How to create a bootable Ubuntu Lucid USB pen drive with persistent storage

This blog explains how to create a bootable Ubuntu Lucid Lynx (10.04) USB pen drive with persistent storage. Persistent storage means that all changes made to the system settings and all files in the user's home directory are saved to the pen drive and are available after system reboot.

Connect your USB pen drive.

The Ubuntu Lucid live system supports persistent storage by default. On an existing Ubuntu Lucid system System / Administration / Startup Disk Creator on an existing Ubuntu Lucid system. If you have an existing Ubuntu Karmic system, run sudo apt-get install usb-creator to install the Startup Disk Creator program, and then run System / Administration / USB Startup Disk Creator.

Make sure that the Stored in reserved extra space is selected (it's selected by default).

Download the live CD ISO image to your hard drive from http://releases.ubuntu.com/lucid/ubuntu-10.04-desktop-i386.iso. If you want to download from a faster mirror, please find the ISO image link on http://releases.ubuntu.com/lucid/. For maximum compatibility, select the Intel x86 (or i386, or 32-bit) version. The download may take 30 minutes or more.

In the startup disk creator window, specify the downloaded .iso file by clicking on the Other... button.

For maximum compatibility, format your pen drive, by clicking on the Format button in the startup disk creator window.

Click on the Make Startup Disk button.

Eject (remove) the USB pen drive in the file manager. Disconnect the pen drive.

Boot the computer from your USB stick as usual. There is now configuration necessary. All files you create in the live system in the user's home directory, and all settings you change get retained through reboots.


How to add (generate) locales on Debian and Ubuntu

This blog post gives instructions to add (and generate) locales on Debian and Ubuntu systems. The instructions given here work on Debian Etch and newer, and Ubuntu Hardy and newer (including Intrepid, Jaunty and Karmic).

To add the locales hu_HU.ISO8859-2 and hu_HU.UTF-8, run

$ echo 'hu_HU.ISO8859-2 ISO-8859-2' | sudo tee -a /var/lib/locales/supported.d/hu
$ echo 'hu_HU.UTF-8 UTF-8' | sudo tee -a /var/lib/locales/supported.d/hu
$ sudo dpkg-reconfigure locales 

To verify that the locales are installed correctly, run the following commands and verify that they don't print anything:

$ LC_ALL=hu_HU.ISO8859-2 perl -e0
$ LC_ALL=hu_HU.UTF-8 perl -e0


An approximation of pi in bc

This blog post shows an approximation of the constant π (3.14...) implemented as a bc program using Machin's formula.

Machin's formula is documented on http://en.wikipedia.org/wiki/Numerical_approximations_of_%CF%80#Machin-like_formulae. The implementation below computes acot using its Taylor series expansion, always rounding down for divisions. The implementation knows the number of good digits by computing an upper bound of the total rounding error.

#! /usr/bin/bc -q
# by pts@fazekas.hu at Sat Jul 17 17:38:25 CEST 2010

/** Return an approximation and lower bound for acot(x) * 10 ^ u. */
define acot(x, u) {
  auto sum, xpower, xx, n, term
  sum = xpower = u / x
  xx = x * x
  n = 3
  for (;;) {
    xpower /= xx
    term = xpower / n
    if (term == 0)
      return sum
    sum -= term
    n += 2
    xpower /= xx
    term = xpower / n
    if (term == 0)
      return sum
    sum += term
    n += 2

/* Return an integer upper bound for the >= 0 error value pi * 10 ^ u - f(u),
 * where u is 10 ^ nd, f(u) is the integer 4 * (4 * acot(5, u) - acot(239, u)).
 * The magic constants in the maxerr implementation were derived from analyzing
 * the acot implementation, taking into account the rounding (truncation) done
 * in each division.
define maxerr(nd) {
  return (286135312 * nd + 41739380) / 10000000

/* Return a string of at most nd characters, prefix of pi,
 * assuming nd >= 4.
define pi(nd) {
  auto u, y
  u = 10 ^ nd
  y = 4 * (4 * acot(5, u) - acot(239, u))
  y /= 10 ^ (length(maxerr(nd)) - 1)
  while (y % 10 == 0) {
    y /= 10
  return y / 10

/* Print pi with increasing precision infinitely (until aborted). */
define pinfinite() {
  auto b, nb, nd, a, na
  print "3."
  b = 3
  nb = 1
  nd = 8
  for (;;) {
    a = pi(nd)
    na = length(a)
    /* Print digits not printed yet in previous iterations. */
    print a % (10 ^ (na - nb))
    b = a
    nb = na
    nd *= 3

pinfinite()  /* Infinite loop. */
Here is the equivalent program in dc: