(Internet via Ethernet) + (SSH via wireless)

= (sustained SSH during MPICH computing)

I've been losing SSH connection after starting process jobs on my new beowulf cluster.  This is my current fix, since my theory is that the network switch is so clogged with MPI-related communication (which does take place via ssh) that there's no bandwidth left for my administrative SSH connection.  Theory supported by observation that when I plug my unrelated control machine into the switch it can't ping google.

assumptions

• Ubuntu 16.04.1 LTS
• working wireless and ethernet: I had to do this and this.

sources

https://web.archive.org/web/20140307210607/http://www.themagpi.com/issue/issue-11/article/turn-your-raspberry-pi-into-a-wireless-access-point
http://askubuntu.com/a/180734
https://seravo.fi/2014/create-wireless-access-point-hostapd

check wifi hardware capability

Run the command 

iw list

And look for a section like the following.  If it includes 'AP' (see emboldened bit), you're golden.  If not, look for a different wireless card.

Supported interface modes:  
         * IBSS 
         * managed  
         * AP 
         * AP/VLAN  
         * monitor 

install dependencies

sudo apt-get install rfkill hostapd hostap-utils iw dnsmasq   

identify interface names

As of ubuntu 16.04, the standard wlan0 and eth0 interface names are no longer in use.  You'll have to identify them specifically.  Use the following command, which lists the contents of the folder for each interface device, and look for the device that has a folder named 'wireless'. src.

ls /sys/class/net/*

Observe the assumptions above to see what I'm calling them.

configure wifi settings

There's three files you'll have to configure.  Since I'm logged in via ssh, I don't want to interrupt my connection until I've created a new access point I can connect to.  So I'll walk through editing each file in turn, then I'll have one command at the end that activates all the changes.  

configure wireless interface: /etc/network/interfaces

Backup your current interface file.

sudo cp /etc/network/interfaces /etc/network/interfaces.bak

and then edit the original

sudo nano /etc/network/interfaces

replace the contents of the file - change the interface names as appropriate.

auto lo
iface lo inet loopback

auto enp2s0
iface enp2s0 inet dhcp

auto wlp1s0
iface wlp1s0 inet static
hostapd /etc/hostapd/hostapd.conf
address 192.168.3.14
netmask 255.255.255.0

Normally I'd say that here's where you restart the interface, but we're saving that for the end.

configure the access point: /etc/hostapd/hostapd.conf

backup the original file - it's ok if there's nothing there.

sudo cp /etc/hostapd/hostapd.conf /etc/hostapd/hostapd.conf.bak

edit the original

sudo nano /etc/hostapd/hostapd.conf

put this in:

interface=wlp1s0
driver=nl80211
ssid=test
hw_mode=g
channel=1
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=3
wpa_passphrase=1234567890
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

Inexplicably, this only seems to produce a detectable wifi access point when the ssid is 'test'.  I tried several other non-keyword names, and none of them worked.  Go back to 'test', and it worked.  Did it several times...magic.

Save and exit.

configure the DHCP server

this is where the access point actually becomes something you can access. backup: 

sudo cp /etc/dnsmasq.conf /etc/dnsmasq.conf.bak

edit original - since the file is so big, I rm'd the original and pasted the contents below into an empty file.

sudo rm /etc/dnsmasq.conf
sudo nano /etc/dnsmasq.conf

make it look like this:

# Never forward plain names (without a #dot or domain part)
domain-needed

# Only listen for DHCP on wlan0
interface=wlp1s0

# create a domain if you want, comment #it out otherwise
# domain=Pi-Point.co.uk

# Create a dhcp range on your /24 wlp1s0 #network with 12 hour lease time
dhcp-range=192.168.3.15,192.168.3.254, 255.255.255.0,12h

Save and exit.

implement changes

this is going to be one big command. if it works, you're in business...if it doesn't, you'll have to login directly to the machine for troubleshooting.

sudo ifdown wlp1s0; sudo ifup wlp1s0; sudo service hostapd restart; sudo service dnsmasq restart

Worked for me: I now have a secondary wireless access to my beowulf cluster for when the ethernet gets clogged with MPI signals.

Install a package without internet

So first of all, this isn't original.  Credit goes here.  But it's fantastic, and I wish I'd known about this a long time ago.  As usual, for my own memory/use: and actually, I'm just going to clean up what the other guy said.  He did a great job.

