Sunday, January 15, 2017

Ubuntu 16.10 is not booting because of error stick: gfxboot.c32: not a COM32R image


When trying to boot Ubuntu 16.10 from USB stick, it fails to boot from following error


Missing parameter in configuration file. Keyword: path
gfxboot.c32: not a COM32R image
boot :

This error had been reported since the Ubuntu versions 14.04. Discussion regarding this can be found here.


Therefore as a solution for this issue, I figured out following workaround.


  1. Whenever this error is getting thrown during startup, press the TAB key
  2. Choose among options like live, live-install etc ... I chose the live option.
  3. Next press enter.
This will take into the live OS and from thereon wards, Ubuntu 16.10, can be installed using USB stick.

How to prepare bootable usb stick for Ubuntu 16.10


In this post I will explain to create a bootable USB disk to install Ubuntu 16.10.

Prerequisites


  • USB Flash disk with at least 2 GB free space.
  • Ubuntu 16.10 ISO image


Steps

Install gparted tool to enable formatting of the USB disk.
Install mksub tool to wipe out the first mega byte of file system and create a new a partition of
  same file system.

- Run Startup Disk Creator/USB Creator


  1. Insert the usb disk and run the Startup Disk Creator.
  2. Choose the image file and make sure to format the USB stick using usb creator's graphical user interface.

 


Once you click the right-most button, eventually it will create a bootable USB disk for Ubuntu 16.10.

Now as the final step after using usb stick for boot-able disk task, in order to restore usb disk to standard storage drive we can use the mksub-nox utility.

Monday, January 9, 2017

How to fix the ERROR 1698 (28000): Access denied for user 'root'@'localhost'


After upgrading from MySQL version 5.5 to 5.7, whenever I tried to log in to the database as non sudo user it throws following error. But I was able to log into the system as sudo user without any issues.



firzhan@firzhan-wso2:/etc/mysql$ mysql -u root -padmin 
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1698 (28000): Access denied for user 'root'@'localhost'


I followed following steps to do a quick fix

  • First connect to the mysql as sudo user.
  • Check the users presently available in the databases's user table.
  1. SELECT User,Host FROM mysql.user;
    +------------------+-----------+
    | User             | Host      |
    +------------------+-----------+
    | admin            | localhost |
    | root             |    *      |
    | root             | %         |
    | mysql.sys        | localhost |
    | root             | localhost |
  • Delete all the entries/accounts related to root user.
  • mysql> DROP USER 'root'@'localhost';
    Query OK, 0 rows affected (0,00 sec)
    
    mysql> DROP USER 'root'@'*';
    Query OK, 0 rows affected (0,00 sec)
    mysql> DROP USER '%';
    Query OK, 0 rows affected (0,00 sec)
  • Again insert an entry for root user in the table.
  • mysql> CREATE USER 'root'@'%' IDENTIFIED BY '';
    Query OK, 0 rows affected (0,00 sec)
  • Grant relevant permissions for that particular user of the database and make sure to flush the privileges.
  • mysql> GRANT ALL PRIVILEGES ON *.* TO 'root'@'%';
    Query OK, 0 rows affected (0,00 sec)
    
    mysql> FLUSH PRIVILEGES;
    Query OK, 0 rows affected (0,01 sec)
  • Exit and try to reconnect to the terminal without sudo.  

Wednesday, February 10, 2016

How to perform correlation during process instance startup



Correlation

Let us assume we have set of BPMN process instances with various values for a given variable "var1". Correlation is a mechanism of identifying the process instance with the given value of variable "var1". Correlation can be done for single/multiple variables. 

In other word, correlation is a process of finding the instance with similar set of variables. More information on correlation and how the REST API provided by WSO2 Business Server 3.5.1 can be used to correlate among various process instances can be found here.

In this article we are going to provide further description on a newly introduced API which aggregates both instances startup and correlation on a single API call. This API provides following functionality. 
  1. If the instance with the given variable state exists, API will return with the existing process instance information.
  2. Or if the instance exist with the searched variable state, API will correlate with the process instance and continue the execution.
  3. Or if there are no instances exist with defined variable state, new instance will be created and returned back to the client.

This use case can be explained using following BPMN workflow diagram.


This diagram has following properties.
  1. A start message :- This message is denoted with "startProcess"
  2. Two intermediate message catching events :- Those are "updateRequest" and "recieveResponse"

Requirements
Once the BPMN Archive file is deployed to the server, BPMN instance can be started by hitting the url https://localhost:9443/bpmn/runtime/process-instances with following request.

Prior to sending the request please make sure to set the following header values.
Those are
  • Content-Type: application/json or application/xml
  • Accept: application/json or application/xml
  • Authorization: Basic base64encode(username:password)

Authorization header has to be set with the base64 encoded values of "username:password".


