diff --git a/.ci/README.md b/.ci/README.md
new file mode 100644
index 00000000000..e2b165cc518
--- /dev/null
+++ b/.ci/README.md
@@ -0,0 +1,9 @@
+# Continuous Integration (CI)
+
+We support several implementations of CI. All these implementations rely on
+[docker](https://docker.com) in some way. This directory contains bits which
+are shared between these CI implementations. The relevant docker files can be
+found in `/docker/`.
+
+* [CircleCI](https://circleci.com) is configured in `/.circleci/`.
+* [GitLab CI](https://gitlab.com) is configured in `/.gitlab-ci.yml`.
diff --git a/.ci/build-docker.sh b/.ci/build-docker.sh
new file mode 100755
index 00000000000..11651e5dd38
--- /dev/null
+++ b/.ci/build-docker.sh
@@ -0,0 +1,46 @@
+#!/bin/bash
+
+# This script gets called from CI to build several flavours of docker images
+# which contain Sage.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+set -ex
+
+[[ -z "$DOCKER_TAG" ]] && DOCKER_TAG=none
+[[ "$DOCKER_TAG" = "master" ]] && DOCKER_TAG=latest
+
+. .ci/setup-make-parallelity.sh
+
+# We speed up the build process by copying built artifacts from ARTIFACT_BASE
+# during docker build. See /docker/Dockerfile for more details.
+ARTIFACT_BASE=${ARTIFACT_BASE:-sagemath/sagemath-dev:latest}
+
+# Seed our cache with $ARTIFACT_BASE if it exists
+docker pull $ARTIFACT_BASE || true
+
+function docker_build {
+    time docker build -f docker/Dockerfile --build-arg "MAKE=${MAKE}" --build-arg ARTIFACT_BASE=$ARTIFACT_BASE $@
+}
+
+# We use a multi-stage build /docker/Dockerfile. For the caching to be
+# effective, we populate the cache by building the make-all target. (Just
+# building the last target is not enough as intermediate targets would be
+# discarded from the cache and therefore the caching would fail for our actual
+# builds below.)
+docker_build --pull --tag make-all --target make-all .
+
+# Build the release image without build artifacts.
+DOCKER_IMAGE_CLI=${DOCKER_USER:-sagemath}/sagemath:$DOCKER_TAG
+docker_build --target sagemath --tag "$DOCKER_IMAGE_CLI" .
+# Build the developer image with the build artifacts intact.
+# Note: It's important to build the dev image last because it might be tagged as ARTIFACT_BASE.
+DOCKER_IMAGE_DEV=${DOCKER_USER:-sagemath}/sagemath-dev:$DOCKER_TAG
+docker_build --target sagemath-dev --tag "$DOCKER_IMAGE_DEV" .
diff --git a/.ci/protect-secrets.sh b/.ci/protect-secrets.sh
new file mode 100755
index 00000000000..a3ae9239988
--- /dev/null
+++ b/.ci/protect-secrets.sh
@@ -0,0 +1,40 @@
+#!/bin/bash
+
+# This script protects all environment variables that start with "SECRET_".
+# It puts them in a temporary file. The name of the variable contains the path
+# of that file.  This filename can then safely be used in `cat` even if `set
+# -x` has been turned on. Also you can run "export" to understand the
+# environment without danger.
+# Be careful, however, not to use this like the following:
+# docker login $DOCKER_USER $(cat $SECRET_DOCKER_PASS)
+# as this would expose the password if `set -x` has been turned on.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+
+set -eo pipefail
+set +x
+
+function encrypt {
+    RET=`mktemp`
+    eval " echo \$$1" > "$RET"
+    echo $RET
+}
+
+for name in `awk 'END { for (name in ENVIRON) { print name; } }' < /dev/null`; do
+case "$name" in 
+  SECRET_*)
+    export $name="$(encrypt $name)"
+    echo "Protected $name"
+    ;;
+esac
+done
+
+unset encrypt
diff --git a/.ci/pull-gitlab.sh b/.ci/pull-gitlab.sh
new file mode 100755
index 00000000000..01bb10cdd08
--- /dev/null
+++ b/.ci/pull-gitlab.sh
@@ -0,0 +1,33 @@
+#!/bin/bash
+
+# This script gets called from CI to pull the Sage docker images that were
+# built during the "build" phase to pull all the connected docker daemon
+# (likely a docker-in-docker.)
+# This script expects a single parameter, the base name of the docker image
+# such as sagemath or sagemath-dev.
