Merge tag 'v1.38.0rc2' into develop

Synapse 1.38.0rc2 (2021-07-09)
==============================

Bugfixes
--------

- Fix bug where inbound federation in a room could be delayed due to not correctly dropping a lock. Introduced in v1.37.1. ([\#10336](https://github.com/matrix-org/synapse/issues/10336))

Improved Documentation
----------------------

- Update links to documentation in the sample config. Contributed by @dklimpel. ([\#10287](https://github.com/matrix-org/synapse/issues/10287))
- Fix broken links in [INSTALL.md](INSTALL.md). Contributed by @dklimpel. ([\#10331](https://github.com/matrix-org/synapse/issues/10331))

6 files changed, 604 insertions, 13 deletions

diff --git a/docs/.sample_config_header.yaml b/docs/.sample_config_header.yaml
index 8c9b31acdb..09e86ca0ca 100644
--- a/docs/.sample_config_header.yaml
+++ b/docs/.sample_config_header.yaml
@@ -8,7 +8,8 @@
 #
 # It is *not* intended to be copied and used as the basis for a real
 # homeserver.yaml. Instead, if you are starting from scratch, please generate
-# a fresh config using Synapse by following the instructions in INSTALL.md.
+# a fresh config using Synapse by following the instructions in
+# https://matrix-org.github.io/synapse/latest/setup/installation.html.
 
 # Configuration options that take a time period can be set using a number
 # followed by a letter. Letters have the following meanings:
diff --git a/docs/MSC1711_certificates_FAQ.md b/docs/MSC1711_certificates_FAQ.md
index ce8189d4ed..283f288aaf 100644
--- a/docs/MSC1711_certificates_FAQ.md
+++ b/docs/MSC1711_certificates_FAQ.md
@@ -14,7 +14,7 @@ upgraded, however it may be of use to those with old installs returning to the
 project.
 
 If you are setting up a server from scratch you almost certainly should look at
-the [installation guide](../INSTALL.md) instead.
+the [installation guide](setup/installation.md) instead.
 
 ## Introduction
 The goal of Synapse 0.99.0 is to act as a stepping stone to Synapse 1.0.0. It
diff --git a/docs/postgres.md b/docs/postgres.md
index f83155e52a..2c0a5b803a 100644
--- a/docs/postgres.md
+++ b/docs/postgres.md
@@ -8,14 +8,14 @@ Synapse will require the python postgres client library in order to
 connect to a postgres database.
 
 -   If you are using the [matrix.org debian/ubuntu
-    packages](../INSTALL.md#matrixorg-packages), the necessary python
+    packages](setup/installation.md#matrixorg-packages), the necessary python
     library will already be installed, but you will need to ensure the
     low-level postgres library is installed, which you can do with
     `apt install libpq5`.
 -   For other pre-built packages, please consult the documentation from
     the relevant package.
 -   If you installed synapse [in a
-    virtualenv](../INSTALL.md#installing-from-source), you can install
+    virtualenv](setup/installation.md#installing-from-source), you can install
     the library with:
 
         ~/synapse/env/bin/pip install "matrix-synapse[postgres]"
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index cbbe7d58d9..a45732a246 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -8,7 +8,8 @@
 #
 # It is *not* intended to be copied and used as the basis for a real
 # homeserver.yaml. Instead, if you are starting from scratch, please generate
-# a fresh config using Synapse by following the instructions in INSTALL.md.
+# a fresh config using Synapse by following the instructions in
+# https://matrix-org.github.io/synapse/latest/setup/installation.html.
 
