Add doc/TROUBLESHOOTING-EN.md

Author: rafael-santiago

doc/TROUBLESHOOTING-EN.md

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+![troubleshooting-glyph](figures/troubleshooting-glyph.png)
+# Troubleshooting
+
+**Abstract**: Guess what? Here you find topics related to troubleshooting.
+
+## Topics
+
+- [I have enabled password-based login but I forgot the password!](#i-have-enabled-password-based-login-but-i-forgot-the-password)
+- [I have changed the Wi-Fi password but now I cannot access Eutherpe via web](#i-have-changed-the-wi-fi-password-but-now-i-cannot-access-eutherpe-via-web)
+
+
+### I have enabled password-based login but I forgot the password!
+
+In order to solve this problem I will log in the computer that is running `Eutherpe` as 
+`root` user.
+
+If you are logged in this machine as a normal user, you can turn into `root` in several ways:
+
+```
+$ sudo su
+```
+
+or:
+
+```
+$ sudo -i
+```
+
+or still if you are not logged in, do the log in as `root`.
+
+Once with a `root` prompt, edit the file `/etc/eutherpe/player.cache`, doing the following:
+
+- Locate in the file the configuration `"Authenticated":true` and change it to `"Authenticated":false`.
+- Still in the file, locate the configuration `"HashKey":"<a bunch of symbols>"` and replace it to
+`"HashKey":""`.
+- Save the changes done in `/etc/eutherpe/player.cache`.
+- From the `root` `prompt` execute `systemctl restart eutherpe`.
+- `Log off` from `root` session (jot down `exit` in the `root` `prompt`).
+- Now browse `Eutherpe` from your `web browser`, it will not ask for password anymore.
+- If you would like to reactivate the authentication and/or reset the password, the current password is from now on `music`.
+
+
+[`Back`](#topics)
+
+### I have changed the Wi-Fi password but now I cannot access Eutherpe via web
+
+You need to log in the `Eutherpe` server as `root`.
+
+If you are logged in this machine as a normal user, you can turn into `root` in several ways:
+
+```
+$ sudo su
+```
+
+or:
+
+```
+$ sudo -i
+```
+
+or still if you are not logged in, do the log in as `root`.
+
+Once it done, edit the file `/etc/eutherpe/player.cache` by doing the following:
+
+- Locate the configuration `"ESSID":"<name of your Wi-Fi network>"` and replace it to `"ESSID":""`.
+- Save the changes done in `/etc/eutherpe/player.cache`.
+- From the `root` `prompt` execute `systemctl restart eutherpe`.
+- Browse `http://<eutherpe server ip address>:8080/eutherpe`. If you have chosen `https` instead
+of `http`, use `https://<eutherpe server ip address>:8080/eutherpe`. If you have changed the
+default port, replace `:8080` to `:<chosen port>`.
+- Once `Eutherpe` accessed by `web` you can update all Wi-Fi credentials info, besides reactivating
+it. After with all info updated, do the reboot and the access to your Wi-Fi will be restablished.
+
+[`Back`](#topics)