+# The variable $DOCKER_IMAGE is set to the full name of the pulled image;
+# source this script to use it.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+
+set -ex
+
+[[ -z "$DOCKER_TAG" ]] && (echo "Can not pull untagged build."; exit 0)
+[[ "$DOCKER_TAG" = "master" ]] && DOCKER_TAG=latest
+
+# Pull the built images from the gitlab registry and give them the original
+# names they had after built.
+# Note that "set -x" prints the $CI_BUILD_TOKEN here but GitLab removes it
+# automatically from the log output.
+docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN $CI_REGISTRY
+docker pull $CI_REGISTRY_IMAGE/$1:$DOCKER_TAG
+DOCKER_IMAGE="${DOCKER_USER:-sagemath}/$1:$DOCKER_TAG"
+docker tag $CI_REGISTRY_IMAGE/$1:$DOCKER_TAG $DOCKER_IMAGE
diff --git a/.ci/push-dockerhub.sh b/.ci/push-dockerhub.sh
new file mode 100755
index 00000000000..ca2c4906eec
--- /dev/null
+++ b/.ci/push-dockerhub.sh
@@ -0,0 +1,30 @@
+#!/bin/bash
+
+# This script gets called from CI to push our docker images to
+# $DOCKER_USER/sagemath* on the Docker Hub.
+# This script expects a single parameter, the base name of the docker image
+# such as sagemath or sagemath-dev.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+
+set -ex
+
+[[ -z "$DOCKER_TAG" ]] && (echo "Can not push untagged build."; exit 0)
+[[ "$DOCKER_TAG" = "master" ]] && DOCKER_TAG=latest
+
+# Push the built images to the docker hub (and fail silently if
+# DOCKER_USER/SECRET_DOCKER_PASS have not been configured.)
+if [[ -z "$DOCKER_USER" || -z "$SECRET_DOCKER_PASS" ]]; then
+    echo "DOCKER_USER/SECRET_DOCKER_PASS variables have not been configured in your Continuous Integration setup. Not pushing built images to Docker Hub."
+else
+  cat "$SECRET_DOCKER_PASS" | docker login -u $DOCKER_USER --password-stdin
+  docker push ${DOCKER_USER:-sagemath}/$1:$DOCKER_TAG
+fi
diff --git a/.ci/push-gitlab.sh b/.ci/push-gitlab.sh
new file mode 100755
index 00000000000..9d98dca7e49
--- /dev/null
+++ b/.ci/push-gitlab.sh
@@ -0,0 +1,27 @@
+#!/bin/bash
+set -ex
+
+# This script gets called from CI to push our docker images to registry
+# configured in GitLab. (Mostly, so we can pull them again to push them to the
+# Docker Hub.)
+# This script expects a single parameter, the base name of the docker image
+# such as sagemath or sagemath-dev.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+
+[[ -z "$DOCKER_TAG" ]] && (echo "Can not push untagged build."; exit 0)
+[[ "$DOCKER_TAG" = "master" ]] && DOCKER_TAG=latest
+
+# Note that "set -x" prints the $CI_BUILD_TOKEN here but GitLab removes it
+# automatically from the log output.
+docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN $CI_REGISTRY
+docker tag ${DOCKER_USER:-sagemath}/$1:$DOCKER_TAG $CI_REGISTRY_IMAGE/$1:$DOCKER_TAG
+docker push $CI_REGISTRY_IMAGE/$1:$DOCKER_TAG
diff --git a/.ci/setup-make-parallelity.sh b/.ci/setup-make-parallelity.sh
new file mode 100644
index 00000000000..12f3a252179
--- /dev/null
+++ b/.ci/setup-make-parallelity.sh
@@ -0,0 +1,26 @@
+#!/bin/bash
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+set -ex
+
+# Determine the number of threads that can run simultaneously on this system
+# (we might not have nproc available.)
+# Note that this value is incorrect for some CI providers (notably CircleCI:
+# https://circleci.com/docs/2.0/configuration-reference/#resource_class) which
+# provision fewer vCPUs than shown in /proc/cpuinfo. Also, setting this value
+# too high can lead to RAM being insufficient, so it's best to set this
+# variable manually in your CI configuration.
+[[ -z "$NTHREADS" ]] && NTHREADS=`grep -E '^processor' /proc/cpuinfo | wc -l` || true
+# Set -j and -l for make (though -l is probably stripped by Sage)
+[[ -z "$MAKEOPTS" ]] && MAKEOPTS="-j $NTHREADS -l $((NTHREADS-1)).8" || true
+# Not all parts of Sage seem to honor MAKEOPTS, so the current way of telling
+# the system which concurrency to use, seems to be setting $MAKE.
