I work with a lot of IIS servers. Keeping track of what sites are present on which servers can sometimes be a daunting task. Heretofore I have been dealing with the rather obnoxious and time consuming process of checking sites and bindings by looking at each one in the IIS console. The other day I thought to myself, surely there must be a more effecient way to do this from the CLI via PowerShell… There is… I quickly found the following code on Stack Overflow after a Google search: (more…)
A lot of my bash scripting experience has been, in one sense, relatively simple. I have several scripts that span several hundred lines and do fairly complex things across multiple systems. From that perspective they aren’t necessarily simple. However it wasn’t until recently that I had to really starting thinking about managing when scripts run and particularly keeping them from “stepping all over each other” when multiple instances of the same script must be run… enter the topic of “Job Control” or “Controlled Execution.”
A common scenario is that your bash script is written to access some shared resource. A few examples of such shared resources:
-An executable file that can only have one running instance at any given time
-A log file that must be written to in a certain order
-Sensitive system files (such as the interfaces file).
What happens if a bash script gets executed once, and then before the first instance finishes running a second instance is fired off? The short answer is typically unexpected/bad stuff that tends to break things.
So the solution is to introduce some job control logic into your scripts. And to that end I want to talk about two methods of controlling job execution that I have started to employ heavily for one of my projects: Simple Lock Files, and the more involved FLOCK application built into most newer Linux distributions. For reference, most of this article is based on a system running Debian Jessie. (more…)
I am working on a project where I need to generate a random value and assign it to a variable…
Initially I was doing this:
var=$(date +%s | sha512sum | base64 | head -c 12 ; echo)
Which was okay until I started executing my script more than once in a short period of time. Suddenly my random variable wasn’t so random and I was getting the same value multiple times in a row. This is a flaw of this method in that it is a hash of the value of the date (represented as an epoch value) at a given second.
UPDATE – 6/28/2016 – Someone pointed out to me that the OpenSSL method below also relies on the value of the date and time. I am not sure why it doesn’t experience the same issues as just using a sha512sum and, as I have a working method, am not going to investigate it further. I just wanted to clarify for the sake of accuracy. I am not an expert with this stuff.
So I had to can that method and that led me to trying this next:
var=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 12 | head -n 1)
This worked perfectly from the shell. Worked great when I executed a test script from the shell using it. However the PHP script that fired off the bash script would freeze whenever I used this. (more…)
I found myself creating security groups for different servers in one of my domains over and over again and using the GUI can get a bit tedious. So I decided to write a quick powershell script that provides an interactive prompt asking for the server name, group type (select from options) and then from there creates a security group called “SERVERNAME-GROUP” in Active Directory. In my case, I had three different groups for each server, local “Admins”, local “Users”, and finally a special group for database admins used in Microsoft SQL Server. This requires the Active Directory module for powershell and must be run from a Domain Controller.
Below is the powershell code: (more…)