Environment Variables

ElectrumX takes no command line arguments, instead its behaviour is controlled by environment variables. Only a few are required to be given, the rest will have sensible defaults if not specified. Many of the defaults around resource usage are conservative; I encourage you to review them.

Note: by default the server will only serve to connections from the same machine. To be accessible to other users across the internet you must set HOST appropriately; see below.

Required

These environment variables are always required:

COIN

Must be a NAME from one of the Coin classes in lib/coins.py.

DB_DIRECTORY

The path to the database directory. Relative paths should be relative to the parent process working directory. This is the directory of the run script if you use it.

DAEMON_URL

A comma-separated list of daemon URLs. If more than one is provided ElectrumX will initially connect to the first, and failover to subsequent ones round-robin style if one stops working.

The generic form of a daemon URL is:

http://username:password@hostname:port/

The leading http:// is optional, as is the trailing slash. The :port part is also optional and will default to the standard RPC port for COIN and NET if omitted.

For the run script

The following are required if you use the run script:

ELECTRUMX

The path to the electrumx_server script. Relative paths should be relative to the directory of the run script.

USERNAME

The username the server will run as.

Miscellaneous

These environment variables are optional:

LOG_FORMAT

The Python logging format string to use. Defaults to %(levelname)s:%(name)s:%(message)s.

ALLOW_ROOT

Set this environment variable to anything non-empty to allow running ElectrumX as root.

NET

Must be a NET from one of the Coin classes in lib/coins.py. Defaults to mainnet.

DB_ENGINE

Database engine for the UTXO and history database. The default is leveldb. The other alternative is rocksdb. You will need to install the appropriate python package for your engine. The value is not case sensitive.

HOST

The host or IP address that the TCP and SSL servers will use when binding listening sockets. Defaults to localhost. To listen on multiple specific addresses specify a comma-separated list. Set to an empty string to listen on all available interfaces (likely both IPv4 and IPv6).

TCP_PORT

If set ElectrumX will serve TCP clients on HOST:TCP_PORT.

Note

ElectrumX will not serve TCP connections until it has fully caught up with your daemon.

SSL_PORT

If set ElectrumX will serve SSL clients on HOST:SSL_PORT. If set then SSL_CERTFILE and SSL_KEYFILE must be defined environment variables with values the filesystem paths to those SSL files.

Note

ElectrumX will not serve SSL connections until it has fully caught up with your daemon.

RPC_HOST

The host or IP address that the RPC server will listen on and defaults to localhost. To listen on multiple specific addresses specify a comma-separated list. Servers with unusual networking setups might want to specify e.g. ::1 or 127.0.0.1 explicitly rather than defaulting to localhost.

An empty string (normally indicating all interfaces) is interpreted as localhost, because allowing access to the server’s RPC interface to arbitrary connections across the internet is not a good idea.

RPC_PORT

ElectrumX will listen on this port for local RPC connections. ElectrumX listens for RPC connections unless this is explicitly set to blank. The default depends on COIN and NET (e.g., 8000 for Bitcoin mainnet) if not set, as indicated in lib/coins.py.

DONATION_ADDRESS

The server donation address reported to Electrum clients. Defaults to empty, which Electrum interprets as meaning there is none.

BANNER_FILE

The path to a banner file to serve to clients in Electrum’s “Console” tab. Relative file paths must be relative to DB_DIRECTORY. The banner file is re-read for each new client.

You can place several meta-variables in your banner file, which will be replaced before serving to a client.

• $SERVER_VERSION is replaced with the ElectrumX version you are running, such as 1.0.10.
• $SERVER_SUBVERSION is replaced with the ElectrumX user agent string. For example, ElectrumX 1.0.10.
• $DAEMON_VERSION is replaced with the daemon’s version as a dot-separated string. For example 0.12.1.
• $DAEMON_SUBVERSION is replaced with the daemon’s user agent string. For example, /BitcoinUnlimited:0.12.1(EB16; AD4)/.
• $DONATION_ADDRESS is replaced with the address from the DONATION_ADDRESS environment variable.

See here for a script that updates a banner file periodically with useful statistics about fees, last block time and height, etc.

TOR_BANNER_FILE

As for BANNER_FILE (which is also the default) but shown to incoming connections believed to be to your Tor hidden service.

ANON_LOGS

Set to anything non-empty to replace IP addresses in logs with redacted text like xx.xx.xx.xx:xxx. By default IP addresses will be written to logs.

LOG_SESSIONS

The number of seconds between printing session statistics to the log. The output is identical to the sessions RPC command except that ANON_LOGS is honoured. Defaults to 3600. Set to zero to suppress this logging.

REORG_LIMIT

The maximum number of blocks to be able to handle in a chain reorganisation. ElectrumX retains some fairly compact undo information for this many blocks in levelDB. The default is a function of COIN and NET; for Bitcoin mainnet it is 200.

EVENT_LOOP_POLICY

The name of an event loop policy to replace the default asyncio policy, if any. At present only uvloop is accepted, in which case you must have installed the uvloop Python package.

If you are not sure what this means leave it unset.

DROP_CLIENT

Set a regular expression to disconnect any client based on their version string. For example to drop versions from 1.0 to 1.2 use the regex 1\.[0-2]\.\d+.

Resource Usage Limits

The following environment variables are all optional and help to limit server resource consumption and prevent simple DoS.

Address subscriptions in ElectrumX are very cheap - they consume about 160 bytes of memory each and are processed efficiently. I feel the two subscription-related defaults below are low and encourage you to raise them.

MAX_SESSIONS

The maximum number of incoming connections. Once reached, TCP and SSL listening sockets are closed until the session count drops naturally to 95% of the limit. Defaults to 1,000.