This is a sample request used for creating a process instance



If we want to enable the correlation during process instance creation along with the initial json/xml request message following Boolean flags should be enabled. Those are
  • skipInstanceCreationIfExist
  • correlate
In addition to this, we did a slight modification to the original request to cater correlation support during process instance creation. That change can be briefed shortly in following way.
  • In the previous process instance creation message contains all the variables with in the variables json array.
  • but with the introduction of correlation, some times not all the variables mentioned within the variables json array is necessary for correlation task.
  • Therefore, we introduced a new json array named "additionalVariables" to include the variables which are not relevant to correlation.
  • But eventually once the correlation is completed and if the process instance is found, before prior to continuing with the execution of the workflow, the process instance will be updated with the variables inside the json array  "additionalVariables".
Last but not least we have included the "messageName" variable to be included in the process instance request message.

Now lets go through the requests.

Scenario 1

As per this scenario we are creating the instance for the first time.




You will get the following response.





Scenario 2

In this scenario, we are not going to correlate with the existing instance. We are just going to look whether are there any instance exist with the given variable state. If there is an instance with the given state, it will return with the instance information.

Note the variable "correlate" has been made false. But "skipInstanceCreationIfExist" has been made true.
So there will be neither instance creation nor correlation.

This is the sample request




You will get the following response





Scenario 3

This scenario mainly focuses on correlation. You can notice that we are only interested in correlating with "corrId" variable. The other both variables are being added to the "additionalVariables" field. 

This is the sample request.





And in the successful completion of execution, you will get HTTP Header with 204 (NO-CONTENT) message.
Eventually, you can notice all the variables are being updated in the instance as well.






This method will only work with message based correlation.

Wednesday, February 3, 2016

How to upgrade the Ubuntu version 13.10 with the updated package repository archives to 14.04


I have been using ubuntu version 13.10 for a while. After some time, ubuntu stops supporting the older version and it keeps throwing error while trying to update the 13.10 packages. 

Therefore in order to fix this issue, you can either update the OS version to the latest one or you can update the package repository archives of archive.ubuntu.com  and  security.ubuntu.compackage repository domain names with  old-releases.ubuntu.com

This has been explained in the post to isolate the Ubuntu update error.

But not it's time to update the Ubutnu to 14.04. In order to perform the update you have to follow the following steps.

The semicolon differentiates each individual commands to let us paste together in the terminal.

sudo apt-get clean ;
cd /var/lib/apt ;
sudo mv lists lists.old_`date '+%Y%m%d_%H%M%S'`   ;
sudo mkdir -p lists/partial ;
sudo apt-get clean ;
sudo apt-get update

Sometimes the above commands may fail. In that case you can execute the following set of commands.
sudo sed -i 's/saucy/trusty/g' /etc/apt/sources.list ; sudo apt-get update ; sudo apt-get upgrade ;

Monday, January 18, 2016

How to perform authorizations during BPMN process instance initialization


When designing the BPMN workflow, users can define either the candidate start users or groups.  This permits only the allowed users to start an instance.

Requirements

Candidate start users/groups can be configured like this in Activiti eclipse designer



candidate users/groups can be defined either directly or by defining variables. T

The direct way is to define the user name or group name like admin1, manager etc ...

On the other hand we can use the variables to define the user name or group name as well like ${user1}, ${mgr1}.

The value for these defined variables can be defined in 2 ways. Those are static way and dynamic way.

Static Way

This is similar to variable declarations. This value can be set under the "Data Objects" section of process definition.





Dynamic Way

When invoking the process definition with the REST start call,  you can define the dynamic variable inside "variables" json array.

When starting the process instance following URL should be hit with the json message request
https://localhost:9443/bpmn/runtime/process-instance.

Prior to sending the request please make sure to set the following header values.
Those are

  • Content-Type: application/json or application/xml
  • Accept: application/json or application/xml
  • Authorization: Basic base64encode(username:password)

Authorization header has to be set with the base64 encoded values of "username:password".


In the event of authorization failure REST API will return with 401.

Monday, January 11, 2016

How to Skip the BPMN instances creation with same variable state in WSO2 BPS


This post describes on how to skip the BPMN instance creation with same variable state in
WSO2 Business Process Server 3.5.1 .

Currently in the BPMN Rest API, process instance start operations are not conditional. But there are occasions, process instances  should not be initialized when ever there is a already created instance with same variables state (variable values).

This is the sample request that we use to start a process instance.



In order to make sure that only single instance is being created for an unique value, we can use the "businessKey" attribute. Although this is the most preferred way this won't work every time.

This may fails on following occasions.

  • Business key attribute value can not be updated during the run time. Therefore, If the business key is not known before the instance creation, we shall not be able to update it.
  • In the event of considering more than one variables to determine the instance state, we can't use the business key attribute.

Therefore as a solution to those issues, WSO2 Business Process Server 3.5.1 introduces a new Boolean flag "skipInstanceCreationIfExist" in the request.  By default the value of the flag is false.

This sample request can be used to start the process instance


This flags looks for the process instances with variables which have the values  defined in the process instance request. In the event of existence of any process instances with the same variables state, instance creation will be skipped.