Golang on OpenWRT MIPS

I have been tracking Golang for quite a while since I came to know about it I guess about 3 years ago primarily because it is very easy to use and build static binaries that just work about anywhere. And no dealing with memory allocation stuff which often lead to frustrations and segmentation fault bugs soaking up hours of your time to solve those.

As a OpenWRT user running a Go program on OpenWRT had been one of my most desired things. So here it is, finally, a hello world program running my TP Link WR740N (which is a MIPS 32 bit CPU, ar71xx in OpenWRT tree):

system type             : Atheros AR9330 rev 1
machine                 : TP-LINK TL-WR741ND v4
processor               : 0
cpu model               : MIPS 24Kc V7.4
BogoMIPS                : 265.42
wait instruction        : yes
microsecond timers      : yes
tlb_entries             : 16
extra interrupt vector  : yes
hardware watchpoint     : yes, count: 4, address/irw mask: &#91;0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa                     : mips1 mips2 mips32r1 mips32r2
ASEs implemented        : mips16
shadow register sets    : 1
kscratch registers      : 0
package                 : 0
core                    : 0
VCED exceptions         : not available
VCEI exceptions         : not available

system type : Atheros AR9330 rev 1

machine : TP-LINK TL-WR741ND v4

processor : 0

cpu model : MIPS 24Kc V7.4

BogoMIPS : 265.42

wait instruction : yes

microsecond timers : yes

tlb_entries : 16

extra interrupt vector : yes

hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]

isa : mips1 mips2 mips32r1 mips32r2

ASEs implemented : mips16

shadow register sets : 1

kscratch registers : 0

package : 0

core : 0

VCED exceptions : not available

VCEI exceptions : not available

package main

import "fmt"

func main() {
        fmt.Println("hello world")
}

package main

import "fmt"

func main() {

fmt.Println("hello world")

}

First I built it with GOOS=linux GOARCH=mips go build hello but it did not run and gave error “Illegal Instruction”. Then I tried it with GOOS=linux GOARCH=mipsle go build hello which again, did not work because the CPU of this TP Link is big endian, not little endian. After a bit of searching I came across this GoMips guide on Golang’s Github which builds it using GOMIPS=softfloat. I tried the same and my program works! It will now be easy to build complex stuff that runs on embedded devices without resorting to C/C++.

$ GOOS=linux GOARCH=mips GOMIPS=softfloat go build hello
$ scp hello root@IP:/tmp/

root@740n-2:/tmp# ./hello
hello world
root@740n-2:/tmp#

$ GOOS=linux GOARCH=mips GOMIPS=softfloat go build hello

$ scp hello root@IP:/tmp/

root@740n-2:/tmp# ./hello

hello world

root@740n-2:/tmp#

February 16, 2020 0

Using privileged mode (become) in Ansible without a password

So I was working on automating some stuff using Ansible when the necessity to have password less superuser access came up. A simple way would be adding the ansible management key to the root account itself and allow SSH to root, but allowing ssh to root is usually a bad idea.

I tried many things – NOPASSWD in sudo entry, requiretty, etc. And after nearly two hours of digging a spark ignited and I found a way – Linux has PAM module called pam_wheel.so which can implicitly allow root access via su when a user is present in the wheel group (the group can be configured in module options). This module is disabled by default on most Linux distributions, in fact Ubuntu doesn’t even have a wheel group. But in this particular case I was managing CentOS which has the wheel group.

Add the Ansible management user to the wheel group and enable the pam_wheel.so module:

# /etc/pam.d/su

# Uncomment the following line to implicitly trust users in the "wheel" group.
auth            sufficient      pam_wheel.so trust use_uid

# /etc/pam.d/su

# Uncomment the following line to implicitly trust users in the "wheel" group.

auth sufficient pam_wheel.so trust use_uid

Now when you SSH to the machine using the ansible user and run su – it will give you root access without asking for password. Consequently, now when you set become_method = su in your Ansible configuration by way of editing config files, setting variables in playbook or inventory, etc. Ansible will become privileged without a password.

