Monthly Archives: December 2017

OpenVPN software repository for Ubuntu 16.04

sudo -s
wget -O - https://swupdate.openvpn.net/repos/repo-public.gpg|apt-key add -
echo "deb http://build.openvpn.net/debian/openvpn/<version> <osrelease> main" > /etc/apt/sources.list.d/openvpn-aptrepo.list
echo "deb http://build.openvpn.net/debian/openvpn/stable xenial main" > /etc/apt/sources.list.d/openvpn-aptrepo.list
apt-get update && apt-get install openvpn

References
https://community.openvpn.net/openvpn/wiki/OpenvpnSoftwareRepos

Android Facebook SDK get Email, Date of Birth and gender of User

GraphRequest request = GraphRequest.newMeRequest(
        accessToken,
        new GraphRequest.GraphJSONObjectCallback() {
            @Override
            public void onCompleted(
                   JSONObject object,
                   GraphResponse response) {
                // Application code
            }
        });
Bundle parameters = new Bundle();
parameters.putString("fields", "id,name,link");
request.setParameters(parameters);
request.executeAsync();

References
https://developers.facebook.com/docs/android/graph
https://stackoverflow.com/questions/29295987/android-facebook-4-0-sdk-how-to-get-email-date-of-birth-and-gender-of-user

Set up OpenConnect VPN Server (ocserv) on Ubuntu 16.04/17.10 with Let’s Encrypt

Installing OpenConnect VPN Server on Ubuntu 16.04/17.10

sudo apt install ocserv

Installing Let’s Encrypt Client (Certbot) on Ubuntu 16.04/17.10 Server

sudo apt install ocserv
sudo apt install software-properties-common
sudo add-apt-repository ppa:certbot/certbot
sudo apt update
sudo apt install certbot

Obtaining a TLS Certificate from Let’s Encrypt

certbot certonly --standalone -d ocserv.example.com

Editing OpenConnect VPN Server Configuration File

sudo nano /etc/ocserv/ocserv.conf
auth = "plain[/etc/ocserv/ocpasswd]"
tcp-port = 443
udp-port = 443
run-as-user = nobody
run-as-group = daemon
socket-file = /var/run/ocserv-socket
server-cert = /etc/letsencrypt/live/ocserv.ml/fullchain.pem
server-key = /etc/letsencrypt/live/ocserv.ml/privkey.pem
ca-cert = /etc/letsencrypt/live/ocserv.ml/chain.pem
max-clients = 8
max-same-clients = 0
try-mtu-discovery = true
device = vpns
dns = 8.8.8.8
dns = 8.8.4.4
cisco-client-compat = true
default-domain = ocserv.example.com
tunnel-all-dns = true

Then comment out all the route directives (add # symbol at the beginning of the following four lines), which will set the server as the default gateway for the clients.

route = 10.10.10.0/255.255.255.0
route = 192.168.0.0/255.255.0.0
route = fef4:db8:1000:1001::/64

no-route = 192.168.5.0/255.255.255.0

Fixing DTLS Handshake Failure

DTLS handshake failed: Resource temporarily unavailable, try again.
sudo cp /lib/systemd/system/ocserv.service /etc/systemd/system/ocserv.service
sudo nano /etc/systemd/system/ocserv.service

Comment out the following two lines.

Requires=ocserv.socket

Also=ocserv.socket
sudo systemctl daemon-reload
sudo systemctl stop ocserv.socket
sudo systemctl disable ocserv.socket
sudo systemctl restart ocserv.service

Creating VPN Accounts

sudo ocpasswd -c /etc/ocserv/ocpasswd username

Enable IP Forwarding

sudo nano /etc/sysctl.conf
net.ipv4.ip_forward = 1
sudo sysctl -p

Configure Firewall for IP Masquerading

ifconfig
sudo iptables -t nat -A POSTROUTING -o ens3 -j MASQUERADE

Preserving Iptables Rules

apt-get install iptables-persistent

If apt-get install iptables-persistent has no effect, run dpkg-reconfigure iptables-persistent instead

Or do it manually :
By default, iptables ruls are lost after reboot. To preserve them, you can switch to root user and then save your rules to a file.

su -

iptables-save > /etc/iptables.rules
nano /etc/systemd/system/iptables-restore.service
[Unit]
Description=Packet Filtering Framework
Before=network-pre.target
Wants=network-pre.target

[Service]
Type=oneshot
ExecStart=/sbin/iptables-restore /etc/iptables.rules
ExecReload=/sbin/iptables-restore /etc/iptables.rules
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
sudo systemctl daemon-reload

sudo systemctl enable iptables-restore

Install and Use OpenConnect VPN client on Ubuntu 16.04/17.10 Desktop

sudo apt install openconnect
sudo openconnect -b vpn.example.com:port-number

-b flag will make it run in the background after connection is established

sudo pkill openconnect
sudo apt install network-manager-openconnect network-manager-openconnect-gnome

References
https://www.linuxbabe.com/ubuntu/openconnect-vpn-server-ocserv-ubuntu-16-04-17-10-lets-encrypt
https://yoursunny.com/t/2017/ocserv-letsencrypt/
https://lowendbox.com/blog/install-openconnect-server-on-ubuntu-16-04/
https://www.digitalocean.com/community/tutorials/how-to-list-and-delete-iptables-firewall-rules

Boost Ubuntu 16.04/17.10 Network Performance by Enabling TCP BBR

Install Linux Kernel 4.9 or Above
TCP BBR is supported by Linux since kernel version 4.9. Use the following command to check your Linux kernel version.

uname -r

Simply install the Hardware Enablement Stack (HWE), which provides newer kernel for Ubuntu LTS releases

sudo apt install --install-recommends linux-generic-hwe-16.04
sudo nano /etc/sysctl.conf
net.core.default_qdisc=fq
net.ipv4.tcp_congestion_control=bbr
sudo sysctl -p

References
https://www.linuxbabe.com/ubuntu/enable-google-tcp-bbr-ubuntu

Combining text & image on a Button on Android

Just use a LinearLayout and pretend it’s a Button – setting background and clickable is the key:

<LinearLayout
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@android:drawable/btn_default"
    android:clickable="true"
    android:orientation="horizontal" >

    <ImageView
        android:id="@+id/img"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="5dp"
        android:src="@drawable/image" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_margin="5dp"
        android:text="Do stuff" />
</LinearLayout>

References
https://stackoverflow.com/questions/1532876/android-combining-text-image-on-a-button-or-imagebutton