Getting Help with Linux Commands

We can use the man command or --help option to get more information on a command. For example, if we want to know more about the cat command usage, then we can issue the commands man cat or cat --help.

Network-related Commands

The following network-related commands are handy in understanding network infrastructure.

wlan0 IEEE 802.11bg ESSID:"ASHWIN"
Mode:Managed Frequency:2.412 GHz Access Point: A2:EC:80:FB:E2:66
Bit Rate=6 Mb/s Tx-Power=20 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:off
Link Quality=45/70 Signal level=-65 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:24 Invalid misc:6 Missed beacon:0

lo no wireless extensions.

eth0 no wireless extensions.

System Information Commands

These commands help us know more about the status of systems and hardware on the Pi.

Architecture: armv7l
Byte Order: Little Endian
CPU(s): 4
On-line CPU(s) list: 0-3
Thread(s) per core: 1
Core(s) per socket: 4
Socket(s): 1
Model name: ARMv7 Processor rev 5 (v7l)
CPU max MHz: 900.0000
CPU min MHz: 600.0000

        total   used     free     shared   buffers  cached
Mem:    996476  210612   785864   7208     15152    113668
-/+ buffers/
cache:  81792   914684
Swap:   102396  0        102396

Linux raspberrypi 4.4.11-v7+ #888 SMP Mon May 23 20:10:33 BST 2016 armv7l GNU/Linux

Filesystem              Size    Used    Avail   Use%    Mounted on
/dev/root               15G     3.6G    11G     26%     /
devtmpfs                483M    0       483M    0%      /dev
tmpfs                   487M    0       487M    0%      /dev/shm
tmpfs                   487M    6.6M    480M    2%      /run
tmpfs                   5.0M    4.0K    5.0M    1%      /run/lock
tmpfs                   487M    0       487M    0%      /sys/fs/cgroup
/dev/mmcblk0p1          63M     21M     43M     33%     /boot
tmpfs                   98M     0       98M     0%      /run/user/1000

Checking the Connectivity with Pi from Another Computer

It is essential that the computer which we are planning to connect to Pi must be in the same network. There should not be any proxy and firewall restrictions between the other computer and the Pi. The best example of this setup is the Pi and the other computer connected under the same router/network switch. To check the connectivity, we can use the ping utility.

1. Open cmd, the Windows command line, on your computer.

2. Turn on the Pi and write down its IP address. Use ifconfig command to find its IP address. Suppose it is 192.168.0.2 (It does not matter whether it is ethernet or WiFi).

3. In cmd, run ping 192.168.0.2 to check the connectivity.

We can use the same ping command on any computer with a Linux distribution or macOS if they are in the same network as Pi.

PuTTY

PuTTY is a free implementation of SSH and Telnet for Windows and Unix platforms, along with an xterm terminal emulator. It is written and maintained primarily by Simon Tatham. You can explore the PuTTY homepage ( www.chiark.greenend.org.uk/~sgtatham/putty/ ) for more information.

PuTTY is open-source software that is available with source code and is developed and supported by a team of volunteers.

Now let’s download and install PuTTY. PuTTY can be downloaded from its download page ( www.chiark.greenend.org.uk/~sgtatham/putty/latest.html ). Download the file PuTTY.exe. Once downloaded, place it in a directory of your choice and create a desktop shortcut (Figure 2-3) for your convenience.

Figure 2-3. PuTTY desktop shortcut

Double-click the putty shortcut and the PuTTY (Figure 2-4) window will open.

Figure 2-4. PuTTY Window

Type the IP address or the host name in the Host Name (or IP address) text box. Make sure SSH is selected as connection type. For future use, you may want to save the settings (I usually do this). Now, click the Open button. It opens a terminal-style window. It will ask you for the username and the password, which are pi and raspberry respectively. While logging in for the first time, it shows the following (Figure 2-5) message dialogue. Click Yes.

Figure 2-5. PuTTY security alert

Once we login, it will show a prompt (Figure 2-6) as follows.

Figure 2-6. PuTTY remote connection window

We can now remotely work with the Pi’s command prompt.

