Why can't I switch from the ad-hoc network settings to the wifi settings?

Question

I followed the instructions from this link to set up an ad hoc network. I get the following strange behaviour.

If my /etc/network/interfaces file is the "wifi - regular" file on boot then everything is great. I can switch between the ad hoc configuration and the wifi one using ifup and ifdown and copying the settings over. However, if I boot with the adhoc configurations the following strange thing happens:

• I cannot switch to the wifi settings successfully. What happens is that although I do ifdown wlan0 copy the interface file over and then ifup wlan0. The wifi does not connect to any networks. I've connected a monitor to the Pi so that's how I'm checking that.

I'm running a Raspberry Pi B+ and the uname -a output is:

Linux raspberrypi 4.1.7+ #817 PREEMPT armv6l GNU/Linux

Any help much appreciated.

These are my configuration files.

/etc/network/interfaces-adhoc:

auto lo
iface lo inet loopback
iface eth0 inet dhcp

auto wlan0
iface wlan0 inet static
  address 192.168.1.1
  netmask 255.255.255.0
  wireless-channel 1
  wireless-essid RPiwireless
  wireless-mode ad-hoc

---

/etc/network/interfaces-wifi:

auto lo
iface lo inet loopback

auto eth0
allow-hotplug eth0
iface etho0 inet manual

auto wlan0
allow-hotplug wlan0
iface wlan0 inet manual
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

auto wlan1
allow-hotplug wlan1
iface wlan1 inet manual
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

---

/etc/dhcp/dhcpd.conf:

ddns-update-style interim;
default-lease-time 600;
max-lease-time 7200;
authoritative;
log-facility local7;
subnet 192.168.1.0 netmask 255.255.255.0 {
    range 192.168.1.5 192.168.1.150;
}

EDIT

To switch the settings once logged in I do:

sudo cp /etc/network/interface-<DESIRED> /etc/network/interface
sudo ifdown wlan0
sudo ifup wlan0

EDIT 2

| on boot          | wifi        | Ad hoc      |
|----------------------------------------------|
| DHCP on boot?    | failed      | active      |
| can switch?      | yes         | no          |
| IP on boot       | 10.0.0.114  | 192.168.1.1 |
| after 1 switch   | 192.168.1.1 | 192.168.1.1 |
| after 2 switches | 192.168.1.1 | 192.168.1.1 |
|----------------------------------------------|

• DHCP on boot: sudo service isc-dhcp-server status
• Whether I can switch between the two interfaces and connect succesfully to the internet.
• What the IP is when I first boot
• What the IP is after 1 switch
• What the IP is after 2 switches

I read the IP from ifconfig wlan0. This is a bit strange given the network is in the 10.0.0.XX range.

1 Starting ISC DHCP server: dhcpdcheck syslog for diagnostics. ... failed!

Answer 1

If you boot with your interfaces-adhoc which contains iface eth0 inet dhcp you effectively disable dhcpcd. This would prevent the interfaces-wifi from running, because this depends on dhcpcd.

You are trying to run 2 incompatible services. It MAY be possible to write a script which shuts down all the services not needed and start others, but you are on your own. It is going to be easier to just reboot.