January 20, 2020 0

LXD OpenVSwitch and VLANs

LXD is a fantastic container virtualization tool that comes by default with Ubuntu. In one of my applications I needed to have many containers each within it’s own VLAN network.
So I used OpenVSwitch in combination with LXD to achieve this.

There is no inherent facility in LXD to provide VLAN tag numbers to the interface. So it is necessary to use a “Fake bridge”. I managed to do it after reading this article by Scott – VLANs with Open vSwitch Fake Bridges

Let’s say the OpenVSwitch bridge is named vm-bridge and we want to add 10 fake bridges ranging from VLAN 20 to 30. Here’s how I did it:

for i in $(seq 20 30); do
ovs-vsctl add-br vlan$i vm-bridge $i
done

for i in $(seq 20 30); do

ovs-vsctl add-br vlan$i vm-bridge $i

done

In LXD you can specify the bridge to which it will connect containers to, so I created 10 containers using a similar loop 😀
Further to bind each container to the fake bridge this step is needed:

for i in $(seq 20 30); do
lxc config device set ct$i eth0 parent vlan$i
done

for i in $(seq 20 30); do

lxc config device set ct$i eth0 parent vlan$i

done

July 5, 2019 2

Ubuntu 18.04 add e1000e Intel driver to dkms

e1000e is an Intel NIC driver which often needs to be updated on servers so that the NIC can operate trouble free.

Note: I assume you have DKMS and the necessary kernel headers to compile the drivers already installed. If not use apt / apt-get to install the same.

Here’s a quick guide on how to add the Intel e1000e driver to DKMS (Dynamic Kernel Module Support) so that it gets installed / uninstalled automatically with future kernel updates and removals.

Download the driver from Intel website https://downloadcenter.intel.com/download/15817

As of my writing this article, the e1000e version is 3.4.2.1. On download the tarball I get e1000e-3.4.2.1.tar.gz.

Extract it to /usr/src:

tar -xzf e1000e-3.4.2.1.tar.gz -C /usr/src

1	tar -xzf e1000e-3.4.2.1.tar.gz -C /usr/src

Create a dkms.conf in /usr/src/e1000e-3.4.2.1 with following contents:

PACKAGE_NAME="e1000e"
PACKAGE_VERSION="3.4.2.1"
AUTOINSTALL=yes
MAKE[0]="make -C src/"
BUILT_MODULE_NAME="e1000e"
BUILT_MODULE_LOCATION="src/"
DEST_MODULE_LOCATION="/kernel/drivers/net/ethernet/intel/e1000e"

PACKAGE_NAME="e1000e"

PACKAGE_VERSION="3.4.2.1"

AUTOINSTALL=yes

MAKE[0]="make -C src/"

BUILT_MODULE_NAME="e1000e"

BUILT_MODULE_LOCATION="src/"

DEST_MODULE_LOCATION="/kernel/drivers/net/ethernet/intel/e1000e"

Next, we have to tell DKMS that such a module has been added and build it for each of the kernels we have on the system:

dkms add -m e1000e/3.4.2.1
for k in /boot/vmlinuz*; do
  dkms install -k ${k##*vmlinuz-} e1000e/3.4.2.1
done

dkms add -m e1000e/3.4.2.1

for k in /boot/vmlinuz*; do

dkms install -k ${k##*vmlinuz-} e1000e/3.4.2.1

done

Finally, reboot the system and the new module should be live.

May 25, 2019 3

Multi-WAN DNS in pfSense

Update: I later figured out there are many other places pfSense restarts Unbound, so this is simply not worth the effort. I reversed the changes & moved Unbound to another box and using just DNS forwarder on pfSense — which is used by the Unbound server.

