Tag Archives: linux

how to count files in subdirectories (linux)

This is one is quick but very helpful

  ls -laR | wc -l

With that, you will count all files under the current and subdirectories.

ext4, is it for you ?

Well, I heard (read to be honest) somewhere that ext4, the evolution of ext3 linux file system, is coming out from development to stable tree (Kernel 2.6.28). However, I was not so sure about the benefits and how this can improve my life and my performance in daily tasks using my 80gb HD laptop. Here is the features I found in my search:

  • Large filesystem: It can support volumes with sizes up to 1 exabyte (1024 GB == 1 Tera. 1024 Tera == 1 Peta. 1024 Peta == 1 Exa). Since Linux kernel version 2.6.25, it also supports files as large as the file system.
  • Backward and forward compatibility: It has backward compatible with ext3, making it possible to mount an ext3 filesystem as ext4 and vice-versa, but the ext4 to ext3 is only possible if extents is not enabled.
  • Delayed allocation: With this feature, ext4 can delay block allocation as long as possible, improving performance and reducing fragmentation, since it will only allocate space with the real file size.
  • Expand the subdirectory limit up to 64000: Shame on you Window$ ;)
  • Faster file system checking: The data structures used in ext4 allows fsck to skip unused blocks of data, which will reduce the time fsck may spend.
  • Undelete: It’s not yet implemented but this feature will also be supported and it’s very handy in many situations.
  • Other fixes…

But the discussion here: is it really for you ? Do you need a filesystem with 1 exabyte limit ? Create more than 32,000 subdirectories ? I mean, of course that there are other performance improvements and they are very important and welcome, thanks. But I’m not so sure about experiment ext4 now, since I’m only with one machine and using it for work. :P   Maybe in few months or with the next Ubuntu release I’ll have it. At least,  I’m already aware of what I can expect about ext4.

For those who want’s to migrate from ext3 to ext4 now, I found this step-by-step article at IBM developerWorks and looks very helpful.

Sources:
– http://ext4.wiki.kernel.org/index.php/Main_Page
- http://en.wikipedia.org/wiki/Ext4

O básico do apt-get

Essa é uma daquelas dicas simples do dia a dia mas que pode ser útil para alguns novatos em uma distribuição debian-based como o Ubuntu. Para instalar programas você pode utilizar o Synaptic, uma ótima ferramenta sim, mas abrir uma ferramenta e fazer a pesquisa pode ser um pouco demorado, principalmente quando se deseja apenas instalar “aquele programinha”, coisa rápida.

Para agilizar podemos utilizar o apt-get que é o mecanismo utilizado pela interface do Synaptic e já conhecido de usuários debian. Para facilitar o uso, vou resumir os principais comandos:

# instalar uma aplicacao
$ apt-get install nome-da-app

# remover uma aplicacao
$ apt-get remove nome-da-app

# pesqusiar por uma aplicacao
$ apt-cache search nome-da-app

# atualizar programas e lista de programas
$ apt-get update

Bom é isso, simples mas para quem está começando, pode ajudar…

Problems with Java Swing applications on Ubuntu 8.04 64bit ?

If you are running java apps based on swing (gui) under linux, you should be experiencing some problems, such as a “a completly blank window” or no components showing… This happens if you are using the desktop effects (even in the “Normal” level).

Common applications that I had problems:

  • Apache JMeter
  • Oracle SQLDeveloper
  • IReport

Ok, here is the simple fix: Add these 2 lines in the script that starts the application (sqldeveloper.sh for example).

export AWT_TOOLKIT="MToolkit"
export HOSTNAME=localhost

More details: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6429775

Looks like the 1.6.1 jdk will have this fixed…