It is often necessary to have the ability to SSH between your Linux Host and your Guest virtual machines. In VirtualBox you can do this by simply configuring a second network interface on the Guest. This type of setup will not only allow SSH sessions between Host and Guest, but also between separate Guests themselves.

First off shutdown your Guest VM so that you can add a second network interface. By default you should have one interface already which is using NAT. Leave this alone as it provides access to the internet. Select the tab “Adapter 2″ and change “attached to” to “Host-only Adapter”.

Now boot up your Guest and pull up a terminal. Run ifconfig to see what base address eth1 has been assigned. You can use this address as a base to assign static IP addresses for each Guest VM. In this case inet addr:192.168.56.101 is the base IP address.
$ sudo ifconfig eth1
Link encap:Ethernet HWaddr XX:XX:XX:XX:XX:XX
inet addr:192.168.56.101 Bcast:192.168.56.255 Mask:255.255.255.0
inet6 addr: XXXX::XXXX:XXXX:XXXX:XXXX/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:296 errors:0 dropped:0 overruns:0 frame:0
TX packets:237 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:32116 (31.3 KiB) TX bytes:37642 (36.7 KiB)


If you rely on DHCP you might get a different IP address each time your Guest VM reboots. If this is a problem, you need to setup a static IP address instead.

On a Debian based system edit /etc/network/interfaces to add the following lines. Change the address to your base IP address.
auto eth1
iface eth1 inet static
address 192.168.56.101
netmask 255.255.255.0


On a redhat based system edit this file /etc/sysconfig/network-scripts/ifcfg-eth1 and add the following lines. Change the IPADDR to your base IP address.
DEVICE=eth1
BOOTPROTO=static
IPADDR=192.168.56.101
NETMASK=255.255.255.0


On your Linux Host you can now open a terminal add ssh to the Guest VM:
$ ssh ryan@192.168.56.101

If you are having problems connecting, make sure that sshd in installed and running, and that the firewall on the is not blocking the SSH service on the VM.

You can create an entry in /etc/hosts so you don’t have to remember the IP address.
192.168.56.101 virtualhost1

This allows you to use the virtual hostname instead.
$ ssh ryan@virtualhost1

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At various times it is necessary to restrict the users which can access a certain host. If your network relies on SSH it is as simple as changing an option in the sshd_config configuration file. You will of course need root access to make the necessary changes to this file and eventually reset the SSH daemon.

This configuration file is usually located here.
/etc/ssh/sshd_config

Open the file as root in order to make changes.

$ sudo vim /etc/ssh/sshd_config

You need to set the AllowUsers keyword followed by the users you want to have access to the machine.

AllowUsers	ryan joe

If you want to do something more complex here is the output from the man page:

AllowUsers
This keyword can be followed by a list of user name patterns, separated by spaces. If specified, login is allowed only for user names that match one of the patterns. ‘*’ and ‘?’ can be used as wildcards in the patterns. Only user names are valid; a numerical user ID is not recognized. By default, login is allowed for all users. If the pattern takes the form USER@HOST then USER and HOST are separately checked, restricting logins to particular users from particular hosts.

Another helpful to set the PermitRootLogin to ‘no’ so that the root account is inaccessible.

PermitRootLogin  no

When these settings have been changed go ahead and restart the SSH daemon.

$ sudo /etc/init.d/sshd restart

There are of course ways around this if other users have access to sudo or the root account. But for the most part it is a good way to restrict user access.

Related posts

1. Securely copy remote files with scp
2. Share a remote filesystem over SSH
3. Setup SSH access between VirtualBox Host and Guest VMs