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..82fb2c87c5a
--- /dev/null
+++ b/.ci/build-docker.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+# 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
+
+# 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:develop}
+
+# Seed our cache with $ARTIFACT_BASE if it exists.
+docker pull "$ARTIFACT_BASE" > /dev/null || true
+
+docker_build() {
+    # Docker's --cache-from does not really work with multi-stage builds: https://github.com/moby/moby/issues/34715
+    # So we just have to rely on the local cache.
+    time docker build -f docker/Dockerfile \
+--build-arg "MAKEOPTS=${MAKEOPTS}" --build-arg "SAGE_NUM_THREADS=${SAGE_NUM_THREADS}" --build-arg "MAKEOPTS_DOCBUILD=${MAKEOPTS}" --build-arg "SAGE_NUM_THREADS_DOCBUILD=${SAGE_NUM_THREADS_DOCBUILD}" --build-arg ARTIFACT_BASE=$ARTIFACT_BASE $@
+}
+
+# We use a multi-stage build /docker/Dockerfile. For the caching to be
+# effective, we populate the cache by building the run/build-time-dependencies
+# and the make-all target. (Just building the last target is not enough as
+# intermediate targets could be discarded from the cache [depending on the
+# docker version] and therefore the caching would fail for our actual builds
+# below.)
+docker_build --target run-time-dependencies --tag run-time-dependencies:$DOCKER_TAG .
+docker_build --target build-time-dependencies --tag build-time-dependencies:$DOCKER_TAG .
+docker_build --target make-all --tag make-all:$DOCKER_TAG .
+
+# Build the release image without build artifacts.
+docker_build --target sagemath --tag "$DOCKER_IMAGE_CLI" .
+# Display the layers of this image
+docker history "$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_build --target sagemath-dev --tag "$DOCKER_IMAGE_DEV" .
+# Display the layers of this image
+docker history "$DOCKER_IMAGE_DEV"
diff --git a/.ci/describe-system.sh b/.ci/describe-system.sh
new file mode 100755
index 00000000000..6bd3b0efd4a
--- /dev/null
+++ b/.ci/describe-system.sh
@@ -0,0 +1,23 @@
+#!/bin/sh
+
+# ****************************************************************************
+#       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 +e -x
+
+docker info
+docker run docker sh -c "
+  set -x
+  uname -a
+  df -h
+  cat /proc/cpuinfo
+  cat /proc/meminfo
+  cat /proc/sys/vm/overcommit_memory
+  cat /proc/sys/vm/overcommit_ratio"
diff --git a/.ci/head-tail.sh b/.ci/head-tail.sh
new file mode 100755
index 00000000000..036161dbc37
--- /dev/null
+++ b/.ci/head-tail.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+
+OFFSET=1024
+# This script reads from stdin and prints to stdout as long as a the output
+# does not exceed a certain number of bytes. When reading an EOF it prints the
+# last $OFFSET lines if they have not been printed normally already.
+# This script expects one argument, the number of bytes.
+
+# Heavily inspired by a simlar strategy in make, https://stackoverflow.com/a/44849696/812379.
+
+# ****************************************************************************
+#       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/
+# ****************************************************************************
+
+stdbuf -i0 -o0 -e0 awk -v limit=$1 -v firstMissingNR=-1 -v offset=$OFFSET -v bytes=0 \
+'{
+  if (bytes < limit) {
+    # this probably gets multi-byte characters wrong, but that probably does
+    # not matter for our purposes. (We add 1 for a UNIX newline.)
+    bytes += length($0) + 1;
+    print;
+  } else {
+    if (firstMissingNR == -1){
+      print "[…output truncated…]";
+      firstMissingNR = NR;
+    }
+    a[NR] = $0;
+    delete a[NR-offset];
+    printf "." > "/dev/stderr"
+  }
+}
+END {
+  if (firstMissingNR != -1) {
+    print "" > "/dev/stderr";
+    for(i = NR-offset+1 > firstMissingNR ? NR-offset-1 : firstMissingNR; i<=NR ; i++){ print a[i]; }
+  }
+}
+'
+
diff --git a/.ci/protect-secrets.sh b/.ci/protect-secrets.sh
new file mode 100755
index 00000000000..527604106ca
--- /dev/null
+++ b/.ci/protect-secrets.sh
@@ -0,0 +1,40 @@
+#!/bin/sh
+
+# 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..58b17016b90
--- /dev/null
+++ b/.ci/pull-gitlab.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+
+# 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
+
+# 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
+export DOCKER_IMAGE="${DOCKER_NAMESPACE:-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..a685ae8dd6e
--- /dev/null
+++ b/.ci/push-dockerhub.sh
@@ -0,0 +1,29 @@
+#!/bin/sh
+
+# This script gets called from CI to push our docker images to
+# $DOCKER_NAMESPACE/sagemath* on the Docker Hub.
+# This script expects a single parameter, the base name of the docker image
+# such as sagemath or sagemath-dev.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+
+set -ex
+
+[ -z "$DOCKER_TAG" ] && (echo "Can not push untagged build."; exit 0)
+
+# Push the built images to the docker hub (and fail silently if
+# DOCKER_USER/SECRET_DOCKER_PASS have not been configured.)
+if [ -z "$DOCKER_USER" -o -z "$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_NAMESPACE:-sagemath}/$1:$DOCKER_TAG
+fi
diff --git a/.ci/push-gitlab.sh b/.ci/push-gitlab.sh
new file mode 100755
index 00000000000..a1609995eed
--- /dev/null
+++ b/.ci/push-gitlab.sh
@@ -0,0 +1,25 @@
+#!/bin/sh
+
+# 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/
+# ****************************************************************************
+
+set -ex
+
+# 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_NAMESPACE:-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 100755
index 00000000000..4e33e11b006
--- /dev/null
+++ b/.ci/setup-make-parallelity.sh
@@ -0,0 +1,65 @@
+#!/bin/sh
+
+# Source this to set CPUTHREADS (the number of apparent cores) and RAMTHREADS
+# (free RAM divided by the maximum amount needed per thread typically)
+# From this this script infers reasonable defaults for SAGE_NUM_THREADS and
+# MAKEOPTS.
+
+# We do exactly the same for CPUTHREADS_DOCBUILD, RAMTHREADS_DOCBUILD,
+# SAGE_NUM_THREADS_DOCBUILD, MAKEOPTS_DOCBUILD. As the docbuild needs
+# substantially more RAM as of May 2018.
