From e19b2e04c75b6df4e3f8a455700aa95fca79bcc3 Mon Sep 17 00:00:00 2001
From: Adrien Ferrand <adferrand@users.noreply.github.com>
Date: Wed, 30 Oct 2019 18:39:45 +0100
Subject: [PATCH] Migrate certbot-auto users on CentOS 6 to Python 3.6 (#7268)

Fixes #7007

Python 3.4 is [EOL](https://www.python.org/dev/peps/pep-0429/), and only Python 3.x version available for CentOS 6 through EPEL is this version, and so is used by `certbot-auto`, the only official way to install Certbot on this platform.

This unpleasant situation becomes a little more uncomfortable, considering that the newest `pip` version (19.2) [just dropped Python 3.4 support](https://github.com/pypa/pip/issues/6685) and will refuse to start on this Python version. We can expect a lot of dependencies to follow this path now.

One direct result of this situation is that a fix to support correctly the ARM platforms requires to upgrade `pip` to 19.2 for `certbot-auto`. So this is not possible right now.

Then, let's upgrade Certbot instances on CentOS 6 to a supported version of Python 3.

This PR proposes a new bootstrap approach for CentOS 6 platform, `BootstrapRpmPython3Legacy`, that will install Python 3.6 from [SCL](https://www.softwarecollections.org) (the latest one available for now on CentOS 6). In term of Python 3 specific bootstrap methods, I take the occasion here to completely separate the bootstrap of CentOS 6 as a legacy system, from the RPM-based newest systems (like Fedora 29+) that are simply dropping support for Python 2.x. This is in prevision of future migration for all systems on Python 3.x, that is a different problematic than supporting old systems.

* Add logic

* Rebuilt letsencrypt-auto

* Fix logic

* Focus on specific packages

* Maintain PATH for further invocations of letsencrypt-auto after bootstrap.

* Various corrections

* Fix farm test for RHEL6

* Working centos6 letsencrypt-auto self tests

* Fix test_sdist for CentOS 6

* Corrections

* Work in progress

* Working configuration

* Fix typo

* Remove EPEL. Add a test.

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Improvements after review

* Improvements

* Add a comment

* Add a test

* Update a test

* Corrections

* Update function return

* Work in progress

* Correct behavior on oracle linux 6.

* Corrections

* Rebuild script

* Add letsencrypt-auto tests for oraclelinux6

* Update tox.ini

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/tests/oraclelinux6_tests.sh

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/tests/oraclelinux6_tests.sh

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Remove specific code for scientific linux

* Change some variables names

* Update letsencrypt-auto-source/tests/oraclelinux6_tests.sh

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Various corrections

* Fix tests

* Add a comment

* Update message

* Fix test message

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update scripts

* More focused assertion

* Add back a test

* Update script

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>

* Check quiet mode

* Add changelog

* Update letsencrypt-auto-source/tests/oraclelinux6_tests.sh

Co-Authored-By: Brad Warren <bmw@users.noreply.github.com>
---
 .travis.yml                                   |   3 +
 CHANGELOG.md                                  |   1 +
 ...{Dockerfile.centos6 => Dockerfile.redhat6} |  21 +-
 letsencrypt-auto-source/letsencrypt-auto      | 212 +++++++++++++-----
 .../letsencrypt-auto.template                 | 106 ++++++---
 .../pieces/bootstrappers/rpm_common_base.sh   |  24 +-
 .../pieces/bootstrappers/rpm_python3.sh       |   7 -
 .../bootstrappers/rpm_python3_legacy.sh       |  75 +++++++
 .../tests/centos6_tests.sh                    | 147 ++++++++----
 .../tests/oraclelinux6_tests.sh               |  85 +++++++
 .../letstest/scripts/test_leauto_upgrades.sh  |   2 +
 tests/letstest/scripts/test_sdists.sh         |  13 ++
 tox.ini                                       |  12 +-
 13 files changed, 540 insertions(+), 168 deletions(-)
 rename letsencrypt-auto-source/{Dockerfile.centos6 => Dockerfile.redhat6} (50%)
 create mode 100644 letsencrypt-auto-source/pieces/bootstrappers/rpm_python3_legacy.sh
 create mode 100644 letsencrypt-auto-source/tests/oraclelinux6_tests.sh

diff --git a/.travis.yml b/.travis.yml
index 4d4ea5f55..b3e26fc79 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -234,6 +234,9 @@ matrix:
     - sudo: required
       env: TOXENV=le_auto_centos6
       services: docker
+    - sudo: required
+      env: TOXENV=le_auto_oraclelinux6
+      services: docker
       <<: *extended-test-suite
     - sudo: required
       env: TOXENV=docker_dev
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ac1263e85..ba301a553 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@ Certbot adheres to [Semantic Versioning](https://semver.org/).
   staging server instead of the live server when `--dry-run` is used.
 * Updated certbot-dns-google to depend on newer versions of
   google-api-python-client and oauth2client.
+* Migrated CentOS 6 certbot-auto users from Python 3.4 to Python 3.6.
 
 ### Fixed
 
diff --git a/letsencrypt-auto-source/Dockerfile.centos6 b/letsencrypt-auto-source/Dockerfile.redhat6
similarity index 50%
rename from letsencrypt-auto-source/Dockerfile.centos6
rename to letsencrypt-auto-source/Dockerfile.redhat6
index 09aa52dcd..d5cdc0458 100644
--- a/letsencrypt-auto-source/Dockerfile.centos6
+++ b/letsencrypt-auto-source/Dockerfile.redhat6
@@ -1,9 +1,13 @@
 # For running tests, build a docker image with a passwordless sudo and a trust
 # store we can manipulate.
 
-FROM centos:6
+ARG REDHAT_DIST_FLAVOR
+FROM ${REDHAT_DIST_FLAVOR}:6
 
-RUN yum install -y epel-release
+ARG REDHAT_DIST_FLAVOR
+
+RUN curl -O https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm \
+ && rpm -ivh epel-release-latest-6.noarch.rpm
 
 # Install pip and sudo:
 RUN yum install -y python-pip sudo
@@ -27,11 +31,18 @@ RUN mkdir -p /home/lea/certbot
 COPY ./tests/certs/ca/my-root-ca.crt.pem /usr/local/share/ca-certificates/
 RUN update-ca-trust
 
-# Copy code:
+# Copy current letsencrypt-auto:
 COPY . /home/lea/certbot/letsencrypt-auto-source
 
+# Fetch previous letsencrypt-auto that was installing python 3.4
+RUN curl https://raw.githubusercontent.com/certbot/certbot/v0.38.0/letsencrypt-auto-source/letsencrypt-auto \
+    -o /home/lea/certbot/letsencrypt-auto-source/letsencrypt-auto_py_34 \
+ && chmod +x /home/lea/certbot/letsencrypt-auto-source/letsencrypt-auto_py_34
+
+RUN cp /home/lea/certbot/letsencrypt-auto-source/tests/${REDHAT_DIST_FLAVOR}6_tests.sh /home/lea/certbot/letsencrypt-auto-source/tests/redhat6_tests.sh \
+ && chmod +x /home/lea/certbot/letsencrypt-auto-source/tests/redhat6_tests.sh
+
 USER lea
 WORKDIR /home/lea
 
