ECE497 Tips and Tricks

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thumb‎ Embedded Linux Class by Mark A. Yoder


Some useful tips and tricks for Linux and the Beagleboard.

Interesting Links

Since we are working with the open source community, you need to know where the action is. Here are some useful links to what's happening in the Beagle community.

Linux

Learn UNIX in 10 Minutes is a quick overview of the most commonly used Linux commands.

Top 10 Tools is a nice summary of 10 of the most useful Linux commands.

Quick Tips

Tip Description
host$ gnome-open
Open a file or directory using the default program
Give the IP address a name Inside /etc/hosts add a line of the form <IP address> <alias> this will allow you to refer to the host by name.
beagle$ ntpdate ntp.org
beagle$ rm /etc/localtime
beagle$ ln -s /usr/share/zoneinfo/America/New_York /etc/localtime
This will go to a network time protocol server and get the current time and set the Beagle to it and set the local time zone. [1]
beagle$ mount -t debugfs debugfs /sys/kernel/debug/
beagle$ cd /sys/kernel/debug
beagle$ ls
Kernel Debug Info

Connecting to RHIT wifi

There is a discussion in the Beagle Google Group about getting wireless working with the bone.

Use these settings for connecting to the Rose-Hulman wireless network:

  • SSID: RHIT-1X
  • Security: WPA & WPA2 Enterprise
  • Leave "anonymous identity" blank
  • CA Certificate: (None)
  • PEAP version: Version 0
  • Inner authentication: MSCHAPv2
  • Use your Rose username and password

bash

Tip Description
Ctrl-r Reverse incremental search
Ctrl-g Abort command
Esc-. Insert last argument from last command

ssh

Suspending ssh

Most programs can be suspended by typing ^z (Ctrl-z). If you have an ssh connection to another machine you can suspend it by entering ~^z. You can resume the connection by entering fg.

ssh and X-windows

When using ssh between two X-windows systems try

host$ ssh -CX root@beagle

The -X set the DISPLAY variable on the remote machine so you can open windows from the beagle on your host machine.

The -C compressed the data over the link. Good for slow connections.

vnc

You can run a vnc server on the Beagle. Install it with:

beagle$ apt-get update
beagle$ apt-get install x11vnc

Install a password with

beagle$ x11vnc -storepasswd

Run it on the Beagle with

beagle$ x11vnc -display :0 -ssl -usepw -forever -q &

On your host, connect to it with:

Applications:Internet:Remote Desktop Viewer

Authorizing ssh

ssh and scp can be set up for automatic authorization so you don't have to enter your password when using these commands. Here's how to do it. First let's see what's already there:

  • On your Beagle run
beagle$ ls ~/.ssh

~/.ssh may not exist, if not, it will be created. If it's there, check the files in it.

  • On your host computer run
host$ ssh-copy-id root@beagle

It will ask for your beagle password and then copy the needed files to it.

  • Back on the beagle to see what has changed:
host$ ssh -CX root@beagle
beagle$ ls ~/.ssh

The ssh command shouldn't ask for a password. What new files appeared?

ssh configuration

Here's a nice tip so you don't have to remember who to login as on the beagle. On your host, put the following in ~/.ssh/config.

Host beagle
   User root
   UserKnownHostsFile /dev/null
   StrictHostKeyChecking no

Before you had to

host$ ssh -CX root@beagle

Now you can just

host$ ssh -CX beagle

Mounting dfs/afs

You can set up your Linux box to directly mount your afs and dfs files. The Rose-Hulman Linux Users' Group has a nice page with the details .

After installing sshfs I added the following to my /etc/fstab file:

sshfs#username@dfs.Rose-hulman.edu:/DFS/MyDocs/username /home/username/MyDocs fuse user,noauto,uid=1000,gid=1000 0 0
sshfs#username@dfs.rose-hulman.edu:/DFS/Users/Y/username /home/username/dfs-home fuse user,noauto,uid=1000,gid=1000 0 0
sshfs#username@afs.rose-hulman.edu: /home/username/afs-home fuse user,noauto,uid=1000,gid=1000 0 0