+[[ -z "$MAKE" ]] && MAKE="make $MAKEOPTS" || true
diff --git a/.ci/test-cli.sh b/.ci/test-cli.sh
new file mode 100755
index 00000000000..a9e8c059ffe
--- /dev/null
+++ b/.ci/test-cli.sh
@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# This script gets called from CI to run minimal tests on the sagemath image.
+
+# Usage: ./test-cli.sh sage-cli-image
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+set -exo pipefail
+
+echo "Checking that Sage starts and can calculate 1+1…"
+# Calculate 1+1 (remove startup messages and leading & trailing whitespace)
+TWO=`docker run "$1" sage -c "'print(1+1)'" | tail -1 | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//'`
+[[ "x$TWO" = "x2" ]]
diff --git a/.ci/test-dev.sh b/.ci/test-dev.sh
new file mode 100755
index 00000000000..60b59d6a5ca
--- /dev/null
+++ b/.ci/test-dev.sh
@@ -0,0 +1,35 @@
+#!/bin/bash
+
+# This script gets called from CI to run minimal tests on the sagemath-dev image.
+# This script expects a single argument, the full name of the docker image to
+# test.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+set -exo pipefail
+
+IMAGE="$1"
+
+. .ci/setup-make-parallelity.sh
+
+# Usage: timed_run limit args
+# Runs $IMAGE with args and check that it terminates with a zero exit code in at most limit seconds.
+function timed_run {
+    START=`date +%s`
+    docker run -e MAKE="$MAKE" "$IMAGE" "$2"
+    END=`date +%s`
+    TOTAL=$((END-START))
+    echo "Checking that \"$2\" was fast…"
+    [[ $TOTAL -lt $1 ]]
+}
+
+timed_run 60 true # runs make build
+# TODO: Can't we get this faster than that?
+timed_run 300 make # runs make build and then make
diff --git a/.ci/test-jupyter.sh b/.ci/test-jupyter.sh
new file mode 100755
index 00000000000..982f06fbeac
--- /dev/null
+++ b/.ci/test-jupyter.sh
@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# This script gets called from CI to run minimal tests on the sagemath-jupyter
+# image.
+
+# Usage: ./test-jupyter.sh sage-jupyter-image [host]
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+set -ex
+
+docker run --name sage-jupyter -p 8888:8888 -d "$1" "sage -n jupyter --no-browser --ip='*' --port=8888"
+echo "Checking that the Jupyter notebook is running…"
+sleep 10 # giving the server some time to start
+docker logs sage-jupyter
+wget --retry-connrefused --tries=10 --wait=3 "http://${2:-localhost}:8888"
diff --git a/.circleci/config.yml b/.circleci/config.yml
new file mode 100644
index 00000000000..13f8b567f5f
--- /dev/null
+++ b/.circleci/config.yml
@@ -0,0 +1,41 @@
+# This file configures automatic builds of Sage on [CircleCI](https://circleci.com).
+# To make the build time not too excessive, we seed the build cache with
+# sagemath/sagemath-dev:latest. When basic SPKGs change, this does not help much
+# and the full build might exceed CircleCI's limits for open source projcets (five
+# hours on 2 vCPUs as of early 2018.)
+# You might want to try to build locally or with GitLab CI, see
+# `.gitlab-ci.yml` for more options.
+# Note that we do not use workflows because it was not clear whether the docker
+# images sizes would not exceed the size limits of CircleCI workspaces. Also,
+# workflows would not make things faster. We do not get more machines for free
+# and the frequent loading of docker images probably exceeds the cost of the
+# actual tests.
+
+version: 2
+jobs:
+  # As https://circleci.com/docs/2.0/docker-layer-caching/ is a paid feature,
+  # we do build & test & release in one step.
+  build:
+    machine: true
+    steps:
+      - checkout
+      - run:
+          # The docker commands sometimes take a while to produce output
+          no_output_timeout: 30m
+          command: |
+            # CircleCI has no mechanism to hide secret variables.
+            # Therefore we roll our own to protect $SECRET_* variables.
