Electrs

We set up Electrs to serve as a full Electrum server for use with your Bitcoin software or hardware wallets.

Difficulty: Medium

Requirements

• Bitcoin Core

• Others

  • Rustup + Cargo

Preparations

Make sure that you have reduced the database cache of Bitcoin Core after a full sync.

Electrs is a replacement for a Fulcrum, these two services cannot be run at the same time (due to the same standard ports used), remember to stop or uninstall Fulcrum by doing "sudo systemctl stop fulcrum".

Install dependencies

• With user admin, update the packages and upgrade to keep up to date with the OS

$ sudo apt update && sudo apt full-upgrade

• Make sure that all necessary software packages are installed

$ sudo apt install libgflags-dev libsnappy-dev zlib1g-dev libbz2-dev liblz4-dev libzstd-dev make g++ clang cmake build-essential

• Install the librocksdb v7.8.3 from the source code. Go to the temporary folder

$ cd /tmp

• Clone the rocksdb GitHub repository

$ git clone -b v7.8.3 --depth 1 https://github.com/facebook/rocksdb

• Enter to the rocksdb folder

$ cd rocksdb

• Compile it. This could take time depending on your system performance, be patient

$ make shared_lib -j $(nproc)

Expected output ⬇️

$DEBUG_LEVEL is 0
$DEBUG_LEVEL is 0
  CC       cache/cache.o
  CC       cache/cache_entry_roles.o
  CC       cache/cache_key.o
  CC       cache/cache_reservation_manager.o
  CC       cache/charged_cache.o
  CC       cache/clock_cache.o
  CC       cache/fast_lru_cache.o
  CC       cache/lru_cache.o
  CC       cache/compressed_secondary_cache.o
  CC       cache/sharded_cache.o
  CC       db/arena_wrapped_db_iter.o
  CC       db/blob/blob_contents.o
  CC       db/blob/blob_fetcher.o
  CC       db/blob/blob_file_addition.o
  CC       db/blob/blob_file_builder.o
  CC       db/blob/blob_file_cache.o
  CC       db/blob/blob_file_garbage.o
  [...]

• Install it

$ sudo make install-shared

Expected output ⬇️

$DEBUG_LEVEL is 0
echo 'prefix=/usr/local' > rocksdb.pc
echo 'exec_prefix=${prefix}' >> rocksdb.pc
echo 'includedir=${prefix}/include' >> rocksdb.pc
echo 'libdir=/usr/local/lib' >> rocksdb.pc
echo '' >> rocksdb.pc
echo 'Name: rocksdb' >> rocksdb.pc
echo 'Description: An embeddable persistent key-value store for fast storage' >> rocksdb.pc
echo Version: 7.8.3 >> rocksdb.pc
echo 'Libs: -L${libdir}  -ldl -Wl,-rpath -Wl,'$ORIGIN' -lrocksdb' >> rocksdb.pc
echo 'Libs.private: -lpthread -lrt -ldl -lsnappy -lgflags -lz -lbz2 -llz4 -lzstd ' >> rocksdb.pc
echo 'Cflags: -I${includedir} -std=c++17  -faligned-new -DHAVE_ALIGNED_NEW -DROCKSDB_PLATFORM_POSIX -DROCKSDB_LIB_IO_POSIX  -DOS_LINUX -fno-builtin-memcmp -DROCKSDB_FALLOCATE_PRESENT -DSNAPPY -DGFLAGS=1 -DZLIB -DBZIP2 -DLZ4 -DZSTD -DROCKSDB_MALLOC_USABLE_SIZE -DROCKSDB_PTHREAD_ADAPTIVE_MUTEX -DROCKSDB_BACKTRACE -DROCKSDB_RANGESYNC_PRESENT -DROCKSDB_SCHED_GETCPU_PRESENT -DROCKSDB_AUXV_GETAUXVAL_PRESENT -DHAVE_UINT128_EXTENSION  -isystem third-party/gtest-1.8.1/fused-src' >> rocksdb.pc
echo 'Requires: ' >> rocksdb.pc
install -d /usr/local/lib
install -d /usr/local/lib/pkgconfig
for header_dir in `find "include/rocksdb" -type d`; do \
        install -d //usr/local/$header_dir; \
done
for header in `find "include/rocksdb" -type f -name *.h`; do \
        install -C -m 644 $header //usr/local/$header; \
done
for header in ; do \
        install -d //usr/local/include/rocksdb/`dirname $header`; \
        install -C -m 644 $header //usr/local/include/rocksdb/$header; \
done
install -C -m 644 rocksdb.pc /usr/local/lib/pkgconfig/rocksdb.pc
install -d /usr/local/lib
install -C -m 755 librocksdb.so.7.8.3 /usr/local/lib
ln -fs librocksdb.so.7.8.3 /usr/local/lib/librocksdb.so.7.8
ln -fs librocksdb.so.7.8.3 /usr/local/lib/librocksdb.so.7
ln -fs librocksdb.so.7.8.3 /usr/local/lib/librocksdb.so

