linux and robert

2010年4月7日星期三

stop on first error (gcc, make)

Just want to see the first compilation error ? Try this:

-> gcc main.c -Wfatal-errors

-Wfatal-errors

This option causes the compiler to abort compilation on the first

error occurred rather than trying to keep going and printing

further error messages.

Ref:

man gcc

2010年1月16日星期六

grub rescue after re-partition by Windows

Situation:

I install Ubuntu9.10 (with grub loader) in /dev/sda10.

(My MBR bootloader is spfdisk)

Someday, I boot the system to Windows (/dev/sda2) and re-partition /dev/sda3 to NTFS.

After rebooting to Ubuntu9.10, a problem comes: some Windows program has changed the disk MBR and my Ubuntu9.10 is no more in /dev/sda10. It's in /dev/sda9 in the new MBR.

So when boot to /dev/sda9, grub can't find linux in /dev/sda10.

It is in /dev/sda9 now !

--------- in grub rescure, manually boot to /dev/sda9 -------

grub rescue>

set prefix=(hd0,9)/boot/grub

insmod (hd0,9)/boot/grub/linux.mod

----- now you can use [tab] auto-completion ---

set root=(hd0,9) linux /boot/vmlinuz26 root=/dev/sda9 initrd /boot/kernel26.img boot

----- this will boot to Ubuntu 9.10 ------

sudo update-grub

sudo grub-install /dev/sda9

(this will update your grub settings, esp. your boot menu,

so that you can boot normally into Ubuntu9.10 next time)

Reference:

1. GRUB2 rescue guide

2. Linux Commands for GRUB2

2010年1月13日星期三

generate a (pseudo) random number in sh

Print a pseudo-random byte (hex) in sh:

cat /dev/urandom | od -t x1 -A n -N 1

->89

-----------

Create a pseudo-random file of size 1 MB:

dd if=/dev/urandom of=a.log bs=1M count=1

Ref:

Re: generating random number in sh

http://linuxcommando.blogspot.com/2008/06/create-file-of-given-size-with-random.html

2010年1月1日星期五

Install a New font in Ubuntu

For instance, I want to install a new font "Crisp" to my Ubuntu 9.10:

1. Create a new directory for your new font:

sudo mkdir /usr/share/fonts/truetype/crisp/

sudo cp ~/download/Crisp.ttf /usr/share/fonts/truetype/crisp/

2. Rebuild the font information files:

sudo fc-cache -f -v | grep -i crisp

-> /usr/share/fonts/truetype/crisp: caching, new cache contents: 1 fonts, 0 dirs

3. Restart the programs in which you want to use the new font.

--------

Ref:

Fonts - Ubuntu Wiki

Crisp font (proggy programming)

2009年12月8日星期二

Pull-up resistor

Pull-up resistors are used in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected.

tri-state (vt)

When outputs are tri-stated (in the Hi-Z state) their influence on the rest of the circuit is removed, and the circuit node will be "floating" if no other circuit element determines its state.

PLL (phase-locked loop)

A PLL is a control system that generates a signal that has a fixed relation to the phase of a "reference" signal.