+            . .ci/protect-secrets.sh
+
+            export DOCKER_TAG=${CIRCLE_TAG:-$CIRCLE_BRANCH}
+            # Build docker images
+            # TODO: Change this line to sagemath/sagemath-dev:latest
+            export ARTIFACT_BASE=saraedum/sagemath-dev:gitlabci
+            . .ci/build-docker.sh
+            # Test that the images work
+            . .ci/test-dev.sh $DOCKER_IMAGE_DEV
+            . .ci/test-cli.sh $DOCKER_IMAGE_CLI
+            . .ci/test-jupyter.sh $DOCKER_IMAGE_CLI localhost
+            # Push docker images to dockerhub if a dockerhub user has been configured
+            . .ci/push-dockerhub.sh sagemath-dev
+            . .ci/push-dockerhub.sh sagemath
diff --git a/.dockerignore b/.dockerignore
new file mode 120000
index 00000000000..3e4e48b0b5f
--- /dev/null
+++ b/.dockerignore
@@ -0,0 +1 @@
+.gitignore
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index 101d349690c..498b92c73b9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -81,3 +81,9 @@ $RECYCLE.BIN/
 ###########
 .ipynb_checkpoints
 Untitled*.ipynb
+
+#############################
+# GitLab CI generated files #
+#############################
+gitlab-build-docker.log
+
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
new file mode 100644
index 00000000000..e256dd1effe
--- /dev/null
+++ b/.gitlab-ci.yml
@@ -0,0 +1,99 @@
+# This file configures automatic builds of Sage on [GitLab](https://gitlab.com).
+# To make the build time not too excessive, we seed the build cache with
+# sagemath/sagemath-dev:latest. When basic SPKGs changed, this does not help
+# much and the full build might the set time limit in GitLab.  You can increase
+# that limit in Settings → CI/CD.
+# You can also provision your own private more powerful runner in the same
+# place; or set up your favourite cloud service to provide an on-demand
+# autoscale runner.
+
+image: docker:latest
+
+stages:
+  - build
+  - test
+  - release
+
+variables:
+  DOCKER_TAG: $CI_COMMIT_REF_SLUG
+  # Builds are very I/O intensive; make sure we have a fast file system.
+  DOCKER_DRIVER: overlay2
+  # TODO: Change this line to sagemath/sagemath-dev:latest
+  ARTIFACT_BASE: saraedum/sagemath-dev:gitlabci
+
+before_script:
+  # GitLab has no mechanism yet to hide secret variables: https://gitlab.com/gitlab-org/gitlab-ce/issues/13784
+  # So we roll our own which protects all variables that start with SECRET_
+  - . .ci/protect-secrets.sh
+
+# We use docker-in-docker to build our docker images.  It can be faster to
+# expose your outer docker daemon by mounting /var/run/docker.sock to
+# /var/run/docker.sock and setting DOCKER_HOST in Settings -> CI/CD -> Secret
+# variable to unix:///var/run/docker.sock
+services:
+- docker:dind
+
+# Build Sage and its documentation.
+# The build starts from the build artifacts of ARTIFACT_BASE which is usually
+# much faster than building from a clean checkout of Sage.
+build-from-latest: &build
+  stage: build
+  artifacts:
+    when: always
+    paths:
+    - gitlab-build-docker.log
+    expire_in: 1 month
+  script:
+    # The output of the build can get larger than gitlab.com's limit; only print the first 3MB.
+    - . .ci/build-docker.sh | tee gitlab-build-docker.log | head -c 3m
+    - . .ci/push-gitlab.sh sagemath-dev
+    - . .ci/push-gitlab.sh sagemath
+  except:
+    - master
+
+# Build Sage and its documentation from a clean checkout of Sage.
+# Note that this takes a very long time. You probably want to run this on your
+# own gitlab-runner and increase the standard GitLab time limit for CI runs.
+build-from-clean:
+  << : *build
+  variables:
+    ARTIFACT_BASE: "source-clean"
+  only:
+    - master
+
+test-dev:
+  stage: test
+  script:
+    - . .ci/pull-gitlab.sh sagemath-dev
+    - . .ci/test-dev.sh "$DOCKER_IMAGE"
+
+test-cli:
+  stage: test
+  script:
+    - . .ci/pull-gitlab.sh sagemath
+    - . .ci/test-cli.sh "$DOCKER_IMAGE"
+
+test-jupyter:
+  stage: test
+  script:
+    # Force usage of docker-in-docker (and don't start docker on a bind-mounted
+    # /var/run/docker.sock set through a proivate GitLab CI variable) so that
+    # the -p flag to docker run works as expected.
+    - export DOCKER_HOST='tcp://docker:2375'
+    - apk update
+    - apk add wget
+    - . .ci/pull-gitlab.sh sagemath
+    - . .ci/test-jupyter.sh "$DOCKER_IMAGE" docker
+
+# Pushes the built images to Docker Hub if the Settings -> CI/CD -> Secret
+# variables DOCKER_USER and SECRET_DOCKER_PASS have been set up.