 # Configuration options that take a time period can be set using a number
 # followed by a letter. Letters have the following meanings:
diff --git a/docs/setup/installation.md b/docs/setup/installation.md
index 8bb1cffd3d..d041d08333 100644
--- a/docs/setup/installation.md
+++ b/docs/setup/installation.md
@@ -1,7 +1,596 @@
-<!--
-  Include the contents of INSTALL.md from the project root without moving it, which may
-  break links around the internet. Additionally, note that SUMMARY.md is unable to 
-  directly link to content outside of the docs/ directory. So we use this file as a 
-  redirection.
--->
-{{#include ../../INSTALL.md}}
\ No newline at end of file
+# Installation Instructions
+
+There are 3 steps to follow under **Installation Instructions**.
+
+- [Installation Instructions](#installation-instructions)
+  - [Choosing your server name](#choosing-your-server-name)
+  - [Installing Synapse](#installing-synapse)
+    - [Installing from source](#installing-from-source)
+      - [Platform-specific prerequisites](#platform-specific-prerequisites)
+        - [Debian/Ubuntu/Raspbian](#debianubunturaspbian)
+        - [ArchLinux](#archlinux)
+        - [CentOS/Fedora](#centosfedora)
+        - [macOS](#macos)
+        - [OpenSUSE](#opensuse)
+        - [OpenBSD](#openbsd)
+        - [Windows](#windows)
+    - [Prebuilt packages](#prebuilt-packages)
+      - [Docker images and Ansible playbooks](#docker-images-and-ansible-playbooks)
+      - [Debian/Ubuntu](#debianubuntu)
+        - [Matrix.org packages](#matrixorg-packages)
+        - [Downstream Debian packages](#downstream-debian-packages)
+        - [Downstream Ubuntu packages](#downstream-ubuntu-packages)
+      - [Fedora](#fedora)
+      - [OpenSUSE](#opensuse-1)
+      - [SUSE Linux Enterprise Server](#suse-linux-enterprise-server)
+      - [ArchLinux](#archlinux-1)
+      - [Void Linux](#void-linux)
+      - [FreeBSD](#freebsd)
+      - [OpenBSD](#openbsd-1)
+      - [NixOS](#nixos)
+  - [Setting up Synapse](#setting-up-synapse)
+    - [Using PostgreSQL](#using-postgresql)
+    - [TLS certificates](#tls-certificates)
+    - [Client Well-Known URI](#client-well-known-uri)
+    - [Email](#email)
+    - [Registering a user](#registering-a-user)
+    - [Setting up a TURN server](#setting-up-a-turn-server)
+    - [URL previews](#url-previews)
+    - [Troubleshooting Installation](#troubleshooting-installation)
+
+
+## Choosing your server name
+
+It is important to choose the name for your server before you install Synapse,
+because it cannot be changed later.
+
+The server name determines the "domain" part of user-ids for users on your
+server: these will all be of the format `@user:my.domain.name`. It also
+determines how other matrix servers will reach yours for federation.
+
+For a test configuration, set this to the hostname of your server. For a more
+production-ready setup, you will probably want to specify your domain
+(`example.com`) rather than a matrix-specific hostname here (in the same way
+that your email address is probably `user@example.com` rather than
+`user@email.example.com`) - but doing so may require more advanced setup: see
+[Setting up Federation](../federate.md).
+
+## Installing Synapse
+
+### Installing from source
+
+(Prebuilt packages are available for some platforms - see [Prebuilt packages](#prebuilt-packages).)
+
+When installing from source please make sure that the [Platform-specific prerequisites](#platform-specific-prerequisites) are already installed.
+
+System requirements:
+
+- POSIX-compliant system (tested on Linux & OS X)
+- Python 3.5.2 or later, up to Python 3.9.
+- At least 1GB of free RAM if you want to join large public rooms like #matrix:matrix.org
+
+
+To install the Synapse homeserver run:
+
+```sh
+mkdir -p ~/synapse
+virtualenv -p python3 ~/synapse/env
+source ~/synapse/env/bin/activate
+pip install --upgrade pip
+pip install --upgrade setuptools
+pip install matrix-synapse
+```
+
+This will download Synapse from [PyPI](https://pypi.org/project/matrix-synapse)
+and install it, along with the python libraries it uses, into a virtual environment
+under `~/synapse/env`.  Feel free to pick a different directory if you
+prefer.
+
+This Synapse installation can then be later upgraded by using pip again with the
+update flag:
+
+```sh
+source ~/synapse/env/bin/activate
+pip install -U matrix-synapse
+```
+
+Before you can start Synapse, you will need to generate a configuration
