Category: PC Tweakage

Having configured ssh on the Raspberry Pi for public keys, the next step is to cut the cord by configuring the USB WiFi dongle to automagically come up with a static IP.

[Update: As of 2017, set a static IP by tweaking /etc/dhcpcd.conf instead. Search the blog for that to find recent descriptions. ]

Make /etc/network/interfaces look like this:

auto lo

iface lo inet loopback

#iface eth0 inet dhcp

auto eth0
#iface eth0 inet static
iface eth0 inet manual
 address 192.168.1.209
 gateway 192.168.1.1
 netmask 255.255.255.0
 network 192.168.1.0
 broadcast 192.168.1.255

allow-hotplug wlan0

#iface wlan0 inet manual
iface wlan0 inet static
 address 192.168.1.9
 gateway 192.168.1.1
 netmask 255.255.255.0
 network 192.168.1.0
 broadcast 192.168.1.255

#wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

iface default inet dhcp

Then set up /etc/wpa_supplicant/wpa_supplicant.conf thusly:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
	ssid="whatever it might be"
	psk="choose your own password"
}

You want different IP addresses for the eth0 and wlan0 devices, because you never know when you’ll be forced to use them at the same time.

Using wpa-conf rather than wpa-roam prevents the machinery from automagically doing things when you’re not watching.

The router can hand out IP addresses based on MACs, but that means bottling up all that configuration in a single device that might go toes up. Forcibly configuring each device to a static IP adds a bit of resilience to the network, right up to the point where you must change all of them at once.

Alas, the router seemed to lose track of the Pi after a day. Pinging from my desktop box reported Destination Host Unreachable, even though signing on through the USB keyboard showed the USB WiFi link (a netis WF2123) was still up. Signing on to the router and refreshing the DHCP list (even though the RPi has a static IP) knocked things loose: suddenly the RPi became pingable.

It seems the WiFi link turns itself off after a while, which can be averted by tweaking the options:

sudo nano /etc/modprobe.d/8192cu.conf
# Disable power saving
options 8192cu rtw_power_mgnt=0 rtw_enusbss=0
  

The WordPress sourcecode tag seems to turn underscores into blanks [Update: on the last line of a sourcecode block, which I’ve now forced to be a blank line] ; the options should read rtw_power_mgmt and rtw_enusbss, respectively.

Anyhow, the rtw_enusbss option prevents the USB interface from going down. It was already zero in the default configuration, but I presume there’s no harm in clearing it again.

Things to remember during Raspberry Pi setups…

You can do some of this through raspi-config.

The NOOBS setup configures the HDMI video parameters to work with the worst possible display, so edit the /boot/config.txt (per the Official Doc):

• Comment out all the NOOBS auto-configuration entires at the bottom
• Set disable_overscan=1

The highest mutually compatible setting for the U2711 monitor was 1920×1080@60Hz, which turned out to be CEA Mode 16 and was automagically selected as the monitor’s “native” mode. Disabling overscan lets the X session use the entire monitor screen, rather than being confined within the (huge) black overscan borders.

That requires a power off-on cycle to take effect. Shut down properly with sudo shutdown -H now or just sudo halt.

To set the default size of the lxterminal window so that it’s big enough to be useful, edit the Exec entry (down near the bottom) in /usr/share/raspi-ui-overrides/applications/lxterminal.desktop to read:

Exec=lxterminal --geometry=80x60

The Droid font family seems more readable than the default selection.

Create a user for yourself, just so SSH will eventually work the way it does for all the other boxes. The group list comes from the default pi user:

sudo adduser ed
sudo usermod -a -G pi,adm,dialout,cdrom,sudo,audio,video,plugdev,games,users,netdev,input,spi,gpio ed

Regrettably, the default pi user has the same numeric ID as the one I use on all the other boxes, which leads to problems with file sharing permissions. I may need to swap numeric IDs to make this work out correctly.

To set a static IP, edit /etc/network/interfaces thusly:

#iface eth0 inet dhcp     <-- comment this out to stop DHCP

auto eth0
iface eth0 inet static
 address 192.168.1.9      <-- obviously, pick your own
 gateway 192.168.1.1
 netmask 255.255.255.0
 network 192.168.1.0
 broadcast 192.168.1.255

Change the hostname in /etc/hostname and /etc/hosts.

Set up SSH for public-key access on an unusual port by editing /etc/ssh/sshd_config:

1. Port 12345 <— choose your own
2. PermitRootLogin no
3. PasswordAuthentication no

Create the ~/.ssh directory and put your own public key in it, which you can do from the remote system:

scp ~/.ssh/id_rsa.pub octopi-1:.ssh/authorized_keys
# a dummy line to reveal underscores in the previous line

Twiddle ~/.ssh/config on the remote box to include the Pi and specify the unusual port:

Host octopi-1 thisone thatone anotherone
	ForwardX11	yes
	Port	12345   <--- pick your own
	User	ed

Using ssh-agent -t 4h helps relieve the tedium of typing your passphrase all the time. Then sudo service ssh restart on the pi will require you to use your key passphrase; it’s a Good Idea to remain signed in through Port 22 with the original authorization while you fiddle with this stuff, then sign out when it all works.

Update with the usual routine:

sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade    <-- for system-level update
sudo apt-get clean           <-- flushes /var/cache/apt/archives to save space