diff --git a/doc/lib/pgBackRestDoc/Common/DocManifest.pm b/doc/lib/pgBackRestDoc/Common/DocManifest.pm
index a441518b2..bc68fdf50 100644
--- a/doc/lib/pgBackRestDoc/Common/DocManifest.pm
+++ b/doc/lib/pgBackRestDoc/Common/DocManifest.pm
@@ -370,7 +370,8 @@ sub variableReplace
 
     foreach my $strName (sort(keys(%{$self->{oVariable}})))
     {
-        my $strValue = $self->{oVariable}{$strName};
+        # If the value is not defined then replace it as an empty string. This means the key *was* defined but no value given.
+        my $strValue = defined($self->{oVariable}{$strName}) ? $self->{oVariable}{$strName} : '';
 
         $strBuffer =~ s/\{\[$strName\]\}/$strValue/g;
     }
diff --git a/doc/xml/user-guide.xml b/doc/xml/user-guide.xml
index 12f6cff0c..470c18067 100644
--- a/doc/xml/user-guide.xml
+++ b/doc/xml/user-guide.xml
@@ -177,6 +177,11 @@
 
         <variable key="host-option">-v /sys/fs/cgroup:/sys/fs/cgroup:rw -v /tmp/$(mktemp -d):/run</variable>
 
+        <!-- Limit host memory to check for memory leaks. Some environments do not allow memory to be set so allow disabling. -->
+        <variable key="host-mem-limit">y</variable>
+        <variable key="host-mem" if="'{[host-mem-limit]}' eq 'y'">-m 512m</variable>
+        <variable key="host-mem" if="'{[host-mem-limit]}' eq 'n'"></variable>
+
         <variable key="host-user" eval="y">use English; getpwuid($UID) eq 'root' ? 'vagrant' : getpwuid($UID) . ''</variable>
         <variable key="host-mount">{[host-repo-path]}:{[pgbackrest-repo-path]}</variable>
         <variable key="image-repo">pgbackrest/test</variable>
@@ -771,10 +776,10 @@
         <title>Introduction</title>
 
         <!-- Create Azure server first to allow it time to boot before being used -->
-        <host-add if="'{[azure-local]}' eq 'y'" id="{[host-azure-id]}" name="{[host-azure]}" user="root" image="{[azure-image]}" os="{[os-type]}" option="-m 128m -v {[fake-cert-path]}/azure-server.crt:/root/public.crt:ro -v {[fake-cert-path]}/azure-server.key:/root/private.key:ro -e AZURITE_ACCOUNTS='{[azure-account]}:{[azure-key]}'" param="azurite-blob --blobPort 443 --blobHost 0.0.0.0 --cert=/root/public.crt --key=/root/private.key" update-hosts="n"/>
+        <host-add if="'{[azure-local]}' eq 'y'" id="{[host-azure-id]}" name="{[host-azure]}" user="root" image="{[azure-image]}" os="{[os-type]}" option="-v {[fake-cert-path]}/azure-server.crt:/root/public.crt:ro -v {[fake-cert-path]}/azure-server.key:/root/private.key:ro -e AZURITE_ACCOUNTS='{[azure-account]}:{[azure-key]}'" param="azurite-blob --blobPort 443 --blobHost 0.0.0.0 --cert=/root/public.crt --key=/root/private.key" update-hosts="n"/>
 
         <!-- Create S3 server first to allow it time to boot before being used -->
-        <host-add if="'{[s3-local]}' eq 'y'" id="{[host-s3-id]}" name="{[host-s3]}" user="root" image="{[s3-image]}" os="{[os-type]}" option="-m 128m -v {[fake-cert-path]}/s3-server.crt:/root/.minio/certs/public.crt:ro -v {[fake-cert-path]}/s3-server.key:/root/.minio/certs/private.key:ro -e MINIO_REGION={[s3-region]} -e MINIO_DOMAIN={[s3-endpoint]} -e MINIO_BROWSER=off -e MINIO_ACCESS_KEY={[s3-key]} -e MINIO_SECRET_KEY={[s3-key-secret]}" param="server /data --address :443" update-hosts="n"/>
+        <host-add if="'{[s3-local]}' eq 'y'" id="{[host-s3-id]}" name="{[host-s3]}" user="root" image="{[s3-image]}" os="{[os-type]}" option="-v {[fake-cert-path]}/s3-server.crt:/root/.minio/certs/public.crt:ro -v {[fake-cert-path]}/s3-server.key:/root/.minio/certs/private.key:ro -e MINIO_REGION={[s3-region]} -e MINIO_DOMAIN={[s3-endpoint]} -e MINIO_BROWSER=off -e MINIO_ACCESS_KEY={[s3-key]} -e MINIO_SECRET_KEY={[s3-key-secret]}" param="server /data --address :443" update-hosts="n"/>
 
