Let’s say you want to change the working directory to the root of the filesystem. You can use the cd command:

root@beaglebone:~# cd /
root@beaglebone:/#

Did you notice that subtle change in the command line prompt? Instead of a tilde, there’s now a forward slash, which indicates we’ve changed from the home directory to the root of the filesystem. To be sure, we can always execute pwd again:

root@beaglebone:/# pwd
/

To change to the current directory’s parent, use cd ..:

root@beaglebone:/# cd ~
root@beaglebone:~# pwd
/root
root@beaglebone:~# cd ..
root@beaglebone:/# pwd
/

The .. notation can also be used when typing out paths. For instance, if you were in the hypothetical path /root/myProject/sound shown in the directory structure in Figure 3-1, you could change to /root/myProject/sound by typing cd ../code.

Figure 3-1. An example directory structure. You can change from /myProject/sound to /myProject/code by typing cd ../code

And now that you’re in the root of the filesystem, list the contents of the current working directory, with the command ls:

root@beaglebone:/# ls
bin   dev  home  lost+found  mnt  proc  run   selinux  sys  usr
boot  etc  lib   media       opt  root  sbin  srv      tmp  var

Now you can see all the directories explained in Table 3-1 (plus a few others). If you’re interested in even more information about the contents of the current working directory, you can add the -l option to the ls command to display them in long format:

root@beaglebone:/# ls -l
total 76
drwxr-xr-x   2 root root  4096 Apr 23 20:35 bin
drwxr-xr-x   3 root root  4096 Apr 23 20:35 boot
drwxr-xr-x  14 root root  3620 Apr 23 20:58 dev
drwxr-xr-x 103 root root  4096 Apr 23 20:58 etc
drwxr-xr-x   3 root root  4096 Apr 23 20:57 home
drwxr-xr-x  15 root root  4096 Apr 11 01:41 lib
drwx------   2 root root 16384 Apr 23 20:21 lost+found
drwxr-xr-x   2 root root  4096 Apr 23 20:20 media
drwxr-xr-x   2 root root  4096 Feb  3 10:24 mnt
drwxr-xr-x   5 root root  4096 Apr 23 20:35 opt
dr-xr-xr-x 115 root root     0 Jan  1  1970 proc
drwx------   3 root root  4096 Apr 23 20:28 root
drwxr-xr-x  23 root root   740 Apr 23 20:58 run
drwxr-xr-x   2 root root  4096 Apr 23 20:40 sbin
drwxr-xr-x   2 root root  4096 Jun 10  2012 selinux
drwxr-xr-x   2 root root  4096 Apr 23 20:14 srv
dr-xr-xr-x  12 root root     0 Apr 23 20:57 sys
drwxrwxrwt   8 root root  4096 Jul 21 15:17 tmp
drwxr-xr-x  10 root root  4096 Feb 21 04:24 usr
drwxr-xr-x  12 root root  4096 Apr 23 20:34 var

This listing gives a more complete picture, showing the permissions, owner, size, and date modified for each file or directory. Next, you’re going to create some files and directories, so let’s go back into the root account’s home directory:

root@beaglebone:/# cd /root
root@beaglebone:~#

Use the command mkdir to create a new directory:

root@beaglebone:~# mkdir myProject

Change to the newly created directory:

root@beaglebone:~# cd myProject
root@beaglebone:~/myProject#

If you want to create a new file and store some text in it, you can do all that with one command:

root@beaglebone:~/myProject# echo 'Hello, world!' > hello.txt

The job of the command echo is to output to the terminal whatever text follows the command. We use the greater than sign to redirect that output to the file hello.txt, which will be created if it doesn’t already exist.

Now if you list the contents of myProject, you’ll see your new file in the listing:

root@beaglebone:~/myProject# ls
hello.txt

To see the contents of the file, you can use the command cat:

root@beaglebone:~/myProject# cat hello.txt
Hello, world!

If you want to append text to the end of a file, the command you type will look like this:

root@beaglebone:~/myProject# echo 'What a beautiful day!' >> hello.txt

Be sure you use two greater than signs, which means to append the output from echo to the end of the file. To see the results, use cat again:

root@beaglebone:~/myProject# cat hello.txt
Hello, world!
What a beautiful day!

Although we’re using cat to display the contents of the file, cat’s main function is to concatenate files. In other words, it will take a series of files and appends one after the other. To try that out, first make a few file:

root@beaglebone:~/myProject# echo 'See you real soon!' > bye.txt

Now let’s use cat to join hello.txt to bye.txt to create a new file called greetings.txt:

root@beaglebone:~/myProject# cat hello.txt bye.txt > greetings.txt

Now when you output the content of greetings.txt, you’ll see the content copied from the first two files:

root@beaglebone:~/myProject# cat greetings.txt
Hello, world!
What a beautiful day!
See you real soon!