+file. To do this, run (in your virtualenv, as before):
+
+```sh
+cd ~/synapse
+python -m synapse.app.homeserver \
+    --server-name my.domain.name \
+    --config-path homeserver.yaml \
+    --generate-config \
+    --report-stats=[yes|no]
+```
+
+... substituting an appropriate value for `--server-name`.
+
+This command will generate you a config file that you can then customise, but it will
+also generate a set of keys for you. These keys will allow your homeserver to
+identify itself to other homeserver, so don't lose or delete them. It would be
+wise to back them up somewhere safe. (If, for whatever reason, you do need to
+change your homeserver's keys, you may find that other homeserver have the
+old key cached. If you update the signing key, you should change the name of the
+key in the `<server name>.signing.key` file (the second word) to something
+different. See the [spec](https://matrix.org/docs/spec/server_server/latest.html#retrieving-server-keys) for more information on key management).
+
+To actually run your new homeserver, pick a working directory for Synapse to
+run (e.g. `~/synapse`), and:
+
+```sh
+cd ~/synapse
+source env/bin/activate
+synctl start
+```
+
+#### Platform-specific prerequisites
+
+Synapse is written in Python but some of the libraries it uses are written in
+C. So before we can install Synapse itself we need a working C compiler and the
+header files for Python C extensions.
+
+##### Debian/Ubuntu/Raspbian
+
+Installing prerequisites on Ubuntu or Debian:
+
+```sh
+sudo apt install build-essential python3-dev libffi-dev \
+                     python3-pip python3-setuptools sqlite3 \
+                     libssl-dev virtualenv libjpeg-dev libxslt1-dev
+```
+
+##### ArchLinux
+
+Installing prerequisites on ArchLinux:
+
+```sh
+sudo pacman -S base-devel python python-pip \
+               python-setuptools python-virtualenv sqlite3
+```
+
+##### CentOS/Fedora
+
+Installing prerequisites on CentOS or Fedora Linux:
+
+```sh
+sudo dnf install libtiff-devel libjpeg-devel libzip-devel freetype-devel \
+                 libwebp-devel libxml2-devel libxslt-devel libpq-devel \
+                 python3-virtualenv libffi-devel openssl-devel python3-devel
+sudo dnf groupinstall "Development Tools"
+```
+
+##### macOS
+
+Installing prerequisites on macOS:
+
+```sh
+xcode-select --install
+sudo easy_install pip
+sudo pip install virtualenv
+brew install pkg-config libffi
+```
+
+On macOS Catalina (10.15) you may need to explicitly install OpenSSL
+via brew and inform `pip` about it so that `psycopg2` builds:
+
+```sh
+brew install openssl@1.1
+export LDFLAGS="-L/usr/local/opt/openssl/lib"
+export CPPFLAGS="-I/usr/local/opt/openssl/include"
+```
+
+##### OpenSUSE
+
+Installing prerequisites on openSUSE:
+
+```sh
+sudo zypper in -t pattern devel_basis
+sudo zypper in python-pip python-setuptools sqlite3 python-virtualenv \
+               python-devel libffi-devel libopenssl-devel libjpeg62-devel
+```
+
+##### OpenBSD
+
+A port of Synapse is available under `net/synapse`. The filesystem
+underlying the homeserver directory (defaults to `/var/synapse`) has to be
+mounted with `wxallowed` (cf. `mount(8)`), so creating a separate filesystem
+and mounting it to `/var/synapse` should be taken into consideration.
+
+To be able to build Synapse's dependency on python the `WRKOBJDIR`
+(cf. `bsd.port.mk(5)`) for building python, too, needs to be on a filesystem
+mounted with `wxallowed` (cf. `mount(8)`).
+
+Creating a `WRKOBJDIR` for building python under `/usr/local` (which on a
+default OpenBSD installation is mounted with `wxallowed`):
+
+```sh
+doas mkdir /usr/local/pobj_wxallowed
+```
+
+Assuming `PORTS_PRIVSEP=Yes` (cf. `bsd.port.mk(5)`) and `SUDO=doas` are
+configured in `/etc/mk.conf`:
+
+```sh
+doas chown _pbuild:_pbuild /usr/local/pobj_wxallowed
+```
+
+Setting the `WRKOBJDIR` for building python:
+
+```sh
+echo WRKOBJDIR_lang/python/3.7=/usr/local/pobj_wxallowed  \\nWRKOBJDIR_lang/python/2.7=/usr/local/pobj_wxallowed >> /etc/mk.conf
+```
+
+Building Synapse:
+
+```sh
+cd /usr/ports/net/synapse
+make install
+```
+
+##### Windows
+
+If you wish to run or develop Synapse on Windows, the Windows Subsystem For
+Linux provides a Linux environment on Windows 10 which is capable of using the
+Debian, Fedora, or source installation methods. More information about WSL can
+be found at <https://docs.microsoft.com/en-us/windows/wsl/install-win10> for