+dockerhub:
+  stage: release
+  only:
+    - branches
+    - tags
+  script:
+    - . .ci/pull-gitlab.sh sagemath-dev
+    - . .ci/push-dockerhub.sh sagemath-dev
+    - . .ci/pull-gitlab.sh sagemath
+    - . .ci/push-dockerhub.sh sagemath
diff --git a/Makefile b/Makefile
index 92457458fe5..d2dfc71256d 100644
--- a/Makefile
+++ b/Makefile
@@ -68,6 +68,7 @@ misc-clean:
 	rm -f build/make/Makefile build/make/Makefile-auto
 	rm -f .BUILDSTART
 
+# TODO: What is a "bdist"? A binary distribution?
 bdist-clean: clean
 	$(MAKE) misc-clean
 
@@ -89,6 +90,31 @@ maintainer-clean: distclean bootstrap-clean
 micro_release: bdist-clean sagelib-clean
 	@echo "Stripping binaries ..."
 	LC_ALL=C find local/lib local/bin -type f -exec strip '{}' ';' 2>&1 | grep -v "File format not recognized" |  grep -v "File truncated" || true
+	@echo "Removing .py files that have a corresponding .pyc or .pyo file as they are not needed when running code with CPython..."
+	find local/lib/python* -name '*.py' | while IFS= read -r fname; do [ -e "$${fname}c" -o -e "$${fname}o" ] && rm "$$fname"; done || true
+	@echo "Removing sphinx artifacts..."
+	rm -rf local/share/doc/sage/doctrees local/share/doc/sage/inventory
+	@echo "Removing unnecessary files & directories - make will not be functional afterwards anymore"
+	@# We need src/sage/ for introspection with "??"
+	@# We need src/sage/bin/ for the scripts that invoke Sage
+	@# We need sage, the script to start Sage
+	@# We need local/, the dependencies and the built Sage library itself.
+	@# We keep VERSION.txt.
+	@# We keep COPYING.txt so we ship a license with this distribution.
+	find . -name . -o -prune ! -name src ! -name sage ! -name local ! -name VERSION.txt ! -name COPYING.txt ! -name build -exec rm -rf \{\} \;
+	cd src && find . -name . -o -prune ! -name sage ! -name bin -exec rm -rf \{\} \;
+
+# Leaves everything that is needed to make the next "make" fast but removes
+# all the cheap build artifacts that can be quickly regenerated.
+fast-rebuild-clean: misc-clean bdist-clean
+	rm -rf upstream/
+	rm -rf src/build/temp.*
+	# Without site-packages/sage sage does not start but copying/compiling
+	# them from src/build is very fast.
+	rm -rf local/lib/python*/site-packages/sage
+	# The .py files in src/build are restored from src/sage without their
+	# mtimes changed.
+	find src/build -name '*.py' -exec rm \{\} \;
 
 TESTALL = ./sage -t --all
 PTESTALL = ./sage -t -p --all
diff --git a/configure.ac b/configure.ac
index 5c61a89704e..2d86803c6c9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -285,9 +285,9 @@ fi
 AC_CHECK_PROG(found_latex, latex, yes, no)
 if test x$found_latex != xyes
 then
-    AC_MSG_WARN([You do not have 'latex', which is recommended, but not])
-    AC_MSG_WARN([required. Latex is only really used for building pdf])
-    AC_MSG_WARN([documents and for %latex mode in the AC_PACKAGE_NAME notebook.])
+    AC_MSG_NOTICE([You do not have 'latex', which is recommended, but not])
+    AC_MSG_NOTICE([required. Latex is only really used for building pdf])
+    AC_MSG_NOTICE([documents and for %latex mode in the AC_PACKAGE_NAME notebook.])
 fi
 
