Miscellaneous

Take care of this when you buy a new laptop bag..

Posted on by Kj / 0 Comment

Just thought of sharing this.

If you buy a new laptop bag, you have to be careful to remove the small sachets that contain small silica balls (or whatever they are. See photo).

I allowed them to remain in the bag (new one from American Tourister),  the sachets broke, and the released silica balls entered the USB, HDMI, LAN and audio slots of the laptop.

While I could get rid of them from other slots, a nasty particle is still stuck in the 3.5 mm audio slot. (Because I didn’t know of it and pushed in the audio jack, which took the darn ball further down the slot)

So yes, remember to to remove such sachets from your laptop bag before you use them.

Notes/Technology

Spring boot + Websockets : Connection getting closed by itself.

Posted on by Kj / 0 Comment

Problem : Getting the message “Websocket already in CLOSED or CLOSING state” from browser console after sending the first message.

Reason: The packet size is larger than the one set for Text/Binary message on Spring WebSocket handler.

Fix: Increase size limit for individual packages/frames in the Spring handler –

[java]
@Override
public void afterConnectionEstablished(WebSocketSession session) throws Exception {
session.setTextMessageSizeLimit(1024 * 1024);
session.setBinaryMessageSizeLimit(1024 * 1024);
log.info("Connection established");
}
[/java]

Notes/Technology

Fixed : “Json Array should begin with [” error on UTF-8 or UTF-16 files

Posted on by Kj / 0 Comment

Problem : JSON file which store top level JSON arrays just wouldn’t parse (using org.json library), and gives out an error message like – “Json Array should begin with [ …..”. Editors like Vim or Gedit or IntelliJ show no errors (or any character before “[” )in these files.

Reason :  Byte order marker character is prefixed to the file content (this was probably added when I converted the files from UTF-16 to UTF-8).

Fix:

  1. Open the file in Vim.
  2. Run command-   :set nobomb
  3. save and exit. (:wq)
Notes/Technology

Bash on VNC session – Tabs do not auto complete

Posted on by Kj / 0 Comment

Problem : Pressing Tab keys not auto-completing when using Bash within a VNC session (to guest VM running on Ubuntu and XFCE.)

Reason : Unknown, possibly tabs are caught and consumed by the window switch handler.

Fix:

  1. vi ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-keyboard-shortcuts.xml
  2. search for
    • <property name=”&lt;Super&gt;Tab” type=”string” value=”switch_window_key”/>
  3. Change the above line to –
    • <property name=”&lt;Super&gt;Tab” type=”empty”/>
  4. Reboot the machine.

Reference : https://ubuntuforums.org/archive/index.php/t-1771058.html

Notes/Technology

Fix: Unable to connect to RabbitMQ server from remote clients

Posted on by Kj / 0 Comment

Problem : When connected from a remote client, this error is thrown (at client) – An unexpected connection driver error occured (Exception message: Socket closed)

Reason : As per default settings, the default user (“guest”) can access only from localhost (or Loop back IP).

Fix: Remove “guest” user from “loopback_users”. This is how –

[bash]
sudo vi /etc/rabbitmq/rabbitmq.config # create new file if in Ubuntu
[{rabbit, [{loopback_users, []}]}]. # Add this line, save and quit vim.

sudo rabbit-server restart # this mostly fails. So we grep & kill in next steps.

ps auxx|grep rabbitmq # gives multiple processes

kill -9 3099 3288 3289 10263 # process-Ids are place holders

sudo rabbitmq-server start

[/bash]

Should be able to connect from remote clients now.

Notes/Technology

Increase Zuul timeouts for backend BOSH or Comet servers

Posted on by Kj / 0 Comment

This is how I could make Spring Zuul work with my backend XMPP (over BOSH) server which had a hanging post of 5 mins.
Please find the relevant settings in application.yml here –

 
[bash]
zuul:
add-host-header: true
host:
connect-timeout-millis: 5000
socket-timeout-millis: 601000

hystrix:
command:
default:
execution:
isolation:
thread:
timeoutInMilliseconds: 601000
xmppServer:
execution:
timeout:
enabled: false;

ribbon:
eureka:
enabled: false
xmppServer:
ribbon:
ReadTimeout: 601000
ConnectTimeout: 601000

[/bash]

Notes/Technology

MySQL Data migration from one server box to another

Posted on by Kj / 0 Comment

 

Here’s a quick way to move data from one MySQL server to another

Let source box be ServerOne, and the target box be ServerTwo. (user-names and schema names are indicative) –

  1. On ServerOne,
    1. mysqldump -u username -p db_name > data-dump.sql  (provide password when asked)
    2. scp data-dump.sql serverTwoUsername@ServerTwo:~/
  2. On ServerTwo
    1. mysql -u username -p
    2. create schema schema-name;
    3. exit
    4. mysql -u username -p -h localhost schema-name < data-dump.sql
    5. verify
      1. mysql -u username -p
      2. use schema-name;
      3. show tables;

Should be done.

Notes/Technology

Fix : Cassandra not accessible from outside the local machine.

Posted on by Kj / 0 Comment

Problem: In Single node setup of cassandra, after installation and starting Cassandra, the native port (9042) is not accessible from outside the local box.

Reason : By default Cassandra binds to the loopback IP or localhost.

Fix:

[bash]

sudo vi /etc/cassandra/cassandra.yaml

# Comment out below line
#listen_address: localhost

# Uncomment below lines
listen_interface: eth0
listen_interface_prefer_ipv6: false

#Comment out below line
# rpc_address: localhost

#Uncomment below lines
rpc_interface: eth0
rpc_interface_prefer_ipv6: false

seeds: "127.0.0.1,192.168.14.49" #Added the LAN address after a comma

[/bash]