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[[Category:Parallella]]

= How-to set up Linaro Nano Root Filesystem for NFS Boot =

This Guide describes the steps to extract and prepare Linaro Saucy nano root filesystem to be NFS mounted on the Parallella.<br />
The Guide supports the [[TFTP Boot and NFS Root Filesystems|How-To on setting up TFTP boot and NFS Filesystems]], and assumes the same convention (naming, IP Addresses, directories) from that page.<br />
The Guide assumes:
* The NFS server is a Debian PC environment.
* A minimal 'headless' nano build. Additional packages may be added as required.
* A USB-serial cable is connected to the Parallella - at least initially.

The following is derived directly from ''shodrucky's'' Linaro Saucy  nano build instructions: [[Parallella Linaro Nano|How-To for setting up a Linaro Nano system]]. There are some simplifications (less to do setting up the SD Card) and minor modifications (to ensure NFS runs smoothly). <br />

== Get the Linaro Saucy nano Image ==
On the NFS Server, download the Linaro Saucy nano image.
<pre>
wget http://releases.linaro.org/14.04/ubuntu/saucy-images/nano/linaro-saucy-nano-20140410-652.tar.gz
</pre>
<pre>md5sum linaro-saucy-nano-20140410-652.tar.gz</pre>
<blockquote><pre>
cded44187fb762ba7ea7b1ee092a0998  linaro-saucy-nano-20140410-652.tar.gz
</pre></blockquote>
* Extract the filesystem image from the download directory into the NFS directory created for the target root filesystem, in this example: ''/srv/nfs/nano''.
<pre>
sudo tar --strip-components=1 -C /srv/nfs/nano/ -xzpf ~/Downloads/linaro-saucy-nano-20140410-652.tar.gz
</pre>
== Modify Configuration Files ==
On the NFS Server, edit the following files in the NFS directory. <br /><br />
'''WARNING! WARNING! WARNING! WARNING! WARNING!''' 
* Make sure you are in the CORRECT NFS directory - edits are with root (sudo) priviledge!!
<br />
* Prevent installation of unnecessary packages
<pre>
sudo nano /srv/nfs/nano/etc/apt/apt.conf.d/00InstallRecommends
</pre>
(Edit and save)
<blockquote><pre>
APT::Install-Recommends "false";
</pre></blockquote>
* Edit the network configuration files. The kernel will be instructed to use DHCP in the ''bootargs'' provided by U-Boot. The Gigabit Ethernet interface will have been set up during boot, so the ''interfaces'' file can be kept simple.
<pre>
sudo nano /srv/nfs/nano/etc/network/interfaces
</pre>
(Edit to contain only the following lines, and save)
<blockquote><pre>
auto lo
iface lo inet loopback
</pre></blockquote>
Set up the nameserver address, as it applies to your network. For example:
<pre>
sudo nano /srv/nfs/nano/etc/resolv.conf 
</pre>
(Edit and save)
<blockquote><pre>
nameserver 192.168.1.1
</pre></blockquote>
* Edit the root filesystem table to mount temporary files in Parallella RAM. Reduces traffic.
<pre>
sudo nano /srv/nfs/nano/etc/fstab
</pre>
(Edit and save)
<blockquote><pre>
# /etc/fstab: static file system information.
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    defaults        0       0
/dev/nfs        /               nfs     defaults        1       1
none            /tmp            tmpfs   defaults        0       0
none            /var/run        tmpfs   defaults        0       0
none            /var/lock       tmpfs   defaults        0       0
none            /var/tmp        tmpfs   defaults        0       0
</pre></blockquote>

== Install SSH ==
To access the Parallella remotely from your PC, add the SSH server package to the nano build. <br />
Any changes to the root filesystem that require maintaining or obtaining new packages need to be run as a session on the Parallella, as root (or by sudo).
* If the USB Serial cable is connected then there is a root session prompt at the console.
* If the HDMI build has been booted, and keyboard/screen are available then log on as Linaro and prepend ''sudo'' to the following commands.<br />
For this sequence, assume that the console has been enabled in the ''bootscript'' This is described in [[TFTP Boot and NFS Root Filesystems|How-To on setting up TFTP boot and NFS Filesystems]].
Boot up the Parallella and the kernel should boot and eventually display the 'root@linaro' prompt at the UART console. Enter the following:
<pre>
apt-get update
apt-get install openssh-server xauth
</pre>
Once successfully updated and SSH installed, shutdown the Parallella.
<pre>
shutdown -h now
</pre> 
After shutdown, power off the Parallella.<br />
<br />
Note: after this sequence, if required, the USB serial cable can be removed, the console argument can be deleted from the ''bootargs'' string, and the ''bootscript'' rebuilt to boot completely 'headless'. <br />
Now you can login to the Parallella from your PC using SSH.<br />
Power on the Parallella, and wait for a minute or so while the boot sequence completes. (That is, wait for the network activity LEDs to calm down, approximately 30 secs).
<br />
On the PC, to connect using SSH to the Parallella, for example, ''para1'', use the IP address, unless 'para1' has been set up in the PC's ''/etc/hosts'' file.
<pre>
ssh linaro@192.168.1.21
password: linaro
</pre> 

== Additional Packages and Maintenance ==
This must be done in a session on the Parallella, either via the UART console or via SSH. For example, to add some recommended packages in an SSH session:
<pre>
sudo apt-get install fake-hwclock wget less unzip
</pre>
Other additions such as adding the Epiphany SDK to the build are described in the [[Parallella Linaro Nano|How-To for setting up a Linaro Nano system]].

== Disable sshd hostname look-up ==
To fix slow SSH connections, on the PC Host (in the correct directory!):
<pre>
sudo nano /srv/nfs/etc/ssh/sshd_config
</pre>
(add to the bottom of the file)
<blockquote>
<pre>
UseDNS no
</pre>
</blockquote>

== Mitigating NFS Timeouts - "Dirty Writes"==
Writing across the network will inevitably be slower than direct to disk, and queues may build up as the kernel optimises/caches IO buffers. Some versions of the kernel flush the cache when it reaches a certain level, say, 40%. This may result in longer waits at the application level, and timeouts may occur. For example, the following message may appear after the command ''apt-get update'':
<pre>
INFO: task apt-get:1587 blocked for more than 20 seconds.
      Not tainted 3.12.0-g0bc9c3a-dirty #6
</pre>
The level at which the cache is flushed can be set lower at, say, 5% or even as low as 1% (so treat as a "tuning opportunity"). <br />
On the NFS server, edit the Parallella NFS root filesystem (i.e. the NFS Client) to adjust the "dirty_ratio" parameter as follows:
<pre>
sudo nano /srv/nfs/nano/etc/sysctl.conf
</pre>
(Edit to add the following lines at the end of the file, and save)
<blockquote><pre>
vm.dirty_background_ratio = 5
vm.dirty_ratio = 5
</pre></blockquote>
Note: this may not be required on newer kernels, or in all cases.


== Back-up/Copy the Root Filesystem ==
At some stage, the root filsystem will be configured as required. <br />
Copy (perhaps to a spare SD card?) or back-up the NFS directory so that it can be restored at a later time.
<br/>

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