+
+# ****************************************************************************
+#       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
+
+if [ -z "$CPUTHREADS" ]; then
+    # Determine the number of threads that can run simultaneously on this system
+    # (we might not have nproc available.)
+    # Note that this value is incorrect for some CI providers (notably CircleCI:
+    # https://circleci.com/docs/2.0/configuration-reference/#resource_class) which
+    # provision fewer vCPUs than shown in /proc/cpuinfo. So it is probably better
+    # to set CPUTHREADS manuall in your CI configuration.
+    CPUTHREADS=`docker run docker cat /proc/cpuinfo | grep -E '^processor' | wc -l`
+fi
+if [ -z "$CPUTHREADS_DOCBUILD" ]; then
+    CPUTHREADS_DOCBUILD=$CPUTHREADS
+fi
+
+if [ -z "$RAMTHREADS" ]; then
+    RAMTHREADS=$(( `docker run docker cat /proc/meminfo | grep MemTotal | awk '{ print $2 }'` / 1048576 ))
+    if [ $RAMTHREADS = 0 ];then
+        RAMTHREADS=1;
+    fi
+fi
+if [ -z "$RAMTHREADS_DOCBUILD" ]; then
+    RAMTHREADS_DOCBUILD=$(( `docker run docker cat /proc/meminfo | grep MemTotal | awk '{ print $2 }'` / 2097152 ))
+    if [ $RAMTHREADS_DOCBUILD = 0 ];then
+        RAMTHREADS_DOCBUILD=1;
+    fi
+fi
+
+# On CI machines with their virtual CPUs, it seems to be quite beneficial to
+# overcommit on CPU usage. We only need to make sure that we do not exceed RAM
+# (as there is no swap.)
+if [ $CPUTHREADS -lt $RAMTHREADS ]; then
+    export SAGE_NUM_THREADS=$((CPUTHREADS + 1))
+else
+    export SAGE_NUM_THREADS=$RAMTHREADS
+fi
+if [ $CPUTHREADS_DOCBUILD -lt $RAMTHREADS_DOCBUILD ]; then
+    export SAGE_NUM_THREADS_DOCBUILD=$((CPUTHREADS_DOCBUILD + 1))
+else
+    export SAGE_NUM_THREADS_DOCBUILD=$RAMTHREADS_DOCBUILD
+fi
+# Set -j and -l for make (though -l is probably ignored by Sage)
+export MAKEOPTS="-j $SAGE_NUM_THREADS -l $((CPUTHREADS - 1)).8"
+export MAKEOPTS_DOCBUILD="-j $SAGE_NUM_THREADS_DOCBUILD -l $((CPUTHREADS_DOCBUILD - 1)).8"
diff --git a/.ci/test-cli.sh b/.ci/test-cli.sh
new file mode 100755
index 00000000000..0ad6a8f3d0a
--- /dev/null
+++ b/.ci/test-cli.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+
+# This script gets called from CI to run minimal tests on the sagemath image.
+
+# Usage: ./test-cli.sh IMAGE-NAME
+
+# ****************************************************************************
+#       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
+
+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" ]
+
+echo "Checking that some binaries that should be distributed with Sage are on the PATH…"
+# We could also run minimal tests on these but we don't yet.
+# Check that Singular and GAP are present
+docker run "$1" which Singular
+docker run "$1" which gap
+# Check that jupyter is present (for binder)
+docker run "$1" which jupyter
diff --git a/.ci/test-dev.sh b/.ci/test-dev.sh
new file mode 100755
index 00000000000..5ba2cce16ca
--- /dev/null
+++ b/.ci/test-dev.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+
+# 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.
+
+# Usage: ./test-dev.sh IMAGE-NAME
+
+# ****************************************************************************
+#       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
+
+IMAGE="$1"
+
+. .ci/setup-make-parallelity.sh
+
+# Usage: timed_run limit args
+# Runs $IMAGE with args and check that it terminates with a zero exit code in at most limit seconds.
+timed_run() {
+    START=`date +%s`
+    docker run -e MAKEOPTS="$MAKEOPTS_DOCBUILD" -e SAGE_NUM_THREADS="$SAGE_NUM_THREADS_DOCBUILD" "$IMAGE" "$2"
+    END=`date +%s`
+    TOTAL=$((END-START))
+    echo "Checking whether running \"$2\" was fast…"
+    [ "$TOTAL" -lt "$1" ]
+}
+
+# Most setup should be done in well under 120 seconds but some CI machines tend
+# to be really slow so we better give them some space here. Better miss a
+# regression at first than create a lot of noise.
+timed_run 120 true # runs make build
+# Building the documentation is quite slow at the moment:
+# Currently, this detects some dependencies as changed that have not changed.
+# The parser in Sphinx fails to parse some .py files and adds the (more
+# recently modified) .pyc files as dependencies instead. (Have a look the
+# changeset that introduced this comment for more details.)
+timed_run $(( 1200/$SAGE_NUM_THREADS_DOCBUILD )) 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..4578fb5cbd8
--- /dev/null
+++ b/.ci/test-jupyter.sh
@@ -0,0 +1,23 @@
+#!/bin/sh
+
+# This script gets called from CI to run minimal tests on the sagemath-jupyter
+# image.
+
+# Usage: ./test-jupyter.sh IMAGE-NAME [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 -d "$1" sage-jupyter
+echo "Checking that the Jupyter notebook is running…"
+sleep 10 # giving the server some time to start
+docker logs sage-jupyter
+docker run --link sage-jupyter alpine sh -c "apk --update add wget; wget --retry-connrefused --tries=10 --wait=3 http://sage-jupyter:8888"
diff --git a/.ci/update-env.sh b/.ci/update-env.sh
new file mode 100755
index 00000000000..470529d742a
--- /dev/null
+++ b/.ci/update-env.sh
@@ -0,0 +1,44 @@
+#!/bin/sh
+
+# This script gets called from CI to establish the name of the current docker
+# tag to build and also the image which is used to seed the cache.
+
+# ****************************************************************************
+#       Copyright (C) 2018 Julian Rüth <julian.rueth@fsfe.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#                  http://www.gnu.org/licenses/
+# ****************************************************************************
+
+set -ex
+
+# The maintainer of the CI environment, e.g., the people administrating the
+# SageMath account on gitlab.com, can decide to inject an arbitrary
+# base64-encoded script early into the CI execution. The script has access to
+# all the CI variables, e.g., to find out which job is being executed, and
+# it could do things such as "exit 1" to fail early, or "git merge" a fix for a
+# known bug in CI. The CI_MONKEY_PATCH could of course also curl a more
+# complicated script and execute that.
