Install scp, rsync and other tools on CentOS

When you do a "minimal" install of CentOS it doesn't install things like rsync and scp by default.

To install them do;

yum install openssh-clients rsync

HOWTO: The Five Minute VPN Guide

UPDATE: 05-06-2012, latest version: VPN v1.03

I posted some time ago a guide for setting up a PPP over SSH vpn but it was a bit clunky and I was never fully happy with it.

So, I have spent some time adding all of the hard work to a fully interactive script that has the following features;

* Automatically configure your client details in a "vpn.conf" file.

* Bi-directional routing between the server and all remote nodes is automatically configured.

* Interactive functions to stop and start the VPN

* Function to check the VPN status, attempts restart if down

* Send email to a specified administrator when the state of the VPN changes.

* Automatic setup of keys for passwordless connections.

* Zero scripting skills required

Audience:

Network admins who want to connect two or more offices using an encrypted, secure VPN over the public Internet. Clients at remote sites will access the Internet directly through their local gateway while all internal traffic is automatically routed via encrypted VPN links back to the central site.

Pre-requisites:

Two debian or ubuntu servers configured as routers, designated as SERVER and CLIENT. Both must be connected to the internet and the SERVER should have a FQDN of some sort (see www.dyndns.com if you don't have your own domain). Assuming you are running a firewall on the server you must poke a hole in it to allow SSH connections from the internet.

Authors Note:

This script started out as a simple clean up of the old one but of course that quickly blew out to a full on rewrite until I ended up with an all singing, all dancing mega-vpn management utility that I reckon is the easiest way to setup a VPN ever. Not one line of the original script remains intact!

Anyway, enough of the chest beating, let's get on with the show!

Step 1: Setting up the Server

Clients connecting to the server will do so using a local account on the server that is specifically used for this purpose.

Create a user called "vpn"

sudo adduser --system --group vpn

The --system parameter has set the vpn users shell to be /bin/false. However, because the vpn user needs to be able to log in via ssh, we must change this to /bin/bash in the /etc/passwd file.

Edit the passwd file;

sudo vi /etc/passwd

Modify the line for the vpn user so that it ends with /bin/bash;

vpn:x:110:110::/home/vpn:/bin/bash

We also need to set a password for the "vpn" account;

sudo passwd vpn

NOTE:

The vpn account password will only be used while doing the initial configuration of your VPN clients. You should choose a reasonably complex (secure) password and not be concerned about making it easy to type or remember.

The vpn user needs to be able to bring the ppp connection up and down as well as modify the system routing table. We will configure sudo to allow access to those commands.

Edit your sudoers file;

sudo visudo

Append these lines to the end of the file;

vpn ALL=NOPASSWD: /usr/sbin/pppd
vpn ALL=NOPASSWD: /sbin/route

Finally, we need to log in as the vpn and set up a few bits in its home folder.

Change to the vpn user;

sudo su vpn

Create an ssh directory;

mkdir .ssh

We need to seed an "active_networks" file with the subnet(s) that the VPN clients should be able to route to (usually the local LAN subnet that your VPN server is on but if you have a more elaborate network there may be multiple subnets. Simply add all the ones that you need remote hosts to route to). The "active_networks" file should be located in the vpn user's home folder (and owned by the vpn user)

Create an active_networks file;

vi ~/active_networks

Add a line for the servers local subnet followed by a hash and the server name.

Example:

10.1.1.0/24 # vpn-server

If you have more than one subnet then you can add them too (on separate lines)

Note:

The active_routes file holds a record of all the remote subnets (VPN network nodes) that the server is connected to. As each client gateway connects to the server it adds it's own LAN subnet to the file. If new routes are added later you can do a "vpn check" on the client gateway which will automatically update the local routing table with any new routes for any other nodes that may have been recently added to your network.

And that's all there is for the server part of this howto!

Yes, seriously.

Step 2: Configuring a Client

Configuring the client is even easier than the server, we just need to download and run my new VPN script.

On the client host, download my vpn client script

Put the vpn script file somewhere in your system path or make a link to wherever you decide to put it.

