Changing default application that start a file

Sometime the default installation of an operating system configuration is not the way you wanted it to be, so with this article, it will show you how to change the application that open a file. Note that this article will work in gnome version 3.4.2 or later.

gui way
This is an easy way if you don't want to dig deep into how is the gnome mechanism file opening work. Just right click on the file, click on Properties. An pop up window associated with the file you selected appeared. On the tab Open With , locate the application you want the file to open with and then select it.

cli way
If you want to dig a little deeper, there are many configuration files located in /usr/share/applications. These files contain information about an application like application name and application exec command to trigger the start of an application. Once you located the application you want a file to be associated to start with, e.g. I would like csv file to be started with libreoffice-calc.desktop , then go to $HOME/.local/share/applications directory, locate another file, mimeapps.list. Open this file with an text editor, under the group [Default Applications] , add an entry like text/csv=libreoffice-calc.desktop. If you want to associated with more files, locate the general mime file at /etc/mime.types, and start to populate your environment with default application.

https://developer.gnome.org/integration-guide/stable/desktop-files.html.en

analysis graph - gangnam style view

So after a year run, everyone on earth should not be alien about gangnam style; the korean kpop hit songs. It's impresive we see this video view in youtube break the most view youtube holder and set itself far ahead than the rest top 10 most view youtube videos.

Numbers speak and represent the popularity of the content, in this case, the song and the singer. With this article, I would like to share my thought and history experience about this song view chart. This is just my analysis and opinion based on this graph.

It was released sometime ago but it has not gain momentum, probably due to just released and new to the people. But from the black circle, this is where the slope is at its highest. At this time, videos played all over the tv, news play over and over in the radio, and even in social networking websites, everyone sharing this songs to everyone. The rate of explosion is tremendous!

Then we continue to see the curve going upward...as indicated in the red circle. There was a time where there is a video circulate in the internet said how the view is generated using a paid service company.. LoL.. lame.. that is, if you want to get your views goes high up, you paid a certain amount to a company, and they click on your video and view and does that continously for you. :-) But I don't think it happen for this song, because this gangnam trend is seem throughout the earth.. though it is korean song, the impact is everywhere, we can see mass public doing mob dance everywhere on earth.. also, the hundred of parodies....

Though the graph is still rising, as seen in blue circle, the rate of view is definitely slow down. somewhere during the period of 2013 april, that's about 6 months run! I think it has done good , considering a good pop song would not last like 2-3months... Nonetheless, true fans of Psy and newbie just watch the video still contributing the view rate. At this stage, Psy and his gangnam style has reach the fame and every household would know him.. maybe your pet, dog and cat too. :-)

The record breaking at almost 1.8billions view after july 2013 is really astonishing and greatest achievement. We see the graph not grow but in fact, if you zoom into the last of light yellow circle, you will see the fall of the view rate. I guesss it is only normal everyone is bored with this pop song. Would it grow any higher and stay steady? Trend and time will tell because we see history, there are pop songs goes back into chart, with gangnam style, there is high possibility too. Thereby push the graph higher.

That's it for my analysis and thank you for reading.

cassandra 2.0 catch 101

This is my experience with cassandra 2.0 and cqlsh, reading through the datastax documentation [1] , sometime you need to play around with the new tool to understand with the nature of the usage. It could be a bug, it could be just some changes, nonetheless, it is my experience reading and experiencing in cassandra 2.0. Some bugs may be fix or change in the later cassandra release and thus render this article invalid.. thus this article is only meant for cassandra 2.0 and cqlsh 4.0.0 . I will add more in my journey to cassandra 2.0


when updating config durable_writes to the keyspace, got a few times error... like below.

cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : false};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : false};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 'false'};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 'false'};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 0};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 0};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 1};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 1};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : '1'};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : '1'};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : '0'};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : '0'};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 'False'};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 'False'};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 'True'};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : 'True'};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : True};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : True};] reason: NullPointerException null
cqlsh:jw_schema1> alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : False};
Bad Request: Failed parsing statement: [alter keyspace jw_schema1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3, durable_writes : False};] reason: NullPointerException null

just specified as one config in the alter keyspace command. It strange alter keyspace is not in the cqlsh help file...

cqlsh:jw_schema1> alter keyspace jw_schema1 with durable_writes = false;
cqlsh:jw_schema1> DESCRIBE KEYSPACE jw_schema1;

CREATE KEYSPACE jw_schema1 WITH replication = {
  'class': 'SimpleStrategy',
  'replication_factor': '3'
} AND durable_writes = 'false';

voila!