+if [ -n "$CI_MONKEY_PATCH" ]; then
+    SCRIPT=$(echo "$CI_MONKEY_PATCH" | base64 -d)
+    $SCRIPT
+fi
+
+# From the docker documentation: "A tag name must be valid ASCII and may
+# contain lowercase and uppercase letters, digits, underscores, periods and
+# dashes. A tag name may not start with a period or a dash and may contain a
+# maximum of 128 characters."
+export DOCKER_TAG=`echo $DOCKER_TAG | tr -d '[:space:]' | tr -c '[:alnum:]_.-' '-' | sed 's/^[-.]*//' | cut -c1-128`
+
+[[ -z "$DOCKER_TAG" ]] && export DOCKER_TAG=none
+[[ "$DOCKER_TAG" = "master" ]] && export DOCKER_TAG=latest
+
+export DOCKER_IMAGE_CLI=${DOCKER_NAMESPACE:-sagemath}/sagemath:$DOCKER_TAG
+export DOCKER_IMAGE_DEV=${DOCKER_NAMESPACE:-sagemath}/sagemath-dev:$DOCKER_TAG
+
+# Seed the build cache with this image (set to source-clean to build from
+# scratch.)
+export ARTIFACT_BASE=${ARTIFACT_BASE:-$DEFAULT_ARTIFACT_BASE}
diff --git a/.circleci/before-script.sh b/.circleci/before-script.sh
new file mode 100644
index 00000000000..51127362f15
--- /dev/null
+++ b/.circleci/before-script.sh
@@ -0,0 +1,26 @@
+#!/bin/sh
+
+# Source this script during a CI run to set environment variables and print
+# some informational messages about the system we are running 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/
+# ****************************************************************************
+
+# CircleCI has no mechanism to hide secret variables.
+# Therefore we roll our own to protect $SECRET_* variables.
+. .ci/protect-secrets.sh
+# Collect debug infos about the system we are running on
+.ci/describe-system.sh
+# Set MAKEOPTS and SAGE_NUM_THREADS 
+. .ci/setup-make-parallelity.sh
+
+# Set DOCKER_TAG according to the current branch/tag
+export DOCKER_TAG=${CIRCLE_TAG:-$CIRCLE_BRANCH}
+. .ci/update-env.sh
diff --git a/.circleci/config.yml b/.circleci/config.yml
new file mode 100644
index 00000000000..2b425783ce6
--- /dev/null
+++ b/.circleci/config.yml
@@ -0,0 +1,89 @@
+# 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:develop. When basic SPKGs change, this does not help much,
+# as the full build will often 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.
+
+# As of early 2018, a run on CircleCI takes usually about 25 minutes. Most of
+# the time is spent pulling/pushing from/to Docker Hub and copying files
+# locally during the docker build. We could probably save five minutes by not
+# building and testing the sagemath-dev image for most branches.
+
+version: 2
+jobs:
+  build-test-release: &build-test-release
+    docker:
+      - image: docker:latest
+    environment:
+      DEFAULT_ARTIFACT_BASE: sagemath/sagemath-dev:develop
+    steps:
+      - run: apk --update add git openssh
+      - checkout
+      - setup_remote_docker:
+          version: 18.05.0-ce
+      - run: &build
+          # The docker commands sometimes take a while to produce output
+          no_output_timeout: 30m
+          name: build
+          command: |
+            . .circleci/before-script.sh
+            .ci/build-docker.sh
+      - run: &test-dev
+          name: test-dev
+          command: |
+            . .circleci/before-script.sh
+            .ci/test-dev.sh $DOCKER_IMAGE_DEV
+      - run: &test-cli
+          name: test-cli
+          command: |
+            . .circleci/before-script.sh
+            .ci/test-cli.sh $DOCKER_IMAGE_CLI
+      - run: &test-jupyter
+          name: test-jupyter
+          command: |
+            . .circleci/before-script.sh
+            .ci/test-jupyter.sh $DOCKER_IMAGE_CLI localhost
+      - run: &release
+          # The docker commands sometimes take a while to produce output
+          no_output_timeout: 30m
+          name: release
+          command: |
+            . .circleci/before-script.sh
+            # Push docker images to dockerhub if a dockerhub user has been configured
+            .ci/push-dockerhub.sh sagemath-dev
+            .ci/push-dockerhub.sh sagemath
+  build-from-latest-test-release:
+    <<: *build-test-release
+  build-from-clean-test-release:
+    <<: *build-test-release
+    environment:
+      ARTIFACT_BASE: source-clean
+
+workflows:
+  version: 2
+  build-branch-from-clean:
+    jobs:
+      - build-from-clean-test-release:
+          filters:
+            branches:
+              only:
+                - master
+                - develop
+  build-tag-from-clean:
+    jobs:
+      - build-from-clean-test-release:
+          filters:
+            branches:
+              ignore: /.*/
+            tags:
+              only: /.*/
+  build-branch-from-latest:
+    jobs:
+      - build-from-latest-test-release:
+          filters:
+            branches:
+              ignore:
+                - master
+                - develop
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..c98ce30b813 100644
--- a/.gitignore
+++ b/.gitignore
@@ -81,3 +81,14 @@ $RECYCLE.BIN/
 ###########
 .ipynb_checkpoints
 Untitled*.ipynb
+
+#############################
+# GitLab CI generated files #
+#############################
+gitlab-build-docker.log
+
+/src/.cython_version
+/src/build
+/src/Makefile
+/src/bin/sage-env-config
+
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
new file mode 100644
index 00000000000..0319ba1c410
--- /dev/null
+++ b/.gitlab-ci.yml
@@ -0,0 +1,173 @@
+# 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:develop. When basic SPKGs changed, this does not help
+# much and the full build might exceed 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
+# https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#use-docker-in-docker-executor;
+# or set up your favourite cloud service to provide an on-demand autoscale
+# runner. More details below.
+
+# As of early 2018 a run on GitLab CI takes about 45 minutes. We could probably
+# save 10 minutes by not building/pushing/testing dev images for branches other
+# than master/develop.
+
+# Note that most of the time during CI is spent with pulling and pushing of
+# docker images and copying files locally as part of the docker build.  At the
+# moment there is no reliable way of passing the docker images to the following
+# stages without explicit pushing/pulling or similar:
+# https://gitlab.com/gitlab-org/gitlab-runner/issues/1107
+
+# The timings mentioned above are typical values. The shared runners provided
+# on gitlab.com are sometimes much slower depending on the runner you are
+# scheduled on. Sometimes it's slower for no apparent reason, probably just an
+# overcommittment of virtual machines on hardware.
