5aaee6b Jan 16, 2017
@kyuupichan @thelazier @cluelessperson
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ElectrumX should run on any flavour of unix. I have run it successfully on MaxOSX and DragonFlyBSD. It won't run out-of-the-box on Windows, but the changes required to make it do so should be small - pull requests are welcome.

Package Notes
Python3 ElectrumX uses asyncio. Python version >= 3.5 is required.
aiohttp Python library for asynchronous HTTP. Version >= 1.0 required; I am using 1.0.5.
pylru Python LRU cache package. I'm using 1.0.9.
DB Engine I use plyvel 0.9, a Python interface to LevelDB. A database engine package is required but others are supported (see Database Engine below).
IRC Python IRC package. Only required if you enable IRC; ElectrumX will happily serve clients that try to connect directly. I use 15.0.4 but older versions likely are fine.
x11_hash Only required for DASH. Python X11 Hash package. Only required if for Dash. Version 1.4 tested.

While not a requirement for running ElectrumX, it is intended to be run with supervisor software such as Daniel Bernstein's daemontools, Gerald Pape's runit package or systemd. These make administration of secure unix servers very easy, and I strongly recommend you install one of these and familiarise yourself with them. The instructions below and sample run scripts assume daemontools; adapting to runit should be trivial for someone used to either.

When building the database form the genesis block, ElectrumX has to flush large quantities of data to disk and its DB. You will have a better experience if the database directory is on an SSD than on an HDD. Currently to around height 447,100 of the Bitcoin blockchain the final size of the leveldb database, and other ElectrumX file metadata comes to just over 18.7GB (17.5 GiB). LevelDB needs a bit more for brief periods, and the block chain is only getting longer, so I would recommend having at least 30-40GB of free space before starting.

Database Engine

You can choose from LevelDB and RocksDB to store transaction information on disk. The time taken and DB size is not significantly different. We tried to support LMDB but its history write performance was much worse.

You will need to install one of:


Install the prerequisites above.

Check out the code from Github:

git clone
cd electrumx

You can install with or run the code from the source tree or a copy of it.

You should create a standard user account to run the server under; your own is probably adequate unless paranoid. The paranoid might also want to create another user account for the daemontools logging process. The sample scripts and these instructions assume it is all under one account which I have called electrumx.

Next create a directory where the database will be stored and make it writeable by the electrumx account. I recommend this directory live on an SSD:

mkdir /path/to/db_directory
chown electrumx /path/to/db_directory

Process limits

You must ensure the ElectrumX process has a large open file limit. During sync it should not need more than about 1,024 open files. When serving it will use approximately 256 for LevelDB plus the number of incoming connections. It is not unusual to have 1,000 to 2,000 connections being served, so I suggest you set your open files limit to at least 2,500.

Note that setting the limit in your shell does NOT affect ElectrumX unless you are invoking ElectrumX directly from your shell. If you are using systemd, you need to set it in the .service file (see samples/systemd/electrumx.service).

Using daemontools

Next create a daemontools service directory; this only holds symlinks (see daemontools documentation). The svscan program will ensure the servers in the directory are running by launching a supervise supervisor for the server and another for its logging process. You can run svscan under the electrumx account if that is the only one involved (server and logger) otherwise it will need to run as root so that the user can be switched to electrumx.

Assuming this directory is called service, you would do one of:

mkdir /service       # If running svscan as root
mkdir ~/service      # As electrumx if running svscan as that a/c

Next create a directory to hold the scripts that the supervise process spawned by svscan will run - this directory must be readable by the svscan process. Suppose this directory is called scripts, you might do:

mkdir -p ~/scripts/electrumx

Then copy the all sample scripts from the ElectrumX source tree there:

cp -R /path/to/repo/electrumx/samples/daemontools ~/scripts/electrumx

This copies 3 things: the top level server run script, a log/ directory with the logger run script, an env/ directory.