+Windows 10 and <https://docs.microsoft.com/en-us/windows/wsl/install-on-server>
+for Windows Server.
+
+### Prebuilt packages
+
+As an alternative to installing from source, prebuilt packages are available
+for a number of platforms.
+
+#### Docker images and Ansible playbooks
+
+There is an official synapse image available at
+<https://hub.docker.com/r/matrixdotorg/synapse> which can be used with
+the docker-compose file available at
+[contrib/docker](https://github.com/matrix-org/synapse/tree/develop/contrib/docker).
+Further information on this including configuration options is available in the README
+on hub.docker.com.
+
+Alternatively, Andreas Peters (previously Silvio Fricke) has contributed a
+Dockerfile to automate a synapse server in a single Docker image, at
+<https://hub.docker.com/r/avhost/docker-matrix/tags/>
+
+Slavi Pantaleev has created an Ansible playbook,
+which installs the offical Docker image of Matrix Synapse
+along with many other Matrix-related services (Postgres database, Element, coturn,
+ma1sd, SSL support, etc.).
+For more details, see
+<https://github.com/spantaleev/matrix-docker-ansible-deploy>
+
+#### Debian/Ubuntu
+
+##### Matrix.org packages
+
+Matrix.org provides Debian/Ubuntu packages of the latest stable version of
+Synapse via <https://packages.matrix.org/debian/>. They are available for Debian
+9 (Stretch), Ubuntu 16.04 (Xenial), and later. To use them:
+
+```sh
+sudo apt install -y lsb-release wget apt-transport-https
+sudo wget -O /usr/share/keyrings/matrix-org-archive-keyring.gpg https://packages.matrix.org/debian/matrix-org-archive-keyring.gpg
+echo "deb [signed-by=/usr/share/keyrings/matrix-org-archive-keyring.gpg] https://packages.matrix.org/debian/ $(lsb_release -cs) main" |
+    sudo tee /etc/apt/sources.list.d/matrix-org.list
+sudo apt update
+sudo apt install matrix-synapse-py3
+```
+
+**Note**: if you followed a previous version of these instructions which
+recommended using `apt-key add` to add an old key from
+`https://matrix.org/packages/debian/`, you should note that this key has been
+revoked. You should remove the old key with `sudo apt-key remove
+C35EB17E1EAE708E6603A9B3AD0592FE47F0DF61`, and follow the above instructions to
+update your configuration.
+
+The fingerprint of the repository signing key (as shown by `gpg
+/usr/share/keyrings/matrix-org-archive-keyring.gpg`) is
+`AAF9AE843A7584B5A3E4CD2BCF45A512DE2DA058`.
+
+##### Downstream Debian packages
+
+We do not recommend using the packages from the default Debian `buster`
+repository at this time, as they are old and suffer from known security
+vulnerabilities. You can install the latest version of Synapse from
+[our repository](#matrixorg-packages) or from `buster-backports`. Please
+see the [Debian documentation](https://backports.debian.org/Instructions/)
+for information on how to use backports.
+
+If you are using Debian `sid` or testing, Synapse is available in the default
+repositories and it should be possible to install it simply with:
+
+```sh
+sudo apt install matrix-synapse
+```
+
+##### Downstream Ubuntu packages
+
+We do not recommend using the packages in the default Ubuntu repository
+at this time, as they are old and suffer from known security vulnerabilities.
+The latest version of Synapse can be installed from [our repository](#matrixorg-packages).
+
+#### Fedora
+
+Synapse is in the Fedora repositories as `matrix-synapse`:
+
+```sh
+sudo dnf install matrix-synapse
+```
+
+Oleg Girko provides Fedora RPMs at
+<https://obs.infoserver.lv/project/monitor/matrix-synapse>
+
+#### OpenSUSE
+
+Synapse is in the OpenSUSE repositories as `matrix-synapse`:
+
+```sh
+sudo zypper install matrix-synapse
+```
+
+#### SUSE Linux Enterprise Server
+
+Unofficial package are built for SLES 15 in the openSUSE:Backports:SLE-15 repository at
+<https://download.opensuse.org/repositories/openSUSE:/Backports:/SLE-15/standard/>
+
+#### ArchLinux
+
+The quickest way to get up and running with ArchLinux is probably with the community package
+<https://www.archlinux.org/packages/community/any/matrix-synapse/>, which should pull in most of
+the necessary dependencies.
+
+pip may be outdated (6.0.7-1 and needs to be upgraded to 6.0.8-1 ):
+
+```sh
+sudo pip install --upgrade pip
+```
+
+If you encounter an error with lib bcrypt causing an Wrong ELF Class:
+ELFCLASS32 (x64 Systems), you may need to reinstall py-bcrypt to correctly
