in case you have forgotten password for btsync Web UI, you can override it in config file.
For example on Debian it is located in: /etc/btsync/debconf-default.conf

Find webui section in configuration and add 2 options: username and password:

“login”: “admin”,
“password”: “password”

So “webui” configuration section will look like this:

        "webui" :
        {
                "directory_root" : "/var/btsync",
                "listen" : "0.0.0.0:8888",
                "force_https" : true,
                "ssl_certificate" : "/etc/btsync/debconf-default.crt",
                "ssl_private_key" : "/etc/btsync/debconf-default.key",
                "login": "admin",
                "password": "password"
        }

Now restart btsync serviceby running:

service btsync restart

You can now login using username “admin” and password “password” and reset password in WebUI.