How Do You List Directories Traits without Traversing into Their Contents?

0 Comments

Problem Scenario
You want to find out the permissions, ownership and groups associated with various subdirectories in Linux. You do not want to display the lengthy contents of these directories. How do you use the ls command to show the attributes of the directories themselves and not the contents of the directories?

Solution
From a Linux command prompt, run this command:  ls -ld /parentdirectory/

For PowerShell to list files without traversing into their contents use either of these two commands:
dir
ls

…

Continue reading “How Do You List Directories Traits without Traversing into Their Contents?”

How Do You Create a New User with DSC?

0 Comments

Problem scenario
You are using Windows Server 2019. You want to create a new local user. You don’t want the user to be a member of the local Administrators group (which allows remote logins). What do you do?

Solution

Prerequisites
i. Install DSC. If you need assistance, see this posting.
ii.a. Make sure the server has been added to its own TrustedHosts configuration settings.

…

Continue reading “How Do You Create a New User with DSC?”

How Do You Troubleshoot Desired State Configuration Problems where Actions Are Not Working or Software Is Not Installing?

0 Comments

Problem scenario

You run a Start-DscConfiguration command in PowerShell like this:

Start-DscConfiguration -Path . -Wait -Verbose

You get an error message that the installation failed. The message may say something like this:

Start-DscConfiguration : The computer name was not specified and the configuration directory does not have any configuration files.

CategoryInfo : NotSpecified … ArgumentException
FullyQualifiedErrorId : System.ArgumentException, Microsoft.PowerShell.DesiredStateConfiguration.Commands.StartDscConfigurationCommand

What should you do?

…

Continue reading “How Do You Troubleshoot Desired State Configuration Problems where Actions Are Not Working or Software Is Not Installing?”

How Do You Create Docker Containers To Have Unique IP Addresses?

0 Comments

Problem scenario
How do you create Docker containers to have unique IP Addresses (but not the default 172.x.x.x type)?

Solution
(If you need help installing Docker, see this posting.)

Create new IP addresses with these commands (with sudo in front of them, preferably, or less preferably as the root user):

ip addr add 33.33.33.38/28 brd + dev eth0
ip addr add 33.33.33.39/28 brd + dev eth0
ip addr add 33.33.33.40/28 brd + dev eth0

# Replace the IP addresses and subnet masks as you desire

Then use a modified version of this command:
docker run -p 33.33.33.38:80:80 repositoryName:versionDesignation /bin/bash
# You can use the “docker images” command to find the “repositoryName” and “versionDesignation”
# The IP address and port mapping (from Linux server to Docker container) can be substituted as needed

Two or more containers on the same Docker host can use port 80 using this method. 

…

Continue reading “How Do You Create Docker Containers To Have Unique IP Addresses?”

How To Create IP Addresses On a Linux Server without Corresponding NICs

0 Comments

If you do not want to create new interfaces, just new IP addresses, use these commands:

ip addr add 33.33.33.38/28 brd + dev eth0
ip addr add 33.33.33.39/28 brd + dev eth0
ip addr add 33.33.33.40/28 brd + dev eth0

# Replace the IP addresses and subnet masks as you desire.

The IP addresses will go away upon rebooting.  You may want multiple IP addresses on new “semi-virtual” interfaces on a Linux server. 

…

Continue reading “How To Create IP Addresses On a Linux Server without Corresponding NICs”

Troubleshooting DSC for Configuration Management (Problem and Solution)

0 Comments

Background:  DSC is a toolkit of PowerShell cmdlets that enable you to do configuration management.  It can allow you to do CM tasks with Windows and Linux machines (https://msdn.microsoft.com/en-us/powershell/dsc/LnxGettingStarted).

Problem/Scenario:  You are trying to use this PowerShell command (e.g., to test your Desired State Configuration tool):

Enter-PSSession -ComputerName goodServer -Credential jdoe

# where goodServer is a Windows server on the network and jdoe is a local user account on the goodServer machine.

…

Continue reading “Troubleshooting DSC for Configuration Management (Problem and Solution)”

What does the I.T. term “bootstrap” mean?

0 Comments

Bootstrap

Definition 1 (transitive verb) of bootstrap:  To turn on a computer so that the operating system is completely functional.  Source:  The fifth definition of “bootstrap” in Dictionary.com is specific to “computers.” 

Definition 2 (transitive verb) of bootstrap:  To intentionally initiate multiple subprocesses (especially a primarily automatic sequence of often incremental subprocesses), as in a batch execution, from a single file or action.

Examples of definition 2: 
“Between the advent of handy tools,

…

Continue reading “What does the I.T. term “bootstrap” mean?”

How Do You Troubleshoot the Docker problem “Error response from daemon: Cannot start container”?

0 Comments

Problem scenario
Sometimes you try to start a Docker container but there is a problem.  For example you try:
docker start <containerID
But you receive this: “Error response from daemon: Cannot start container <containerID: failed to create endpoint <nameon network bridge: ip tables failed: iptables –wait -t nat -A DOCKER -p tcp -d 0/0 –dport 80 -j DNAT –to-destination x.x.x.x:80 ! -i docker0: iptables: No chain/target/match by that name.”
​
Solution
cd /var/lib/docker/network/files/
ls -lh /tmp/forposterity
mkdir /tmp/backupdir
mv /var/lib/docker/network/files/ /tmp/backupdir
systemctl restart docker #change this command depending on your distribution and version of Linux to restart Docker services

…

Continue reading “How Do You Troubleshoot the Docker problem “Error response from daemon: Cannot start container”?”

How To Port Forward (redirect traffic destined for an IP address to a specific port)

0 Comments

Scenario:  On a Linux server, it can be useful to send traffic destined to a certain IP address to a different port on the server.  The listening service could be unique insofar as its port number has been designated.  The listening service could be a Docker container or a guest virtual machine.
Method:  iptables -t nat -A PREROUTING -i eth3 -p tcp –dport 80 -j DNAT –to 91.91.91.91:81
Explanation: 

…

Continue reading “How To Port Forward (redirect traffic destined for an IP address to a specific port)”

Saving a Docker Image and Using It On A Different Server

0 Comments

Problem Scenario
Sometimes the “docker save” command does not work as you would expect.  You run the command on a Docker host, but it does not work.  You might even try the -o flag or the –output=/tmp/destinationFileName.tar option.  But the response may be an surprising error “Cowardly refusing to save to a terminal. Use the -o flag or redirect.”  You want to copy a Docker image from one machine to another computer but problems get in your way. 

…

Continue reading “Saving a Docker Image and Using It On A Different Server”