doc: update/improve automatic tor section of tor.md

Author: jonatack

doc/tor.md

@@ -117,37 +117,94 @@ for normal IPv4/IPv6 communication, use:
 
 ## 3. Automatically create a Bitcoin Core onion service
 
-Starting with Tor version 0.2.7.1 it is possible, through Tor's control socket
-API, to create and destroy 'ephemeral' onion services programmatically.
-Bitcoin Core has been updated to make use of this.
-
-This means that if Tor is running (and proper authentication has been configured),
-Bitcoin Core automatically creates an onion service to listen on. This will positively
-affect the number of available .onion nodes.
-
-This new feature is enabled by default if Bitcoin Core is listening (`-listen`), and
-requires a Tor connection to work. It can be explicitly disabled with `-listenonion=0`
-and, if not disabled, configured using the `-torcontrol` and `-torpassword` settings.
-To show verbose debugging information, pass `-debug=tor`.
-
-Connecting to Tor's control socket API requires one of two authentication methods to be
-configured. It also requires the control socket to be enabled, e.g. put `ControlPort 9051`
-in `torrc` config file. For cookie authentication the user running bitcoind must have read
-access to the `CookieAuthFile` specified in Tor configuration. In some cases this is
-preconfigured and the creation of an onion service is automatic. If permission problems
-are seen with `-debug=tor` they can be resolved by adding both the user running Tor and
-the user running bitcoind to the same group and setting permissions appropriately. On
-Debian-based systems the user running bitcoind can be added to the debian-tor group,
-which has the appropriate permissions. Before starting bitcoind you will need to re-login
-to allow debian-tor group to be applied. Otherwise you will see the following notice: "tor:
-Authentication cookie /run/tor/control.authcookie could not be opened (check permissions)"
-on debug.log.
-
-An alternative authentication method is the use
-of the `-torpassword=password` option. The `password` is the clear text form that
-was used when generating the hashed password for the `HashedControlPassword` option
-in the tor configuration file. The hashed password can be obtained with the command
-`tor --hash-password password` (read the tor manual for more details).
+Bitcoin Core makes use of Tor's control socket API to create and destroy
+ephemeral onion services programmatically. This means that if Tor is running and
+proper authentication has been configured, Bitcoin Core automatically creates an
+onion service to listen on. The goal is to increase the number of available
+onion nodes.
+
+This feature is enabled by default if Bitcoin Core is listening (`-listen`) and
+it requires a Tor connection to work. It can be explicitly disabled with
+`-listenonion=0`. If it is not disabled, it can be configured using the
+`-torcontrol` and `-torpassword` settings.
+
+To see verbose Tor information in the bitcoind debug log, pass `-debug=tor`.
+
+### Control Port
+
+You may need to set up the Tor Control Port. On Linux distributions there may be
+some or all of the following settings in `/etc/tor/torrc`, generally commented
+out by default (if not, add them):
+
+```
+ControlPort 9051
+CookieAuthentication 1
+CookieAuthFileGroupReadable 1
+```
+
+Add or uncomment those, save, and restart Tor (usually `systemctl restart tor`
+or `sudo systemctl restart tor` on most systemd-based systems, including recent
+Debian and Ubuntu, or just restart the computer).
+
+On some systems (such as Arch Linux), you may also need to add the following
+line:
+
+```
+DataDirectoryGroupReadable 1
+```
+
+### Authentication
+
+Connecting to Tor's control socket API requires one of two authentication
+methods to be configured: cookie authentication or bitcoind's `-torpassword`
+configuration option.
+
+#### Cookie authentication
+
+For cookie authentication, the user running bitcoind must have read access to
+the `CookieAuthFile` specified in the Tor configuration. In some cases this is
+preconfigured and the creation of an onion service is automatic. Don't forget to
+use the `-debug=tor` bitcoind configuration option to enable Tor debug logging.
+
+If a permissions problem is seen in the debug log, e.g. `tor: Authentication
+cookie /run/tor/control.authcookie could not be opened (check permissions)`, it
+can be resolved by adding both the user running Tor and the user running
+bitcoind to the same Tor group and setting permissions appropriately.
+
+On Debian-derived systems, the Tor group will likely be `debian-tor` and one way
+to verify could be to list the groups and grep for a "tor" group name:
+
+```
+getent group | cut -d: -f1 | grep -i tor
+```
+
+You can also check the group of the cookie file. On most Linux systems, the Tor
+auth cookie will usually be `/run/tor/control.authcookie`:
+
+```
+stat -c '%G' /run/tor/control.authcookie
+```
+
+Once you have determined the `${TORGROUP}` and selected the `${USER}` that will
+run bitcoind, run this as root:
+
+```
+usermod -a -G ${TORGROUP} ${USER}
+```
+
+Then restart the computer (or log out) and log in as the `${USER}` that will run
+bitcoind.
+
+#### `torpassword` authentication
+
+For the `-torpassword=password` option, the password is the clear text form that
+was used when generating the hashed password for the `HashedControlPassword`
+option in the Tor configuration file.
+
+The hashed password can be obtained with the command `tor --hash-password
+password` (refer to the [Tor Dev
+Manual](https://2019.www.torproject.org/docs/tor-manual.html.en) for more
+details).
 
 ## 4. Privacy recommendations