You'll have to replace username with your login name. Then create the mount points:

host$ cd ~
host$ mkdir MyDocs
host$ mkdir dfs-home
host$ mkdir afs-home

Now you can mount your files by using:

host$ cd ~
host$ mount dfs-home
host$ cd dfs-home
host$ ls

You should now see your dfs files. You can unmount using:

host$ cd ~
host$ sudo umount dfs-home

byobu - A Screen Manager

For years Unix has had screen which is a screen manager. byobu is wrapper for screen that puts a nice face on it. You can run byobu on your host computer and on the Beagle. With byobu you can start a long running program (bitbake for example) in one terminal and detach from the terminal and the program will keeping running in the background. Using byobu you can later attach to the program (possibly from another terminal) and see how the program is progressing.

Install byobu with:

host$ sudo apt-get update
host$ sudo apt-get install byobu

Now you can run it.

beagle$ byobu

You'll see a command prompt. You'll also see some status information on the bottom two lines. Type Ctrl-A ? for help. Type Ctrl-A Ctrl-D to detach from the session. Running byobu again will reattach you to the session. Try running byobu in two windows at the same time. You should see the same session in both.

Backing up an SD card with dd

Here's the command I use to backup an SD card. I use System:Administration:Disk Utility to figure out the path to the card. In this case it's /dev/sdc

host$ sudo time dd if=/dev/sdc of=FIE2011.img bs=4M count=1000
host$ sudo chown yoder:yoder FIE2011.img
host$ md5sum FIE2011.img > FIE2011.img.md5
host$ bzip2 -k FIE2011.img

It takes about 5 minutes to dd a 4G card, 1.2 minutes for md5 and bzip2 takes about 23 minutes.

It looks like the 7z compression is becoming popular. Use it via

host$  7za a FIE2011.img.7z IFE2011.img

It took 16 minutes. The file size is 454M compared to 628M. Wow, faster and smaller.

Local Ubuntu Update Mirror

Darryl Mouck in CSSE has passed this on...

We host a local mirror for all ubuntu updates. This is from the current distro back to hardy; it hosts every distro that ubuntu currently supports.

In order to get your system to point to our mirror follow the directions here.

Using pico DLP with BBB

Put this in uEnv.txt to use the BBB with a pico DLP.

optargs=video=HDMI-A-1:640x480@60

systemd journal taking too much time/space

If you are running out of space because of the systemd journal try this Google Group Suggestion

Getting the BeagleBone to work with unusual network managers

If you plugged in your BeagleBone, but you just can't get it to pop up a page at 192.168.7.2 (aka your browser says "could not connect" or "time out"), then the following steps should help.


First run

host$ ip a

This will list a bunch of network interfaces. You should see one that looks odd and long like

enp0s29u1u5

That is the interface for the BeagleBone. Now, to get the BeagleBone to communicate with your host over USB serial, run

host$ sudo dhcpcd enp0s29u1u5

If this is successful, you should see your interface in the output of the command below. Its state should be UP.

host$ ifconfig

Windows

Most of the work is done under Linux; however there are some handy Windows-based tools.

Serial Port

SecureCRT is a good program that gives you both access to a serial port and is also an ssh client. Rose has a license for SecureCRT.

Tera Term also gives you access to the serial port and it's free.

Notepad++

Notepad++ is a nice text editor for Windows.

Mac OS X

Mounting the BeagleBone filesystem locally

1. Download and install OSXFUSE and SSHFS from github official page in the respective order.

2. In Terminal do

host$ mkdir /Volumes/Beagle
host$ sshfs root@beagleIPaddr:/ /Volumes/Beagle

Set up on the BeagleBoard

Accessing the Beagle via the Serial Port

During boot up the Beagle logs various messages on the serial port. You can see these messages by:

  • See what USB/tty devices are already attached to your host
host$ ls /dev/ttyU*
  • Attach a serial to USB converter to your host computer and the Beagle's serial port.
  • See what new USB/tty devices appeared
host$ ls /dev/ttyU*
  • On my host, /dev/ttyUSB1 appeared. On the host computer run
host$ screen /dev/ttyUSB1 115200

where ttyUSB1 is what appeared when you plugged in your converter.