Having multiple broadband connections at home, I have a pfSense which takes care of load balancing and firewalling. pfSense is pretty good in almost everything, except one thing that was annoying me a lot — That it restarted the DNS Resolver (Unbound) every time either of my WAN connections restarted (one of my ISPs restarts the connection periodically), and the traffic originating from the box itself cannot be load balanced across multiple connections due to a limitation in FreeBSD’s implementation of pf itself – it is unable to set the correct source address.

It’s quite annoying that – even when you use the forwarding mode of Unbound, your DNS still goes through a single WAN interface. Moreover, Unbound doesn’t seem to do parallel querying across DNS servers. So if you have listed multiple DNS servers as forwarders it will try them one by one as they fail. Suppose, the WAN interface from which DNS traffic is outgoing is running at full capacity – a download or somebody is streaming a video, then your browsing becomes slow as well – but the browsing itself may go through another WAN connection. Notably, for having a stable multi-WAN setup in pfSense – you have to use forwarding mode. The gateway switching for the box itself doesn’t work reliably in my experience, due to which I’ve had to face “host not found” error messages even when one of the connections was up.

Continue reading “Multi-WAN DNS in pfSense” →

May 6, 2018 0

Monitoring your internet connections with OpenWRT and a Telegram Bot

For the past 5 years or so, I have been using a single ISP at home and mobile data for backup when it went down. But since last few months, the ISP service became a bit unreliable – this is more related to the rainy season. Mobile data doesn’t give fiber like constant speeds I get on the wire. It’s very annoying to browse at < 10 Mbps on mobile data when you are used to 100 Mbps on the wire.

I decided to get another fiber pipe from a local ISP. One needs to be very unlucky to have both going down at the same time – I hope that never happens. Now the question is how to monitor the two connections: Why do I need monitoring? – so that I can inform the ISP when it goes down, with the fail-over happening automatically thanks to OpenWRT’s mwan3 package, I won’t ever know when I am using which ISP (unless I am checking the public IP address, of course).

Continue reading “Monitoring your internet connections with OpenWRT and a Telegram Bot” →

August 25, 2017 2

Asterisk PJSIP wizard and phone provisioning

So after setting up Asterisk with a working DAHDI configuration for the PBX project, next was configuration for IP phones using PJSIP and provisioning them.

Asterisk has a built-in module called res_phoneprov which handles HTTP based phone provisioning but that didn’t work for me – I just couldn’t have it generate XML configuration for the phones that we had, i.e. Grandstream GXP1625.

The server on which I had configured PBX was multi-homed, as in it was part of multiple networks. But there was no reason to run the service on all interfaces except the VLAN on which we were going to connect the phones.

Continue reading “Asterisk PJSIP wizard and phone provisioning” →

July 20, 2017 5

Asterisk PBX with Reliance PRI Line using Digium TE131F

So I got an opportunity to set up Asterisk PBX with a Reliance Communications E1 line. I have worked with Asterisk PBX, but without PSTN interfacing. This post is about what all stuff I have done to get a Reliance E1 line with Digium TE131F card.

Having explored a lot of other distributions like Fedora, Arch, Gentoo, Sabayon, etc. since I ventured into Linux world and learning the internals of Linux and how different components are stitched together I settled on Ubuntu. It’s my favorite these days because everything seems to work out of the box… except when it doesn’t, then you have PPAs. 😛 For this project I have installed Ubuntu 16.04 server edition.

Continue reading “Asterisk PBX with Reliance PRI Line using Digium TE131F” →

July 14, 2017 0

Category: Linux

Golang on OpenWRT MIPS

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Using privileged mode (become) in Ansible without a password

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LXD OpenVSwitch and VLANs

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Ubuntu 18.04 add e1000e Intel driver to dkms

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Multi-WAN DNS in pfSense

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Monitoring your internet connections with OpenWRT and a Telegram Bot

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Asterisk PJSIP wizard and phone provisioning

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Asterisk PBX with Reliance PRI Line using Digium TE131F

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