19095: Add upgrade note about singularity version.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@curii.com>

diff --git a/doc/admin/upgrading.html.textile.liquid b/doc/admin/upgrading.html.textile.liquid
index 226c8667d67a710283c436db321dc1f26246593d..f686eec8bd2d453249db4e4e5c1db37c6ad86eb1 100644 (file)
--- a/doc/admin/upgrading.html.textile.liquid
+++ b/doc/admin/upgrading.html.textile.liquid
@@ -32,6 +32,10 @@ h2(#main). development main (as of 2022-04-08)
 
 "previous: Upgrading to 2.4.0":#v2_4_0
 
+h3. Now recommending Singularity 3.9.9
+
+The compute image builder now installs Singularity 3.9.9 instead of 3.7.4. The newer version includes a bugfix that should resolve "intermittent loopback device errors":https://dev.arvados.org/issues/18489 when running containers.
+
 h2(#v2_4_0). v2.4.0 (2022-04-08)
 
 "previous: Upgrading to 2.3.1":#v2_3_1