 # Check that perl is available, with version 5.8.0 or later.
diff --git a/docker/.gitignore b/docker/.gitignore
new file mode 100644
index 00000000000..a38152cb5ee
--- /dev/null
+++ b/docker/.gitignore
@@ -0,0 +1,2 @@
+# Stores the commit that was used to create a sagemath-dev image
+commit
diff --git a/docker/Dockerfile b/docker/Dockerfile
new file mode 100644
index 00000000000..503f9eb579f
--- /dev/null
+++ b/docker/Dockerfile
@@ -0,0 +1,176 @@
+################################################################################
+# SageMath images for Docker                                                   #
+################################################################################
+# This is a description of the layout of this Dockerfile; for details on the   #
+# created docker images, see the README.md please.                             #
+#                                                                              #
+# This Dockerfile builds sagemath (for end-users) and sagemath-dev (for        #
+# developers) it consists of lots of intermediate targets, mostly to shrink    #
+# the resulting images but also to make this hopefully easier to maintain.     #
+# The aims of this Dockerfile are:                                             #
+# (1) Make it build in reasonable time.                                        #
+# (2) It should be self-contained and work on its own, i.e., just by invoking  #
+# docker build without any external orchestration script.                      #
+#                                                                              #
+# The idea to achieve (1) is to reuse the build artifacts from the latest      #
+# master build. This is slightly against the philosophy of a Dockerfile (which #
+# should produce perfectly reproducible outputs) but building Sage from scratch#
+# just takes too long at the moment to do this all the time. ARTIFACT_BASE     #
+# controls which build artifacts are used. You probably want to set this to    #
+# sagemath/sagemath-dev:latest which takes the latest build from the official  #
+# master branch. The default is source-clean which builds Sage from scratch.   #
+# If you want to understand how this works, have a look at source-from-context #
+# which merges ARTIFACT_BASE with the context, i.e., the contents of the sage  #
+# source directory.                                                            #
+################################################################################
+
+
+ARG ARTIFACT_BASE=source-clean
+
+################################################################################
+# Image containing the run-time dependencies for Sage                          #
+################################################################################
+FROM ubuntu:xenial as run-time-dependencies
+LABEL maintainer="Erik M. Bray <erik.bray@lri.fr>, Julian Rüth <julian.rueth@fsfe.org>"
+# Set sane defaults for common environment variables.
+ENV LC_ALL C.UTF-8
+ENV LANG C.UTF-8
+ENV SHELL /bin/bash
+# Create symlinks for sage and sagemath - we copy a built sage to the target of these symlinks later.
+ARG SAGE_ROOT=/home/sage/sage
+RUN ln -s "$SAGE_ROOT/sage" /usr/bin/sage
+RUN ln -s /usr/bin/sage /usr/bin/sagemath
+# Sage needs the fortran libraries at run-time because we do not build gfortran
+# with Sage but use the system's.
+# We also install sudo for the sage user, see below.
+RUN apt-get update -qq \
+    && apt-get install -y --no-install-recommends gfortran sudo \
+    && apt-get clean \
+    && rm -r /var/lib/apt/lists/*
+# Sage refuses to build as root, so we add a "sage" user that can sudo without a password.
+# We also want this user at runtime as some commands in sage know about the user that was used during build.
+ARG HOME=/home/sage
+RUN adduser --quiet --shell /bin/bash --gecos "Sage user,101,," --disabled-password --home "$HOME" sage \
+    && echo "sage ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers.d/01-sage \
+    && chmod 0440 /etc/sudoers.d/01-sage
+# Run everything from now on as the sage user in sage's home
+USER sage
+ENV HOME $HOME
+WORKDIR $HOME
+
+################################################################################
+# Image containing everything so that a make in a clone of the Sage repository #
+# completes without errors                                                     #
+################################################################################
+FROM run-time-dependencies as build-time-dependencies
+# Install the build time dependencies & git
+RUN sudo apt-get update -qq \
+    && sudo apt-get install -y wget build-essential automake m4 dpkg-dev sudo python libssl-dev git \
+    && sudo apt-get clean \
+    && sudo rm -r /var/lib/apt/lists/*
+
+################################################################################
+# Image with an empty git repository in $SAGE_ROOT.                            #
+################################################################################
+FROM build-time-dependencies as source-clean
+ARG SAGE_ROOT=/home/sage/sage
+RUN mkdir -p "$SAGE_ROOT"
+WORKDIR $SAGE_ROOT
+RUN git init
+RUN git remote add trac git@trac.sagemath.org:sage.git
+
+################################################################################
+# Image with the build context added, i.e., the directory from which `docker   #
+# build` has been called in a separate directory so we can copy files from     #
+# there.                                                                       #
+# This blows up the size of this docker image significantly, but we only use   #
+# this image to create artifacts for our final image.                          #
+# Warning: If you set ARTIFACT_BASE to something else than source-clean, the   #
+# build is not going to use the build-time-dependencies target but rely on     #
+# whatever tools are installed in ARTIFACT_BASE.                               #
+################################################################################
+FROM $ARTIFACT_BASE as source-from-context
+WORKDIR $HOME
+COPY --chown=sage:sage . sage-context
+# Checkout the commit that is in $HOME/sage-context
+ARG SAGE_ROOT=/home/sage/sage
+WORKDIR $SAGE_ROOT
+RUN git fetch "$HOME/sage-context" HEAD \
+    && git reset FETCH_HEAD \
+    && git checkout -f FETCH_HEAD \
+    && git log -1 --format=%H > docker/commit \
+    && rm -rf .git
+# Copy over all the untracked/staged/unstaged changes from sage-context
+WORKDIR $HOME/sage-context
+RUN if git status --porcelain | read CHANGES; then \
+        git -c user.name=docker-build -c user.email=docker-build@sage.invalid stash -u \
+        && git stash show -p > "$HOME"/sage-context.patch; \
+    else \
+        touch "$HOME"/sage-context.patch; \
+    fi
+WORKDIR $SAGE_ROOT
+RUN patch -p1 < "$HOME"/sage-context.patch
+
+################################################################################
+# Image with a built sage but without sage's documentation.                    #
+################################################################################
+FROM source-from-context as make-build
+# Make sure that the results runs on most CPUs.