E.g. sudo ln -s /store/scripts/vpn /usr/sbin/vpn

Install dependencies;

sudo apt-get install ipcalc ppp

And finally, execute the script with the "setup" directive;

sudo ./vpn setup

This will create a default config for your VPN. If this will be the first or only client node to be connected to your VPN server then the only required value is the SERVER_HOSTNAME for the VPN server. This should be a FQDN that is pingable from the Internet. For 99% of scenarios the rest of the default settings will work perfectly fine.

Once you have finished the setup, you can start the vpn;

sudo ./vpn start
Starting vpn to vpn.tuxnetworks.net on port 22 - Using interface ppp0
Connect: ppp0 <--> /dev/pts/1
Deflate (15) compression enabled
local  IP address 192.168.2.2
remote IP address 192.168.2.1
Setting static routes
Added route to 10.1.1.0/24
Added route to 10.48.17.0/24

Check the status of your VPN connection;

sudo ./vpn status
---------------------------------------------------------
Local network : 10.1.3.1/255.255.255.0 [eth0]
Connected to  : vpn.tuxnetworks.net
Remote IP     : 192.168.2.1
Local IP      : 192.168.2.2
PID           : 25493

To have your client check whether the VPN is up (and automatically restart it if it's not) add an entry to your system crontab;

sudo vi /etc/crontab

Add a line like so;

*  *    * * *   root    vpn check >> /dev/null 2>&1

This will run every minute, check the vpn status as well as update any new routes to new nodes that have been added since the last time it was run.

Note:

Of course the vpn script file will need to be in your system path for this cronjob to execute. (See above)

If you also configure an administrator email address (and your system is able to send emails of course) then it will email the administrator every time the VPN link goes down, and again when it comes back up.

I've tried to make the script as simple as possible to use and I hope I have covered all the possible failure scenarios gracefully.

Give it a go and let me know in the comments or send me an email to the address contained in the script header and tell me what you think.

Any and all feedback is welcome.

Cheers!

HOWTO: Setting up a vpn using ssh and pppd

For this we need two systems, one is designated as the server, the other the client. The server needs to have a static IP address or dynamic dns name from a free service such as https://www.dyndns.com/. Also, ensure that all firewalls are turned off or port 22 forwarding is enabled for both hosts.

Configuring the SSH accounts;

On the "server" machine;

Firstly, if you have not already installed ssh server do so now.
sudo apt-get install openssh-server

I use port 443 for VPN connections because this is usually the easiest port to get through a firewall that you don't control.

Edit your ssh server config;

sudo vi /etc/ssh/sshd_config

Change the line;

Port 22

to

Port 443

and restart your SSH server;

sudo /etc/init.d/ssh restart

Now, we create a user called "vpn";

sudo adduser --system --group vpn

The --system parameter sets vpn's shell to /bin/false but because the vpn user needs to log in via ssh, we must change this to /bin/bash in the /etc/passwd file.

sudo vi /etc/passwd

Here is an example;

vpn:x:110:110::/home/vpn:/bin/bash

The account password will only be used during this howto. You can choose a complex (secure) one now or a simpler temporary one and change it later.

Creating a password;

sudo passwd vpn

You should be able to login to the account from the client now;

ssh vpn@hostname

The next step is to create a ssh keypair for the root user on the client machine and place that public key in the vpn users authorized_keys file. Use this guide to configure passwordless ssh but remember to use the vpn user on the server instead of the root user as is shown in that guide.

Once you have passwordless SSH properly configured between root@client and vpn@server you should change the password to a more secure (random) one if you haven't already done so it will no longer be needed.

Time to set up the actual VPN.

Configuring the VPN;

The pppd daemon we will use needs to run as root, but we don't want to give our vpn user complete access to the system. To do that we configure sudo to give minimal access rights.

On the Server, open the visudo editor

visudo

Add these three lines to the end of the file

vpn ALL=NOPASSWD: /usr/sbin/pppd
vpn ALL=NOPASSWD: /sbin/iptables
vpn ALL=NOPASSWD: /sbin/route


This allows our vpn user to execute the pppd command to start the vpn and use the "route" command to set the return routes (if required).
If you are setting up a router<->router connection you will need to set the appropriate return routes to the client on the server.