You need to configure the environment variables under env/ to your setup, as explained in ENVIRONMENT.rst. ElectrumX server currently takes no command line arguments; all of its configuration is taken from its environment which is set up according to env/ directory (see 'envdir' man page). Finally you need to change the log/run script to use the directory where you want the logs to be written by multilog. The directory need not exist as multilog will create it, but its parent directory must exist.

Now start the 'svscan' process. This will not do much as the service directory is still empty:

svscan ~/service & disown

svscan is now waiting for services to be added to the directory:

cd ~/service
ln -s ~/scripts/electrumx electrumx

Creating the symlink will kick off the server process almost immediately. You can see its logs with:

tail -F /path/to/log/dir/current | tai64nlocal

Using systemd

This repository contains a sample systemd unit file that you can use to setup ElectrumX with systemd. Simply copy it to /etc/systemd/system:

cp samples/systemd/electrumx.service /etc/systemd/system/

The sample unit file assumes that the repository is located at /home/electrumx/electrumx. If that differs on your system, you need to change the unit file accordingly.

You need to set a few configuration variables in /etc/electrumx.conf, see ENVIRONMENT.rst for the list of required variables.

Now you can start ElectrumX using systemctl:

systemctl start electrumx

You can use journalctl to check the log output:

journalctl -u electrumx -f

Once configured you may want to start ElectrumX at boot:

systemctl enable electrumx

Warning: systemd is aggressive in forcibly shutting down processes. Depending on your hardware, ElectrumX can need several minutes to flush cached data to disk during initial sync. You should set TimeoutStopSec to at least 10 mins in your .service file.

Sync Progress

Time taken to index the blockchain depends on your hardware of course. As Python is single-threaded most of the time only 1 core is kept busy. ElectrumX uses Python's asyncio to prefill a cache of future blocks asynchronously to keep the CPU busy processing the chain without pausing.

Consequently there will probably be only a minor boost in performance if the daemon is on the same host. It may even be beneficial to have the daemon on a separate machine so the machine doing the indexing has its caches and disk I/O tuned to that task only.

The CACHE_MB environment variable controls the total cache size ElectrumX uses; see ENVIRONMENT.rst for caveats.

Here is my experience with the current codebase, to given heights and rough wall-time. The period from heights 363,000 to 378,000 is the most sluggish:

               Machine A     Machine B
181,000          25m 00s      5m 30s
283,500                       1h 00m
321,800                       1h 40m
357,000          12h 32m      2h 41m
386,000          21h 56m      4h 25m
414,200       1d 12h 29m      6h 30m
447,168       2d 13h 20m      9h 47m

Machine A: a low-spec 2011 1.6GHz AMD E-350 dual-core fanless CPU, 8GB RAM and a DragonFlyBSD UFS fileystem on an SSD. It requests blocks over the LAN from a bitcoind on machine B. DB_CACHE the default of 1,200. LevelDB.

Machine B: a late 2012 iMac running Sierra 10.12.2, 2.9GHz quad-core Intel i5 CPU with an HDD and 24GB RAM. Running bitcoind on the same machine. DB_CACHE set to 1,800. LevelDB.

For chains other than bitcoin-mainnet sychronization should be much faster.

Terminating ElectrumX

The preferred way to terminate the server process is to send it the stop RPC command, or alternatively on Unix the INT or TERM signals. For a daemontools supervised process this can be done by bringing it down like so:

svc -d ~/service/electrumx

ElectrumX will note receipt of the signals in the logs, and ensure the block chain index is flushed to disk before terminating. You should be patient as flushing data to disk can take many minutes.

ElectrumX uses the transaction functionality, with fsync enabled, of the databases. I have written it with the intent that, to the extent the atomicity guarantees are upheld by the DB software, the operating system, and the hardware, the database should not get corrupted even if the ElectrumX process if forcibly killed or there is loss of power. The worst case should be having to restart indexing from the most recent UTXO flush.

Once the process has terminated, you can start it up again with:

svc -u ~/service/electrumx

You can see the status of a running service with:

svstat ~/service/electrumx

svscan can of course handle multiple services simultaneously from the same service directory, such as a testnet or altcoin server. See the man pages of these various commands for more information.

Understanding the Logs

You can see the logs usefully like so:

tail -F /path/to/log/dir/current | tai64nlocal

Here is typical log output on startup:

INFO:BlockProcessor:switching current directory to /crucial/server-good
INFO:BlockProcessor:using leveldb for DB backend
INFO:BlockProcessor:created new database
INFO:BlockProcessor:creating metadata diretcory
INFO:BlockProcessor:software version: ElectrumX 0.10.2
INFO:BlockProcessor:DB version: 5
INFO:BlockProcessor:coin: Bitcoin
INFO:BlockProcessor:network: mainnet
INFO:BlockProcessor:height: -1
INFO:BlockProcessor:tip: 0000000000000000000000000000000000000000000000000000000000000000
INFO:BlockProcessor:tx count: 0
INFO:BlockProcessor:sync time so far: 0d 00h 00m 00s
INFO:BlockProcessor:reorg limit is 200 blocks
INFO:Daemon:daemon at
INFO:BlockProcessor:flushing DB cache at 1,200 MB
INFO:Controller:RPC server listening on localhost:8000
INFO:Prefetcher:catching up to daemon height 447,187...
INFO:Prefetcher:verified genesis block with hash 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
INFO:BlockProcessor:our height: 9 daemon: 447,187 UTXOs 0MB hist 0MB
INFO:BlockProcessor:our height: 52,509 daemon: 447,187 UTXOs 9MB hist 14MB
INFO:BlockProcessor:our height: 85,009 daemon: 447,187 UTXOs 12MB hist 31MB
INFO:BlockProcessor:our height: 102,384 daemon: 447,187 UTXOs 15MB hist 47MB
INFO:BlockProcessor:our height: 133,375 daemon: 447,187 UTXOs 80MB hist 222MB
INFO:BlockProcessor:our height: 134,692 daemon: 447,187 UTXOs 96MB hist 250MB
INFO:BlockProcessor:flushed to FS in 0.7s
INFO:BlockProcessor:flushed history in 16.3s for 1,124,512 addrs
INFO:BlockProcessor:flush #1 took 18.7s.  Height 134,692 txs: 941,963
INFO:BlockProcessor:tx/sec since genesis: 2,399, since last flush: 2,400
INFO:BlockProcessor:sync time: 0d 00h 06m 32s  ETA: 1d 13h 03m 42s

Under normal operation these cache stats repeat once or twice a minute. UTXO flushes can take several minutes and look like this:

INFO:BlockProcessor:our height: 378,745 daemon: 447,332 UTXOs 1,013MB hist 184MB
INFO:BlockProcessor:our height: 378,787 daemon: 447,332 UTXOs 1,014MB hist 194MB
INFO:BlockProcessor:flushed to FS in 0.3s
INFO:BlockProcessor:flushed history in 13.4s for 934,933 addrs
INFO:BlockProcessor:flushed 6,403 blocks with 5,879,440 txs, 2,920,524 UTXO adds, 3,646,572 spends in 93.1s, committing...
INFO:BlockProcessor:flush #120 took 226.4s.  Height 378,787 txs: 87,695,588
INFO:BlockProcessor:tx/sec since genesis: 1,280, since last flush: 359
INFO:BlockProcessor:sync t ime: 0d 19h 01m 06s  ETA: 3d 21h 17m 52s
INFO:BlockProcessor:our height: 378,812 daemon: 447,334 UTXOs 10MB hist 10MB

The ETA shown is just a rough guide and in the short term can be quite volatile. It tends to be a little optimistic at first; once you get to height 280,000 is should be fairly accurate.