal-outputs '(console))))
   (file-systems (cons (file-system
-                        (device (file-system-label "my-root"))
                         (mount-point "/")
+                        (device "/dev/vda1")
                         (type "ext4"))
                       %base-file-systems))
 
-  ;; This is where user accounts are specified.  The "root"
-  ;; account is implicit, and is initially created with the
-  ;; empty password.
-  (users %base-user-accounts)
+  (users (cons (user-account
+                (name "guest")
+                (comment "GNU Guix Live")
+                (password "")                     ;no password
+                (group "users")
+                (supplementary-groups '("wheel" "netdev"
+                                        "audio" "video")))
+               %base-user-accounts))
 
-  ;; Globally-installed packages.
-  (packages (append (list nvi fdisk
-                          ;; mostly so xrefs to its manual work
-                          grub
-                          ;; partprobe
-                          parted)
-                    %base-packages))
+  (packages (append (list nvi wget) %base-packages))
 
-  (services (modify-services %base-services
-              (login-service-type config =>
-                                  (login-configuration
-                                    (inherit config)
-                                    (motd vm-image-motd))))))
+  (services
+   (append (list (service xfce-desktop-service-type)
+
+                 ;; Copy this file to /etc/config.scm in the OS.
+                 (simple-service 'config-file etc-service-type
+                                 `(("config.scm" ,this-file)))
+
+                 ;; Choose SLiM, which is lighter than the default GDM.
+                 (service slim-service-type
+                          (slim-configuration
+                           (auto-login? #t)
+                           (default-user "guest")
+                           (xorg-configuration
+                            (xorg-configuration
+                             (keyboard-layout keyboard-layout))))))
+
+           ;; Remove GDM.
+           (remove (lambda (service)
+                     (eq? gdm-service-type (service-kind service)))
+                   (modify-services %desktop-services
+                     (login-service-type config =>
+                                         (login-configuration
+                                          (inherit config)
+                                          (motd vm-image-motd)))))))
+
+  ;; Allow resolution of '.local' host names with mDNS.
+  (name-service-switch %mdns-host-lookup-nss))