Error: Could not create the Java Virtual Machine

Apparently on some versions of Java checking the Java version will give you the following error.

root@local:~# java -v
Unrecognized option: -v
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
root@local:~#

The issue being the -v or –version options are not recognized. On newer versions of Java it is recognized.

The proper way to do it is -version with only one dash

root@local:~# java -version
openjdk version "1.8.0_252"
OpenJDK Runtime Environment (build 1.8.0_252-8u252-b09-1ubuntu1-b09)
OpenJDK 64-Bit Server VM (build 25.252-b09, mixed mode)
root@local:~#

https://askubuntu.com/questions/324858/installed-jdk-by-and-have-error-could-not-create-the-java-virtual-machine

Unity Hub Failing to Launch Unity Project

While trying to launch a project in Unity I kept getting met with, nothing… Click on the project the Hub disappears and nothing happens… Tried uninstalling and reinstalling both Unity and the Unity hub.

I did receive an error similar to the following when trying to launch Unity directly.

windows\system32\msvcp120.dll is either not designed to run on windows or it contains an error

Doing some digging online shows that it has to do with the Visual C++ Redistributable runtime package which can be downloaded here

https://www.microsoft.com/en-us/download/details.aspx?id=40784

Unity was back to working normal after installing that.

More information is available at the following link.

https://forum.unity.com/threads/unity-exe-bad-image.500938/

Install Element (Matrix Client) on Ubuntu

https://element.io/get-started

Installing the Matrix client Element is fairly straight forward on Ubuntu. You should be able to copy and paste the following commands in a terminal.

sudo wget -O /usr/share/keyrings/riot-im-archive-keyring.gpg https://packages.riot.im/debian/riot-im-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/riot-im-archive-keyring.gpg] https://packages.riot.im/debian/ default main" | sudo tee /etc/apt/sources.list.d/riot-im.list
sudo apt update
sudo apt install element-desktop

fatal: [matrix2.host.com]: UNREACHABLE! => changed=false

Error while attempting to run playbook
ansible-playbook -i inventory/hosts setup.yml --tags=setup-system-user --ask-become-pass

Looks like the above issue is that Ansible is not able to authenticate with the server. By default it looks to try and use ssh keys, but I don’t have any passwordless ssh keys set up for Ansible to use so it fails while attempting to connect. The work around it to make sure you have sshpass installed and then specify –ask-pass to the end of the command.

ansible-playbook -i inventory/hosts setup.yml --tags=setup-system-user --ask-become-pass --ask-pass

When the command runs it’ll ask you for the ssh password and then use that.

[WARNING]: Could not match supplied host pattern, ignoring: matrix_servers

Error while trying to run playbook

If you get the above error when you try running

ansible-playbook -i inventory/hosts setup.yml --tags=setup-system-user

Check and verify that you have [matrix_servers] in your inventory/hosts file

That file should contain the following.

[matrix_servers]
matrix. ansible_host= ansible_ssh_user=root

Backup Matrix Synapse PostgreSQL Database

This is part of a series of posts on backing up and restoring a backup for Matrix Synapse server. Synapse was installed using the matrix-docker-ansible deployment which while a little complicated can greatly ease management later on down the road. All the main components are in docker containers so we need to use docker to access.

https://github.com/spantaleev/matrix-docker-ansible-deploy/blob/master/docs/maintenance-postgres.md#backing-up-postgresql

As the root user run

docker exec --env-file=/matrix/postgres/env-postgres-psql matrix-postgres pg_dumpall -h matrix-postgres | gzip -c > /matrix/postgres.sql.gz

This will dump the Postgres database in /matrix/postgres.sql.gz
We can use this later to restore to a new server or keep as a backup.

Configure rsnapshot on Ubuntu Server

rsnapshot is a utility that uses rsync to backup files locally or it can backup files from a remote server.

While trying to figure out a good solution for backing up an Ubuntu Server I decided to try rsnapshot, however since it can either create a local backup or pull a remote backup it needs to be configured to do that on the backup server side. It does not “push” a backup to a backup server.

Some helpful snippits from the man file.

rsnapshot will typically be invoked as root by a cron job, or series of cron jobs. It is possible, however, to run as any    arbitrary user with an alternate configuration file.
...
USAGE
        rsnapshot can be used by any user, but for system-wide backups you will probably want to run it as root.
...
NOTES
        Make sure your /etc/rsnapshot.conf file has all elements separated by tabs.  See
        /usr/share/doc/rsnapshot/examples/rsnapshot.conf.default.gz for a working example file.
    Make sure you put a trailing slash on the end of all directory references.  If you don't, you may have extra directories    created in your snapshots.  For more information on how the trailing slash is handled, see the rsync(1) manpage.

Overview

Scenario

Host A runs xyz application and host B is the backup server. We create a backup user on host A, host B then uses that user to ssh and rsync backups to itself.

  1. Create backup user
  2. Configure rysnc to be used without a password
  3. Setup SSH Key, aka Passwordless authentication (On backup server)
  4. Setup rsnapshot config (On backup server)
  5. Configure rsnapshot in crontab (On backup server)
  6. Final Testing

Create backup user

The following commands are fairly straight forward. Change backupuser to whatever you want to call your backup user.

sudo useradd -m backupuser
passwd backupuser
sudo usermod -a -G sudo backupuser

Configure rysnc to be used without a password

We need to setup the backup user to be able to use “sudo rsync” without having to input the user password. If we don’t use sudo we can’t access system files for backups. And if we have to manually input the password every time rsync runs, then the backups would not be automatic. The following link was helpful.

https://unix.stackexchange.com/questions/325100/proper-way-to-set-up-rsnapshot-over-ssh

All we need to do is create a file in /etc/sudoers.d/username and then tell it we don’t need to enter a password when “sudo rsync” is run.

sudo tee /etc/sudoers.d/backupuser <<<'backupuser ALL = (root) NOPASSWD: /usr/bin/rsync'

Setup SSH Key, aka Passwordless authentication (On backup server)

Log into the backup server

Create SSH keys. Note that since rsnapshot wants to run as root, we create the key and copy it as the root user.

sudo ssh-keygen

Accept all the defaults so we can login from the backup server without having to enter in a password.

Copy ssh key to the server we are wanting to back up

sudo ssh-copy-id backupuser@ip

enter in the password and the the key should get copied it over. Once complete, verify that you can login without having to enter in a password.

Setup rsnapshot config (On backup server)

Open up the rsnapshot config file and modify where appropriate. /etc/rsnapshot.conf

Change the path to where the snapshots are stored. By default it stores them under /.snapshots. I moved it under a local user as I am not needing to use rsnapshot to backup the local backup server files.


# SNAPSHOT ROOT DIRECTORY
snapshot_root /home/user/rsnapshot/snapshots/

Add a daily backup option under Backup levels

# BACKUP LEVELS / INTERVAL #
retain daily 6

Setup remote server to get a backup from. Replace ipaddress and directories as needed. hostname is the sever name. You can change to whatever you want.

### BACKUP POINTS / SCRIPTS ###
# LOCALHOST
# Comment or delete entries unless you want to backup those as well
# EXAMPLE.COM
backup  backupuser@ipaddress:/home/     hostname/       +rsync_long_args=--rsync-path="sudo rsync"

If you would like to back up multiple locations you can create multiple entries with different remote paths. Example locations to add

backup  backupuser@ipaddress:/etc/     hostname/       +rsync_long_args=--rsync-path="sudo rsync"
backup  backupuser@ipaddress:/usr/local/     hostname/       +rsync_long_args=--rsync-path="sudo rsync"

Verify that the config is good with

sudo rsnapshot configtest

It should return Syntax OK

Setup Crontab

sudo crontab -e

Add the following line to run rsnapshot at 3AM every day. More information about crontab can be found here.

0 3 * * * /usr/bin/rsnapshot daily

Final Testing

Manually run a backup to verify everything is set up correctly.

sudo rsnapshot daily

After it runs you can check the directory you specified in the config file to verify that the files did get copied.

GTX 1070 – ETH Hashrate and Power Consumption

Nvidia GTX 1070 ETH Hashrate and Power Consumption

The following is the estimated Hashrate and power consumption of a GTX 1070 based on web sources.

GTX 1070

Cost

Cost Used (eBay)
February 2021: $300 – $500

Hasrate for Ethash and Power Consumption

Hashrate: 26/Mhs

Power Consumption
Average: 130 W


Average Mhs Per Watt : 0.2/Mhs
Average Watts Per Mhs: 5 W

Profitability is about $2.97/day as of February 9, 2021

https://whattomine.com/coins/151-eth-ethash?hr=26&p=130&fee=0.0&cost=0.1&hcost=0.0&commit=Calculate