Add a Troubleshooting page

docs/administration/5_troubleshooting.md

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+---
+title: Troubleshooting
+parent: Administration
+permalink: /administration/troubleshooting
+---
+
+# Troubleshooting
+
+If your Dendrite installation is acting strangely, there are a few things you should
+check before seeking help.
+
+## 1. Logs
+
+Dendrite, by default, will log all warnings and errors to stdout, in addition to any
+other locations configured in the `dendrite.yaml` configuration file. Often there will
+be clues in the logs.
+
+You can increase this log level to the more verbose `debug` level if necessary by adding
+this to the config and restarting Dendrite:
+
+```
+logging:
+- type: std
+  level: debug
+```
+
+Look specifically for lines that contain `level=error` or `level=warning`.
+
+## 2. Federation tester
+
+If you are experiencing problems federating with other homeservers, you should check
+that the [Federation Tester](https://federationtester.matrix.org) is passing for your
+server.
+
+Common reasons that it may not pass include:
+
+1. Incorrect DNS configuration;
+2. Misconfigured DNS SRV entries or well-known files;
+3. Invalid TLS/SSL certificates;
+4. Reverse proxy configuration issues (if applicable).
+
+Correct any errors if shown and re-run the federation tester to check the results.
+
+## 3. System time
+
+Matrix relies heavily on TLS which requires the system time to be correct. If the clock
+drifts then you may find that federation no works reliably (or at all) and clients may
+struggle to connect to your Dendrite server.
+
+Ensure that your system time is correct and consider syncing to a reliable NTP source.
+
+## 4. Database connections
+
+If you are using the PostgreSQL database, you should ensure that Dendrite's configured
+number of database connections does not exceed the maximum allowed by PostgreSQL.
+
+Open your `postgresql.conf` configuration file and check the value of `max_connections`
+(which is typically `100` by default). Then open your `dendrite.yaml` configuration file
+and ensure that:
+
+1. If you are using the `global.database` section, that `max_open_conns` does not exceed
+   that number;
+2. If you are **not** using the `global.database` section, that the sum total of all
+   `max_open_conns` across all `database` blocks does not exceed that number.
+
+## 5. File descriptors
+
+Dendrite requires a sufficient number of file descriptors for every connection it makes
+to a remote server, every connection to the database engine and every file it is reading
+or writing to at a given time (media, logs etc). We recommend ensuring that the limit is
+no lower than 65535 for Dendrite.
+
+Dendrite will check at startup if there are a sufficient number of available descriptors.
+If there aren't, you will see a log lines like this:
+
+```
+level=warning msg="IMPORTANT: Process file descriptor limit is currently 65535, it is recommended to raise the limit for Dendrite to at least 65535 to avoid issues"
+```
+
+Follow the [Optimisation](../installation/10_optimisation.md) instructions to correct the
+available number of file descriptors.