• Update the shared library cache. Wait until the prompt comes back to show

$ sudo ldconfig

• Come back to the /tmp folder

$ cd ..

• Delete rocksdb folder

$ sudo rm -r rocksdb

• Check if you already have Rustc installed

$ rustc --version

Expected output:

> rustc 1.71.0 (8ede3aae2 2023-07-12)

• And cargo installed

$ cargo -V

Expected output:

> cargo 1.71.0 (cfd3bbd8f 2023-06-08)

If you obtain "command not found" outputs, you need to follow the Rustup + Cargo bonus section to install it and then come back to continue with the guide

Reverse proxy & Firewall

In the Security section, we already set up Nginx as a reverse proxy. Now we can add the Electrs configuration.

• With user admin, create the reverse proxy configuration

$ sudo nano /etc/nginx/streams-available/electrs-reverse-proxy.conf

• Paste the complete following configuration. Save and exit

upstream electrs {
  server 127.0.0.1:50001;
}
server {
  listen 50002 ssl;
  proxy_pass electrs;
}

• Create the symbolic link that points to the directory streams-enabled

$ sudo ln -s /etc/nginx/streams-available/electrs-reverse-proxy.conf /etc/nginx/streams-enabled/

• Test the Nginx configuration

$ sudo nginx -t

Expected output:

> nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
> nginx: configuration file /etc/nginx/nginx.conf test is successful

• Reload the Nginx configuration to apply changes

$ sudo systemctl reload nginx

• Configure the firewall to allow incoming requests to the SSL and TCP ports

$ sudo ufw allow 50002/tcp comment 'allow Electrs SSL from anywhere'

$ sudo ufw allow 50001/tcp comment 'allow Electrs TCP from anywhere'

Installation

There are no precompiled binaries available, so we will compile the application ourselves.

Build from the source code

• With user admin, go to the temporary folder

$ cd /tmp

• Set a temporary version environment variable to the installation

$ VERSION=0.10.4

• Download the source code

$ git clone --branch v$VERSION https://github.com/romanz/electrs.git

• Go to the electrs folder

$ cd electrs

• To avoid using bad source code, verify that the release has been properly signed by the main developer Roman Zeyde

$ curl https://romanzey.de/pgp.txt | gpg --import

Expected output:

>   % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
>                                    Dload  Upload   Total   Spent    Left  Speed
> 100  1255  100  1255    0     0   3562      0 --:--:-- --:--:-- --:--:--  3555
> gpg: key 87CAE5FA46917CBB: public key "Roman Zeyde <[email protected]>" imported
> gpg: Total number processed: 1
> gpg:               imported: 1

• Verify the release

$ git verify-tag v$VERSION

Expected output:

> gpg: Signature made Thu 03 Nov 2022 03:37:23 PM UTC
> gpg:                using ECDSA key 15C8C3574AE4F1E25F3F35C587CAE5FA46917CBB
> gpg:                issuer "[email protected]"
> gpg:  from "Roman Zeyde <[email protected]>" [unknown]
> gpg:                 aka "Roman Zeyde <[email protected]>" [unknown]
> gpg: WARNING: This key is not certified with a trusted signature!
> gpg:          There is no indication that the signature belongs to the owner.
> Primary key fingerprint: 15C8 C357 4AE4 F1E2 5F3F  35C5 87CA E5FA 4691 7CBB

• Now compile the source code into an executable binary

$ ROCKSDB_INCLUDE_DIR=/usr/local/include ROCKSDB_LIB_DIR=/usr/local/lib cargo build --locked --release

Example of expected output 🔽

info: syncing channel updates for '1.63.0-x86_64-unknown-linux-gnu'
info: latest update on 2022-08-11, rust version 1.63.0 (4b91a6ea7 2022-08-08)
info: downloading component 'cargo'
info: downloading component 'clippy'
info: downloading component 'rust-docs'
info: downloading component 'rust-std'
info: downloading component 'rustc'
info: downloading component 'rustfmt'
info: installing component 'cargo'
info: installing component 'clippy'
info: installing component 'rust-docs'
info: installing component 'rust-std'
info: installing component 'rustc'
info: installing component 'rustfmt'
    Updating crates.io index
  Downloaded hex_lit v0.1.1
  Downloaded humantime v2.1.0
  Downloaded bitflags v1.3.2
  Downloaded getrandom v0.2.10
  Downloaded rand_chacha v0.3.1
  Downloaded is-terminal v0.4.7
  Downloaded lock_api v0.4.10
  Downloaded libloading v0.7.4
  Downloaded jsonrpc v0.14.1
  Downloaded jobserver v0.1.26
  Downloaded thiserror-impl v1.0.40
  Downloaded autocfg v1.1.0
  Downloaded dirs-sys-next v0.1.2
  Downloaded dirs-next v2.0.0
  Downloaded httpdate v1.0.2
  Downloaded configure_me v0.4.0
  Downloaded lazycell v1.3.0
  Downloaded num_cpus v1.16.0
[...]

• Install it

$ sudo install -m 0755 -o root -g root -t /usr/local/bin ./target/release/electrs

• Check the correct installation

$ electrs --version

Example of expected output:

> v0.10.0

• Return to the home folder and delete the folder /electrs to be ready for the next update

$ cd

• Delete the temporal electrs folder

$ sudo rm -r /tmp/electrs

If you come to update this is the final step

Configuration

• Create the electrs user

$ sudo adduser --disabled-password --gecos "" electrs

• Make to the electrs user a member of the "bitcoin" group

$ sudo adduser electrs bitcoin

• Create the Electrs data directory

$ sudo mkdir /data/electrs

• Assign as the owner to the electrs user

$ sudo chown electrs:electrs /data/electrs

• Switch to the electrs user

$ sudo su - electrs

• Create the electrs config file

$ nano /data/electrs/electrs.conf

• Enter the complete next content

# MiniBolt: electrs configuration
# /data/electrs/electrs.conf

# Bitcoin Core settings
network = "bitcoin"
cookie_file= "/data/bitcoin/.cookie"

# Electrs settings
electrum_rpc_addr = "0.0.0.0:50001"
db_dir = "/data/electrs/db"
server_banner = "Welcome to electrs (Electrum Rust Server) running on a MiniBolt node!"
skip_block_download_wait = true

# Logging
log_filters = "INFO"
timestamp = true

• Exit electrs user session to return to the "admin" user session

$ exit

Create systemd service

• As user admin, create the Electrs systemd unit

$ sudo nano /etc/systemd/system/electrs.service

• Enter the complete following configuration. Save and exit

# MiniBolt: systemd unit for electrs
# /etc/systemd/system/electrs.service

[Unit]
Description=Electrs
Wants=bitcoind.service
After=bitcoind.service

[Service]
ExecStart=/usr/local/bin/electrs --conf /data/electrs/electrs.conf --skip-default-conf-files