+
+# GitLab provides several flavours of shared runners (as of early 2018):
+# * runners tagged as "do" (digitalocean.com) provide about 60GB of HDD, two
+#   cores, but only 2GB of RAM. The RAM is sometimes not sufficient to build
+#   the documentation.
+# * runners tagged as "gce" (Google Compute Engine) provide about 22GB of HDD,
+#   a single core, 4GB of RAM. Since we are relying on OverlayFS, the disk
+#   space is not sufficient to build sage from scratch.
+# The shared runners are terminated after three hours. Currently, this is often
+# insufficient to build sage from scratch.
+
+# If you want to provide your own runners, make sure to tag them as follows:
+# * "big" (60GB of disk space are available) to make build-from-clean pass.
+
+image: docker:latest
+
+stages:
+  - build
+  - test
+  - release
+
+variables:
+  DOCKER_TAG: $CI_COMMIT_REF_NAME
+  # Builds are very I/O intensive; make sure we have a fast file system.
+  DOCKER_DRIVER: overlay2
+  DEFAULT_ARTIFACT_BASE: sagemath/sagemath-dev:develop
+
+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
+  # Collect debug infos about the system we are running on
+  - .ci/describe-system.sh
+  # Set DOCKER_TAG according to the current branch/tag
+  - . .ci/update-env.sh
+  # Set MAKEOPTS and SAGE_NUM_THREADS according to the machine we are running on
+  - . .ci/setup-make-parallelity.sh
+
+# We use docker-in-docker to build our docker images, i.e., we run a
+# docker:dind "service" container and link to it from the container running the
+# actual scripts below.
+# Our scripts automatically connect to this service (unless you override it by
+# setting DOCKER_HOST.) For example, each RUN statement in the Dockerfile
+# spawns a docker container inside the docker:dind container to perform the RUN
+# command there.
+# 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. (The
+# speedup is mostly due to sharing layers of intermediate images.) However,
+# this is only possible if you provision your own runners. Shared gitlab
+# runners, do not bind mount /var/run/docker.sock. Also, docker:dind provides
+# better isolation. If you expect many builds to run simultaneously on a host,
+# conflicting tags can cause issues with a mounted DOCKER_HOST.
+services:
+- docker:18.05.0-ce-dind
+
+# Build Sage and its documentation.
+# The build starts from the build artifacts of DEFAULT_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:
+    - apk --update add coreutils
+    # The output of the build can get larger than gitlab.com's limit; only print the first 3MB (and the last 80 lines.)
+    - .ci/build-docker.sh | tee gitlab-build-docker.log | .ci/head-tail.sh 3145728
+    - .ci/push-gitlab.sh sagemath-dev
+    - .ci/push-gitlab.sh sagemath
+  except:
+    - master
+    - develop
+    - tags
+
+# Build Sage and its documentation from a clean checkout of Sage.
+# Note that this takes several hours. You probably want to run this on your own
+# gitlab-runner and increase the standard GitLab time limit for CI runs.
+# Some of the shared runners provided by GitLab for free do not have enough
+# disk space for this to work. If a build fails with "no space left on device",
+# you could just retry it and hope to be scheduled on a machine with more disk
+# space, or provision your own runner.
+build-from-clean:
+  << : *build
+  variables:
+    ARTIFACT_BASE: "source-clean"
+  only:
+    - master
+    - develop
+    - tags
+  except: []
+  tags:
+    # 60 GB of HDD are available
+    - big
+  # This build takes several CPU hours. It is very unlikely that there are any
+  # actual build errors for a tagged release but the (discounted) cloud
+  # machines this is running on might be preempted during the long build time.
+  # So let's try three times before we give up.
+  retry: 2
+
+test-dev:
+  stage: test
+  script:
+    - . .ci/pull-gitlab.sh sagemath-dev
+    - sh .ci/test-dev.sh "$DOCKER_IMAGE"
+
+test-cli:
+  stage: test
+  script:
+    - . .ci/pull-gitlab.sh sagemath
+    - sh .ci/test-cli.sh "$DOCKER_IMAGE"
+
+test-jupyter:
+  stage: test
+  script:
+    - . .ci/pull-gitlab.sh sagemath
+    - sh .ci/test-jupyter.sh "$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.
+push-dockerhub:
+  stage: release
+  only:
+    refs:
+      - branches
+      - tags
+    variables:
+      - $SECRET_DOCKER_PASS
+  script:
+    - . .ci/pull-gitlab.sh sagemath
+    - sh .ci/push-dockerhub.sh sagemath
+
+# Pushes the built dev images to Docker Hub if the Settings -> CI/CD -> Secret
+# variables DOCKER_USER and SECRET_DOCKER_PASS have been set up.
+push-dockerhub-dev:
+  stage: release
+  only:
+    refs:
+      - master
+      - develop
+      - tags
+    variables:
+      - $SECRET_DOCKER_PASS
+  script:
+    - . .ci/pull-gitlab.sh sagemath-dev
+    - sh .ci/push-dockerhub.sh sagemath-dev
diff --git a/Makefile b/Makefile
index d81d450ef4e..89ac3e4ecf1 100644
--- a/Makefile
+++ b/Makefile
@@ -104,9 +104,44 @@ bootstrap-clean:
 maintainer-clean: distclean bootstrap-clean
 	rm -rf upstream
 
+# Remove everything that is not necessary to run Sage and pass all its
+# doctests.
 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 sphinx artifacts..."
+	rm -rf local/share/doc/sage/doctrees local/share/doc/sage/inventory
+	@echo "Removing documentation. Inspection in IPython still works."
+	rm -rf local/share/doc local/share/*/doc local/share/*/examples local/share/singular/html
+	@echo "Removing unnecessary files & directories - make will not be functional afterwards anymore"
+	@# We need src/doc/common, src/doc/en/introspect for introspection with "??"
+	@# We keep src/sage for some doctests that it expect it to be there and
+	@# also because it does not add any weight with rdfind below.
