How to add more swap space on Linux

An easy method if you don't want to repartition the whole disk.

dd if=/dev/zero of=/tmp/swap.img bs=1M count=256

Set up a loop device and connect the dummy file with that device:

losetup /dev/loop3 /tmp/swap.img


Then, it's just formatting the loop device:

mkswap /dev/loop3


It also needs activation:

swapon /dev/loop3


Voilá, there is a new swap partition.

To remove it:

swapoff /dev/loop3
losetup -d /dev/loop3
rm /tmp/swap.img


Enable LAN access for Oracle XE admin web on Ubuntu

Edit your .bashrc file to include the lines:

ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
PATH=$PATH:$ORACLE_HOME/bin
export ORACLE_HOME
export ORACLE_SID=XE
export PATH


Log out. Log in again.

Then start up sqlplus:

sqlplus sys as sysdba


And then just execute:

SQL> exec dbms_xdb.setListenerLocalAccess (l_access => FALSE);


Generating unique file names with SimpleDateFormat and Random

Sometimes it is necessary use an unique file name when writing a voice recording with Cisco IP IVR or Cisco Unified Contact Center Express (UCCX). The CCX Editor does support Java, so we can easily do this: let's just create a timestamp with the date and time including milliseconds, then just append a random number between 0 and 9999. Yes, I know there is still some chance this will generate the same string, but this isn't something I cannot live with.

First, create the timeStamp string using this code block:


{
String DATE_FORMAT="yyyyMMdd_HHmmss-SSS";
java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat(DATE_FORMAT);
return sdf.format(new Date());
}


Then generate a random number with this code:


{
java.util.Random nahcis = new java.util.Random();
return nahcis.nextInt(9999).toString();
}


And in the end just concatenate:


"recording_" + timeStamp + "_" + randomNumber


This will create a string like:

"recording_20100120_134541-214_6592"


And this is something you can use as the file name.

Servlets cannot look into their own install directory? Solution.

This applies to a Tomcat 5.5 installation running on a Ubuntu 8.04 server (and, all Ubuntu versions I know).

If you write a servlet that needs to read a file which is in the servlet's WEB-INF directory, for instance, a config.xml, Tomcat, or more precisely, the Java Security Manager will not let you.

(Interestingly, Tomcat that comes with CentOS, will do. Hmm.)

What I did is turning off the security manager in the /etc/init.d/tomcat5.5 file.

Task for the rest of the week: find out how to enable the required thing without turning off the Security Manager.

Using apt behind a proxy in Ubuntu

It's really easy. All you have to do is:


http_proxy='http://someproxy:someport"
$export http_proxy


and voila, you can apt-get update, apt-get install, whatever.