+compile it under the right architecture. (This should not be needed if
+installing under virtualenv):
+
+```sh
+sudo pip uninstall py-bcrypt
+sudo pip install py-bcrypt
+```
+
+#### Void Linux
+
+Synapse can be found in the void repositories as 'synapse':
+
+```sh
+xbps-install -Su
+xbps-install -S synapse
+```
+
+#### FreeBSD
+
+Synapse can be installed via FreeBSD Ports or Packages contributed by Brendan Molloy from:
+
+- Ports: `cd /usr/ports/net-im/py-matrix-synapse && make install clean`
+- Packages: `pkg install py37-matrix-synapse`
+
+#### OpenBSD
+
+As of OpenBSD 6.7 Synapse is available as a pre-compiled binary. The filesystem
+underlying the homeserver directory (defaults to `/var/synapse`) has to be
+mounted with `wxallowed` (cf. `mount(8)`), so creating a separate filesystem
+and mounting it to `/var/synapse` should be taken into consideration.
+
+Installing Synapse:
+
+```sh
+doas pkg_add synapse
+```
+
+#### NixOS
+
+Robin Lambertz has packaged Synapse for NixOS at:
+<https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/misc/matrix-synapse.nix>
+
+## Setting up Synapse
+
+Once you have installed synapse as above, you will need to configure it.
+
+### Using PostgreSQL
+
+By default Synapse uses an [SQLite](https://sqlite.org/) database and in doing so trades
+performance for convenience. Almost all installations should opt to use [PostgreSQL](https://www.postgresql.org)
+instead. Advantages include:
+
+- significant performance improvements due to the superior threading and
+  caching model, smarter query optimiser
+- allowing the DB to be run on separate hardware
+
+For information on how to install and use PostgreSQL in Synapse, please see
+[docs/postgres.md](../postgres.md)
+
+SQLite is only acceptable for testing purposes. SQLite should not be used in
+a production server. Synapse will perform poorly when using
+SQLite, especially when participating in large rooms.
+
+### TLS certificates
+
+The default configuration exposes a single HTTP port on the local
+interface: `http://localhost:8008`. It is suitable for local testing,
+but for any practical use, you will need Synapse's APIs to be served
+over HTTPS.
+
+The recommended way to do so is to set up a reverse proxy on port
+`8448`. You can find documentation on doing so in
+[docs/reverse_proxy.md](../reverse_proxy.md).
+
+Alternatively, you can configure Synapse to expose an HTTPS port. To do
+so, you will need to edit `homeserver.yaml`, as follows:
+
+- First, under the `listeners` section, uncomment the configuration for the
+  TLS-enabled listener. (Remove the hash sign (`#`) at the start of
+  each line). The relevant lines are like this:
+
+```yaml
+  - port: 8448
+    type: http
+    tls: true
+    resources:
+      - names: [client, federation]
+  ```
+
+- You will also need to uncomment the `tls_certificate_path` and
+  `tls_private_key_path` lines under the `TLS` section. You will need to manage
+  provisioning of these certificates yourself.
+
+  If you are using your own certificate, be sure to use a `.pem` file that
+  includes the full certificate chain including any intermediate certificates
+  (for instance, if using certbot, use `fullchain.pem` as your certificate, not
+  `cert.pem`).
+
+For a more detailed guide to configuring your server for federation, see
+[federate.md](../federate.md).
+
+### Client Well-Known URI
+
+Setting up the client Well-Known URI is optional but if you set it up, it will
+allow users to enter their full username (e.g. `@user:<server_name>`) into clients
+which support well-known lookup to automatically configure the homeserver and
+identity server URLs. This is useful so that users don't have to memorize or think
+about the actual homeserver URL you are using.
+
+The URL `https://<server_name>/.well-known/matrix/client` should return JSON in
+the following format.
+
+```json
+{
+  "m.homeserver": {
+    "base_url": "https://<matrix.example.com>"
+  }
+}
+```
+
+It can optionally contain identity server information as well.
+
+```json
+{
+  "m.homeserver": {
+    "base_url": "https://<matrix.example.com>"
+  },
+  "m.identity_server": {
+    "base_url": "https://<identity.example.com>"
+  }
+}
+```
+
+To work in browser based clients, the file must be served with the appropriate
+Cross-Origin Resource Sharing (CORS) headers. A recommended value would be
+`Access-Control-Allow-Origin: *` which would allow all browser based clients to
+view it.
+