# Process management
####################
Type=simple
TimeoutSec=300
KillMode=process

# Directory creation and permissions
####################################
RuntimeDirectory=electrs
RuntimeDirectoryMode=0710
User=electrs
Group=electrs

# Hardening Measures
####################
PrivateTmp=true
ProtectSystem=full
ProtectHome=true
PrivateDevices=true
MemoryDenyWriteExecute=true

[Install]
WantedBy=multi-user.target

• Enable autoboot (optional)

$ sudo systemctl enable electrs

• Prepare "electrs" monitoring by the systemd journal and check log logging output. You can exit monitoring at any time with Ctrl-C

$ journalctl -f -u electrs

Run

To keep an eye on the software movements, start your SSH program (eg. PuTTY) a second time, connect to the MiniBolt node, and log in as admin. Commands for the second session start with the prompt $2 (which must not be entered).

• Start the service

$2 sudo systemctl start electrs

• Monitor the systemd journal at the first session created to check if everything works fine

Example of expected output on the first terminal with $ journalctl -f -u electrs ⬇️

Starting electrs  on x86_64 linux with Config { network: Bitcoin, db_path: "/data/electrs/db/bitcoin", daemon_dir: "/data/bitcoin", daemon_auth: CookieFile("/data/bitcoin/.cookie"), daemon_rpc_addr: 127.0.0.1:8332, daemon_p2p_addr: 127.0.0.1:8333, electrum_rpc_addr: 0.0.0.0:50001, monitoring_addr: 127.0.0.1:4224, wait_duration: 10s, jsonrpc_timeout: 15s, index_batch_size: 10, index_lookup_limit: None, reindex_last_blocks: 0, auto_reindex: true, ignore_mempool: false, sync_once: false, disable_electrum_rpc: false, server_banner: "Welcome to electrs (Electrum Rust Server) running on a MiniBolt node!", args: [] }
[2021-11-09T07:09:42.744Z INFO  electrs::metrics::metrics_impl] serving Prometheus metrics on 127.0.0.1:4224
[2021-11-09T07:09:42.744Z INFO  electrs::server] serving Electrum RPC on 0.0.0.0:50001
[2021-11-09T07:09:42.812Z INFO  electrs::db] "/data/electrs/db/bitcoin": 0 SST files, 0 GB, 0 Grows
[2021-11-09T07:09:43.174Z INFO  electrs::index] indexing 2000 blocks: [1..2000]
[2021-11-09T07:09:44.665Z INFO  electrs::chain] chain updated: tip=00000000dfd5d65c9d8561b4b8f60a63018fe3933ecb131fb37f905f87da951a, height=2000
[2021-11-09T07:09:44.986Z INFO  electrs::index] indexing 2000 blocks: [2001..4000]
[2021-11-09T07:09:46.191Z INFO  electrs::chain] chain updated: tip=00000000922e2aa9e84a474350a3555f49f06061fd49df50a9352f156692a842, height=4000
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 2000 blocks: [4001..6000]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c5a5, height=6000
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 2000 blocks: [6001..8000]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c5a6, height=8000
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 2000 blocks: [8001..10000]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c5a7, height=10000
[...]
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 65 blocks: [756001..756065]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c510, height=756065
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting config compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting headers compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting txid compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting funding compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting spending compaction
[...]