-RUN sudo chmod +x certbot/letsencrypt-auto-source/tests/centos6_tests.sh
-CMD sudo certbot/letsencrypt-auto-source/tests/centos6_tests.sh
+CMD ["sudo", "certbot/letsencrypt-auto-source/tests/redhat6_tests.sh"]
diff --git a/letsencrypt-auto-source/letsencrypt-auto b/letsencrypt-auto-source/letsencrypt-auto
index ff1fbe8c3..c0f7466ae 100755
--- a/letsencrypt-auto-source/letsencrypt-auto
+++ b/letsencrypt-auto-source/letsencrypt-auto
@@ -256,20 +256,28 @@ DeprecationBootstrap() {
   fi
 }
 
-MIN_PYTHON_VERSION="2.7"
-MIN_PYVER=$(echo "$MIN_PYTHON_VERSION" | sed 's/\.//')
+MIN_PYTHON_2_VERSION="2.7"
+MIN_PYVER2=$(echo "$MIN_PYTHON_2_VERSION" | sed 's/\.//')
+MIN_PYTHON_3_VERSION="3.5"
+MIN_PYVER3=$(echo "$MIN_PYTHON_3_VERSION" | sed 's/\.//')
 # Sets LE_PYTHON to Python version string and PYVER to the first two
-# digits of the python version
+# digits of the python version.
+# MIN_PYVER and MIN_PYTHON_VERSION are also set by this function, and their
+# values depend on if we try to use Python 3 or Python 2.
 DeterminePythonVersion() {
   # Arguments: "NOCRASH" if we shouldn't crash if we don't find a good python
   #
   # If no Python is found, PYVER is set to 0.
   if [ "$USE_PYTHON_3" = 1 ]; then
+    MIN_PYVER=$MIN_PYVER3
+    MIN_PYTHON_VERSION=$MIN_PYTHON_3_VERSION
     for LE_PYTHON in "$LE_PYTHON" python3; do
       # Break (while keeping the LE_PYTHON value) if found.
       $EXISTS "$LE_PYTHON" > /dev/null && break
     done
   else
+    MIN_PYVER=$MIN_PYVER2
+    MIN_PYTHON_VERSION=$MIN_PYTHON_2_VERSION
     for LE_PYTHON in "$LE_PYTHON" python2.7 python27 python2 python; do
       # Break (while keeping the LE_PYTHON value) if found.
       $EXISTS "$LE_PYTHON" > /dev/null && break
@@ -285,7 +293,7 @@ DeterminePythonVersion() {
     fi
   fi
 
-  PYVER=`"$LE_PYTHON" -V 2>&1 | cut -d" " -f 2 | cut -d. -f1,2 | sed 's/\.//'`
+  PYVER=$("$LE_PYTHON" -V 2>&1 | cut -d" " -f 2 | cut -d. -f1,2 | sed 's/\.//')
   if [ "$PYVER" -lt "$MIN_PYVER" ]; then
     if [ "$1" != "NOCRASH" ]; then
       error "You have an ancient version of Python entombed in your operating system..."
@@ -368,7 +376,9 @@ BootstrapDebCommon() {
 
 # Sets TOOL to the name of the package manager
 # Sets appropriate values for YES_FLAG and QUIET_FLAG based on $ASSUME_YES and $QUIET_FLAG.
-# Enables EPEL if applicable and possible.
+# Note: this function is called both while selecting the bootstrap scripts and
+# during the actual bootstrap. Some things like prompting to user can be done in the latter
+# case, but not in the former one.
 InitializeRPMCommonBase() {
   if type dnf 2>/dev/null
   then
@@ -388,26 +398,6 @@ InitializeRPMCommonBase() {
   if [ "$QUIET" = 1 ]; then
     QUIET_FLAG='--quiet'
   fi
-
-  if ! $TOOL list *virtualenv >/dev/null 2>&1; then
-    echo "To use Certbot, packages from the EPEL repository need to be installed."
-    if ! $TOOL list epel-release >/dev/null 2>&1; then
-      error "Enable the EPEL repository and try running Certbot again."
-      exit 1
-    fi
-    if [ "$ASSUME_YES" = 1 ]; then
-      /bin/echo -n "Enabling the EPEL repository in 3 seconds..."
-      sleep 1s
-      /bin/echo -ne "\e[0K\rEnabling the EPEL repository in 2 seconds..."
-      sleep 1s
-      /bin/echo -e "\e[0K\rEnabling the EPEL repository in 1 second..."
-      sleep 1s
-    fi
-    if ! $TOOL install $YES_FLAG $QUIET_FLAG epel-release; then
-      error "Could not enable EPEL. Aborting bootstrap!"
-      exit 1
-    fi
-  fi
 }
 
 BootstrapRpmCommonBase() {
@@ -488,13 +478,88 @@ BootstrapRpmCommon() {
   BootstrapRpmCommonBase "$python_pkgs"
 }
 
+# If new packages are installed by BootstrapRpmPython3 below, this version
+# number must be increased.
+BOOTSTRAP_RPM_PYTHON3_LEGACY_VERSION=1
+
+# Checks if rh-python36 can be installed.
+Python36SclIsAvailable() {
+  InitializeRPMCommonBase >/dev/null 2>&1;
+
+  if "${TOOL}" list rh-python36 >/dev/null 2>&1; then
+    return 0
+  fi
+  if "${TOOL}" list centos-release-scl >/dev/null 2>&1; then
+    return 0
+  fi
+  return 1
+}
+
+# Try to enable rh-python36 from SCL if it is necessary and possible.
+EnablePython36SCL() {
+  if "$EXISTS" python3.6 > /dev/null 2> /dev/null; then
+      return 0
+  fi
+  if ! scl --list 2>/dev/null | grep -q rh-python36; then
+      return 0
+  fi
+  set +e
+  . scl_source enable rh-python36
+  set -e
+}
+
+# This bootstrap concerns old RedHat-based distributions that do not ship by default
+# with Python 2.7, but only Python 2.6. We bootstrap them by enabling SCL and installing
+# Python 3.6. Some of these distributions are: CentOS/RHEL/OL/SL 6.
+BootstrapRpmPython3Legacy() {
+  # Tested with:
+  #   - CentOS 6
+
+  InitializeRPMCommonBase
+
+  if ! "${TOOL}" list rh-python36 >/dev/null 2>&1; then
+    echo "To use Certbot on this operating system, packages from the SCL repository need to be installed."
+    if ! "${TOOL}" list centos-release-scl >/dev/null 2>&1; then
+      error "Enable the SCL repository and try running Certbot again."
+      exit 1
+    fi
+    if [ "${ASSUME_YES}" = 1 ]; then
+      /bin/echo -n "Enabling the SCL repository in 3 seconds... (Press Ctrl-C to cancel)"
+      sleep 1s
+      /bin/echo -ne "\e[0K\rEnabling the SCL repository in 2 seconds... (Press Ctrl-C to cancel)"
+      sleep 1s
+      /bin/echo -e "\e[0K\rEnabling the SCL repository in 1 second... (Press Ctrl-C to cancel)"
+      sleep 1s
+    fi
+    if ! "${TOOL}" install "${YES_FLAG}" "${QUIET_FLAG}" centos-release-scl; then
+      error "Could not enable SCL. Aborting bootstrap!"
+      exit 1
+    fi
+  fi
+
+  # CentOS 6 must use rh-python36 from SCL
+  if "${TOOL}" list rh-python36 >/dev/null 2>&1; then
+    python_pkgs="rh-python36-python
+      rh-python36-python-virtualenv
+      rh-python36-python-devel
+    "
+  else
+    error "No supported Python package available to install. Aborting bootstrap!"
+    exit 1
+  fi
+
+  BootstrapRpmCommonBase "${python_pkgs}"
+
+  # Enable SCL rh-python36 after bootstrapping.
+  EnablePython36SCL
+}
+
 # If new packages are installed by BootstrapRpmPython3 below, this version
 # number must be increased.
 BOOTSTRAP_RPM_PYTHON3_VERSION=1
 