+ENV SAGE_FAT_BINARY yes
+# Just to be sure Sage doesn't try to build its own GCC (even though
+# it shouldn't with a recent GCC package from the system and with gfortran)
+ENV SAGE_INSTALL_GCC no
+# Make everything in the build use multiple cores (this causes trouble for some packages outside Sage but it still seems to be they way Sage is doing this.)
+ARG MAKE="make -j2"
+ENV MAKE $MAKE
+RUN make build
+
+################################################################################
+# Image with a full build of sage and its documentation.                       #
+################################################################################
+FROM make-build as make-all
+RUN make
+
+################################################################################
+# Image with a full build of sage and its documentation but everything         #
+# stripped that can be quickly rebuild by make.                                #
+################################################################################
+FROM make-all as make-fast-rebuild-clean
+RUN make fast-rebuild-clean
+
+################################################################################
+# A releasable (relatively small, but still huge) image of this build with all #
+# the build artifacts intact so developers can make changes and rebuild        #
+# quickly                                                                      #
+################################################################################
+FROM source-clean as sagemath-dev
+ARG SAGE_ROOT=/home/sage/sage
+COPY --chown=sage:sage --from=make-fast-rebuild-clean $SAGE_ROOT $SAGE_ROOT
+COPY ./docker/entrypoint-dev.sh /usr/local/bin/sage-entrypoint
+ENTRYPOINT ["/usr/local/bin/sage-entrypoint"]
+CMD ["bash"]
+
+################################################################################
+# Image with a full build of sage, ready to release, i.e., with stripped       #
+# binaries and some extras to run the jupyter notebook.                        #
+################################################################################
+FROM make-all as make-release
+RUN sage -pip install terminado "notebook>=5" "ipykernel>=4.6"
+RUN sage -i gap_jupyter singular_jupyter pari_jupyter
+RUN make micro_release
+
+################################################################################
+# A releasable (relatively small) image which contains a copy of sage without  #
+# temporary build artifacts which is set up to start the command line          #
+# interface if no parameters are passed in.                                    #
+################################################################################
+FROM run-time-dependencies as sagemath
+ARG SAGE_ROOT=/home/sage/sage
+COPY --chown=sage:sage --from=make-release $SAGE_ROOT/ $SAGE_ROOT/
+# Put scripts to start gap, gp, maxima, ... in /usr/bin
+WORKDIR $SAGE_ROOT
+RUN sudo sage --nodotsage -c "install_scripts('/usr/bin')"
+COPY ./docker/entrypoint.sh /usr/local/bin/sage-entrypoint
+ENTRYPOINT ["/usr/local/bin/sage-entrypoint"]
+EXPOSE 8888
+CMD ["sage"]
diff --git a/docker/README.md b/docker/README.md
new file mode 100644
index 00000000000..9b653689031
--- /dev/null
+++ b/docker/README.md
@@ -0,0 +1,51 @@
+[![License: GPL v3](https://img.shields.io/badge/License-GPL%20v3-blue.svg)](https://github.com/sagemath/sage/COPYING.txt) [![Maintained](https://img.shields.io/maintenance/yes/2018.svg)](https://github.com/sagemath/sage/commits/master) [![CircleCI](https://circleci.com/gh/saraedum/sage.svg?style=svg)](https://circleci.com/gh/saraedum/sage) [![GitLab CI](https://gitlab.com/saraedum/sage/badges/gitlabci/pipeline.svg)](https://gitlab.com/saraedum/sage/commits/gitlabci)
+
+# Supported tags
+
+* `latest` — the stable `master` branch
+* `x.x.x` — all stable releases of Sage are tagged with their version number.
+* `develop` — the current development version of Sage which gets merged into the `master` branch when a new version of Sage is released
+
+# What is SageMath
+
+SageMath is a free open-source mathematics software system licensed under the GPL. It builds on top of many existing open-source packages: NumPy, SciPy, matplotlib, Sympy, Maxima, GAP, FLINT, R and many more. Access their combined power through a common, Python-based language or directly via interfaces or wrappers. 
