Submitted upstream: https://github.com/canonical/lightdm/pull/312

diff --git a/src/vnc-server.c b/src/vnc-server.c
index d3500764..00a2fc02 100644
--- a/src/vnc-server.c
+++ b/src/vnc-server.c
@@ -126,18 +126,10 @@ vnc_server_start (VNCServer *server)
 
     g_return_val_if_fail (server != NULL, FALSE);
 
-    g_autoptr(GError) ipv4_error = NULL;
-    priv->socket = open_tcp_socket (G_SOCKET_FAMILY_IPV4, priv->port, priv->listen_address, &ipv4_error);
-    if (ipv4_error)
-        g_warning ("Failed to create IPv4 VNC socket: %s", ipv4_error->message);
-
-    if (priv->socket)
-    {
-        GSource *source = g_socket_create_source (priv->socket, G_IO_IN, NULL);
-        g_source_set_callback (source, (GSourceFunc) read_cb, server, NULL);
-        g_source_attach (source, NULL);
-    }
-
+    // Bind to IPv6 first, as this implies binding to 0.0.0.0 in the
+    // Linux kernel default configuration, which would otherwise cause
+    // IPv6 clients to fail with "Error binding to address [::]:5900:
+    // Address already in use" (#266).
     g_autoptr(GError) ipv6_error = NULL;
     priv->socket6 = open_tcp_socket (G_SOCKET_FAMILY_IPV6, priv->port, priv->listen_address, &ipv6_error);
     if (ipv6_error)
@@ -150,6 +142,18 @@ vnc_server_start (VNCServer *server)
         g_source_attach (source, NULL);
     }
 
+    g_autoptr(GError) ipv4_error = NULL;
+    priv->socket = open_tcp_socket (G_SOCKET_FAMILY_IPV4, priv->port, priv->listen_address, &ipv4_error);
+    if (ipv4_error)
+        g_warning ("Failed to create IPv4 VNC socket: %s", ipv4_error->message);
+
+    if (priv->socket)
+    {
+        GSource *source = g_socket_create_source (priv->socket, G_IO_IN, NULL);
+        g_source_set_callback (source, (GSourceFunc) read_cb, server, NULL);
+        g_source_attach (source, NULL);
+    }
+
     if (!priv->socket && !priv->socket6)
         return FALSE;
 
on>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=12d8efb1a98a803c4de4368cb0890dbffeb2f619'>root</a>/<a href='/guix/log/gnu?id=12d8efb1a98a803c4de4368cb0890dbffeb2f619'>gnu</a>/<a href='/guix/log/gnu/system?id=12d8efb1a98a803c4de4368cb0890dbffeb2f619'>system</a>/<a href='/guix/log/gnu/system/mapped-devices.scm?id=12d8efb1a98a803c4de4368cb0890dbffeb2f619'>mapped-devices.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/system/mapped-devices.scm?id=12d8efb1a98a803c4de4368cb0890dbffeb2f619&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-04-08 18:14:35 +0200'>2022-04-08</span></td><td><a href='/guix/commit/gnu/system/mapped-devices.scm?id=931f13840bad7bd3cb98b7806f09ca2b3cf7cd10'>mapped-devices: Ensure 'cryptsetup open' gets a tty.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://issues.guix.gnu.org/54770&gt;.
Regression introduced in 400c9ed3d779308e56038305d40cd93acb496180.

Previously, for an encrypted /home (say), "cryptsetup open" would be
invoked by shepherd, with /dev/null as its standard input.  It would
thus run in non-interactive mode and, instead of asking for a
passphrase, fail with:

  Nothing to read on input.

This change ensures it runs in interactive mode.

* gnu/build/file-systems.scm (system*/console, system*/tty): New
procedures.
* gnu/system/mapped-devices.scm (open-luks-device): Use 'system*/tty'
instead of 'system*'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-12-01 17:51:37 +0100'>2021-12-01</span></td><td><a href='/guix/commit/gnu/system/mapped-devices.scm?id=adce91a3ec0cb2912daa6eefe9324c15ff3126f7'>gnu: system: Add LUKS2 support for the root file system.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/bootloader/grub.scm (grub-configuration-file): Add 'insmod
luks2'.
* gnu/system/mapped-devices.scm (open-luks-device): Create
'/run/cryptsetup/' directory.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Josselin Poiret</td></tr>
ts/substitute.scm (%default-substitute-urls): Likewise.
* guix/store.scm (%default-substitute-urls): Likewise.
* guix/self.scm (miscellaneous-files): Add "ci.guix.gnu.org".
</span></span></td><td>Ludovic Courtès</td></tr>