MAX_SEND

The maximum size of a response message to send over the wire, in bytes. Defaults to 1,000,000 (except for AuxPoW coins, which default to 10,000,000). Values smaller than 350,000 are taken as 350,000 because standard Electrum protocol header “chunk” requests are almost that large.

The Electrum protocol has a flaw in that address histories must be served all at once or not at all, an obvious avenue for abuse. MAX_SEND is a stop-gap until the protocol is improved to admit incremental history requests. Each history entry is approximately 100 bytes so the default is equivalent to a history limit of around 10,000 entries, which should be ample for most legitimate users. If you use a higher default bear in mind one client can request history for multiple addresses. Also note that the largest raw transaction you will be able to serve to a client is just under half of MAX_SEND, as each raw byte becomes 2 hexadecimal ASCII characters on the wire. Very few transactions on Bitcoin mainnet are over 500KB in size.

MAX_SUBS

The maximum number of address subscriptions across all sessions. Defaults to 250,000.

MAX_SESSION_SUBS

The maximum number of address subscriptions permitted to a single session. Defaults to 50,000.

BANDWIDTH_LIMIT

Per-session periodic bandwidth usage limit in bytes. This is a soft, not hard, limit. Currently the period is hard-coded to be one hour. The default limit value is 2 million bytes.

Bandwidth usage over each period is totalled, and when this limit is exceeded each subsequent request is stalled by sleeping before handling it, effectively giving higher processing priority to other sessions.

The more bandwidth usage exceeds this soft limit the longer the next request will sleep. Sleep times are a round number of seconds with a minimum of 1. Each time the delay changes the event is logged.

Bandwidth usage is gradually reduced over time by “refunding” a proportional part of the limit every now and then.

SESSION_TIMEOUT

An integer number of seconds defaulting to 600. Sessions with no activity for longer than this are disconnected. Properly functioning Electrum clients by default will send pings roughly every 60 seconds.

Peer Discovery

In response to the server.peers.subscribe() RPC call, ElectrumX will only return peer servers that it has recently connected to and verified basic functionality.

If you are not running a Tor proxy ElectrumX will be unable to connect to onion server peers, in which case rather than returning no onion peers it will fall back to a hard-coded list.

To give incoming clients a full range of onion servers you will need to be running a Tor proxy for ElectrumX to use.

ElectrumX will perform peer-discovery by default and announce itself to other peers. If your server is private you may wish to disable some of this.

PEER_DISCOVERY

This environment variable is case-insensitive and defaults to on.

If on, ElectrumX will occasionally connect to and verify its network of peer servers.

If off, peer discovery is disabled and a hard-coded default list of servers will be read in and served. If set to self then peer discovery is disabled and the server will only return itself in the peers list.

PEER_ANNOUNCE

Set this environment variable to empty to disable announcing itself. If not defined, or non-empty, ElectrumX will announce itself to peers.

If peer discovery is disabled this environment variable has no effect, because ElectrumX only announces itself to peers when doing peer discovery if it notices it is not present in the peer’s returned list.

FORCE_PROXY

By default peer discovery happens over the clear internet. Set this to non-empty to force peer discovery to be done via the proxy. This might be useful if you are running a Tor service exclusively and wish to keep your IP address private.

TOR_PROXY_HOST

The host where your Tor proxy is running. Defaults to localhost.

If you are not running a Tor proxy just leave this environment variable undefined.

TOR_PROXY_PORT

The port on which the Tor proxy is running. If not set, ElectrumX will autodetect any proxy running on the usual ports 9050 (Tor), 9150 (Tor browser bundle) and 1080 (socks).

BLACKLIST_URL

URL to retrieve a list of blacklisted peers. If not set, a coin- specific default is used.

Server Advertising

These environment variables affect how your server is advertised by peer discovery (if enabled).

REPORT_HOST

The clearnet host to advertise. If not set, no clearnet host is advertised.

REPORT_TCP_PORT

The clearnet TCP port to advertise if REPORT_HOST is set. Defaults to TCP_PORT. 0 disables publishing a TCP port.

REPORT_SSL_PORT

The clearnet SSL port to advertise if REPORT_HOST is set. Defaults to SSL_PORT. 0 disables publishing an SSL port.

REPORT_HOST_TOR

If you wish run a Tor service, this is the Tor host name to advertise and must end with .onion.

REPORT_TCP_PORT_TOR

The Tor TCP port to advertise. The default is the clearnet REPORT_TCP_PORT, unless disabled or it is 0, otherwise TCP_PORT. 0 disables publishing a Tor TCP port.

REPORT_SSL_PORT_TOR

The Tor SSL port to advertise. The default is the clearnet REPORT_SSL_PORT, unless disabled or it is 0, otherwise SSL_PORT. 0 disables publishing a Tor SSL port.

Note

Certificate-Authority signed certificates don’t work over Tor, so you should set REPORT_SSL_PORT_TOR to 0 if yours is not self-signed.

Cache

If synchronizing from the Genesis block your performance might change by tweaking the cache size. Cache size is only checked roughly every minute, so the cache can grow beyond the specified size. Moreover, the Python process is often quite a bit fatter than the cache size, because of Python overhead and also because leveldb consumes a lot of memory when flushing. So I recommend you do not set this over 60% of your available physical RAM:

CACHE_MB

The amount of cache, in MB, to use. The default is 1,200.

A portion of the cache is reserved for unflushed history, which is written out frequently. The bulk is used to cache UTXOs.

Larger caches probably increase performance a little as there is significant searching of the UTXO cache during indexing. However, I don’t see much benefit in my tests pushing this too high, and in fact performance begins to fall, probably because LevelDB already caches, and also because of Python GC.

I do not recommend raising this above 2000.