On the Internet-less computer:

In the terminal enter:

PACKAGENAME=<The name of the Package to install>

and then

apt-get -qqs install $PACKAGENAME | grep Inst | awk '{print $2}' | xargs apt-cache show | grep 'Filename: ' | awk '{print $2}' | while read filepath; do echo "wget \"http://archive.ubuntu.com/ubuntu/${filepath}\""; done >downloader.sh

A ready-to-use downloader for the package has now been created in the home folder.  Open your home directory in the file browser and move the file downloader.sh to the top-level directory of your flash drive.  Then eject your flash drive.

On the computer with Internet:

Insert your flash drive, and open your flash drive in the file browser.  Copy the location of your flash drive:

[CTRL]-L

[CTRL] C 

Move into the directory of the flash drive.  In a terminal this time, type:

cd [CTRL]+[SHIFT]+V 

Run the downloader:

bash ./downloader.sh

Wait for the download to complete and eject your flash drive.

Back to the Internet-less computer:

Open your flash drive in the file browser.  In the browser, type the following to copy the file location of the flash drive.

[CTRL]-L

[CTRL]-C

Move into the directory of the flash drive.  In a terminal this time, type:

cd [CTRL]+[SHIFT]+V 
sudo dpkg --install *.deb

That's it!

Setting up OpenBSD (updated for 6.0)

A few notes on how I set up my OpenBSD installation.  This will be an ongoing compilation.

Installation

Had to do this with a USB connected CD drive.  Followed the instructions for a flash drive, but the installation itself didn't want to play ball.  I forget the exact scenario; it was confusing.

Wireless

I'm on an Acer Aspire One from a long time ago - I believe it's a D250 model.  It uses the athn0 wifi driver.  Set it up by putting this into your /etc/hostname.ath0 file (copy the whole thing into the command prompt and run it):

echo "
nwid 'foo'
wpakey 'bar'
dhcp 
" > /etc/hostname.ath0

Replace the text as required with your own information...specifically, the stuff that says foo and bar.  :)  After that's added, run:

sh /etc/netstart

...because it won't start automatically.  Don't know why.  I used this link to figure out how to get it running.

Ethernet

If you have ethernet access, internet is somewhat simpler.  Find out what the ethernet device name is:

ifconfig

Mine is fxp0.  Using DHCP makes things easy.  All this command does is put dhcp in the device's config file.

echo dhcp > /etc/hostname.fxp0

Reboot, and you should be online.  Any problems, visit http://www.openbsd.org/faq/faq6.html#Setup
and http://www.openbsd.org/faq/faq6.html#DHCP.

Package Installation

See http://www.openbsd.org/faq/faq15.html#Intro for an excellent explanation of how all this works.

Setting up the Package Mirror

Being able to install packages is always nice.  On OpenBSD, you have to specify the mirror you want to search from and download from manually.  You can set this variable after startup every time, or put it in your .profile.  I used the MIT mirror; it's not going anywhere anytime soon. [edit: ok, it did go.  They didn't keep the 5.9 mirror once 6.0 came out; here's the link to the 6.0 packages.]

vi ./.profile

Now add (I stuck it in the middle of the file):

export PKG_PATH=http://mirrors.mit.edu/pub/OpenBSD/$(uname -r)/packages/$(uname -m)/

Except that in my case this didn't work.  OpenBSD read that as

mirrors.mit.edu/pub/OpenBSD/OpenBSD/packages/i386/

which doesn't make sense.  Instead, I had to do

export PKG_PATH=http://mirrors.mit.edu/pub/OpenBSD/6.0/packages/$(uname -m)/

which destroys flexibility when I upgrade to 6.0 (whenever that comes out). Changed for compatibility with 6.0.

Installing a Package

Now I can do

pkg_add python-2.7.11

to install python 2.7 - but to get that full package name, I have to do CTRL-F in the mirror webpage and figure out what's available.  I'm pretty sure there's a way to search that on the command line, but I haven't figured it out yet.  If only the package name, and not the exact version number, is known, then just use that.  The following successfully installs nano.

pkg_add nano

Turning the Computer Off

Restarting

Restarting is simple: 

reboot

Shutting Down

You'd think this would be simple, eh?  Linux works with a straightforward

shutdown now

but that eventually brings you right back to the shell on my computer's OpenBSD installation.  I have to use 

halt

Though, and I haven't tried this yet, something like

shutdown -h now

is also supposed to work.  This thread has more details.