To do this, create a script in the vpn user directory on the server.

vi /home/vpn/returnroutes.sh

Place the appropriate route commands to the subnet(s) at the clients end. If you don't want return routes then just don't enter any route commands. Here is mine;

#!/bin/sh
sudo route add -net 10.48.0.0/16 gw 192.168.0.1
sudo route add -net 10.0.0.0/16 gw 192.168.0.1


This script must be executable

chmod +x /home/vpn/returnroutes.sh

and owned by the vpn user

chown vpn:vpn /home/vpn/returnroutes.sh

We can also check that the pppd permissions are set up properly by logging in as the vpn user and issuing this command;

sudo /usr/sbin/pppd noauth

You should see a bunch of hieroglyphics such as this.

~�}#�!}!}!} }4}"}&} } } } }%}&����}'}"}(}"��~

You can kill the process from another terminal or just wait 30 secs or so for it to finish on its own.

Now we can configure the client (logged in as root)
Firstly, we need to use a script to connect to the server. You can locate the script anywhere you like, I put it in /usr/local/bin

You can download a copy of the connect script or simply
copy and paste this text into a file


#!/bin/sh
# SCRIPT: vpn-connect version 2.2
# LOCATION: /usr/local/bin/vpn-connect
# DESCRIPTION: This script initiates a ppp-ssh vpn connection.
# see the VPN PPP-SSH HOWTO on http://www.linuxdoc.org
# for more information.
# NOTES: This script uses port 443 so your VPN server should be
# configured to listen for ssh on Port 443
#
# revision history:
# 1.6 11-Nov-1996 miquels@cistron.nl
# 1.7 20-Dec-1999 bart@jukie.net
# 2.0 16-May-2001 bronson@trestle.com
# 2.2 27-Sep-2009 brettg@tuxnetworks.com
#
# You will need to change these variables...
#
# The host name or IP address of the SSH server that we are
# sending the connection request to:
SERVER_HOSTNAME=tuxnetworks.homelinux.net

# The username on the VPN server that will run the tunnel.
# For security reasons, this should NOT be root. (Any user
# that can use PPP can intitiate the connection on the client)
SERVER_USERNAME=vpn

# The VPN network interface on the server should use this address:
SERVER_IFIPADDR=192.168.3.2

# ...and on the client, this address:
CLIENT_IFIPADDR=192.168.3.1

# This tells ssh to use unprivileged high ports, even though it's
# running as root. This way, you don't have to punch custom holes
# through your firewall.
LOCAL_SSH_OPTS="-P"

PATH=/usr/local/sbin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/bin/X11/:

## required commands...

PPPD=/usr/sbin/pppd
SSH=/usr/bin/ssh
RETURNROUTES=/home/vpn/zenroutes.sh

if ! test -f $PPPD ; then echo "can't find $PPPD"; exit 3; fi
if ! test -f $SSH ; then echo "can't find $SSH"; exit 4; fi

case "$1" in
start)
# echo -n "Starting vpn to $SERVER_HOSTNAME: "
${PPPD} updetach noauth passive pty "${SSH} -p 443 ${LOCAL_SSH_OPTS} ${SERVER_HOSTNAME} -l${SERVER_USERNAME} -o Batchmode=yes sudo ${PPPD} nodetach notty noauth" ipparam vpn ${CLIENT_IFIPADDR}:${SERVER_IFIPADDR}
${SSH} -p 443 ${SERVER_HOSTNAME} -l ${SERVER_USERNAME} ${RETURNROUTES}
route add -net 10.1.0.0 netmask 255.255.0.0 gw $SERVER_IFIPADDR
# route add -net 10.2.0.0 netmask 255.255.0.0 gw $SERVER_IFIPADDR
# route add -net 192.0.0.0/8 gw $SERVER_IFIPADDR
;;

stop)
# echo -n "Stopping vpn to $SERVER_HOSTNAME: "
PID=`ps ax | grep "${SSH} -p 443 ${LOCAL_SSH_OPTS} ${SERVER_HOSTNAME} -l${SERVER_USERNAME} -o" | grep -v ' passive ' | grep -v 'grep ' | awk '{print $1}'`
if [ "${PID}" != "" ]; then
kill $PID
echo "disconnected."
else
echo "Failed to find PID for the connection"
fi
;;

config)
echo "SERVER_HOSTNAME=$SERVER_HOSTNAME"
echo "SERVER_USERNAME=$SERVER_USERNAME"
echo "SERVER_IFIPADDR=$SERVER_IFIPADDR"
echo "CLIENT_IFIPADDR=$CLIENT_IFIPADDR"
;;