You are now talking to your Beagle's serial port. Login quickly. There appears to be a bug that makes garbage appear on your screen if you wait too long. Try

beagle$ shutdown -r now

You will see the shutdown messages, followed by the U-boot messages. After a 3 second (or so) delay you will see the kernel booting.

Tip 1: Ctrl-a H will cause the data on the serial port to be logged. See

host$ man screen

for help.

Tip 2: <F6> will disconnect from the session. You can reconnect later.

Setup a USB Wireless Device on Beagle

(Here are instructions on setting up a Belkin USB dongle.)

The device I used to setup a wireless connection on the Beagle Board was the Linksys Compact Wireless-G USB Network Adapter with SpeedBooster.

I first opened the wpa_supplicant.conf file to setup my networks:

beagle$ cd /etc
beagle$ gedit wpa_supplicant.conf &

This file is filled with numerous examples of possible wireless configurations for you to basically fill in. After looking at the examples, I scrolled down to the bottom of the page and set up two networks: one for home and one for school. Here are examples of my setup networks:

#Home Network
network={
        ssid="YourHomeNetworkName"
        psk="YourHomeNetworkPassword"
}

#School Network
network={
        ssid="RHIT-1X"
        proto=WPA
        key_mgmt=WPA-EAP
        pairwise=CCMP
        group=TKIP
        eap=PEAP
        phase1="peapver=0 peaplabel=0"
        phase2="auth=MSCHAPV2"
        scan_ssid=1
        identity="YourSchoolUsername"
        password="YourSchoolPassword"
}

For the network examples above,the quotation marks actually belong there but replace the Your.... areas with your corresponding information. No <space> before the first quotation mark.When finished editing save and exit this file. The information for the RHIT school network was found here:RHLUG

Now you must specify that this is the file to use for the wireless device:

beagle$ cd network
beagle$ gedit interfaces &

This file will display all of the different types of Internet connections you have setup. To use the wpa_supplicant.conf file, scroll down to around line 42 of the code and uncomment the configuration for wpasupplicant. After doing this make sure all of the above lines mentioning anything about wlan0 are commented out. Return back to where it says "iface wlan0 inet dhcp" that you uncommented around line 42. Add "auto wlan0" above this line, make sure the line "wpa-conf /etc/wpa_supplicant.conf" is uncommented below the iface line, and change the wpa-driver line below that line to wext. So after all of that the code in this file for the wireless device should be the following:

auto wlan0 
  iface wlan0 inet dhcp
     wpa-conf /etc/wpa_supplicant.conf
     wpa-driver wext

NOTE: the auto wlan0 command in this file means that this device will load at boot time. You can take the time in here now to comment out any interfaces you don't use like auto usb0 to make these devices not load at boot time, which will increase the speed at which you boot up. Save and exit this file

Once you have finished this you can either restart the Beagle Board or:

beagle$ cd
beagle$ /etc/init.d/networking restart

I've found that a lot of the time the interface doesn't receive an IP address when it boots up. If you run ifconfig in the terminal you should see your wireless device connected to a network. If it is connected but no IP address I do the following:

beagle$ ifdown wlan0
# it will report messages here and then
beagle$ ifup wlan0
# more messages and it should report connecting and having an IP address

This ifdown ifup method has worked every time for me so far but if anyone can find a way to prevent having to do this almost every time please feel free to edit this

Fixing Problems

Kernel Boot Problems

Here is a link with some suggestions of what to do if your kernel isn't booting properly.

Serial port garbage

If you are having trouble with garbage on the console, this might help. Sometimes the serial port times out. Most of the time it just generates some junk which can be cleared with CTRL-U or backspace. However, if it happens at the login prompt then getty thinks the terminal is 7-bit with parity (rather than 8-bit raw). If this happens and you continue to login the whole session appears to be scrambled - if you press CTRL-D you can login again provided you don't stop typing... :] I have simply added the following two lines to root's .profile:

stty -parenb -parodd cs8 -inpck -istrip 
echo 0 > /sys/class/tty/ttyS2/device/sleep_timeout

A better fix would probably be to just add the second line to a rc.d startup script somewhere.

This suggestion came from this posting.

Getting help from a news group

Here's a nice tip on what to do before posting a question to a news group.




thumb‎ Embedded Linux Class by Mark A. Yoder