Electrs will now index the whole Bitcoin blockchain so that it can provide all necessary information to wallets. With this, the wallets you use no longer need to connect to any third-party server to communicate with the Bitcoin peer-to-peer network

• Ensure electrs service is working and listening at the default TCP 50001 port, the monitoring 14224 port (not used on MiniBolt) and

$2 sudo ss -tulpn | grep LISTEN | grep electrs

Expected output:

tcp   LISTEN 0      128          0.0.0.0:50001      0.0.0.0:*    users:(("electrs",pid=54749,fd=4))
tcp   LISTEN 0      128        127.0.0.1:14224      0.0.0.0:*    users:(("electrs",pid=54749,fd=3))

• And the SSL 50002 port

$2 sudo ss -tulpn | grep LISTEN | grep 50002

Expected output:

> tcp   LISTEN 0   511   0.0.0.0:50002   0.0.0.0:*    users:(("nginx",pid=719,fd=5),("nginx",pid=718,fd=5),("nginx",pid=717,fd=5),("nginx",pid=716,fd=5),("nginx",pid=715,fd=5))

Electrs must first fully index the blockchain and compact its database before you can connect to it with your wallets. This can take a few hours. Only proceed with the next section once Electrs is ready

Extras (optional)

Remote access over Tor

To use your Electrum server when you're on the go, you can easily create a Tor hidden service. This way, you can connect the BitBoxApp or Electrum wallet remotely, or even share the connection details with friends and family. Note that the remote device needs to have Tor installed as well.

• Ensure that you are logged in with the user admin, edit the torrc file

$ sudo nano /etc/tor/torrc

• Add the following lines in the "location hidden services" section, below "## This section is just for location-hidden services ##" in the torrc file. Save and exit

# Hidden Service Electrs TCP & SSL
HiddenServiceDir /var/lib/tor/hidden_service_electrs_tcp_ssl/
HiddenServiceVersion 3
HiddenServicePoWDefensesEnabled 1
HiddenServicePort 50001 127.0.0.1:50001
HiddenServicePort 50002 127.0.0.1:50002

• Reload the Tor configuration to apply changes

$ sudo systemctl reload tor

• Get your Onion address

$ sudo cat /var/lib/tor/hidden_service_electrs_tcp_ssl/hostname

Expected output:

> abcdefg..............xyz.onion

• You should now be able to connect to your Electrs server remotely via Tor using your hostname and port 50002 (SSL) or 50001 (TCP)

Migrate BTC RPC Explorer to Electrs API connection

To get address balances, either an Electrum server or an external service is necessary. Your local Electrs server can provide address transaction lists, balances, and more.

• As user admin, open the btcrpcexplorer service

$ sudo nano /etc/systemd/system/btcrpcexplorer.service

• Replace the "After=fulcrum.service" with the "After=electrs.service" parameter. Save and exit

After=electrs.service

• Restart the BTC RPC Explorer service to apply the changes

$ sudo systemctl restart btcrpcexplorer

Upgrade

• First, ensure that you have the latest Rustc version following the Upgrade section of the Rustup + Cargo bonus guide

• Follow the complete Build from the source code section

• When you finish, restart Electrs to apply the new version

$ sudo systemctl restart electrs

• Check logs and pay attention to the next log if that attends to the new version installed

$ journalctl -fu electrs

Example of expected output ⬇️

Starting electrs 0.10.0 on x86_64 linux with Config { network: Bitcoin, db_path: "/data/electrs/db/bitcoin", daemon_dir: "/data/bitcoin", daemon_auth: CookieFile("/data/bitcoin/.cookie"), daemon_rpc_addr: 127.0.0.1:8332, daemon_p2p_addr: 127.0.0.1:8333, electrum_rpc_addr: 0.0.0.0:50001, monitoring_addr: 127.0.0.1:4224, wait_duration: 10s, jsonrpc_timeout: 15s, index_batch_size: 10, index_lookup_limit: None, reindex_last_blocks: 0, auto_reindex: true, ignore_mempool: false, sync_once: false, disable_electrum_rpc: false, server_banner: "Welcome to electrs (Electrum Rust Server) running on a MiniBolt node!", args: [] }
[2021-11-09T07:09:42.744Z INFO  electrs::metrics::metrics_impl] serving Prometheus metrics on 127.0.0.1:4224
[2021-11-09T07:09:42.744Z INFO  electrs::server] serving Electrum RPC on 0.0.0.0:50001
[2021-11-09T07:09:42.812Z INFO  electrs::db] "/data/electrs/db/bitcoin": 0 SST files, 0 GB, 0 Grows
[2021-11-09T07:09:43.174Z INFO  electrs::index] indexing 2000 blocks: [1..2000]
[2021-11-09T07:09:44.665Z INFO  electrs::chain] chain updated: tip=00000000dfd5d65c9d8561b4b8f60a63018fe3933ecb131fb37f905f87da951a, height=2000
[2021-11-09T07:09:44.986Z INFO  electrs::index] indexing 2000 blocks: [2001..4000]
[2021-11-09T07:09:46.191Z INFO  electrs::chain] chain updated: tip=00000000922e2aa9e84a474350a3555f49f06061fd49df50a9352f156692a842, height=4000
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 2000 blocks: [4001..6000]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c5a5, height=6000
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 2000 blocks: [6001..8000]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c5a6, height=8000
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 2000 blocks: [8001..10000]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c5a7, height=10000
[...]
[2021-11-09T07:09:46.481Z INFO  electrs::index] indexing 65 blocks: [756001..756065]
[2021-11-09T07:09:47.581Z INFO  electrs::chain] chain updated: tip=00000000dbbb79792303bdd1c6c4d7ab9c21bba0667213c2eca955e11230c510, height=756065
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting config compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting headers compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting txid compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting funding compaction
[2021-11-09T07:09:47.581Z INFO  electrs::db] starting spending compaction
[...]

Uninstall

Uninstall service & user

• Ensure you are logged in with the user admin, stop, disable, and delete the service

$ sudo systemctl stop electrs

$ sudo systemctl disable electrs

$ sudo rm /etc/systemd/system/electrs.service

• Ensure you are logged in with the user admin. Delete the electrs user. Don't worry about userdel: electrs mail spool (/var/mail/electrs) not found output, the uninstall has been successful

$ sudo userdel -rf electrs

• Delete electrs directory

$ sudo rm -rf /data/electrs/

Uninstall Tor hidden service

• Ensure that you are logged in with the user admin , edit the torrc config file

$ sudo nano /etc/tor/torrc

• Delete or comment on the following lines in the "location hidden services" section, below "## This section is just for location-hidden services ##" in the torrc file. Save and exit

# Hidden Service Electrs TCP & SSL
#HiddenServiceDir /var/lib/tor/hidden_service_electrs_tcp_ssl/
#HiddenServiceVersion 3
#HiddenServicePoWDefensesEnabled 1
#HiddenServicePort 50001 127.0.0.1:50001
#HiddenServicePort 50002 127.0.0.1:50002

• Reload the Tor configuration to apply changes

$ sudo systemctl reload tor

Uninstall reverse proxy & FW configuration

• Ensure you are logged in with the user admin, delete the reverse proxy config file

$ sudo rm /etc/nginx/sites-available/electrs-reverse-proxy.conf

• Delete the simbolic link

$ sudo rm /etc/nginx/sites-enabled/electrs-reverse-proxy.conf

• Test Nginx configuration

$ sudo nginx -t

Expected output:

> nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
> nginx: configuration file /etc/nginx/nginx.conf test is successful

• Reload the Nginx configuration to apply changes

$ sudo systemctl reload nginx

• Display the UFW firewall rules, and note the numbers of the rules for Electrs (e.g., X and Y below)

$ sudo ufw status numbered

Expected output:

> [Y] 50001       ALLOW IN    Anywhere          # allow Electrs TCP from anywhere
> [X] 50002       ALLOW IN    Anywhere          # allow Electrs SSL from anywhere

• Delete the rule with the correct number and confirm with "yes"

$ sudo ufw delete X

Port reference

Port	Protocol	Use
50001	TCP	Default port
50002	TCP (SSL)	Encrypted port