+In nginx this would be something like:
+
+```nginx
+location /.well-known/matrix/client {
+    return 200 '{"m.homeserver": {"base_url": "https://<matrix.example.com>"}}';
+    default_type application/json;
+    add_header Access-Control-Allow-Origin *;
+}
+```
+
+You should also ensure the `public_baseurl` option in `homeserver.yaml` is set
+correctly. `public_baseurl` should be set to the URL that clients will use to
+connect to your server. This is the same URL you put for the `m.homeserver`
+`base_url` above.
+
+```yaml
+public_baseurl: "https://<matrix.example.com>"
+```
+
+### Email
+
+It is desirable for Synapse to have the capability to send email. This allows
+Synapse to send password reset emails, send verifications when an email address
+is added to a user's account, and send email notifications to users when they
+receive new messages.
+
+To configure an SMTP server for Synapse, modify the configuration section
+headed `email`, and be sure to have at least the `smtp_host`, `smtp_port`
+and `notif_from` fields filled out.  You may also need to set `smtp_user`,
+`smtp_pass`, and `require_transport_security`.
+
+If email is not configured, password reset, registration and notifications via
+email will be disabled.
+
+### Registering a user
+
+The easiest way to create a new user is to do so from a client like [Element](https://element.io/).
+
+Alternatively, you can do so from the command line. This can be done as follows:
+
+ 1. If synapse was installed via pip, activate the virtualenv as follows (if Synapse was
+    installed via a prebuilt package, `register_new_matrix_user` should already be
+    on the search path):
+    ```sh
+    cd ~/synapse
+    source env/bin/activate
+    synctl start # if not already running
+    ```
+ 2. Run the following command:
+    ```sh
+    register_new_matrix_user -c homeserver.yaml http://localhost:8008
+    ```
+
+This will prompt you to add details for the new user, and will then connect to
+the running Synapse to create the new user. For example:
+```
+New user localpart: erikj
+Password:
+Confirm password:
+Make admin [no]:
+Success!
+```
+
+This process uses a setting `registration_shared_secret` in
+`homeserver.yaml`, which is shared between Synapse itself and the
+`register_new_matrix_user` script. It doesn't matter what it is (a random
+value is generated by `--generate-config`), but it should be kept secret, as
+anyone with knowledge of it can register users, including admin accounts,
+on your server even if `enable_registration` is `false`.
+
+### Setting up a TURN server
+
+For reliable VoIP calls to be routed via this homeserver, you MUST configure
+a TURN server. See
+[docs/turn-howto.md](../turn-howto.md)
+for details.
+
+### URL previews
+
+Synapse includes support for previewing URLs, which is disabled by default.  To
+turn it on you must enable the `url_preview_enabled: True` config parameter
+and explicitly specify the IP ranges that Synapse is not allowed to spider for
+previewing in the `url_preview_ip_range_blacklist` configuration parameter.
+This is critical from a security perspective to stop arbitrary Matrix users
+spidering 'internal' URLs on your network. At the very least we recommend that
+your loopback and RFC1918 IP addresses are blacklisted.
+
+This also requires the optional `lxml` python dependency to be  installed. This
+in turn requires the `libxml2` library to be available - on  Debian/Ubuntu this
+means `apt-get install libxml2-dev`, or equivalent for your OS.
+
+### Troubleshooting Installation
+
+`pip` seems to leak *lots* of memory during installation. For instance, a Linux
+host with 512MB of RAM may run out of memory whilst installing Twisted. If this
+happens, you will have to individually install the dependencies which are
+failing, e.g.:
+
+```sh
+pip install twisted
+```
+
+If you have any other problems, feel free to ask in
+[#synapse:matrix.org](https://matrix.to/#/#synapse:matrix.org).
diff --git a/docs/upgrade.md b/docs/upgrade.md
index 011aadf638..db0450f563 100644
--- a/docs/upgrade.md
+++ b/docs/upgrade.md
@@ -16,7 +16,7 @@ this document.
     summaries.
 
 -   If Synapse was installed using [prebuilt
-    packages](../setup/INSTALL.md#prebuilt-packages), you will need to follow the
+    packages](setup/installation.md#prebuilt-packages), you will need to follow the
     normal process for upgrading those packages.
 
 -   If Synapse was installed from source, then: