CodeMarvels – All's the Code !

Change the datacenter set in cassandra-rackdc on Ubuntu

Posted on July 19, 2021 by Kj / 0 Comment

Problem: Changing just the datacenter name in cassandra-rackdc.properties gives the error:

Cannot start node if snitch's data center [newName] differs from previous data center [oldName]. Please fix the snitch configuration, decommission and rebootstrap this node or use the flag -Dcassandra.ignore_dc=true.

Solution:
If you are just beginning to setup you cassandra cluster, and is ok to reset the data to bootstrapped state, do this

sudo service cassandra stop
sudo rm -R /var/lib/cassandra
sudo mkdir /var/lib/cassandra
sudo chown cassandra /var/lib/cassandra
sudo service cassandra start

If you need to persist the existing data, do this

sudo vi /etc/cassandra/cassandra-env.sh
# edit the JVM_OPTS line to make it look like below
JVM_OPTS=\"$JVM_OPTS -Dcassandra.ignore_rack=true -Dcassandra.ignore_dc=true\"

sudo service cassandra restart

This should normally resolve the dc name correction in rack-dc properties file.

Notes/Technology

RabbitMQ installation fails in in the last leg of setting up in ubuntu 20.04

Posted on June 2, 2021 by Kj / 0 Comment

Error:

Setting up rabbitmq-server (3.8.16-1) …
Job for rabbitmq-server.service failed because the control process exited with 
error code.
See "systemctl status rabbitmq-server.service" and "journalctl -xe" for details.
invoke-rc.d: initscript rabbitmq-server, action "start" failed.

Reason: libtinfo.so library missing.

Solution:

sudo apt install libncurses5

Note: No need to reattempt the installation.

Uncategorized

An “eat dosa!” reminder for busy kids :)

Posted on May 24, 2021 by Kj / 0 Comment

Here is a one hour HTML app that you can use to repeat recorded audio to remind your busy kids they have to finish that food on the table, while watching their favorite videos on YouTube.

Launch Dosa Reminder HTML App

To use the app is this simple –

Click on record button. Give permission to access microphone if it asks for it.
The recording automatically stops in 4 seconds and replays what it recorded. You can re-record till you are satisfied with the playback.
Now you can set the number of seconds of interval, between which the above audio has to be repeated.
Click on “Start Reminder” button to start the reminders.
When your kid is done eating, you can stop the reminders by clicking “Stop Reminder” button

Happy parenting !

Miscellaneous

Enable dark mode for Chrome on desktop

Posted on May 3, 2021 by Kj / 0 Comment

Dark mode is great to protect your eyes, more so if you are a coder.

Here is how you can apply dark more on chrome on your desktop –

In the address bar paste this address : chrome://flags/#enable-force-dark
Change the setting “Force Dark Mode for Web Contents” from default to “enabled”

That’s it. Now you can have easy on eyes theme on Chrome, just like your IDE !

Uncategorized

NPM install gives error : Cannot find module ‘semver’

Posted on March 20, 2021 by Kj / 0 Comment

Problem:
We get this error when we do npm install –

Error: Cannot find module ‘semver’
Require stack:

/usr/share/npm/lib/utils/unsupported.js
/usr/share/npm/bin/npm-cli.js
at Function.Module._resolveFilename (node:internal/modules/cjs/loader:924:15)
at Function.Module._load (node:internal/modules/cjs/loader:769:27)
at Module.require (node:internal/modules/cjs/loader:996:19)
at require (node:internal/modules/cjs/helpers:92:18)
at Object. (/usr/share/npm/lib/utils/unsupported.js:2:14)

Reason:
Version issues

Fix:
Run these commands

sudo rm -rf /usr/local/bin/npm /usr/local/share/man/man1/node* ~/.npm
sudo rm -rf /usr/local/lib/node*
sudo rm -rf /usr/local/bin/node*
sudo rm -rf /usr/local/include/node*

sudo apt-get purge nodejs npm
sudo apt autoremove
sudo apt-get install nodejs npm

Try now. Should be fixed !

Notes/Technology

Fix : Docker node down after restart

Posted on November 5, 2020 by Kj / 0 Comment

Problem: One of the docker nodes does not start up after restart. Error in the log is

msg="error removing task " error="incompatible value"

Reason: Docker swarm and network stack sucks.

Fix:

 
sudo service docker stop 
rm -rf /var/lib/docker/swarm
sudo service docker start
docker swarm init

Notes/Technology

IP Telephony – bit rates of audio formats, and other notes

Posted on October 29, 2020 by Kj / 0 Comment

The bit rates for the most common audio formats –

ALAW	8 BITS
ULAW	8 BITS
PCM	16 BITS SIGNED/UNSIGNED
ADPCM	8 BITS

The endian-ness for more than one byte systems:

Motorola Processors	Big Endian
Intel Processors	Small Endian

Notes/Technology

Fix: Cannot start container Subnet sandbox join failed error from docker

Posted on October 27, 2020 by Kj / 0 Comment

Error : Few docker containers don’t start up. In the /var/log/syslog they give the error “Cannot start container Subnet sandbox join failed…”

Fix: Restart the machine !

Optionally you can try the steps mentioned here, and see that they don’t work, and restart the machine anyway 🙂

Notes/Technology

React Ajax call on load gives : “Error: Should not already be working.”

Posted on September 2, 2020 by Kj / 0 Comment

Problem : On page refreshes, the ajax calls in the componentDidMount functions throws the error : “Error: Should not already be working.”

Reason : Probably the ajax request is called before the react’s async calls framework is initialized.

Fix: Run within a timeout function
Eg –

componentDidMount() {
    setTimeout(() => {
      $.ajax(...);
    }, 400);
  }

Notes/Technology

Fix : The repository ‘http://archive.ubuntu.com/ubuntu disco-backports Release’ no longer has a Release file.

Posted on July 26, 2020 by Kj / 0 Comment

Issue : When doing an apt update, we get the this error.
The repository ‘http://archive.ubuntu.com/ubuntu disco-backports Release’ no longer has a Release file. N: Updating from such a repository can’t be done securely, and is therefore disabled by default.

fix :

[bash] vi /etc/apt/sources.list replace all occurrences of archive.ubuntu.com to old-releases.ubuntu.com [/bash]