*)
echo "Usage: vpn {start|stop|config}"
exit 1
;;
esac
exit 0


You need to change the SERVER_HOSTNAME variable in the above script. You may also need to change SERVER_IFIPADDR and CLIENT_IFIPADDR depending on your existing network landscape.

Now we need to make the script executable

chmod +x /usr/local/bin/vpn-client

To start the vpn, at the client type

/usr/local/sbin/vpn-client start

You can check if it is up using the "ifconfig" command

ifconfig ppp0

Note: if you already have a ppp connection, such as to your ISP, then you may need to do "ifconfig ppp1". To see all your current ppp connections enter

ifconfig | grep ppp

If you want the vpn connection to be permanently up you can create a script to check the status and restart it if required.

vi /usr/local/sbin/vpn-check

Code;

#!/bin/sh
EMAIL=brettg@tuxnetworks.com
DAEMON=pppd

if [ "$(/bin/pidof $DAEMON)" = "" ]; then
/usr/local/sbin/vpn-client start
wait
if ! [ "$(/bin/pidof $DAEMON)" = "" ]; then
echo "VPN restarted $(date +%m-%d-%Y)"
fi
fi


Now, add an entry to the system crontab to run the script every minute

vi /etc/crontab

Add this line

* * * * * root /usr/local/sbin/vpn-check

Cron will automatically restart so we don't need to do that.

Now, assuming all has gone well if you issue the command

/usr/local/sbin/vpn-client stop

and wait for about a minute the vpn client should automatically reconnect!

Source:
http://www.faqs.org/docs/Linux-mini/ppp-ssh.html#AEN237

HOWTO: Passwordless SSH using a public key

If you find yourself logging in to machines regularly or you want to include ssh commands in a script, for example using rsync to backup then you don't want to have to enter a password every time. In such cases you can use a public key.

The first thing we need to do is create a ssh key pair on the client host. Make sure that you login as the user who will be connecting to the server. In this case I am using the root user.

Warning: If your user already has a key pair then you should skip this step otherwise you may overwrite your existing key and potentially cause problems for other services that may already rely on them.

First, we should check whether there is already a keypair for our user;

ls -al ~/.ssh/
known_hosts

If there are files id_rsa and id_rsa.pub (or similar) listed then you already have a keypair and you should skip this step.

Creating an ssh key pair (press [enter] for each question asked);

ssh-keygen

Note: It is important that you don't enter a passphrase when asked to! If you did just run the command again, it will overwrite the key you just created.

You can check your new keys by looking in the .ssh folder

root@client:~# ls .ssh/
id_rsa id_rsa.pub known_hosts

The one we are interested in here is the public key which ends with .pub. We need to copy this file to /root on the server.

Note: You can do this via scp or copy it onto a thumbdrive or even type it in from a printout if you like! I will leave it up to you to decide the best method in your situation.

On the server, we will need to login as the root user;

Now, we should have the public key file that we copied earlier in our root directory. Let's double check that;

root@server:~# ls -al *.pub
-rw-r--r-- 1 root root 392 2010-08-02 08:22 id_rsa.pub

Great, it is there! We need to add this key to the root users authorized_keys file;

cat id_rsa.pub >> .ssh/authorized_keys

We can test that this worked by going back to our client PC and logging into the server via ssh;

root@client:~# ssh root@server
Linux server 2.6.32-25-generic-pae #44-Ubuntu SMP Fri Sep 17 21:57:48 UTC 2010 i686 GNU/Linux
Ubuntu 10.04.1 LTS

Welcome to Ubuntu!
* Documentation: https://help.ubuntu.com/
Last login: Thu Oct 14 15:38:57 2010 from client
root@server:~#

If it didn't ask you to enter a password then you are cooking with gas!