+	@# 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 ! -name doc -exec rm -rf \{\} \;
+	if command -v rdfind > /dev/null; then \
+		echo "Hardlinking identical files."; \
+		rdfind -makeresultsfile false -makehardlinks true .; \
+	else \
+		echo "rdfind not installed. Not hardlinking identical files."; \
+	fi
+
+# 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 5a830e50f25..a5540ef97be 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..579da245b87
--- /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..4c8bc553959
--- /dev/null
+++ b/docker/Dockerfile
@@ -0,0 +1,265 @@
+################################################################################
+# 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      #
+# develop 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:develop which takes the latest build from the official #
+# develop 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.                                                            #
+################################################################################
+
+################################################################################
+# HOWTO use this file for local builds                                         #
+################################################################################
+# If you don't mind downloading a 2GB docker image from time to time, you      #
+# could use this file for local Sage development. As of early 2018 each build  #
+# takes about five minutes but you don't have to go through the sadly frequent #
+# rebuilds the whole Sage distribution...                                      #
+# To build Sage, run this command from your sage/ directory:                   #
+# $ docker build --build-arg MAKEOPTS="-j4" --build-arg SAGE_NUM_THREADS="4" --build-arg ARTIFACT_BASE="sagemath/sagemath-dev:develop" -f docker/Dockerfile --target=make-build --tag sage .
+# To run Sage:                                                                 #
+# $ docker run -it sage                                                        #
+# To run doctests:                                                             #
+# $ docker run -e "MAKEOPTS=-j4" -e "SAGE_NUM_THREADS=4" -it sage sage -tp src/sage
+# Make sure that you always have the latest develop branch merged into your    #
+# local branch for this to work.                                               #
+################################################################################
+
+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 "$SAGE_ROOT/sage" /usr/bin/sage
+RUN ln -s /usr/bin/sage /usr/bin/sagemath
+# Sage needs the fortran libraries at run-time because we do not build gfortran
+# with Sage but use the system's.
+# We need gcc/g++ and libstdc++-5-dev to allow compilation of cython at run-time from the notebook.
+# We also install sudo for the sage user, see below.
+RUN apt-get -qq update \
+    && apt-get -qq install -y --no-install-recommends gfortran gcc g++ libstdc++-5-dev sudo openssl \
+    && apt-get -qq clean \
+    && rm -r /var/lib/apt/lists/*
+# Sage refuses to build as root, so we add a "sage" user that can sudo without a password.
+# We also want this user at runtime as some commands in sage know about the user that was used during build.
+ARG HOME=/home/sage
+RUN adduser --quiet --shell /bin/bash --gecos "Sage user,101,," --disabled-password --home "$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 & rdfind
+RUN sudo apt-get -qq update \
+    && sudo apt-get -qq install -y wget build-essential automake m4 dpkg-dev python libssl-dev git rdfind \
+    && sudo apt-get -qq 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 checked out in $HOME/sage-context
+# This is a bit complicated because our local .git/ is empty and we want to
+# make sure that we only change the mtimes of a minimal number of files.
+# 1) Restore the git checkout ARTIFACT_BASE was built from, recorded in
+#    docker/.commit. (Or go directly to FETCH_HEAD if there is no history to
+#    restore, i.e., set ARTIFACT_BASE=source-clean if you want to build from
+#    scratch.)
+# 2) Merge in FETCH_HEAD but only if it is a fast-forward, i.e., if it is an
+#    ancestor of the commit restored in 1. If we would not do that we would get
+#    a new commit hash in docker/.commit that is not known outside of this build
+#    run. Since docker/.commit was in the history of FETCH_HEAD this should
+#    automatically be a fast-forward.
+# 3) Trash .git again to save some space.
+ARG SAGE_ROOT=/home/sage/sage
+WORKDIR $SAGE_ROOT
+# We create a list of all files present in the artifact-base (with a timestamp
+# of now) so we can find out later which files were added/changed/removed.
+RUN find . -type f > $HOME/artifact-base.manifest
+RUN git fetch "$HOME/sage-context" HEAD \
+    && if [ -e docker/.commit ]; then \
+          git reset `cat docker/.commit` \
+          || ( echo "Could not find commit `cat docker/.commit` in your local Git history. Please merge in the latest built develop branch to fix this: git fetch trac && git merge `cat docker/.commit`." && exit 1 ) \
+       else \
+          echo "You are building from $ARTIFACT_BASE which has no docker/.commit file. That's a bug unless you are building from source-clean or something similar." \
+          && git reset FETCH_HEAD \
+          && git checkout -f FETCH_HEAD; \
+       fi \
+    && git merge --ff-only FETCH_HEAD \
+    && git log -1 --format=%H > docker/.commit \
+    && rm -rf .git
+# Copy over all the untracked/staged/unstaged changes from sage-context. This
+# is relevant for non-CI invocations of this Dockerfile.
+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 result 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
+# Set MAKEOPTS and SAGE_NUM_THREADS to build things in parallel during the
+# docker build. Note that these do not leak into the sagemath and sagemath-dev
+# images.
+ARG MAKEOPTS="-j2"
+ENV MAKEOPTS $MAKEOPTS
+ARG SAGE_NUM_THREADS="2"
+ENV SAGE_NUM_THREADS $SAGE_NUM_THREADS
+RUN make build
+
+################################################################################
+# Image with a full build of sage and its documentation.                       #
+################################################################################
+FROM make-build as make-all
+# The docbuild needs quite some RAM (as of May 2018). It sometimes calls
+# os.fork() to spawn an external program which then exceeds easily the
+# overcommit limit of the system (no RAM is actually used, but this limit is
+# very low because there is not even swap on most CI systems.)
+ARG MAKEOPTS_DOCBUILD=$MAKEOPTS
+ENV MAKEOPTS_DOCBUILD $MAKEOPTS_DOCBUILD
+ARG SAGE_NUM_THREADS_DOCBUILD=$SAGE_NUM_THREADS
+ENV SAGE_NUM_THREADS_DOCBUILD $SAGE_NUM_THREADS_DOCBUILD
+RUN make
+
+################################################################################
+# 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 HOME=/home/sage
+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
+RUN sudo $SAGE_ROOT/sage --nodotsage -c "install_scripts('/usr/bin')"
+COPY ./docker/entrypoint.sh /usr/local/bin/sage-entrypoint
+WORKDIR $HOME
+ENTRYPOINT ["/usr/local/bin/sage-entrypoint"]
+EXPOSE 8888
+CMD ["sage"]
+
+################################################################################
+# Image with a full build of sage and its documentation but everything         #
+# stripped that can be quickly rebuild by make.                                #
+################################################################################
+FROM make-all as make-fast-rebuild-clean
+RUN make fast-rebuild-clean
+
+################################################################################
+# Depending on whether we built from source-clean or not, this image is either #
+# identical to make-fast-rebuild-clean or contains a "patch" which can be used #
+# to upgrade ARTIFACT_BASE to make-fast-rebuild-clean.                         #
+################################################################################
+FROM make-fast-rebuild-clean as sagemath-dev-patch
+ARG ARTIFACT_BASE=source-clean
+ARG SAGE_ROOT=/home/sage/sage
+# Build a patch containing of a tar file which contains all the modified files
+# and a list of all modified files (added/updated/removed).
