Linux

Sometimes when you are running Linux and have a weird bug, you wish you would know what the process is doing. For example, which files it is opening and such ...

The strace command is very useful.

Use case 1: Simple command as argument

However, its common use cases is when you have a single process running. Usually, you would run strace and your command as an argument, like so:

strace your_program 

Use case 2: Tracing a running command

On August 12th, I did a presentation on OpenWRT for the KW Linux Users Group.

The slides from this presentation are attached below, and the audio for the presentation is available as a podcast.

Hope it is of use for some.

In that presentation I mentioned wrtbwmon, the bandwidth monitoring script for OpenWRT. You can download my modified version from here.

Years ago, I wrote about the various tools available for monitoring bandwidth usage for individual devices in a home network.

Now, I have a definitive solution that will help with the questions: wrtbwmon. This is based on several variants that are floating around the internet, each a fork of another.

Here is an excerpt from the README file:

Description
===========

If you have a VPS at Linode, then you have free Dynamic DNS. You can use that from a regular Linux machine, or from a router that runs OpenWRT.

This article describes how to setup an OpenWRT router with Linode Dynamic DNS.

First, the script itself, which goes into the file: /etc/custom/linodedns.sh

#!/bin/ash
 
BASE=`basename $0 .sh`
DIR=`dirname $0`

OUTPUT1=/tmp/$BASE-1.out
OUTPUT2=/tmp/$BASE-2.out

# Read the configuration file
CONF=$DIR/$BASE.conf
if [ -r "$CONF" ]; then
  . $CONF
else 

Update 2020-07-09: With the latest 19.07.3, syslog-ng is no longer the preferred option. Instead, read my other article on using rsyslog with OpenWRT.

Update 2014-10-08: If you upgraded to the stable Barrier Breaker 14.07, and Syslog-NG is not available, or if don't want to use Syslog-NG for any other reason, please check our other article on using the built in logging feature of OpenWRT to write the log to a file.

We wrote earlier on OpenWRT on D-Link DIR-835. Now, we need to expand the functionality a bit more.

On OpenWRT, the default logging mechanism is an in-memory circular buffer. The user interface for it is the logread command. The log buffer default size is 16 kB. There are a couple of directives that can be set in the system configuration for OpenWRT, but because of the limited size of flash and the non-permanence of RAM, you need another solution if you want to store logs for anything longer than a day or two.

Syslog-NG

Syslog-NG is a good system logging program that is available for OpenWRT.

If you are using Ubuntu 12.04 on an older computer with a Semperon CPU, you will soon find that Flash is not working and therefore Youtube videos will not work either.

Adobe Flash built with SSE2 flag

This is because Adobe has build the recent Flash versions with the SSE2 flags enabled, yet many Semperons lack this particular flag.

$ cat /proc/cpuinfo
vendor_id : AuthenticAMD
cpu family : 6
model : 8
model name : AMD Sempron(tm) 2600+
...

I previously wrote about reducing CPU usage for Firefox by disabling Firebug. Later, I wrote on disabling the YSlow extension also reducing CPU usage.

Now, the laptop is able to exceed 4 hours of battery time under Kubuntu Linux 12.04:

Four hours, seven minutes:

09:37:27 localhost pm-utils: Power source switched to battery, Battery: discharging, A/C adapter: off-line

This is a quick how to for installing OpenWRT custom firmware on a D-Link DIR-835 router.

Though these instructions were tested on the DIR-835, they apply to many other router models from Linksys, Netgear, ASUS, and many other brands.

Check if your hardware is supported

Update: 2017-Nov-19: See the last section for automated installation and upgrading, which is now possible.

To read my RSS feeds, I use Tiny Tiny RSS, which worked fine until 21 Feb 2014.

On 22 Feb 2014, Ubuntu pushed Firefox 27, Tiny Tiny RSS stopped working, with a Javascript error. After logging in, there would be a pop up error referring to getCookie and tracing to prototype.js.

To solve this, I went back to the ESR (Extended Support Release). This was quite a few steps, so I am documenting them here.

To have better fonts in Firefox, you need to disable anti-aliasing, and clear all font caches.

Do achieve this, run the following commands from a terminal:

Clear the cached fonts in your home directory

cd ~
rm -f .fonts.conf .fonts.cache-1 .fontconfig/*

Disable antialiasing

cd /etc/fonts/
sudo mv 10-antialias.conf disabled-10-antialias.conf 

Reconfigure the fonts

sudo dpkg-reconfigure fontconfig

Now, restart FIrefox and check if the fonts look better ...