All these command line tools can make it fairly easy to work with files, but sometimes you might just want to get inside a file to view and edit its contents. For that, I recommend the text editor nano. To open your file in nano, simply type nano followed by the file you want to open.

root@beaglebone:~/myProject# nano greetings.txt

Within nano, you can use your arrow keys to move the cursor around to delete and insert text. To save, type Control-O and to exit, type Control-X. Nano can do a lot of stuff including searching, clipboard operations, and spell check. To view the help information within nano, type Control-G.

Of course, you can also create new files with nano. Just type the name of the file you want to create after the nano command and that file will be written when you save within nano.

Copying and moving files around from the command line is fairly straightforward. To try it out, create a new directory called archive inside ~/myProject:

root@beaglebone:~/myProject# mkdir archive

To copy a file into the archive directory, use the command cp followed by the name of the file you want to copy and then its destination:

root@beaglebone:~/myProject# cp hello.txt archive

Now try moving a file with the mv command. It’s used the same way as cp, except of course it moves the file instead of copying it.

root@beaglebone:~/myProject# mv bye.txt archive

You can also use mv to rename a file but keep it in the same spot. Here’s how to rename greetings.txt to salutations.txt:

root@beaglebone:~/myProject# mv greetings.txt salutations.txt

Use the command rm to delete files.

root@beaglebone:~/myProject# rm salutations.txt

If you want to delete an entire directory and its contents, use rm with the option -r. Be careful when using this since there’s no way to undelete!

root@beaglebone:~/myProject# rm -r archive

Most computers have a real time clock, a piece of hardware that keeps track of the date and time. RTCs frequently have a battery backup so that they can keep time even when there’s no power supplied to the computer. Although the BeagleBone doesn’t have an RTC, whenever it’s connected to the Internet, it will attempt to set the time. To see what time the BeagleBone thinks it is, try running the date command:

root@beaglebone:~# date
Mon Jul 21 15:36:39 UTC 2014

Note that the timezone is set to UTC. If this isn’t your timezone, you’ll need to do is set your timezone. Type the command dpkg-reconfigure tzdata, and select your timezone from the menu that appears. For example, if you are in San Francisco, you’d choose US→Pacific Ocean. You could also have chosen America and picked your city or, if it doesn’t appear, another city in your timezone.

If your BeagleBone has a connection to the Internet, you can easily install or upgrade software and code libraries. The software comes in packages and Debian uses the utility apt-get to manage the process of installing and updating packages.

apt keeps a list of available package versions within the BeagleBone’s filesystem, so it’s important to update this list before attempting to install or update software. To update the list of available packages, simply execute:

root@beaglebone:~# apt-get update

You’ll see some text scroll by as it downloads all the latest listings. If you want to update the software, the apt-get command upgrade will upgrade all of your installed packages if there are new versions available. Depending on how many software packages have been upgraded since the release of the software you’re running, this process may take a very long time (a few hours, even):

root@beaglebone:~# apt-get upgrade

If there’s a particular piece of software or code library that you want to install, you can also install it by name using apt-get. To install the unzip utility for uncompressing ZIP files at the command line, you would type:

root@beaglebone:~# apt-get install unzip

By default, your BeagleBone identifies itself with the hostname beaglebone on your network so that you can access it via the web with http://beaglebone.local or SSH with ssh [email protected]. (On some networks, you might need to use beaglebone.home.) In most cases, you won’t need to change this, but if you start to use many BeagleBones on the same network, you’ll want to distinguish one from another.

To edit the hostname, execute the following, keeping in mind that the hostname can only contain letters, numbers, or a hyphen. It cannot contain any other characters such as $, #, or a space:

root@beaglebone:~# echo 'your-hostname' > /etc/hostname

So that your BeagleBone recognizes its own hostname as itself, you’ll also want to edit the hosts file as well:

root@beaglebone:~# nano /etc/hosts

Change the line that says 127.0.0.1 beaglebone, replacing beaglebone with your hostname. After you save the file and quit nano, you need to reboot your BeagleBone. After you log in again, you should see your custom hostname in the prompt.

By default, there’s no password set for the user root in the Linux images provided by BeagleBoard.org. If you exclusively use the BeagleBone via USB or on your own private network, you don’t need to set one, but it’s probably a good idea to set a unique password if you use the BeagleBone on a network that you share with others.

To set or change the password, use the command passwd:

root@xively-box:~# passwd
Enter new UNIX password: [hidden]
Retype new UNIX password: [hidden]
passwd: password updated successfully