The ability to remotely SSH into a machine running an Ubuntu LiveCD can come in handy in many situations. The LiveCD supports a large variety of hardware and can be used to troubleshoot system problems on a machine where you have limited or no access. A user with limited skills can easily setup remote access and allow a trusted friend to troubleshoot the system from another location.

The first thing to start the process is to open a terminal. Follow these menus:

Applications -> Accessories -> Terminal

In the terminal install the ssh server on your LiveCD system.

$ sudo apt-get install openssh-server

The server is started automatically after installing.

To login remotely, you’ll need to set the password for the default ubuntu user.

$ sudo passwd ubuntu
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully

You should now be able to login to the system running the LiveCD. But first you need to find the IP address of the machine so you can connect to it.

The ifconfig command will list your network interfaces and along with it your IP address.

$ ifconfig

eth0      ...
          inet addr:192.168.1.1  Bcast:192.168.2.255  Mask:255.255.255.0
          ...

The inet addr entry is your IP address which you need to log into the LiveCD system. As you an see above the IP address begins with “192.168” which indicates that the IP address is only valid on the local network. It was an address assigned to the machine by the router. This is fine if you plan on logging in from another machine on this local network.

If you need to access the machine from outside your local network you have a couple of options. The first is to remove any router between you and the Internet. This should give you a valid IP address which is accessible from outside your local network. You may also be able to access your router’s administration panel and tell it to pass SSH traffic to the IP address of the LiveCD system. You will then use the router’s IP address instead for the next step.

If your IP address already begins with something other than “192.168” then you are safe as well. You should be able to access the LiveCD system from any location, local or not.

Using the IP address from the previous step you can now log into the LiveCD system as the ubuntu user. Use the password you created earler.

$ ssh ubuntu@<IP Address>

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In C or C++ it is fairly simple to find the IP address of the remote end of a TCP socket.

The following example shows how to do this using the getpeername() and inet_ntoa() system calls.

int sockfd;
int len;
char * hostip;
struct sockaddr_in sin;

len = sizeof(sin);

if (0 != getpeername(sockfd, (struct sockaddr *) &sin, &len))
        perror("getpeername");
}

hostip = inet_ntoa(sin.sin_addr);

printf("client IP: %s\n", hostip);

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You can find the IP address of your system at the command line by using the ifconfig command. The ifconfig command will show you information on all your network interfaces. If no arguments are given ifconfig displays the status of the currently active interfaces.

You have to run this command as root or use sudo.

# ifconfig

wlan0     Link encap:Ethernet  HWaddr a1:b2:c3:d4:e5:f6
          inet addr:192.168.2.11  Bcast:192.168.2.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1492  Metric:1
          RX packets:4007 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4246 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3292271 (3.1 MiB)  TX bytes:994922 (971.6 KiB)

Your IP address is displayed in the inet addr field.

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Here is a good way to determine the hostname and IP address of the local machine in C.

You first have to grab the hostname with gethostname().

char hostbuf[256];
gethostname(hostbuf,sizeof(hostbuf));

Take the hostname and use it to grab the hostent struct with gethostbyname().

struct hostent *hostentry;
hostentry = gethostbyname(hostbuf);

Finally you have to take the hostent that is returned and pull out the IP address. It is in network byte order, so you have to convert it to a string with inet_ntoa().

char * ipbuf;
ipbuf = inet_ntoa(*((struct in_addr *)hostentry->h_addr_list[0]));

Put all this together into a working programs.

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main()
{
        char hostbuf[256];
        char * ipbuf;
        struct hostent *hostentry;
        int ret;

        ret = gethostname(hostbuf,sizeof(hostbuf));

        if(-1 == ret){
                perror("gethostname");
                exit(1);
        }

        hostentry = gethostbyname(hostbuf);

        if(NULL == hostentry){
                perror("gethostbyname");
                exit(1);
        }

        ipbuf = inet_ntoa(*((struct in_addr *)hostentry->h_addr_list[0]));

        if(NULL == ipbuf){
                perror("inet_ntoa");
                exit(1);
        }

        printf("Hostname: %s Host IP: %s\n", hostbuf, ipbuf);

        return 0;
}

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