Accessing Raspberry Pi Desktop Remotely

Raspberry Pi desktop is LXDE (Lightweight X11 Desktop Environment ). We can access it from Windows computer remotely using an RDP (Remote Desktop Protocol ) client. For that, we need to install xrdp on Pi. Install it by running sudo apt-get install xrdp. Reboot the Pi after the installation.

We have to use Windows Remote Desktop Client to connect to the Pi now. The client can be found with the Search option in Windows. Click the Remote Desktop Client icon to open it.

In the dialog box below (Figure 2-7), click Options to expand it.

Figure 2-7. Remote Desktop Connection

It expands and shows various options (Figure 2-8). Enter the IP address of the Pi and pi as user name. Click the checkbox and the Save button to save the same configuration for future use.

Figure 2-8. Remote Desktop Connection options

When logging in, it will prompt for the password. Enter the password. If we are connecting to the Pi with a Windows computer for the very first time, then it will display the following dialog box (Figure 2-9). Select the checkbox so it will not ask us again and then click Yes.

Figure 2-9. First time remote login

It will display the Raspberry Pi desktop. Speed of operations will be a bit slow as the Pi is streaming the desktop over a network. However, it works pretty well.

This is how we can access the Pi’s desktop with a Windows computer/laptop. However, none of the methods we have learned allows us to transfer a file between a Windows computer and the Pi. We will learn how to do it in the next section of this chapter.

WinSCP

For file transfers between a Windows computer and a Raspberry Pi, we will use WinSCP ( https://winscp.net/eng/index.php ). WinSCP is a free open-source SFTP and FTP client for Windows. Its main function is the secure file transfer between local and remote computers.

Download its setup ( https://winscp.net/eng/download.php ) and install it. Create its shortcut on the Windows desktop. Open WinSCP by double-clicking the icon (Figure 2-10).

Figure 2-10. WinSCP window

Enter the IP address of the Pi in the host name text box. Also, enter pi as the username and raspberry as the password.

We can also save the settings for future use. The save session (Figure 2-11) dialog box is as follows.

Figure 2-11. Save session

Once we login, if we are connecting for the first time then the following dialog box (Figure 2-12) is displayed. Click the Add button to continue.

Figure 2-12. First time login dialog box

Once we login, the following window (Figure 2-13) is displayed.

Figure 2-13. WinSCP file transfer window

The file system of the local Windows computer is in the left panel and Raspberry Pi’s pi user’s home directory i.e. /home/pi is in the right panel. We can transfer files between both computers now.

Remote Login with SSH

SSH is built into Linux distributions and macOS. We can use SSH to connect to the Pi from a Linux computer (which could also be another Raspberry Pi) or from the Mac terminal, without installing additional software.

Open the terminal in your Linux computer or Mac and type the following command:

ssh [email protected]

192.168.0.2 is my Pi’s IP address. Replace it with the IP address of your Pi. Once we press Enter, it will show a security/authenticity warning prompt. Type yes to continue. This warning is shown only when we connect for the first time.

Now it will prompt for the password. Enter pi user’s default password raspberry. We will see the Raspberry Pi prompt which will be identical to the one found on the Raspberry Pi itself.

Forwarding Using SSH

We can also forward our X11 session over SSH to allow use of graphical applications by using the -Y flag in the ssh command as follows,

ssh -Y [email protected]

Let’s access a graphical program like scratch remotely. Run the following command,

scratch &

It will start a new X11 session of the Pi program scratch in a new window on a Linux computer or Mac. The & makes the command run in the background.

SCP for File Transfer

In Windows, we used WinSCP for the file transfer between the Windows computer and the Pi. In the same way, we can transfer files between a Linux computer/Mac and the Pi. We need to use the scp utility for that. It is built into all Linux distributions and macOS.

To copy a file from the Pi to a Linux computer or Mac, we have to run the following command in the terminal on the Linux computer or the Mac:

scp [email protected]:/home/pi/test.txt /home/ashwin

The command above copies test.txt from /home/pi directory of Pi to /home/ashwin directory of our Linux computer or Mac.

In the same way, we might want to copy a file from a Linux computer or Mac to the Pi. To do that, run the following command in the terminal of the Linux computer or the Mac:

scp /home/ashwin/test_again.txt [email protected]:/home/pi

You can read more about the scp command in detail on www.computerhope.com/unix/scp.htm .