Print four beamer slides per sheet

Of course, on Linux CLI:
pdfnup --landscape --nup 2x2 --frame true --no-tidy --delta '5mm 5mm' --scale 0.95 input.pdf

Clean up filled up partitions in Linux: mount subdirectories elsewhere

I have two major partitions in my Linux box: / and /home. My root partition was getting dangerously crowded and I got a "disk full" error a number of times.

I had the following idea: mount some large subdirectory from / in /home. In particular, I decided to move there my /usr/local/lib/R/site-library directory (R packages, in the order of 1GB).

Here is how I did it. First, I moved move the required directories:

su -
cd /usr/local/lib/R/
mv site-library /home

Then, I edited the /etc/fstab file adding the line

tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0

to it in order to persist the changes. (Mind that the spaces are actually tabs).

Finally, I ran

mount -a

Get better performance and life from your SSD in Linux-based systems

I recently purchased a new laptop which came with a 24GB SSD disk. In order to get the most of this technology and prevent unnnecessary writes (which affects the longevity of these systems) I kind of followed the superb advice given at Get better performance and life from your SSD in Linux-based systems.

In particular, I mounted the /home directory in the tradicional HD and moved temporary directories (e.g., /tmp) to RAM.

Works as a charm!

Google link converter

Links provided in the search results of Google look something like

http://www.google.co.uk/url?sa=t&source=web&cd=1&ved=0A&url=http%3A%2F%2Fabc.go.com%2F&rct=j&q=abc&ei=kuw&cad=rja

when the URL it links to is simply

http://abc.go.com/

This tool allows users to transform the former into the later for easier copying and pasting.

Apache ignoring mod_rewrite rules?

Then it is very likely in the site configuration file, usually at
/etc/apache/sites-available 
you have directives such as
AllowOverride None 
Change them to
AllowOverride All 
and try again.

Unique rows in vim

Simple! Just

:sort u

Sending UTF-8 mail with PHP

I was facing issues sending mail encoded as UTF-8 via PHP. In order to do it properly, you need to set UTF-8 as the encoding for the mail function (first line of code below). Then, mail can be sent (second line).

mb_internal_encoding("UTF-8");
mb_send_mail( 'myrecipient@wherever.com', 'Polite subject', $message, $headers );


Apache module modwsgi 3.3 on Ubuntu Lucid

A bit of library hell on Linux. I tried to install modwsgi on Ubuntu Lucid. I downloaded the Debian version. However,

root@virt251:/tmp# dpkg -i libapache2-mod-wsgi_3.3-2+b2_i386.deb 
...
dpkg: dependency problems prevent configuration of libapache2-mod-wsgi:
 libapache2-mod-wsgi depends on libpython2.7 (>= 2.7); however:
  Package libpython2.7 is not installed.
dpkg: error processing libapache2-mod-wsgi (--install):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 libapache2-mod-wsgi

You cannot install Python 2.7 (easily, at least) on Lucid, but you can install Python 3.1. Use apt-get and that will do the trick.

Automatic creation of regular expressions in different computing languages

Regular expressions are a powerful tool, albeit they can become difficult to build. This page, text2re, helps you build complex re's and provides code in a number of computing languages such as Python, Perl, etc.

Modifying Xubuntu application menu

One of the most disturbing features of my Xubuntu desktop is the apparent inability to modify the application menu. In particular, I had a huge settings submenu with duplicated entries: many already appeared in the system submenu.

So I edited the file /etc/xdg/menus/xfce-applications.menu and changed the section

    <Menu>
        <Name>Settings</Name>
        <Directory>xfce-settings.directory</Directory>
        <Include>
            <Category>Settings</Category>
        </Include>

        <Layout>
            <Filename>xfce-settings-manager.desktop</Filename>
            <Separator/>
            <Merge type="all"/>
        </Layout>

        <Menu>
            <Name>Screensavers</Name>
            <Directory>xfce-screensavers.directory</Directory>
            <Include>
                <Category>Screensaver</Category>
            </Include>
        </Menu>
    </Menu>

into

    <Menu>
        <Name>Settings</Name>
        <Directory>xfce-settings.directory</Directory>
        <Include>
            <Category>Settings</Category>
        </Include>
        <Exclude>
            <Or>
                <Category>System</Category>
            </Or>
        </Exclude>

        <Layout>
            <Filename>xfce-settings-manager.desktop</Filename>
            <Separator/>
            <Merge type="all"/>
        </Layout>

        <Menu>
            <Name>Screensavers</Name>
            <Directory>xfce-screensavers.directory</Directory>
            <Include>
                <Category>Screensaver</Category>
            </Include>
        </Menu>
    </Menu>

This is a simple example of what can be achieved if you (very carefully) edit the file.

Tweaking Xubuntu application menu

One of the things I find less appealing on my Xubuntu desktop is the apparent inability to modify your application menu. In particular, I had a huge settings submenu with duplicated entries, which already appeared in the system submenu.

So I edited the file

/etc/xdg/menus/xfce-applications.menu

and changed the section


Settings
xfce-settings.directory

Settings



xfce-settings-manager.desktop





Screensavers
xfce-screensavers.directory

Screensaver





into

    
        Settings
        xfce-settings.directory
        
            Settings
        
        
            
                System
            
        

        
            xfce-settings-manager.desktop
            
            
        

        
            Screensavers
            xfce-screensavers.directory
            
                Screensaver
            
        
    

Too many files in a directory hurting performance in Linux?

Some colleagues of mine have come to a situation where they believe that storing many files (in the order of hundreds of thousands) in a single UNIX directory (sorry, I ignore the file system that particular proprietary UNIX brand uses) seriously impairs performance.

Apparently, ls and related utils show a dismaying performance there. So I wanted to check that for myself on my own Linux backup directory on my ext3 external disk, where I store 100.000 files approx. (Note: I keep time stamped copies of my directory structure with hard links to a single directory where I store the actual files so as to avoid data multiplication).

True, ls and ls -lrt are slow, very slow there. However, ls -lrt > /tmp/ls.txt is as fast as you could expect for a 7.5MB file. Also, touch kk and rm kk are as fast as in an empty directory.

In summary, standard tools such as ls and find may not be ready to deal with huge directories. The sorting abilities of ls may scale as bad as O(n^2) in some circumstances. Also, shell expansion (for *, say) may not be very efficient. However, accessing files for creation, editing or deletion may be blazingly fast even in relatively oldish file systems such as ext3 on the cheapest hardware.

Inserting Google visualizations in Wordpress blogs

I tried to insert a Google visualization into my (other) blog. I run into problems that Google itself solved.

The solution? Use the Custom fields shortcode plugin for Wordpress: first, install and activate it. Then, wherever your visualization goes, insert

[cf]this_is_my_tag_name[/cf]

If your plugin is properly inserted, at the bottom of the page you will see a form with title "Custom fields". Add a new custom field with name this_is_my_tag_name and paste the code for your visualization into the adjacent field.

The plugin will replace your tag with the code you inserted and your visualization will be properly shown in your entry.

Padding text with leading zeros in Teradata

In order to pad a number with leading zero Teradata you can do as follows:

create set table my_table ,no fallback ,
no before journal,
no after journal,
checksum = default
( a integer )
primary index ( a );

insert into my_table select 25;
insert into my_table select 12345;
insert into my_table select 0;

select substr(
'00000' || cast( a as varchar(5) ),
characters( cast( a as varchar(5) ) ),
5 )
from my_table;

The relevant part lies in the use of the functions substr and characters.

A open(er) web 2.0 chaintool

I am planning to migrate from my standard set of web 2.0 tools to something more open and collaborative. This will mean:

• Less Twitter and more identi.ca
• Less Google and more blekko
• Less Google Maps and more OpenStreetMap
• Less FB and more beer!

Table sizes and disk utilization in Teradata

The analysis of table sizes and disk utilization per AMP in Teradata is based on table dbc.tablesize.

Two typical queries are:

select
vproc,
databasename,
sum(currentperm) / 2**30 as cp,
sum( peakperm ) / 2**30 pp
from dbc.tablesize
group by 1,2;

to find space utilization by AMP and

select
tablename,
databasename,
sum(currentperm) / 2**30 as cp,
sum( peakperm ) / 2**30 pp
from dbc.tablesize
group by 1,2;

to find out the sizes of tables.

More of git for remote server deployment of webpages

This is a brief tutorial on how to deploy your webpage to a remote server using git.

My (minimalistic) vi cheatsheet

:set (no)wrapscan

:set (no)nu

:set (no)ignorecase

\< \> to search for full words

set softtabstop=2
set shiftwidth=2
set tabstop=4
set expandtab

Nice feature of OpenOffice's brush

I have just discovered a nice feature of OpenOffice's brush: unlike MS Word's, it does not copy formats but named styles.

If you want to use a given format in different places, why not creating a specific custom style? You can spread it over your document using the brush and later, if you need to change it, just edit the style and... voilá!

Query to select last observation by date for each customer

Sometimes you have a table with a list of transactions of each, say, customer and you need the latest picture of each customer. The so called window functions in SQL2003 are instrumental in order to write neat, concise SQL for such purpose.

It would work as follows (in Teradata's SQL dialect):

select
  cust_id,
  status,
  status_date,
row_number() over (partition by cust_id order by status_date desc ) as ranking
from customer_status
qualify ranking = 1;