+RUN if [ x"$ARTIFACT_BASE" != x"source-clean" ]; then \
+        mkdir -p $HOME/patch \
+        && find . -type f > $HOME/make-fast-rebuild-clean.manifest \
+        && cat $HOME/make-fast-rebuild-clean.manifest $HOME/artifact-base.manifest | sort | uniq -u > $HOME/obsolete \
+        && find . -type f -cnewer $HOME/artifact-base.manifest > $HOME/modified \
+        && tar -cJf $HOME/patch/modified.tar.xz -T $HOME/modified \
+        && cat $HOME/obsolete $HOME/modified | xz > $HOME/patch/modified.xz \
+        && rm -rf $SAGE_ROOT \
+        && mkdir -p $SAGE_ROOT \
+        && mv $HOME/patch $SAGE_ROOT/; \
+    fi
+
+################################################################################
+# 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 $ARTIFACT_BASE as sagemath-dev
+ARG SAGE_ROOT=/home/sage/sage
+# If docker is backed by aufs, then the following command adds the size of
+# ARTIFACT_BASE to the image size. As of mid 2018 this is notably the case with
+# the docker instances provided by setup_remote_docker on CircleCI. As a
+# result, the sagemath-dev images that are "build-from-latest" are twice as big
+# as the ones that are build on GitLab:
+# https://github.com/moby/moby/issues/6119#issuecomment-268870519
+COPY --chown=sage:sage --from=sagemath-dev-patch $SAGE_ROOT $SAGE_ROOT
+ARG ARTIFACT_BASE=source-clean
+# Apply the patch from sagemath-dev-patch if we created one.
+RUN if [ x"$ARTIFACT_BASE" != x"source-clean" ]; then \
+        echo "Applying `du -hs patch/modified.tar.xz` patch" \
+        && xzcat patch/modified.xz | xargs rm -rvf \
+        && tar -Jxf patch/modified.tar.xz \
+        && rm -rf patch; \
+    fi
+COPY ./docker/entrypoint-dev.sh /usr/local/bin/sage-entrypoint
+ENTRYPOINT ["/usr/local/bin/sage-entrypoint"]
+CMD ["bash"]
diff --git a/docker/README.md b/docker/README.md
new file mode 100644
index 00000000000..216fcc77364
--- /dev/null
+++ b/docker/README.md
@@ -0,0 +1,59 @@
+[![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)
+
+# Supported tags
+
+* `latest` — the stable `master` branch [![GitHub last commit (branch)](https://img.shields.io/github/last-commit/sagemath/sage/master.svg)](https://github.com/sagemath/sage/commits/master) [![CircleCI branch](https://img.shields.io/circleci/project/github/sagemath/sage/master.svg)](https://circleci.com/gh/sagemath/sage/tree/master) [![GitLab CI](https://gitlab.com/sagemath/sage/badges/master/pipeline.svg)](https://gitlab.com/sagemath/sage/commits/master)
+* `x.x` — all stable releases of Sage are tagged with their version number.
+* `x.x.{beta,rc}x` - betas and release candidates of Sage as [tagged in our git repository](https://github.com/sagemath/sage/tags).
+* `develop` — the current development version of Sage which gets merged into the `master` branch when a new version of Sage is released [![GitHub last commit (branch)](https://img.shields.io/github/last-commit/sagemath/sage/develop.svg)](https://github.com/sagemath/sage/commits/develop) [![CircleCI branch](https://img.shields.io/circleci/project/github/sagemath/sage/master.svg)](https://circleci.com/gh/sagemath/sage/tree/master) [![GitLab CI](https://gitlab.com/sagemath/sage/badges/develop/pipeline.svg)](https://gitlab.com/sagemath/sage/commits/develop)
+
+
+# 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/latest.svg)](https://hub.docker.com/r/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-jupyter
+    ```
+* [`sagemath/sagemath-dev`![image size](https://img.shields.io/microbadger/image-size/sagemath/sagemath-dev.svg)](https://hub.docker.com/r/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:develop
+    ```
+    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 $(cat docker/.commit)
+    ```
+
+# How to build your own SageMath images
+
+Run `docker build -f docker/Dockerfile --build-arg ARTIFACT_BASE=sagemath/sagemath-dev:develop --target TARGET .` in the Sage repository with `TARGET` one of `sagemath` or `sagemath-dev`.
+
+# How these images get updated
+
+Every push to our [github repository](https://github.com/sagemath/sage) triggers a build in [CircleCI](https://circleci.com) which builds and pushes the docker images.
+A push to master also triggers a "build" on our [Docker Hub](https://hub.docker.com) repositories. The latter build is mostly disabled by the `hooks/` and only updates the `README.md`.
+
+Every push to our [GitLab repository](https://gitlab.com/sagemath/sage) triggers a pipeline in GitLab CI. This build also pushes images to Docker Hub.
+
+Have a look at `.circleci/` and `.gitlab-ci.yml` if you want to setup either continuous integration service for your own fork of the SageMath repository.
+
+# Report bugs and issues
+
+Please tell us of any bugs or omissions at our [Issue Tracker](https://trac.sagemath.org) or contact us through the [sage-support](https://groups.google.com/forum/#!forum/sage-support) or the [sage-devel](https://groups.google.com/forum/#!forum/sage-devel) mailing lists.
+
+# License
+
+The whole Sage software distribution is licensed under the General Public License, version 3. More details can be found in our [COPYING.txt](https://github.com/sagemath/sage/blob/master/COPYING.txt)
+
+[//]: # (Please don't break long lines in this files as dockerhub then gets the formatting of this file wrong.)
diff --git a/docker/entrypoint-dev.sh b/docker/entrypoint-dev.sh
new file mode 100755
index 00000000000..67299a5a92d
--- /dev/null
+++ b/docker/entrypoint-dev.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+set -e
+make build
+exec "$@"
diff --git a/docker/entrypoint.sh b/docker/entrypoint.sh
new file mode 100755
index 00000000000..bc841382eaf
--- /dev/null
+++ b/docker/entrypoint.sh
@@ -0,0 +1,9 @@
+#!/bin/bash
+if [ x"$1" = x"sage-jupyter" ]; then
+    # If "sage-jupyter" is given as a first argument, we start a jupyter notebook
+    # with reasonable default parameters for running it inside a container.
+    shift
+    exec sage -n jupyter --no-browser --ip='*' --port=8888 "$@"
+else
+    exec sage -sh -c "$*"
+fi
diff --git a/docker/hooks/build b/docker/hooks/build
new file mode 100644
index 00000000000..b23e55619b2
--- /dev/null
+++ b/docker/hooks/build
@@ -0,0 +1 @@
+#!/bin/true
diff --git a/docker/hooks/push b/docker/hooks/push
new file mode 100644
index 00000000000..b23e55619b2
--- /dev/null
+++ b/docker/hooks/push
@@ -0,0 +1 @@
+#!/bin/true
diff --git a/src/.gitignore b/src/.gitignore
deleted file mode 100644
index e85aa7f89e4..00000000000
--- a/src/.gitignore
+++ /dev/null
@@ -1,4 +0,0 @@
-/.cython_version
-/build
-/Makefile
-/bin/sage-env-config
diff --git a/src/Makefile.in b/src/Makefile.in
index 81a28b3758e..0233601cbbc 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -37,7 +37,7 @@ sage:
 	    SAGE_DOC_SRC=/doesnotexist                            \
 	    SAGE_BUILD_DIR=/doesnotexist                          \
 	    SAGE_PKGS=$(abs_top_srcdir)/build/pkgs                \
-	&& sage-python23 -u setup.py --no-user-cfg build install
+	&& sage-python23 -u setup.py --quiet --no-user-cfg build install
 	if [ "$$UNAME" = "CYGWIN" ]; then                         \
 	    sage-rebase.sh "$$SAGE_LOCAL" 2>/dev/null;            \
 	fi
diff --git a/src/sage_setup/docbuild/__init__.py b/src/sage_setup/docbuild/__init__.py
index 5877b5b2a76..7dc8ff783c5 100644
--- a/src/sage_setup/docbuild/__init__.py
+++ b/src/sage_setup/docbuild/__init__.py
@@ -265,35 +265,29 @@ def clean(self, *args):
     # import the customized builder for object.inv files
     inventory = builder_helper('inventory')
 
-if NUM_THREADS > 1:
-    def build_many(target, args):
-        from multiprocessing import Pool
-        pool = Pool(NUM_THREADS, maxtasksperchild=1)
-        # map_async handles KeyboardInterrupt correctly. Plain map and
-        # apply_async does not, so don't use it.
-        x = pool.map_async(target, args, 1)
-        try:
-            ret = x.get(99999)
-            pool.close()
-            pool.join()
-        except Exception:
-            pool.terminate()
-            if ABORT_ON_ERROR:
-                raise
-        return ret
-else:
-    def build_many(target, args):
-        results = []
-
-        for arg in args:
-            try:
-                results.append(target(arg))
-            except Exception:
-                if ABORT_ON_ERROR:
-                    raise
-
-        return results
-
+def build_many(target, args):
+    # Pool() uses an actual fork() to run each new instance. This is important
+    # for performance reasons, i.e., don't use a forkserver when it becomes
+    # available with Python 3: Here, sage is already initialized which is quite
+    # costly, with a forkserver we would have to reinitialize it for every
+    # document we build. At the same time, don't serialize this by taking the
+    # pool (and thus the call to fork()) out completely: The call to Sphinx
+    # leaks memory, so we need to build each document in its own process to
+    # control the RAM usage.
+    from multiprocessing import Pool
+    pool = Pool(NUM_THREADS, maxtasksperchild=1)
+    # map_async handles KeyboardInterrupt correctly. Plain map and
+    # apply_async does not, so don't use it.
+    x = pool.map_async(target, args, 1)
+    try:
+        ret = x.get(99999)
+        pool.close()
+        pool.join()
+    except Exception:
+        pool.terminate()
+        if ABORT_ON_ERROR:
+            raise
+    return ret
 
 ##########################################
 #      Parallel Building Ref Manual      #
@@ -940,7 +934,12 @@ 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)
diff --git a/src/sage_setup/docbuild/ext/sage_autodoc.py b/src/sage_setup/docbuild/ext/sage_autodoc.py
index f241e09f8a5..2c399bad51b 100644
--- a/src/sage_setup/docbuild/ext/sage_autodoc.py
+++ b/src/sage_setup/docbuild/ext/sage_autodoc.py
@@ -988,7 +988,12 @@ def generate(self, more_content=None, real_modname=None,
             self.analyzer.find_attr_docs()
         except PycodeError as err:
             self.env.app.debug('[autodoc] module analyzer failed: %s', err)
-            # no source file -- e.g. for builtin and C modules
+            # A few things could have happened here:
+            # * there is no source file -- e.g. for builtin and C modules
+            # * the source file contains syntax that Sphinx can not parse,
+            #   e.g., "print(1, end=' ')"; see
+            #   https://github.com/sphinx-doc/sphinx/issues/1641,
+            #   fixed in Sphinx 1.7.
             self.analyzer = None
             # at least add the module.__file__ as a dependency
             if hasattr(self.module, '__file__') and self.module.__file__:
diff --git a/src/sage_setup/docbuild/sphinxbuild.py b/src/sage_setup/docbuild/sphinxbuild.py
index 6b7ac9e8947..da29430dd75 100644
--- a/src/sage_setup/docbuild/sphinxbuild.py
+++ b/src/sage_setup/docbuild/sphinxbuild.py
@@ -2,7 +2,7 @@
 r"""
 This is Sage's version of the sphinx-build script
 
-We redirect stdout to our own logger, and remove some unwanted chatter.
+We redirect stdout and stderr to our own logger, and remove some unwanted chatter.
 """
 # ****************************************************************************
 #       Copyright (C) 2013-2014 Volker Braun <vbraun.name@gmail.com>
@@ -32,8 +32,8 @@ def term_width_line(text):
 
 class SageSphinxLogger(object):
     r"""
-    This implements the file object interface to serve as sys.stdout
-    replacement.
+    This implements the file object interface to serve as
+    ``sys.stdout``/``sys.stderr`` replacement.
     """
     ansi_color = re.compile(r'\x1b\[[0-9;]*m')
     ansi_reset = re.compile(r'\x1b\[39;49;00m')
@@ -60,26 +60,57 @@ def __init__(self, stream, prefix):
         self._error = None
 
     def _init_chatter(self):
-        # useless_chatter: regular expressions to be filtered from
-        # Sphinx output.
-        self.useless_chatter = (
+        # We drop any messages from the output that match these regular
+        # expressions. These just bloat the output and do not contain any
+        # information that we care about.