+
+**Mission**: *Creating a viable free open source alternative to Magma, Maple, Mathematica and Matlab.*
+
+# What's in this image
+
+There are several flavours of this image.
+
+* [`sagemath/sagemath`![image size](https://img.shields.io/microbadger/image-size/sagemath/sagemath.svg)](https://hub.docker.com/sagemath/sagemath) contains everything necessary to run Sage on the command line. Run it with:
+    ```
+    docker run -it sagemath/sagemath:latest
+    ```
+    You can start a graphical [Jupyter Notebook](https://jupyter.org) at http://localhost:8888 instead. To use the notebook, follow the instructions printed when you run:
+    ```
+    docker run -p8888:8888 sagemath/sagemath:latest "sage -n jupyter --no-browser --ip='*' --port=8888"
+    ```
+* [`sagemath/sagemath-dev`![image size](https://img.shields.io/microbadger/image-size/sagemath/sagemath-dev.svg)](https://hub.docker.com/sagemath/sagemath-dev) contains all the build artifacts to rebuild Sage quickly. This version is probably only relevant for Sage developers. Run this image with:
+    ```
+    docker run -it sagemath/sagemath-dev:latest
+    ```
+    This triggers a rebuild and drops you in a shell afterwards. Note that the git repository has been emptied to save space. If you want to use git, fetch from your git repository with `git fetch trac` and go to the commit that was used to create this image with
+    ```
+    git reset $(cat docker/commit)
+    ```
+
+# How to build your own SageMath images
+
+Run `docker build -f docker/Dockerfile --target TARGET .` in the Sage repository with `TARGET` one of `sage`, `sage-jupyter`, or `dev`.
+
+# How these images get updated
+
+Every push to our [github repository](https://github.com/sagemath/sage) triggers a build in [CircleCI](https://circleci.com) which builds and pushes the docker images.
+A push to master also triggers a "build" on our [Docker Hub](https://hub.docker.com) repositories. The latter build is mostly disabled by the `hooks/` and only updates the `README.md`.
+
+Every push to our [GitLab repository](https://gitlab.com/sagemath/sage) triggers a pipeline in GitLab CI. This build also pushes images to Docker Hub.
+
+Have a look at `.circleci/` and `.gitlab-ci.yml` if you want to setup either continuous integration service for your own fork of the SageMath repository.
+
+# License
+
+The whole Sage software distribution is licensed under the General Public License, version 3. More details can be found in our [COPYING.txt](https://github.com/sagemath/sage/blob/master/COPYING.txt)
diff --git a/docker/entrypoint-dev.sh b/docker/entrypoint-dev.sh
new file mode 100755
index 00000000000..67299a5a92d
--- /dev/null
+++ b/docker/entrypoint-dev.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+set -e
+make build
+exec "$@"
diff --git a/docker/entrypoint.sh b/docker/entrypoint.sh
new file mode 100755
index 00000000000..692b5c83390
--- /dev/null
+++ b/docker/entrypoint.sh
@@ -0,0 +1,2 @@
+#!/bin/bash
+exec sage -sh -c "$*"
diff --git a/docker/hooks/build b/docker/hooks/build
new file mode 100644
index 00000000000..b23e55619b2
--- /dev/null
+++ b/docker/hooks/build
@@ -0,0 +1 @@
+#!/bin/true
diff --git a/docker/hooks/push b/docker/hooks/push
new file mode 100644
index 00000000000..b23e55619b2
--- /dev/null
+++ b/docker/hooks/push
@@ -0,0 +1 @@
+#!/bin/true
diff --git a/src/sage_setup/docbuild/__init__.py b/src/sage_setup/docbuild/__init__.py
index b8f79c2269a..bf48bf57cdf 100644
--- a/src/sage_setup/docbuild/__init__.py
+++ b/src/sage_setup/docbuild/__init__.py
@@ -911,7 +911,12 @@ def get_new_and_updated_modules(self):
             except ImportError as err:
                 logger.error("Warning: Could not import %s %s", module_name, err)
                 raise
-            newtime = os.path.getmtime(sys.modules[module_name].__file__)
+
+            module_filename = sys.modules[module_name].__file__
+            if (module_filename.endswith('.pyc') or module_filename.endswith('.pyo')):
+                source_filename = module_filename[:-1]
+                if (os.path.exists(source_filename)): module_filename = source_filename
+            newtime = os.path.getmtime(module_filename)
 
             if newtime > mtime:
                 updated_modules.append(module_name)