         <p>This user guide is intended to be followed sequentially from beginning to end &amp;mdash; each section depends on the last. For example, the <link section="/restore">Restore</link> section relies on setup that is performed in the <link section="/quickstart">Quick Start</link> section. Once <backrest/> is up and running then skipping around is possible but following the user guide in order is recommended the first time through.</p>
 
@@ -869,7 +874,7 @@
 
         <p if="{[os-type-is-rhel]}">{[user-guide-os]} packages for <backrest/> are available from <link url="{[crunchy-url-base]}">Crunchy Data</link> or <link url="http://yum.postgresql.org">yum.postgresql.org</link>, but it is also easy to download the source and install manually.</p>
 
-        <host-add id="{[host-build-id]}" name="{[host-build]}" user="{[host-build-user]}" image="{[host-build-image]}" os="{[os-type]}" mount="{[host-build-mount]}" option="-m 256m {[host-option]}"/>
+        <host-add id="{[host-build-id]}" name="{[host-build]}" user="{[host-build-user]}" image="{[host-build-image]}" os="{[os-type]}" mount="{[host-build-mount]}" option="{[host-option]}"/>
 
         <p>When building from source it is best to use a build host rather than building on production.  Many of the tools required for the build should generally not be installed in production.  <backrest/> consists of a single executable so it is easy to copy to a new host once it is built.</p>
 
@@ -941,7 +946,7 @@
 
         <p>A new host named <host>{[host-pg1]}</host> is created to contain the demo cluster and run <backrest/> examples.</p>
 
-        <host-add id="{[host-pg1-id]}" name="{[host-pg1]}" user="{[host-pg1-user]}" image="{[host-pg1-image]}" os="{[os-type]}" mount="{[host-pg1-mount]}" option="-m 512m {[host-option]}"/>
+        <host-add id="{[host-pg1-id]}" name="{[host-pg1]}" user="{[host-pg1-user]}" image="{[host-pg1-image]}" os="{[os-type]}" mount="{[host-pg1-mount]}" option="{[host-mem]} {[host-option]}"/>
 
         <!-- <execute-list if="{[pg-version]} >= 11" host="{[host-pg1]}">
             <title>Create <user>{[br-user]}</user> user</title>
@@ -2397,7 +2402,7 @@
 
             <admonition type="note">The <backrest/> version installed on the <host>repository</host> host must exactly match the version installed on the <postgres/> host.</admonition>
 
-            <host-add id="{[host-repo1-id]}" name="{[host-repo1]}" user="{[host-repo1-user]}" image="{[host-repo1-image]}" os="{[os-type]}" mount="{[host-repo1-mount]}" option="-m 512m {[host-option]}"/>
+            <host-add id="{[host-repo1-id]}" name="{[host-repo1]}" user="{[host-repo1-user]}" image="{[host-repo1-image]}" os="{[os-type]}" mount="{[host-repo1-mount]}" option="{[host-mem]} {[host-option]}"/>
 
             <p>The <user>{[br-user]}</user> user is created to own the <backrest/> repository.  Any user can own the repository but it is best not to use <user>postgres</user> (if it exists) to avoid confusion.</p>
 
@@ -2812,7 +2817,7 @@
 
             <p>A new host named <host>{[host-pg2]}</host> is created to run the standby.</p>
 
-            <host-add id="{[host-pg2-id]}" name="{[host-pg2]}" user="{[host-pg2-user]}" image="{[host-pg2-image]}" os="{[os-type]}" mount="{[host-pg2-mount]}" option="-m 512m {[host-option]}"/>
+            <host-add id="{[host-pg2-id]}" name="{[host-pg2]}" user="{[host-pg2-user]}" image="{[host-pg2-image]}" os="{[os-type]}" mount="{[host-pg2-mount]}" option="{[host-mem]} {[host-option]}"/>
 
             <!-- <execute-list if="{[pg-version]} >= 11" host="{[host-pg2]}">
                 <title>Create <user>{[br-user]}</user> user</title>