+        self._useless_chatter = (
             re.compile('^$'),
             re.compile('^Running Sphinx v'),
             re.compile('^loading intersphinx inventory from '),
+            re.compile('^loading pickled environment... done'),
+            re.compile('^loading cross citations... done \([0-9]* citations\).'),
             re.compile('^Compiling a sub-document'),
             re.compile('^updating environment: 0 added, 0 changed, 0 removed'),
             re.compile('^looking for now-outdated files... none found'),
             re.compile('^building \[.*\]: targets for 0 source files that are out of date'),
-            re.compile('^loading pickled environment... done'),
-            re.compile('^loading cross citations... done \([0-9]* citations\).'),
+            re.compile('^building \[.*\]: targets for 0 po files that are out of date'),
+            re.compile('^building \[.*\]: targets for 0 mo files that are out of date'),
+            re.compile('^pickling environment... done'),
+            re.compile('^dumping object inventory... done'),
+            # We still have "Build finished."
+            re.compile('^build succeeded.'),
+            re.compile('^checking consistency... done'),
+            re.compile('^preparing documents... done'),
+            re.compile('^copying extra files... done'),
+            re.compile('^writing additional pages... search'),
+            re.compile('^Writing js search indexes...writing additional pages... .*'),
+            re.compile('^generating indices... .*'),
+            re.compile('^dumping search index in .* ... done'),
+            re.compile('^linking _static directory'),
+            re.compile('^copying static files... done'),
+            re.compile('^copying extra files... done'),
+            re.compile('^loading translations \[.*\]... done'),
+            re.compile('^Compiling the master document'),
+            re.compile('^Saved pickle file: citations.pickle'),
+            re.compile('^writing output... \[.*\] '),
+            re.compile('^copying images... \[.*\] '),
+            re.compile('^reading sources... \[.*\] '),
+            re.compile('language "hu" not supported'),
+            re.compile('^$'),
+            re.compile('^WARNING:$'),
+            )
+
+        # We fail whenever a line starts with "WARNING:", however, we ignore
+        # these warnings, as they are not relevant.
+        self._ignored_warnings = (
             re.compile('WARNING: favicon file \'favicon.ico\' does not exist'),
             re.compile('WARNING: html_static_path entry .* does not exist'),
             re.compile('WARNING: while setting up extension'),
             re.compile('WARNING: Any IDs not assiend for figure node'),
             re.compile('WARNING: .* is not referenced'),
             re.compile('WARNING: Build finished'),
-            re.compile('language "hu" not supported'),
             )
+        self._useless_chatter += self._ignored_warnings
 
         # replacements: pairs of regular expressions and their replacements,
         # to be applied to Sphinx output.
@@ -89,10 +120,12 @@ def _init_chatter(self):
         if 'inventory' in sys.argv:
             # When building the inventory, ignore warnings about missing
             # citations and the search index.
-            self.useless_chatter += (
+            ignored = (
                 re.compile('WARNING: citation not found:'),
                 re.compile('WARNING: search index couldn\'t be loaded, but not all documents will be built: the index will be incomplete.')
                 )
+            self._ignored_warnings += ignored
+            self._useless_chatter += ignored
 
         # Regular expressions indicating a problem with docbuilding. Raise an
         # exception if any of these occur.
@@ -109,18 +142,19 @@ def _init_chatter(self):
         # - undefined labels upon the first pass of the compilation: some
         #   cross links may legitimately not yet be resolvable at this point.
         if 'latex' not in sys.argv:
+            self._error_patterns += (re.compile('WARNING:'),)
             if 'multidoc_first_pass=1' in sys.argv:
-                # Catch all warnings except 'WARNING: undefined label'
-                self._error_patterns += (re.compile('WARNING: (?!undefined label)'),)
-            else:
-                self._error_patterns += (re.compile('WARNING:'),)
+                ignore = (re.compile('WARNING: undefined label'),)
+                self._ignored_warnings += ignore
+                self._useless_chatter += ignore
 
     def _filter_out(self, line):
         if self._error is not None and self._is_stdout:
             # swallow non-errors after an error occurred
             return True
         line = re.sub(self.ansi_color, '', line)
-        for regex in self.useless_chatter:
+        line = line.strip()
+        for regex in self._useless_chatter:
             if regex.search(line) is not None:
                 return True
         return False
@@ -139,15 +173,19 @@ def _check_errors(self, line):
             sage: logger.raise_errors()
             Traceback (most recent call last):
             ...
-            OSError: [doctestin] Segmentation fault!
+            OSError: Segmentation fault!
 
         """
         if self._error is not None:
             return  # we already have found an error
-        for regex in self._error_patterns:
-            if regex.search(line) is not None:
-                self._error = line
-                return
+        for error in self._error_patterns:
+            if error.search(line) is not None:
+                for ignored in self._ignored_warnings:
+                    if ignored.search(line) is not None:
+                        break
+                else:
+                    self._error = line
+                    return
 
     def _log_line(self, line):
         r"""
@@ -183,16 +221,16 @@ def _log_line(self, line):
             [#25160   ] Exception: artificial exception
 
         """
-        if self._filter_out(line):
-            return
+        skip_this_line = self._filter_out(line)
+        self._check_errors(line)
         for (old, new) in self.replacements:
             line = old.sub(new, line)
         line = self._prefix + ' ' + line.rstrip() + '\n'
         if not self._color:
             line = self.ansi_color.sub('', line)
-        self._stream.write(line)
-        self._stream.flush()
-        self._check_errors(line)
+        if not skip_this_line:
+            self._stream.write(line)
+            self._stream.flush()
 
     def raise_errors(self):
         r"""
@@ -209,7 +247,7 @@ def raise_errors(self):
             sage: logger.raise_errors()
             Traceback (most recent call last):
             ...
-            OSError: [doctestin] This is a SEVERE error
+            OSError: This is a SEVERE error
 
         """
         if self._error is not None:
@@ -272,6 +310,11 @@ def runsphinx():
     try:
         sys.stdout = SageSphinxLogger(sys.stdout, os.path.basename(output_dir))
         sys.stderr = SageSphinxLogger(sys.stderr, os.path.basename(output_dir))
+        # Note that this call as of eraly 2018 leaks memory. So make sure that
+        # you don't call runsphinx() several times in a row. (i.e., you want to
+        # fork() somewhere before this call.)
+        # We don't use subprocess here, as we don't want to re-initialize Sage
+        # for every docbuild as this takes a while.
         sphinx.cmdline.main(sys.argv[1:])
         sys.stderr.raise_errors()
         sys.stdout.raise_errors()