How Do You Install R on a RHEL Instance of AWS?

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Problem scenario
You have a RedHat Enterprise version of Linux.  You want to install the R programming language.  What do you do?

Solution
1.  Run these six commands:

sudo yum -y install wget
cd /tmp
wget ftp://rpmfind.net/linux/epel/7/x86_64/e/epel-release-7-10.noarch.rpm
sudo rpm -ivh epel-release-7-10.noarch.rpm
sudo yum-config-manager –enable rhui-REGION-rhel-server-extras rhui-REGION-rhel-server-optional
sudo yum -y install R

2.  This is an optional step to complete these instructions. 

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How Do You Install Scala on a RHEL Instance of AWS?

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Problem scenario
You want to install Scala to a Red Hat Enterprise Linux instance of AWS.  How do you do this?

Solution
1.  Install Java:  sudo yum -y install java-1.8*

2.  Log off and log back on.

3.  Run these three commands:
curl https://bintray.com/sbt/rpm/rpm | sudo tee /etc/yum.repos.d/bintray-sbt-rpm.repo
sudo yum -y install sbt
sbt new scala/hello-world.g8

4. 

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How Do You Troubleshoot the Java Error “java.lang.Error: Properties init: Could not determine current working directory”?

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Problem scenario
You run this command:
javac -version

But you receive this error:  “Error occurred during initialization of VM java.lang.Error: Properties init: Could not determine current working directory.”

How do you solve this problem?

Solution
Log out of Linux and log back in.

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How Do You Automate a Sequence of GUI Operations to Use Sikulix as a Proof-of-Concept?

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Problem scenario
You want to try Sikulix to test it.  What do you do to implement a prototype of GUI automation of a basic procedure?

Solution
Prerequisite #1
This assumes that Sikulix has been installed.  If you do not know how, see this posting.

Prerequisite #2 (specific to this example only)
For this example we will set up an automation to open a web browser,

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How Do You Connect to Your Apache Spark Deployment in AWS?

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Problem scenario
You have recently deployed Apache Spark to AWS.  You see the EC-2 instances were created.  But you cannot access them over the web UI (even over ports 4140, 8088, or 50070).  You cannot access the instances via Putty.  You changed your normal Security Group to allow TCP communication from your work station’s IP address.  What should you do to connect to your new Spark instance for the first time?

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How Do You Deploy an Apache Spark Cluster in AWS?

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Problem scenario
You want to deploy Apache Spark to AWS.  How do you do this?

Solution
1.  Log into the AWS management console.  Once in, go to this link.

2.  Click “Create cluster” and then “Quick Create”

3. For Software Configuration, choose “Spark:…”

4. For “Security and access”, for EC2 key pair, choose the key pair you desire.

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How Do You Change the Password of the PostgreSQL Instance Account Named “Postgres”?

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Problem scenario
You want to change the password at the SQL level — not with the OS — of the user named Postgres in your PostgreSQL install.  How do you change this password?

Solution
1.  Enter the SQL database to run a DDL command.
2.  Run this command to change the user named “postgres” to the password “abcd1234” with no quotes:

ALTER USER “postgres” WITH PASSWORD ‘abcd1234’;

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How Do You Solve the Problem with Apache Web Server That Says “Invalid Mutex directory in argument file:${APACHE_LOCK_DIR}”?

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Problem scenario
Your website is not working.  When you browse to the login page, the browser loads forever.  There seems to be a problem with the web server itself.

On the back end, you run this command from the operating system’s command line:
netstat -anlp | apache2

It produces output like this:

“
[Sun Aug 06 21:03:22.088579 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_LOCK_DIR} is not defined
[Sun Aug 06 21:03:22.088682 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_PID_FILE} is not defined
[Sun Aug 06 21:03:22.088697 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_RUN_USER} is not defined
[Sun Aug 06 21:03:22.088701 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_RUN_GROUP} is not defined
[Sun Aug 06 21:03:22.088712 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sun Aug 06 21:03:22.099496 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sun Aug 06 21:03:22.099764 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sun Aug 06 21:03:22.099775 2017] [core:warn] [pid 30144] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
AH00526: Syntax error on line 74 of /etc/apache2/apache2.conf:
Invalid Mutex directory in argument file:${APACHE_LOCK_DIR}
“

What should you do to fix this?

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