I have been encountering problems regarding my raspberry pi 2. I've been following the instructions given @ https://learn.adafruit.com/pi-thermal-printer/overview

when I change parameters in my /boot/cmdline.txt and assuming that i have to disable [email protected] in exchange to commenting out the /etc/initab file. I still get a boot error: unable to mount root fs on unknown-block(179 2).

The sd card is fine, I just need to mount an image and it will run again.

I followed the instructions one by one and it seems that when I edit my cmdline.txt and disable my getty-service (in exchange of editing /etc/inittab) I reboot and get the error.

  • Welcome -- but rather than asking other people to read through a tutorial you have read and followed, you need to explain exactly what it is you did and what problems resulted. "Unable to mount root fs" implies an incorrect image on the SD card. Did it ever work? When did it stop working? Etc.
    – goldilocks
    Commented Jan 31, 2016 at 10:27
  • 1
    Hello and welcome. Please check the following related questions (one suggests power issues: raspberrypi.stackexchange.com/questions/39395/… and raspberrypi.stackexchange.com/questions/38882/… The error unknown-block(179 2) is however related to the SD card and needs separate fixing (but could be induced by some brown out during operation, which makes it even more a power issue).
    – Ghanima
    Commented Jan 31, 2016 at 10:27

1 Answer 1


when I change parameters in my /boot/cmdline.txt

You did this wrong. You must make sure cmdline.txt still includes:

root=/dev/mmcblk0p2 rootfstype=ext4


  • That there is a space between each parameter, but no spaces within a parameter (most of them are key=value but they can be one term with no =).
  • That there is only ONE line in the file. There must be no linebreaks.

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