Synapse

Admin FAQ

How do I become a server admin?

If your server already has an admin account you should use the User Admin API to promote other accounts to become admins.

If you don't have any admin accounts yet you won't be able to use the admin API, so you'll have to edit the database manually. Manually editing the database is generally not recommended so once you have an admin account: use the admin APIs to make further changes.

UPDATE users SET admin = 1 WHERE name = '@foo:bar.com';

What servers are my server talking to?

Run this sql query on your db:

SELECT * FROM destinations;

What servers are currently participating in this room?

Run this sql query on your db:

SELECT DISTINCT split_part(state_key, ':', 2)
    FROM current_state_events AS c
    INNER JOIN room_memberships AS m USING (room_id, event_id)
    WHERE room_id = '!cURbafjkfsMDVwdRDQ:matrix.org' AND membership = 'join';

What users are registered on my server?

SELECT NAME from users;

Manually resetting passwords

Users can reset their password through their client. Alternatively, a server admin can reset a user's password using the admin API.

I have a problem with my server. Can I just delete my database and start again?

Deleting your database is unlikely to make anything better.

It's easy to make the mistake of thinking that you can start again from a clean slate by dropping your database, but things don't work like that in a federated network: lots of other servers have information about your server.

For example: other servers might think that you are in a room, your server will think that you are not, and you'll probably be unable to interact with that room in a sensible way ever again.

In general, there are better solutions to any problem than dropping the database. Come and seek help in https://matrix.to/#/#synapse:matrix.org.

There are two exceptions when it might be sensible to delete your database and start again:

• You have never joined any rooms which are federated with other servers. For instance, a local deployment which the outside world can't talk to.
• You are changing the server_name in the homeserver configuration. In effect this makes your server a completely new one from the point of view of the network, so in this case it makes sense to start with a clean database. (In both cases you probably also want to clear out the media_store.)

I've stuffed up access to my room, how can I delete it to free up the alias?

Using the following curl command:

curl -H 'Authorization: Bearer <access-token>' -X DELETE https://matrix.org/_matrix/client/r0/directory/room/<room-alias>

<access-token> - can be obtained in riot by looking in the riot settings, down the bottom is: Access Token:<click to reveal>

<room-alias> - the room alias, eg. #my_room:matrix.org this possibly needs to be URL encoded also, for example %23my_room%3Amatrix.org

How can I find the lines corresponding to a given HTTP request in my homeserver log?

Synapse tags each log line according to the HTTP request it is processing. When it finishes processing each request, it logs a line containing the words Processed request: . For example:

2019-02-14 22:35:08,196 - synapse.access.http.8008 - 302 - INFO - GET-37 - ::1 - 8008 - {@richvdh:localhost} Processed request: 0.173sec/0.001sec (0.002sec, 0.000sec) (0.027sec/0.026sec/2) 687B 200 "GET /_matrix/client/r0/sync HTTP/1.1" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36" [0 dbevts]"

Here we can see that the request has been tagged with GET-37. (The tag depends on the method of the HTTP request, so might start with GET-, PUT-, POST-, OPTIONS- or DELETE-.) So to find all lines corresponding to this request, we can do:

grep 'GET-37' homeserver.log

If you want to paste that output into a github issue or matrix room, please remember to surround it with triple-backticks (```) to make it legible (see https://help.github.com/en/articles/basic-writing-and-formatting-syntax#quoting-code).

What do all those fields in the 'Processed' line mean?

See Request log format.

What are the biggest rooms on my server?

SELECT s.canonical_alias, g.room_id, count(*) AS num_rows 
FROM 
  state_groups_state AS g, 
  room_stats_state AS s 
WHERE g.room_id = s.room_id 
GROUP BY s.canonical_alias, g.room_id
ORDER BY num_rows desc 
LIMIT 10;

You can also use the List Room API and order_by state_events.

People can't accept room invitations from me

The typical failure mode here is that you send an invitation to someone to join a room or direct chat, but when they go to accept it, they get an error (typically along the lines of "Invalid signature"). They might see something like the following in their logs:

2019-09-11 19:32:04,271 - synapse.federation.transport.server - 288 - WARNING - GET-11752 - authenticate_request failed: 401: Invalid signature for server <server> with key ed25519:a_EqML: Unable to verify signature for <server>

This is normally caused by a misconfiguration in your reverse-proxy. See the reverse proxy docs and double-check that your settings are correct.

Help!! Synapse is slow and eats all my RAM/CPU!

First, ensure you are running the latest version of Synapse, using Python 3 with a PostgreSQL database.

Synapse's architecture is quite RAM hungry currently - we deliberately cache a lot of recent room data and metadata in RAM in order to speed up common requests. We'll improve this in the future, but for now the easiest way to either reduce the RAM usage (at the risk of slowing things down) is to set the almost-undocumented SYNAPSE_CACHE_FACTOR environment variable. The default is 0.5, which can be decreased to reduce RAM usage in memory constrained environments, or increased if performance starts to degrade.

However, degraded performance due to a low cache factor, common on machines with slow disks, often leads to explosions in memory use due backlogged requests. In this case, reducing the cache factor will make things worse. Instead, try increasing it drastically. 2.0 is a good starting value.

Using libjemalloc can also yield a significant improvement in overall memory use, and especially in terms of giving back RAM to the OS. To use it, the library must simply be put in the LD_PRELOAD environment variable when launching Synapse. On Debian, this can be done by installing the libjemalloc1 package and adding this line to /etc/default/matrix-synapse:

LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.1

This made a significant difference on Python 2.7 - it's unclear how much of an improvement it provides on Python 3.x.

If you're encountering high CPU use by the Synapse process itself, you may be affected by a bug with presence tracking that leads to a massive excess of outgoing federation requests (see discussion). If metrics indicate that your server is also issuing far more outgoing federation requests than can be accounted for by your users' activity, this is a likely cause. The misbehavior can be worked around by disabling presence in the Synapse config file: see here.

Running out of File Handles

If Synapse runs out of file handles, it typically fails badly - live-locking at 100% CPU, and/or failing to accept new TCP connections (blocking the connecting client). Matrix currently can legitimately use a lot of file handles, thanks to busy rooms like #matrix:matrix.org containing hundreds of participating servers. The first time a server talks in a room it will try to connect simultaneously to all participating servers, which could exhaust the available file descriptors between DNS queries & HTTPS sockets, especially if DNS is slow to respond. (We need to improve the routing algorithm used to be better than full mesh, but as of March 2019 this hasn't happened yet).

If you hit this failure mode, we recommend increasing the maximum number of open file handles to be at least 4096 (assuming a default of 1024 or 256). This is typically done by editing /etc/security/limits.conf

Separately, Synapse may leak file handles if inbound HTTP requests get stuck during processing - e.g. blocked behind a lock or talking to a remote server etc. This is best diagnosed by matching up the 'Received request' and 'Processed request' log lines and looking for any 'Processed request' lines which take more than a few seconds to execute. Please let us know at #synapse:matrix.org if you see this failure mode so we can help debug it, however.