 BootstrapRpmPython3() {
   # Tested with:
-  #   - CentOS 6
   #   - Fedora 29
 
   InitializeRPMCommonBase
@@ -505,12 +570,6 @@ BootstrapRpmPython3() {
       python3-virtualenv
       python3-devel
     "
-  # EPEL uses python34
-  elif $TOOL list python34 >/dev/null 2>&1; then
-    python_pkgs="python34
-      python34-devel
-      python34-tools
-    "
   else
     error "No supported Python package available to install. Aborting bootstrap!"
     exit 1
@@ -769,31 +828,50 @@ elif [ -f /etc/redhat-release ]; then
      RPM_DIST_VERSION=0
   fi
 
-  # Starting to Fedora 29, python2 is on a deprecation path. Let's move to python3 then.
-  # RHEL 8 also uses python3 by default.
-  if [ "$RPM_DIST_NAME" = "fedora" -a "$RPM_DIST_VERSION" -ge 29 -o "$PYVER" -eq 26 ]; then
-    RPM_USE_PYTHON_3=1
-  elif [ "$RPM_DIST_NAME" = "rhel" -a "$RPM_DIST_VERSION" -ge 8 ]; then
-    RPM_USE_PYTHON_3=1
-  elif [ "$RPM_DIST_NAME" = "centos" -a "$RPM_DIST_VERSION" -ge 8 ]; then
-    RPM_USE_PYTHON_3=1
-  else
-    RPM_USE_PYTHON_3=0
-  fi
+  # Handle legacy RPM distributions
+  if [ "$PYVER" -eq 26 ]; then
+    # Check if an automated bootstrap can be achieved on this system.
+    if ! Python36SclIsAvailable; then
+      INTERACTIVE_BOOTSTRAP=1
+    fi
 
-  if [ "$RPM_USE_PYTHON_3" = 1 ]; then
     Bootstrap() {
-      BootstrapMessage "RedHat-based OSes that will use Python3"
-      BootstrapRpmPython3
+      BootstrapMessage "Legacy RedHat-based OSes that will use Python3"
+      BootstrapRpmPython3Legacy
     }
     USE_PYTHON_3=1
-    BOOTSTRAP_VERSION="BootstrapRpmPython3 $BOOTSTRAP_RPM_PYTHON3_VERSION"
+    BOOTSTRAP_VERSION="BootstrapRpmPython3Legacy $BOOTSTRAP_RPM_PYTHON3_LEGACY_VERSION"
+
+    # Try now to enable SCL rh-python36 for systems already bootstrapped
+    # NB: EnablePython36SCL has been defined along with BootstrapRpmPython3Legacy in certbot-auto
+    EnablePython36SCL
   else
-    Bootstrap() {
-      BootstrapMessage "RedHat-based OSes"
-      BootstrapRpmCommon
-    }
-    BOOTSTRAP_VERSION="BootstrapRpmCommon $BOOTSTRAP_RPM_COMMON_VERSION"
+    # Starting to Fedora 29, python2 is on a deprecation path. Let's move to python3 then.
+    # RHEL 8 also uses python3 by default.
+    if [ "$RPM_DIST_NAME" = "fedora" -a "$RPM_DIST_VERSION" -ge 29 ]; then
+      RPM_USE_PYTHON_3=1
+    elif [ "$RPM_DIST_NAME" = "rhel" -a "$RPM_DIST_VERSION" -ge 8 ]; then
+      RPM_USE_PYTHON_3=1
+    elif [ "$RPM_DIST_NAME" = "centos" -a "$RPM_DIST_VERSION" -ge 8 ]; then
+      RPM_USE_PYTHON_3=1
+    else
+      RPM_USE_PYTHON_3=0
+    fi
+
+    if [ "$RPM_USE_PYTHON_3" = 1 ]; then
+      Bootstrap() {
+        BootstrapMessage "RedHat-based OSes that will use Python3"
+        BootstrapRpmPython3
+      }
+      USE_PYTHON_3=1
+      BOOTSTRAP_VERSION="BootstrapRpmPython3 $BOOTSTRAP_RPM_PYTHON3_VERSION"
+    else
+      Bootstrap() {
+        BootstrapMessage "RedHat-based OSes"
+        BootstrapRpmCommon
+      }
+      BOOTSTRAP_VERSION="BootstrapRpmCommon $BOOTSTRAP_RPM_COMMON_VERSION"
+    fi
   fi
 
   LE_PYTHON="$prev_le_python"
@@ -1078,8 +1156,15 @@ if [ "$1" = "--le-auto-phase2" ]; then
     # If the selected Bootstrap function isn't a noop and it differs from the
     # previously used version
     if [ -n "$BOOTSTRAP_VERSION" -a "$BOOTSTRAP_VERSION" != "$PREV_BOOTSTRAP_VERSION" ]; then
-      # if non-interactive mode or stdin and stdout are connected to a terminal
-      if [ \( "$NONINTERACTIVE" = 1 \) -o \( \( -t 0 \) -a \( -t 1 \) \) ]; then
+      # Check if we can rebootstrap without manual user intervention: this requires that
+      # certbot-auto is in non-interactive mode AND selected bootstrap does not claim to
+      # require a manual user intervention.
+      if [ "$NONINTERACTIVE" = 1 -a "$INTERACTIVE_BOOTSTRAP" != 1 ]; then
+        CAN_REBOOTSTRAP=1
+      fi
+      # Check if rebootstrap can be done non-interactively and current shell is non-interactive
+      # (true if stdin and stdout are not attached to a terminal).
+      if [ \( "$CAN_REBOOTSTRAP" = 1 \) -o \( \( -t 0 \) -a \( -t 1 \) \) ]; then
         if [ -d "$VENV_PATH" ]; then
           rm -rf "$VENV_PATH"
         fi
@@ -1090,12 +1175,21 @@ if [ "$1" = "--le-auto-phase2" ]; then
           ln -s "$VENV_PATH" "$OLD_VENV_PATH"
         fi
         RerunWithArgs "$@"
+      # Otherwise bootstrap needs to be done manually by the user.
       else
-        error "Skipping upgrade because new OS dependencies may need to be installed."
-        error
-        error "To upgrade to a newer version, please run this script again manually so you can"
-        error "approve changes or with --non-interactive on the command line to automatically"
-        error "install any required packages."
+        # If it is because bootstrapping is interactive, --non-interactive will be of no use.
+        if [ "$INTERACTIVE_BOOTSTRAP" = 1 ]; then
+          error "Skipping upgrade because new OS dependencies may need to be installed."
+          error "This requires manual user intervention: please run this script again manually."
+        # If this is because of the environment (eg. non interactive shell without
+        # --non-interactive flag set), help the user in that direction.
+        else
+          error "Skipping upgrade because new OS dependencies may need to be installed."
+          error
+          error "To upgrade to a newer version, please run this script again manually so you can"
+          error "approve changes or with --non-interactive on the command line to automatically"
+          error "install any required packages."
+        fi
         # Set INSTALLED_VERSION to be the same so we don't update the venv
         INSTALLED_VERSION="$LE_AUTO_VERSION"
         # Continue to use OLD_VENV_PATH if the new venv doesn't exist
diff --git a/letsencrypt-auto-source/letsencrypt-auto.template b/letsencrypt-auto-source/letsencrypt-auto.template
index 31c5bb134..bc4b92092 100755
--- a/letsencrypt-auto-source/letsencrypt-auto.template
+++ b/letsencrypt-auto-source/letsencrypt-auto.template
@@ -256,20 +256,28 @@ DeprecationBootstrap() {
   fi
 }
 
-MIN_PYTHON_VERSION="2.7"
-MIN_PYVER=$(echo "$MIN_PYTHON_VERSION" | sed 's/\.//')
+MIN_PYTHON_2_VERSION="2.7"
+MIN_PYVER2=$(echo "$MIN_PYTHON_2_VERSION" | sed 's/\.//')
+MIN_PYTHON_3_VERSION="3.5"
+MIN_PYVER3=$(echo "$MIN_PYTHON_3_VERSION" | sed 's/\.//')
 # Sets LE_PYTHON to Python version string and PYVER to the first two
-# digits of the python version
+# digits of the python version.
+# MIN_PYVER and MIN_PYTHON_VERSION are also set by this function, and their
+# values depend on if we try to use Python 3 or Python 2.
 DeterminePythonVersion() {
   # Arguments: "NOCRASH" if we shouldn't crash if we don't find a good python
   #
   # If no Python is found, PYVER is set to 0.
   if [ "$USE_PYTHON_3" = 1 ]; then
+    MIN_PYVER=$MIN_PYVER3
+    MIN_PYTHON_VERSION=$MIN_PYTHON_3_VERSION
     for LE_PYTHON in "$LE_PYTHON" python3; do
       # Break (while keeping the LE_PYTHON value) if found.
       $EXISTS "$LE_PYTHON" > /dev/null && break
     done
   else
+    MIN_PYVER=$MIN_PYVER2
+    MIN_PYTHON_VERSION=$MIN_PYTHON_2_VERSION
     for LE_PYTHON in "$LE_PYTHON" python2.7 python27 python2 python; do
       # Break (while keeping the LE_PYTHON value) if found.
       $EXISTS "$LE_PYTHON" > /dev/null && break
@@ -285,7 +293,7 @@ DeterminePythonVersion() {
     fi
   fi
 
-  PYVER=`"$LE_PYTHON" -V 2>&1 | cut -d" " -f 2 | cut -d. -f1,2 | sed 's/\.//'`
+  PYVER=$("$LE_PYTHON" -V 2>&1 | cut -d" " -f 2 | cut -d. -f1,2 | sed 's/\.//')
   if [ "$PYVER" -lt "$MIN_PYVER" ]; then
     if [ "$1" != "NOCRASH" ]; then
       error "You have an ancient version of Python entombed in your operating system..."
@@ -298,6 +306,7 @@ DeterminePythonVersion() {
 {{ bootstrappers/deb_common.sh }}
 {{ bootstrappers/rpm_common_base.sh }}
 {{ bootstrappers/rpm_common.sh }}
+{{ bootstrappers/rpm_python3_legacy.sh }}
 {{ bootstrappers/rpm_python3.sh }}
 {{ bootstrappers/suse_common.sh }}
 {{ bootstrappers/arch_common.sh }}
@@ -344,31 +353,50 @@ elif [ -f /etc/redhat-release ]; then
      RPM_DIST_VERSION=0
   fi
 
-  # Starting to Fedora 29, python2 is on a deprecation path. Let's move to python3 then.
-  # RHEL 8 also uses python3 by default.
-  if [ "$RPM_DIST_NAME" = "fedora" -a "$RPM_DIST_VERSION" -ge 29 -o "$PYVER" -eq 26 ]; then
-    RPM_USE_PYTHON_3=1
-  elif [ "$RPM_DIST_NAME" = "rhel" -a "$RPM_DIST_VERSION" -ge 8 ]; then
-    RPM_USE_PYTHON_3=1
-  elif [ "$RPM_DIST_NAME" = "centos" -a "$RPM_DIST_VERSION" -ge 8 ]; then
-    RPM_USE_PYTHON_3=1
-  else
-    RPM_USE_PYTHON_3=0
-  fi
+  # Handle legacy RPM distributions
+  if [ "$PYVER" -eq 26 ]; then
+    # Check if an automated bootstrap can be achieved on this system.
+    if ! Python36SclIsAvailable; then
+      INTERACTIVE_BOOTSTRAP=1
+    fi
 
-  if [ "$RPM_USE_PYTHON_3" = 1 ]; then
     Bootstrap() {
-      BootstrapMessage "RedHat-based OSes that will use Python3"
-      BootstrapRpmPython3
+      BootstrapMessage "Legacy RedHat-based OSes that will use Python3"
+      BootstrapRpmPython3Legacy
     }
     USE_PYTHON_3=1
-    BOOTSTRAP_VERSION="BootstrapRpmPython3 $BOOTSTRAP_RPM_PYTHON3_VERSION"
+    BOOTSTRAP_VERSION="BootstrapRpmPython3Legacy $BOOTSTRAP_RPM_PYTHON3_LEGACY_VERSION"
+
+    # Try now to enable SCL rh-python36 for systems already bootstrapped
+    # NB: EnablePython36SCL has been defined along with BootstrapRpmPython3Legacy in certbot-auto
+    EnablePython36SCL
   else
-    Bootstrap() {
-      BootstrapMessage "RedHat-based OSes"
-      BootstrapRpmCommon
-    }
-    BOOTSTRAP_VERSION="BootstrapRpmCommon $BOOTSTRAP_RPM_COMMON_VERSION"
+    # Starting to Fedora 29, python2 is on a deprecation path. Let's move to python3 then.
+    # RHEL 8 also uses python3 by default.
+    if [ "$RPM_DIST_NAME" = "fedora" -a "$RPM_DIST_VERSION" -ge 29 ]; then
+      RPM_USE_PYTHON_3=1
+    elif [ "$RPM_DIST_NAME" = "rhel" -a "$RPM_DIST_VERSION" -ge 8 ]; then
+      RPM_USE_PYTHON_3=1
+    elif [ "$RPM_DIST_NAME" = "centos" -a "$RPM_DIST_VERSION" -ge 8 ]; then
+      RPM_USE_PYTHON_3=1
+    else
+      RPM_USE_PYTHON_3=0
+    fi
+
+    if [ "$RPM_USE_PYTHON_3" = 1 ]; then
+      Bootstrap() {
+        BootstrapMessage "RedHat-based OSes that will use Python3"
+        BootstrapRpmPython3
+      }
+      USE_PYTHON_3=1
+      BOOTSTRAP_VERSION="BootstrapRpmPython3 $BOOTSTRAP_RPM_PYTHON3_VERSION"
+    else
+      Bootstrap() {
+        BootstrapMessage "RedHat-based OSes"
+        BootstrapRpmCommon
+      }
+      BOOTSTRAP_VERSION="BootstrapRpmCommon $BOOTSTRAP_RPM_COMMON_VERSION"
+    fi
   fi
 
   LE_PYTHON="$prev_le_python"
@@ -545,8 +573,15 @@ if [ "$1" = "--le-auto-phase2" ]; then
     # If the selected Bootstrap function isn't a noop and it differs from the
     # previously used version
     if [ -n "$BOOTSTRAP_VERSION" -a "$BOOTSTRAP_VERSION" != "$PREV_BOOTSTRAP_VERSION" ]; then
-      # if non-interactive mode or stdin and stdout are connected to a terminal
-      if [ \( "$NONINTERACTIVE" = 1 \) -o \( \( -t 0 \) -a \( -t 1 \) \) ]; then
+      # Check if we can rebootstrap without manual user intervention: this requires that
+      # certbot-auto is in non-interactive mode AND selected bootstrap does not claim to
+      # require a manual user intervention.
+      if [ "$NONINTERACTIVE" = 1 -a "$INTERACTIVE_BOOTSTRAP" != 1 ]; then
+        CAN_REBOOTSTRAP=1
+      fi
+      # Check if rebootstrap can be done non-interactively and current shell is non-interactive
+      # (true if stdin and stdout are not attached to a terminal).
+      if [ \( "$CAN_REBOOTSTRAP" = 1 \) -o \( \( -t 0 \) -a \( -t 1 \) \) ]; then
         if [ -d "$VENV_PATH" ]; then
           rm -rf "$VENV_PATH"
         fi
@@ -557,12 +592,21 @@ if [ "$1" = "--le-auto-phase2" ]; then
           ln -s "$VENV_PATH" "$OLD_VENV_PATH"
         fi
         RerunWithArgs "$@"
+      # Otherwise bootstrap needs to be done manually by the user.
       else
-        error "Skipping upgrade because new OS dependencies may need to be installed."
-        error
-        error "To upgrade to a newer version, please run this script again manually so you can"
-        error "approve changes or with --non-interactive on the command line to automatically"
-        error "install any required packages."
+        # If it is because bootstrapping is interactive, --non-interactive will be of no use.
+        if [ "$INTERACTIVE_BOOTSTRAP" = 1 ]; then
+          error "Skipping upgrade because new OS dependencies may need to be installed."
+          error "This requires manual user intervention: please run this script again manually."
+        # If this is because of the environment (eg. non interactive shell without
+        # --non-interactive flag set), help the user in that direction.
+        else
+          error "Skipping upgrade because new OS dependencies may need to be installed."
+          error
+          error "To upgrade to a newer version, please run this script again manually so you can"
+          error "approve changes or with --non-interactive on the command line to automatically"
+          error "install any required packages."
+        fi
         # Set INSTALLED_VERSION to be the same so we don't update the venv
         INSTALLED_VERSION="$LE_AUTO_VERSION"
         # Continue to use OLD_VENV_PATH if the new venv doesn't exist
diff --git a/letsencrypt-auto-source/pieces/bootstrappers/rpm_common_base.sh b/letsencrypt-auto-source/pieces/bootstrappers/rpm_common_base.sh
index 326ad8b3f..2b00b199b 100644
--- a/letsencrypt-auto-source/pieces/bootstrappers/rpm_common_base.sh
+++ b/letsencrypt-auto-source/pieces/bootstrappers/rpm_common_base.sh
@@ -3,7 +3,9 @@
 
 # Sets TOOL to the name of the package manager
 # Sets appropriate values for YES_FLAG and QUIET_FLAG based on $ASSUME_YES and $QUIET_FLAG.
-# Enables EPEL if applicable and possible.
+# Note: this function is called both while selecting the bootstrap scripts and
+# during the actual bootstrap. Some things like prompting to user can be done in the latter
+# case, but not in the former one.
 InitializeRPMCommonBase() {
   if type dnf 2>/dev/null
   then
@@ -23,26 +25,6 @@ InitializeRPMCommonBase() {
   if [ "$QUIET" = 1 ]; then
     QUIET_FLAG='--quiet'
   fi
-
-  if ! $TOOL list *virtualenv >/dev/null 2>&1; then
-    echo "To use Certbot, packages from the EPEL repository need to be installed."
-    if ! $TOOL list epel-release >/dev/null 2>&1; then
-      error "Enable the EPEL repository and try running Certbot again."
-      exit 1
-    fi
-    if [ "$ASSUME_YES" = 1 ]; then
-      /bin/echo -n "Enabling the EPEL repository in 3 seconds..."
-      sleep 1s
-      /bin/echo -ne "\e[0K\rEnabling the EPEL repository in 2 seconds..."
-      sleep 1s
-      /bin/echo -e "\e[0K\rEnabling the EPEL repository in 1 second..."
-      sleep 1s
-    fi
-    if ! $TOOL install $YES_FLAG $QUIET_FLAG epel-release; then
-      error "Could not enable EPEL. Aborting bootstrap!"
-      exit 1
-    fi
-  fi
 }
 
 BootstrapRpmCommonBase() {
diff --git a/letsencrypt-auto-source/pieces/bootstrappers/rpm_python3.sh b/letsencrypt-auto-source/pieces/bootstrappers/rpm_python3.sh
index f33b07ca9..ac0553db5 100644
--- a/letsencrypt-auto-source/pieces/bootstrappers/rpm_python3.sh
+++ b/letsencrypt-auto-source/pieces/bootstrappers/rpm_python3.sh
@@ -4,7 +4,6 @@ BOOTSTRAP_RPM_PYTHON3_VERSION=1
 
 BootstrapRpmPython3() {
   # Tested with:
-  #   - CentOS 6
   #   - Fedora 29
 
   InitializeRPMCommonBase
@@ -15,12 +14,6 @@ BootstrapRpmPython3() {
       python3-virtualenv
       python3-devel
     "
-  # EPEL uses python34
-  elif $TOOL list python34 >/dev/null 2>&1; then
-    python_pkgs="python34
-      python34-devel
-      python34-tools
-    "
   else
     error "No supported Python package available to install. Aborting bootstrap!"
     exit 1
diff --git a/letsencrypt-auto-source/pieces/bootstrappers/rpm_python3_legacy.sh b/letsencrypt-auto-source/pieces/bootstrappers/rpm_python3_legacy.sh
new file mode 100644
index 000000000..0935c1b94
--- /dev/null
+++ b/letsencrypt-auto-source/pieces/bootstrappers/rpm_python3_legacy.sh
@@ -0,0 +1,75 @@
+# If new packages are installed by BootstrapRpmPython3 below, this version
+# number must be increased.
+BOOTSTRAP_RPM_PYTHON3_LEGACY_VERSION=1
+
+# Checks if rh-python36 can be installed.
+Python36SclIsAvailable() {
+  InitializeRPMCommonBase >/dev/null 2>&1;
+
+  if "${TOOL}" list rh-python36 >/dev/null 2>&1; then
+    return 0
+  fi
+  if "${TOOL}" list centos-release-scl >/dev/null 2>&1; then
+    return 0
+  fi
+  return 1
+}
+
+# Try to enable rh-python36 from SCL if it is necessary and possible.
+EnablePython36SCL() {
+  if "$EXISTS" python3.6 > /dev/null 2> /dev/null; then
+      return 0
+  fi
+  if ! scl --list 2>/dev/null | grep -q rh-python36; then
+      return 0
+  fi
+  set +e
+  . scl_source enable rh-python36
+  set -e
+}
+
+# This bootstrap concerns old RedHat-based distributions that do not ship by default
+# with Python 2.7, but only Python 2.6. We bootstrap them by enabling SCL and installing
+# Python 3.6. Some of these distributions are: CentOS/RHEL/OL/SL 6.
+BootstrapRpmPython3Legacy() {
+  # Tested with:
+  #   - CentOS 6
+
+  InitializeRPMCommonBase
+
+  if ! "${TOOL}" list rh-python36 >/dev/null 2>&1; then
+    echo "To use Certbot on this operating system, packages from the SCL repository need to be installed."
+    if ! "${TOOL}" list centos-release-scl >/dev/null 2>&1; then
+      error "Enable the SCL repository and try running Certbot again."
+      exit 1
+    fi
+    if [ "${ASSUME_YES}" = 1 ]; then
+      /bin/echo -n "Enabling the SCL repository in 3 seconds... (Press Ctrl-C to cancel)"
+      sleep 1s
+      /bin/echo -ne "\e[0K\rEnabling the SCL repository in 2 seconds... (Press Ctrl-C to cancel)"
+      sleep 1s
+      /bin/echo -e "\e[0K\rEnabling the SCL repository in 1 second... (Press Ctrl-C to cancel)"
+      sleep 1s
+    fi
+    if ! "${TOOL}" install "${YES_FLAG}" "${QUIET_FLAG}" centos-release-scl; then
+      error "Could not enable SCL. Aborting bootstrap!"
+      exit 1
+    fi
+  fi
+
+  # CentOS 6 must use rh-python36 from SCL
+  if "${TOOL}" list rh-python36 >/dev/null 2>&1; then
+    python_pkgs="rh-python36-python
+      rh-python36-python-virtualenv
+      rh-python36-python-devel
+    "
+  else
+    error "No supported Python package available to install. Aborting bootstrap!"
+    exit 1
+  fi
+
+  BootstrapRpmCommonBase "${python_pkgs}"
+
+  # Enable SCL rh-python36 after bootstrapping.
+  EnablePython36SCL
+}
diff --git a/letsencrypt-auto-source/tests/centos6_tests.sh b/letsencrypt-auto-source/tests/centos6_tests.sh
index 2c6dcf734..c15cd80ec 100644
--- a/letsencrypt-auto-source/tests/centos6_tests.sh
+++ b/letsencrypt-auto-source/tests/centos6_tests.sh
@@ -1,81 +1,140 @@
 #!/bin/bash
 # Start by making sure your system is up-to-date:
-yum update -y > /dev/null
-yum install -y centos-release-scl > /dev/null
-yum install -y python27 > /dev/null 2> /dev/null
+yum update -y >/dev/null
+yum install -y centos-release-scl >/dev/null
+yum install -y python27 >/dev/null 2>/dev/null
 
+LE_AUTO_PY_34="certbot/letsencrypt-auto-source/letsencrypt-auto_py_34"
 LE_AUTO="certbot/letsencrypt-auto-source/letsencrypt-auto"
 
+# Last version of certbot-auto that was bootstraping Python 3.4 for CentOS 6 users
+INITIAL_CERTBOT_VERSION_PY34="certbot 0.38.0"
+
 # we're going to modify env variables, so do this in a subshell
 (
-source /opt/rh/python27/enable
+  . scl_source enable python27
 
-# ensure python 3 isn't installed
-python3 --version 2> /dev/null
-RESULT=$?
-if [ $RESULT -eq 0 ]; then
-  error "Python3 is already installed."
-  exit 1
-fi
+  # ensure python 3 isn't installed
+  python3 --version >/dev/null 2>/dev/null
+  RESULT=$?
+  if [ $RESULT -eq 0 ]; then
+    echo "ERROR: Python3 is already installed."
+    exit 1
+  fi
 
-# ensure python2.7 is available
-python2.7 --version 2> /dev/null
-RESULT=$?
-if [ $RESULT -ne 0 ]; then
-  error "Python3 is not available."
-  exit 1
-fi
+  # ensure python2.7 is available
+  python2.7 --version >/dev/null 2>/dev/null
+  RESULT=$?
+  if [ $RESULT -ne 0 ]; then
+    echo "ERROR: Python2.7 is not available."
+    exit 1
+  fi
 
-# bootstrap, but don't install python 3.
-"$LE_AUTO" --no-self-upgrade -n > /dev/null 2> /dev/null
+  # bootstrap, but don't install python 3.
+  "$LE_AUTO" --no-self-upgrade -n >/dev/null 2>/dev/null
 
-# ensure python 3 isn't installed
-python3 --version 2> /dev/null
-RESULT=$?
-if [ $RESULT -eq 0 ]; then
-  error "letsencrypt-auto installed Python3 even though Python2.7 is present."
-  exit 1
-fi
+  # ensure python 3 isn't installed
+  python3 --version >/dev/null 2>/dev/null
+  RESULT=$?
+  if [ $RESULT -eq 0 ]; then
+    echo "ERROR: letsencrypt-auto installed Python3 even though Python2.7 is present."
+    exit 1
+  fi
 
-echo ""
-echo "PASSED: Did not upgrade to Python3 when Python2.7 is present."
+  echo "PASSED: Did not upgrade to Python3 when Python2.7 is present."
 )
 
 # ensure python2.7 isn't available
-python2.7 --version 2> /dev/null
+python2.7 --version >/dev/null 2>/dev/null
 RESULT=$?
 if [ $RESULT -eq 0 ]; then
-  error "Python2.7 is still available."
+  error "ERROR: Python2.7 is still available."
   exit 1
 fi
 
 # Skip self upgrade due to Python 3 not being available.
 if ! "$LE_AUTO" 2>&1 | grep -q "WARNING: couldn't find Python"; then
-  echo "Python upgrade failure warning not printed!"
+  echo "ERROR: Python upgrade failure warning not printed!"
   exit 1
 fi
 
-# bootstrap, this time installing python3
-"$LE_AUTO" --no-self-upgrade -n > /dev/null 2> /dev/null
+# bootstrap from the old letsencrypt-auto, this time installing python3.4
+"$LE_AUTO_PY_34" --no-self-upgrade -n >/dev/null 2>/dev/null
 
-# ensure python 3 is installed
-python3 --version > /dev/null
+# ensure python 3.4 is installed
+python3.4 --version >/dev/null 2>/dev/null
 RESULT=$?
 if [ $RESULT -ne 0 ]; then
-  error "letsencrypt-auto failed to install Python3 when only Python2.6 is present."
+  echo "ERROR: letsencrypt-auto failed to install Python3.4 using letsencrypt-auto < 0.37.0 when only Python2.6 is present."
   exit 1
 fi
 
-echo "PASSED: Successfully upgraded to Python3 when only Python2.6 is present."
-echo ""
+echo "PASSED: Successfully upgraded to Python3.4 using letsencrypt-auto < 0.37.0 when only Python2.6 is present."
 
-export VENV_PATH=$(mktemp -d)
-"$LE_AUTO" -n --no-bootstrap --no-self-upgrade --version >/dev/null 2>&1
-if [ "$($VENV_PATH/bin/python -V 2>&1 | cut -d" " -f2 | cut -d. -f1)" != 3 ]; then
-  echo "Python 3 wasn't used with --no-bootstrap!"
+# As "certbot-auto" (so without implicit --non-interactive flag set), check that the script
+# refuses to install SCL Python 3.6 when run in a non interactive shell (simulated here
+# using | tee /dev/null) if --non-interactive flag is not provided.
+cp "$LE_AUTO" /tmp/certbot-auto
+# NB: Readline has an issue on all Python versions for CentOS 6, making `certbot --version`
+# output an unprintable ASCII character on a new line at the end.
+# So we take the second last line of the output.
+version=$(/tmp/certbot-auto --version 2>/dev/null | tee /dev/null | tail -2 | head -1)
+
+if [ "$version" != "$INITIAL_CERTBOT_VERSION_PY34" ]; then
+  echo "ERROR: certbot-auto upgraded certbot in a non-interactive shell with --non-interactive flag not set."
   exit 1
 fi
-unset VENV_PATH
+
+echo "PASSED: certbot-auto did not upgrade certbot in a non-interactive shell with --non-interactive flag not set."
+
+if [ -f /opt/rh/rh-python36/enable ]; then
+  echo "ERROR: certbot-auto installed Python3.6 in a non-interactive shell with --non-interactive flag not set."
+  exit 1
+fi
+
+echo "PASSED: certbot-auto did not install Python3.6 in a non-interactive shell with --non-interactive flag not set."
+
+# now bootstrap from current letsencrypt-auto, that will install python3.6 from SCL
+"$LE_AUTO" --no-self-upgrade -n >/dev/null 2>/dev/null
+
+# Following test is exectued in a subshell, to not leak any environment variable
+(
+  # enable SCL rh-python36
+  . scl_source enable rh-python36
+
+  # ensure python 3.6 is installed
+  python3.6 --version >/dev/null 2>/dev/null
+  RESULT=$?
+  if [ $RESULT -ne 0 ]; then
+    echo "ERROR: letsencrypt-auto failed to install Python3.6 using current letsencrypt-auto when only Python2.6/Python3.4 are present."
+    exit 1
+  fi
+
+  echo "PASSED: Successfully upgraded to Python3.6 using current letsencrypt-auto when only Python2.6/Python3.4 are present."
+)
+
+# Following test is exectued in a subshell, to not leak any environment variable
+(
+  export VENV_PATH=$(mktemp -d)
+  "$LE_AUTO" -n --no-bootstrap --no-self-upgrade --version >/dev/null 2>&1
+  if [ "$($VENV_PATH/bin/python -V 2>&1 | cut -d" " -f2 | cut -d. -f1-2)" != "3.6" ]; then
+    echo "ERROR: Python 3.6 wasn't used with --no-bootstrap!"
+    exit 1
+  fi
+)
+
+# Following test is exectued in a subshell, to not leak any environment variable
+(
+  # enable SCL rh-python36
+  . scl_source enable rh-python36
+
+  # ensure everything works fine with certbot-auto bootstrap when python 3.6 is already enabled
+  export VENV_PATH=$(mktemp -d)
+  if ! "$LE_AUTO" --no-self-upgrade -n --version >/dev/null 2>/dev/null; then
+    echo "ERROR: Certbot-auto broke when Python 3.6 SCL is already enabled."
+    exit 1
+  fi
+)
 
 # test using python3
 pytest -v -s certbot/letsencrypt-auto-source/tests
diff --git a/letsencrypt-auto-source/tests/oraclelinux6_tests.sh b/letsencrypt-auto-source/tests/oraclelinux6_tests.sh
new file mode 100644
index 000000000..f3fd952f3
--- /dev/null
+++ b/letsencrypt-auto-source/tests/oraclelinux6_tests.sh
@@ -0,0 +1,85 @@
+#!/bin/bash
+set -eo pipefail
+# Start by making sure your system is up-to-date:
+yum update -y >/dev/null
+
+LE_AUTO_PY_34="certbot/letsencrypt-auto-source/letsencrypt-auto_py_34"
+LE_AUTO="certbot/letsencrypt-auto-source/letsencrypt-auto"
+
+# Apply installation instructions from official documentation:
+# https://certbot.eff.org/lets-encrypt/centosrhel6-other
+cp "$LE_AUTO" /usr/local/bin/certbot-auto
+chown root /usr/local/bin/certbot-auto
+chmod 0755 /usr/local/bin/certbot-auto
+LE_AUTO=/usr/local/bin/certbot-auto
+
+# Last version of certbot-auto that was bootstraping Python 3.4 for CentOS 6 users
+INITIAL_CERTBOT_VERSION_PY34="certbot 0.38.0"
+
+# Check bootstrap from current certbot-auto will fail, because SCL is not enabled.
+set +o pipefail
+if ! "$LE_AUTO" -n 2>&1 | grep -q "Enable the SCL repository and try running Certbot again."; then
+  echo "ERROR: Bootstrap was not aborted although SCL was not installed!"
+  exit 1
+fi
+set -o pipefail
+
+echo "PASSED: Bootstrap was aborted since SCL was not installed."
+
+# Bootstrap from the old letsencrypt-auto, Python 3.4 will be installed from EPEL.
+"$LE_AUTO_PY_34" --no-self-upgrade -n --install-only >/dev/null 2>/dev/null
+
+# Ensure Python 3.4 is installed
+if ! command -v python3.4 &>/dev/null; then
+  echo "ERROR: old letsencrypt-auto failed to install Python3.4 using letsencrypt-auto < 0.37.0 when only Python2.6 is present."
+  exit 1
+fi
+
+echo "PASSED: Bootstrap from old letsencrypt-auto succeeded and installed Python 3.4"
+
+# Expect certbot-auto to skip rebootstrapping with a warning since SCL is not installed.
+if ! "$LE_AUTO" --non-interactive --version 2>&1 | grep -q "This requires manual user intervention"; then
+  echo "FAILED: Script certbot-auto did not print a warning about needing manual intervention!"
+  exit 1
+fi
+
+echo "PASSED: Script certbot-auto did not rebootstrap."
+
+# NB: Readline has an issue on all Python versions for OL 6, making `certbot --version`
+# output an unprintable ASCII character on a new line at the end.
+# So we take the second last line of the output.
+version=$($LE_AUTO --version 2>/dev/null | tail -2 | head -1)
+
+if [ "$version" != "$INITIAL_CERTBOT_VERSION_PY34" ]; then
+  echo "ERROR: Script certbot-auto upgraded certbot in a non-interactive shell while SCL was not enabled."
+  exit 1
+fi
+
+echo "PASSED: Script certbot-auto did not upgrade certbot but started it successfully while SCL was not enabled."
+
+# Enable SCL
+yum install -y oracle-softwarecollection-release-el6 >/dev/null
+
+# Expect certbot-auto to bootstrap successfully since SCL is available.
+"$LE_AUTO" -n --version &>/dev/null
+
+if [ "$(/opt/eff.org/certbot/venv/bin/python -V 2>&1 | cut -d" " -f2 | cut -d. -f1-2)" != "3.6" ]; then
+  echo "ERROR: Script certbot-auto failed to bootstrap and install Python 3.6 while SCL is available."
+  exit 1
+fi
+
+if ! /opt/eff.org/certbot/venv/bin/certbot --version > /dev/null 2> /dev/null; then
+  echo "ERROR: Script certbot-auto did not install certbot correctly while SCL is enabled."
+  exit 1
+fi
+
+echo "PASSED: Script certbot-auto correctly bootstraped Certbot using rh-python36 when SCL is available."
+
+# Expect certbot-auto will be totally silent now that everything has been correctly boostraped.
+OUTPUT_LEN=$("$LE_AUTO" --install-only --no-self-upgrade --quiet 2>&1 | wc -c)
+if [ "$OUTPUT_LEN" != 0 ]; then
+    echo certbot-auto produced unexpected output!
+    exit 1
+fi
+
+echo "PASSED: Script certbot-auto did not print anything in quiet mode."
diff --git a/tests/letstest/scripts/test_leauto_upgrades.sh b/tests/letstest/scripts/test_leauto_upgrades.sh
index 541f54f6b..fc7632793 100755
--- a/tests/letstest/scripts/test_leauto_upgrades.sh
+++ b/tests/letstest/scripts/test_leauto_upgrades.sh
@@ -117,6 +117,8 @@ if ! diff letsencrypt-auto letsencrypt-auto-source/letsencrypt-auto ; then
 fi
 
 if [ "$RUN_RHEL6_TESTS" = 1 ]; then
+    # Add the SCL python release to PATH in order to resolve python3 command
+    PATH="/opt/rh/rh-python36/root/usr/bin:$PATH"
     if ! command -v python3; then
         echo "Python3 wasn't properly installed"
         exit 1
diff --git a/tests/letstest/scripts/test_sdists.sh b/tests/letstest/scripts/test_sdists.sh
index 347589e04..c8ce9fe7f 100755
--- a/tests/letstest/scripts/test_sdists.sh
+++ b/tests/letstest/scripts/test_sdists.sh
@@ -1,8 +1,21 @@
 #!/bin/sh -xe
 
 cd letsencrypt
+
+# If we're on a RHEL 6 based system, we can be confident Python is already
+# installed because the package manager is written in Python.
+if command -v python && [ $(python -V 2>&1 | cut -d" " -f 2 | cut -d. -f1,2 | sed 's/\.//') -eq 26 ]; then
+    # RHEL/CentOS 6 will need a special treatment, so we need to detect that environment
+    RUN_RHEL6_TESTS=1
+fi
+
 letsencrypt-auto-source/letsencrypt-auto --install-only -n --debug
 
+if [ "$RUN_RHEL6_TESTS" = 1 ]; then
+  # Enable the SCL Python 3.6 installed by letsencrypt-auto bootstrap
+  PATH="/opt/rh/rh-python36/root/usr/bin:$PATH"
+fi
+
 PLUGINS="certbot-apache certbot-nginx"
 PYTHON_MAJOR_VERSION=$(/opt/eff.org/certbot/venv/bin/python --version 2>&1 | cut -d" " -f 2 | cut -d. -f1)
 TEMP_DIR=$(mktemp -d)
diff --git a/tox.ini b/tox.ini
index 04715cc2f..952204a9e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -206,7 +206,17 @@ passenv = DOCKER_*
 # At the moment, this tests under Python 2.6 only, as only that version is
 # readily available on the CentOS 6 Docker image.
 commands =
-    docker build -f letsencrypt-auto-source/Dockerfile.centos6 -t lea letsencrypt-auto-source
+    docker build -f letsencrypt-auto-source/Dockerfile.redhat6 --build-arg REDHAT_DIST_FLAVOR=centos -t lea letsencrypt-auto-source
+    docker run --rm -t -i lea
+whitelist_externals =
+    docker
+passenv = DOCKER_*
+
+[testenv:le_auto_oraclelinux6]
+# At the moment, this tests under Python 2.6 only, as only that version is
+# readily available on the Oracle Linux 6 Docker image.
+commands =
+    docker build -f letsencrypt-auto-source/Dockerfile.redhat6 --build-arg REDHAT_DIST_FLAVOR=oraclelinux -t lea letsencrypt-auto-source
     docker run --rm -t -i lea
 whitelist_externals =
     docker