[1] http://www.datastax.com/documentation/cassandra/2.0/webhelp/index.html#cassandra/configuration/configStorage_r.html#reference_ds_itw_wkz_1k
[2] http://cassandra.apache.org/doc/cql3/CQL.html#alterKeyspaceStmt

disk usage via command df

I'm pretty sure all of us have bunch of collections files like documents, audio and video in our computer and what is the simple way to check if the disk space usage is exceed the capacity that physical disk provided? For starter, I'm using a command called df, it cames from the package coreutils if you are using Fedora.

What is df?
df displays the amount of disk space available on the file system containing each file name argument.

Example of usage of df?

$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/vg_super-lv_root
                      51606140   9213992  39770708  19% /
tmpfs                  1977424      2348   1975076   1% /dev/shm
/dev/sda5               495844     68681    401563  15% /boot
/dev/mapper/vg_super-lv_home
                      92792824  60272440  27806708  69% /home


$ df /usr/share/man/man1/df.1.gz
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/vg_super-lv_root
                      51606140   9214012  39770688  19% /

df in techical
- Disk space is shown in 1K blocks by default, unless the environment variable POSIXLY_CORRECT is set, in which case 512-byte blocks are used.
- if the partition is not mounted, it will not shown in the df report.


Based on the example usage shown above, the output shown is not human readable, we have to add additional parameters to the command df to make the report much more readable, I summarize some of the parameters with description which I frequently used but if you want a full list, man df to get an all parameters available to command df.

-h, with this parameter, it output human readable size, such as KiB, MiB

-H, with this parameter, it output human readable size too but use power of 1000 not 1024. You could probably noticed that the hard disk normally use this unit to measure its capacity.

-T, with this parameter, it show additional column called type to shown the type of filesystem it is formatted.

--total, with this parameter, it give you a grand total of all the mounted filesystem in the report.

[debian] installing and removing with the same command

When you need to install a package and remove a package, you can do it with a single command than two separate commands. This can be achieve by appending a suffix to the package name. When the aptitude install command is used, a '-' to the suffix of the package name is to remove the package while an aptitude command remove with a '+' suffix to the package name is to install the package.

# aptitude install package1 package2-

# aptitude remove package1+ package2

what pages in memory context?

When a process uses some memory, the CPU is marking the RAM as used by that process. For efficiency, the CPU allocate RAM by chunks of 4K bytes (it's the default value on many platforms). Those chunks are named pages. Those pages can be swapped to disk, etc.

cassandra

I've been studying cassandra recently and would like to share my findings.

What is cassandra?

Apache Cassandra is an open source, distributed, decentralized, elastically scalable, highly available, fault-tolerant, tuneably consistent, column-oriented database.

Cassandra is an open source distributed database management system. It is designed to handle very large amounts of data spread out across many commodity servers while providing a highly available service with no single point of failure.

Cassandra provides a structured key-value store with eventual consistency. Keys map to multiple values, which are grouped into column families. The column families are fixed when a Cassandra database is created, but columns can be added to a family at any time. Furthermore, columns are added only to specified keys, so different keys can have different numbers of columns in any given family. The values from a column family for each key are stored together, making Cassandra a hybrid between a column-oriented DBMS and a row-oriented store.

where is cassandra use?
well, you can store whatever you want, for example, we used cassandra to store the call detail record.

where do i get started to learn cassandra?
i suggest you start with a cassandra book for beginner or person coming from RDBMS. Because there are new terminology with is introduced in cassandra. When you get a hold on cassandra, you should really get the source from apache cassandra website and they have a great information in their wiki page.

where do i get help if i have question?
they have mailing list where you can find if your question is asked before or you can contact me. :-)