Superhero Ninja

Category: Tips

  • Remove host from SSH KnownHosts file without seeing the hostname

    This post is mostly a bookmark for myself. I’ve been using search engines way too often to find this command..
    The command to remove a host from a knownhosts file without seeing the actual hostname in the knownhosts file is the following:
    [code]ssh-keygen -R HOSTNAME[/code]
    (more…)

  • Comparing sed stream output in linux

    Sed is very very powerful, which is a good thing to be aware of.
    I was looking to compare the output of a sed command to the original file before I wanted to execute the sed command directly on the file and came across this handy trick.
    It works by using temporary named pipes inside the diff command.
    Contents of file:
    [code title=”contents of numbers.txt:”]
    One
    Two
    Three
    Four
    Five
    [/code]
    If I just want to remove the line which begins with “Four”, I can check my sed command like this:
    [code title=”Terminal output:”]
    joris@beanie ~
    $ diff <(sed ‘/Four/d’ numbers.txt) numbers.txt
    3a4
    > Four
    [/code]
    Awesome possum, now I know my sed command won’t destroy anything.

  • Fedora Gnome-shell abnormal high CPU usage in combination with Intel GM 4000 videocard

    I’ve been using my trustworthy thinkpad for a couple of years now, but as soon as I installed Fedora on it, it became quite slow due to gnome-shell using a huge amount of CPU power.
    My thinkpad isn’t the quickest out there, it’s a dual core machine from around 2006, but 50% CPU on two cores for just Gnome was a bit excessive.
    I’ve been searching a lot, and didn’t found any solution, until I started fiddling with Gnome-tweak-tool and saw the “Background logo” entry.
    If you haven’t yet; Install gnome-tweak-tool with the following command:
    sudo yum install gnome-tweak-tool
    The background logo is an PNG overlay on your desktop, and that overlay doesn’t work well with Intel GM cards.
    Start gnome-tweak-tool, disable that extention and see your CPU usage drop to 2%, which is what it should be.
    Selection_001

  • Easily switch between java versions using alternatives in Linux

    This approach works in several distros, I’ve been using it in Ubuntu for a while and just used it in Fedora as well.
    As a developer, you might need to switch between java versions often, this approach will come in handy then.
    We will be using the command “alternatives”, in this case to check the configuration of your Java installation. The default is most often OpenJDK, while you might need Oracle Java.
    Run “alternatives –display java” to see which versions you can currently choose from:
    [code gutter=”false”]
    [joris@today ~]$ alternatives –display java
    java – status is manual.
    link currently points to /usr/java/latest/bin/java
    Current `best’ version is /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.31-3.b13.fc21.x86_64/jre/bin/java.
    [joris@today ~]$
    [/code]
    There’s no Oracle Java yet, make sure you’ve installed Oracle Java. If you haven’t, you can check this blog post: Install Oracle Java in Fedora, Red Hat or CentOS using Yum and RPM
    When Oracle Java is installed, you can add it to your alternatives: “sudo alternatives –install /usr/bin/java java /usr/java/latest/bin/java 20000”
    Please note: I used “latest” in the command above, another options is to specifically set the version you want. This way you can install several JDK’s and switch as shown below.
    When that is finished, you can select your current flavour of Java:
    [code gutter=”false”]
    [joris@today ~]$ sudo alternatives –config java
    There are 2 programs which provide ‘java’.
    Selection Command
    ———————————————–
    * 1 /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.31-3.b13.fc21.x86_64/jre/bin/java
    + 2 /usr/java/latest/bin/java
    Enter to keep the current selection[+], or type selection number:
    [/code]
    Choose the option you want to switch between Java versions.
    As mentioned by enkouyami, please check if you need to use update-java-alternatives instead of alternatives. The use of alternatives was valid when I wrote the post, but might not be working anymore!

