Marcus Folkesson

Embedded Linux Artist

Embedded Linux Conference 2019

Embedded Linux Conference 2019 Here we go again! This trip got exited even before it begun. I checked my passport the day before we should leave and noticed that my passport has expired. Outch. Fortunately I was able to get a temporary passport at the airport. I must admit that I'm not traveling that often and do not have these 'must-checks' in my muscle memory.. This time we were heading Lyon in France.

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Posted by Marcus Folkesson on Thursday, October 31, 2019

ligsegfault.so

libsegfault.so The dynamic linker [1] in a Linux system is using several environment variables to customize it's behavior. The most commonly used is probably LD_LIBRARY_PATH which is a list of directories where it search for libraries at execution time. Another variable I use quite often is LD_TRACE_LOADED_OBJECTS to let the program list its dynamic dependencies, just like ldd(1). For example, consider the following output $ LD_TRACE_LOADED_OBJECTS=1 /bin/bash linux-vdso.so.1 (0x00007ffece29e000) libreadline.

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Posted by Marcus Folkesson on Thursday, December 13, 2018

Embedded Linux Conference 2018

Embedded Linux Conference 2018 OK, time for another conference. This time in Edinburgh, Scotland. My travel is limited to Edinburgh, but this city has a lot of things to see, including Edinburgh Castle, the Royal Botanic Garden, the clock that is always is 3 minutes wrong [1] and lots of more. A side note, yes I've tried Haggis as it's a must-try-thing and so should you. But be prepared to buy a backup-meal.

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Posted by Marcus Folkesson on Tuesday, October 23, 2018

Lund Linux Conference 2018

Lund Linux Conference 2018 It's just two weeks from now til the Lund Linux Conference (LLC) [1] begins! LLC is a two-day conference with the same layout as the bigger Linux conferences - just smaller, but just as nice. There will be talks about PCIe, The serial device bus, security in cars and a few more topics. My highlights this year is to hear about the XDP (eXpress Data Path) [2] to get really fast packet processing with standard Linux.

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Posted by Marcus Folkesson on Friday, April 20, 2018

OOM-killer

OOM-killer When the system is running out of memory, the Out-Of-Memory (OOM) killer picks a process to kill based on the current memory footprint. In case of OOM, we will calculate a badness score between 0 (never kill) and 1000 for each process in the system. The process with the highest score will be killed. A score of 0 is reserved for unkillable tasks such as the global init process (see [1]) or kernel threads (processes with PF_KTHREAD flag set).

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Posted by Marcus Folkesson on Friday, December 1, 2017

Embedded Linux course in Linköping

Embedded Linux course in Linköping I tech in our Embedded Linux course on a regular basis, this time in Linköping. It's a fun course with interesting labs where you will write your own linux device driver for a custom board. The course itself is quite moderate, but with talented participants, we easily slip over to more interesting things like memory management, the MTD subsystem, how ftrace works internally and how to use it, different contexts, introduce perf and much more.

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Posted by Marcus Folkesson on Sunday, November 19, 2017

FIT vs legacy image format

FIT vs legacy image format U-Boot supports several image formats when booting a kernel. However, a Linux system usually need multiple files for booting. Such files may be the kernel itself, an initrd and a device tree blob. A typical embedded Linux system have all these files in at least two-three different configurations. It's not uncommon to have a Default configuration Rescue configuration Development configuration Production configuration ... Only these four configurations may end up with unmanageable amount of different files.

Posted by Marcus Folkesson on Wednesday, October 18, 2017

Magic SysRq

Magic SysRq Every kernel-hacker should knows about the magic SysRQ. Period. To enable the magic, make sure CONFIG_MAGIC_SYSRQ is set in your Kernel hacking tab. I use this feature a lot, mostly for set loglevel and reboot the system. But it is also very useful to get information out of the system even if it is completely frozen. As everybody is using GNU Screen (what else?) as their TTY terminal, the keyboard combination is: ctrl+A B.

Posted by Marcus Folkesson on Sunday, August 27, 2017

Take control of your Buffalo Linkstation NAS

Take control of your Buffalo Linkstation NAS I finally bought a NAS for all of my super-important stuff. It became a Buffalo Linkstation LS200, most because of the price ($300 for 4TB). It supports all of the standard protocols such as FTP, SAMBA, ATP and so on. However, it would be really useful to use some sane protocols like sftp so you could use rsync for your backup scripts.

Posted by Marcus Folkesson on Sunday, August 27, 2017

NAT with Linux

NAT with Linux To share an internet connection may sometimes be very practical when working with embedded devices. The network may have restrictions/authentications that stops you from plug in your device into the network of the big company you are working for. But what about creating your own network and use your computer as NAT (Network Address Translation)? It's not that hard to setup, it's actually just a few command lines away.

Posted by Marcus Folkesson on Thursday, July 27, 2017