  • Select an XML tag or node using Oracle PL SQL

    Hi guys,
    I’ve been using this trick for a while and it’s quite useful when querying Oracle Service Bus logs. I found myself trying to explain this one to a colleague and thought it made a nice post 🙂
    Let’s start with the basic command:
    extractvalue
    Which translates into:
    [code language=”sql”]
    SELECT EXTRACTVALUE(
    xmltype(xml_val),
    ‘/xml-fragment/tns:product’,
    ‘xmlns:tns="http://example.org/"’,
    ‘xmlns:ans="http://anothernamespace.org/"’,
    ‘xmlns:yans="http://yetanothernamespace.org/"’
    )
    x
    FROM xml_table
    [/code]
    Note: the first argument is being cast from CLOB to XMLTYPE and that you can keep adding namespaces at the end by adding commas.
    I’ve added three rows in my table “XML_TABLE” for this example:
    [code language=”XML”]
    ROW1:
    <book category="WEB">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
    </book>
    ROW2:
    <book category="CHILDREN">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
    </book>
    ROW3:
    <book category="WEB">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
    </book>
    [/code]
    Next we’ll query our XML_TABLE:
    [code language=”sql”]
    SELECT
    EXTRACTVALUE( xmltype(xmlval), ‘/book/title’ ) AS title,
    EXTRACTVALUE( xmltype(xmlval), ‘/book/author’ ) AS author,
    EXTRACTVALUE( xmltype(xmlval), ‘/book/year’ ) AS year,
    EXTRACTVALUE( xmltype(xmlval), ‘/book/price’ ) AS price
    FROM xml_table;
    [/code]
    Which results in this output:
    Workspace 1_034
    Awesome, right!? 🙂
    (more…)

  • Bash: Shortcuts to your favorite directories with CDPATH

    This is a fairly handy trick.
    I’m always logging in to different servers, which all have a different location for their logs. With this trick you can login and just type “cd logs” from anywhere.
    First we will add our directory to the CDPATH variable:
    [code language=”Bash”]
    joris@badattitude /data/share/my_domain
    $ echo $CDPATH
    joris@badattitude /data/share/my_domain
    $ export CDPATH=/data/share/my_domain
    joris@badattitude /data/share/my_domain
    $ echo $CDPATH
    /data/share/my_domain
    [/code]
    Then we’ll check if it is working:
    [code language=”Bash”]
    joris@badattitude ~
    $ cd logs
    /data/share/my_domain/logs
    joris@badattitude /data/share/my_domain/logs
    $
    [/code]
    Awesome, we’ve arrived in our logs directory straight from our homedir!

  • SSH Remote Execute command, multiple command and with interaction

    This article shows how to execute remote commands via ssh, but you’ll send the commands from your own shell.
    [code highlight=”1″]
    ssh my_server ‘ls -l /home/my_home_dir’
    [/code]
    This will result in this output:
    [code highlight=”1″]
    $ ssh ae2 ‘ls -lha ~’
    total 36K
    drwxr-xr-x 2 joris joris 4.0K Jan 23 11:42 .
    drwxr-xr-x. 5 root root 4.0K Jan 23 11:41 ..
    -rw-r–r– 1 joris joris 54 Jan 23 11:41 .bash_logout
    -rw-r–r– 1 joris joris 507 Jan 23 11:41 .bash_profile
    -rw-r–r– 1 joris joris 213 Jan 23 11:41 .bashrc
    -rw——- 1 joris joris 51 Jan 23 11:42 .history
    -rw-r–r– 1 joris joris 171 Jan 23 11:41 .kshrc
    -rw-r–r– 1 joris joris 375 Jan 23 11:41 .profile
    -rw-r–r– 1 joris joris 153 Jan 23 11:41 .vimrc
    [/code]
    What’s even better, is that you can run multiple commands separated with a semi colon, like this:
    [code highlight=”1″]
    ssh my_server ‘ls -l /home/my_home_dir;whoami’
    [/code]
    And the best trick is this one, user input with an interactive command, sending input and output back and forth!
    [code highlight=”1″]
    ssh -t my_server ‘vi ~/.bash_profile’
    [/code]

  • Start JDeveloper on Ubuntu Linux for Fusion Middleware SOA Suite 12c

    Okay, this was a bit awkward, I installed the quick start 12c Fusion Middleware and was well underway to getting it all up and running.
    Untill I closed JDev and couldn’t find the executable anymore..!
    For anyone who had the same embarrassing situation, it’s located here:

    *MiddlewareInstallationFolder*/jdeveloper/jdev/bin/jdev

  • Find Java JRE location on Ubuntu Linux

    Everybody knows that the java executable is located in /usr/bin/java , but what if you need the JDK / JRE location itself?
    Just using “whereis” will not get you there, that will point you to the /usr/bin/java point.
    joris@howlingmad: ~_011
     
    So, let’s find out a but more about /usr/bin/java:

    ls -l /usr/bin |grep java

    joris@howlingmad: ~_012
     
    Awesome, this will lead us somewhere, it’s a symlink to /etc/alternatives/java
    So let’s do the same there:

    ls -l /etc/alternatives/ |grep java

    And we’ve hit the jackpot, among the lines here, there’s a bunch of lines pointing us to the JRE location:
    joris@howlingmad: ~_013
     
    As you can see in the screenshit, our java executable within the JRE location is:

    /usr/lib/jvm/java-7-oracle/jre/bin/java

    Which means the JRE location is:

    /usr/lib/jvm/java-7-oracle/jre

     
     
     

  • Oracle SQL Developer 4 does not run on Oracle Java 7 on Ubuntu 14.04

    Wow, ain’t this awkward :-). I cannot run Oracle SQL Developer 4 (4.0.2) on Ubuntu with Oracle JDK 7..

    To be complete: when running SQL Developer with JDK 7 from Oracle itself, displays the following error;

    joris@dipshit:~/programs/sqldeveloper$ ./sqldeveloper.sh
    Oracle SQL Developer
     Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
    LOAD TIME : 968#
    # A fatal error has been detected by the Java Runtime Environment:
    #
    # SIGSEGV (0xb) at pc=0x6aa69be0, pid=9537, tid=1836366656
    #
    # JRE version: Java(TM) SE Runtime Environment (7.0_65-b17) (build 1.7.0_65-b17)
    # Java VM: Java HotSpot(TM) Server VM (24.65-b04 mixed mode linux-x86 )
    # Problematic frame:
    # C 0x6aa69be0
    #
    # Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
    #
    # An error report file with more information is saved as:
    # /home/joris/programs/sqldeveloper/sqldeveloper/bin/hs_err_pid9537.log
    #
    # If you would like to submit a bug report, please visit:
    # http://bugreport.sun.com/bugreport/crash.jsp
    #
    /home/joris/programs/sqldeveloper/sqldeveloper/bin/../../ide/bin/launcher.sh: line 1193: 9537 Aborted (core dumped) ${JAVA} "${APP_VM_OPTS[@]}" ${APP_ENV_VARS} -classpath ${APP_CLASSPATH} ${APP_MAIN_CLASS} "${APP_APP_OPTS[@]}"

    Solution: Run Oracle SQL Developer with OpenJDK

    First we’ll need to install OpenJDK:

    sudo apt-get install openjdk-7-jdk 

    Then we’ll need to change the path which SQL Developer uses. This was asked once when you first started it and it is saved in the following path:

    ~/.sqldeveloper/4.0.0/product.conf

    The file [[ product.conf ]] contains the value SetJavaHome, we need to change this to the OpenJDK path;

    If you're running 32 bit Ubuntu:

    SetJavaHome /usr/lib/jvm/java-7-openjdk-i386

    Or if you're running 64 bit Ubuntu:

    SetJavaHome /usr/lib/jvm/java-7-openjdk-amd64

    After saving this change, you can start SQL Developer on Ubuntu 14.04 and it will use OpenJDK 7, without changing your regular Java settings!