Turing, Turing Machine, Turing Alan Mathison

Turing, Alan Mathison |ˈt(y)o͝oriNG| (1912–54), English mathematician. He developed the concept of a theoretical computing machine and carried out important code-breaking work during World War II. He also investigated artificial intelligence.
Turing machinea mathematical model of a hypothetical computing machine that can use a predefined set of rules to determine a result from a set of input variables.Turing testa test for intelligence in a computer, requiring that a human being should be unable to distinguish the machine from another human being by using the replies to questions put to both.
In colloquial usage, the terms "Turing complete" or "Turing equivalent" are used to mean that any real-world general-purpose computer or computer language can approximately simulate the computational aspects of any other real-world general-purpose computer or computer language.
Real computers constructed so far are essentially similar to a single-tape Turing machine; thus the associated mathematics can apply by abstracting their operation far enough. However, real computers have limited physical resources, so they are only linear bounded automaton complete. In contrast, a universal computer is defined as a device with a Turing complete instruction set, infinite memory, and infinite available time.

In computability theory, several closely related terms are used to describe the computational power of a computational system (such as an abstract machine or programming language):

Turing completeness

A computational system that can compute every Turing-computable function is called Turing-complete (or Turing-powerful). Alternatively, such a system is one that can simulate a universal Turing machine.

Turing equivalence

A Turing-complete system is called Turing equivalent if every function it can compute is also Turing computable; i.e., it computes precisely the same class of functions as do Turing machines. Alternatively, a Turing-equivalent system is one that can simulate, and be simulated by, a universal Turing machine. (All known Turing-complete systems are Turing equivalent, which adds support to the Church–Turing thesis.)

(Computational) universality

A system is called universal with respect to a class of systems if it can compute every function computable by systems in that class (or can simulate each of those systems). Typically, the term universality is tacitly used with respect to a Turing-complete class of systems. The term "weakly universal" is sometimes used to distinguish a system (e.g. a cellular automaton) whose universality is achieved only by modifying the standard definition of Turing machine so as to include input streams with infinitely many 1s.

get zookeeper stable version from its distribution web site

Run the following command at one line:

zkver=$(curl http://www.apache.org/dist/zookeeper/stable/
|grep -o 'zookeeper-[0-9].[0-9].[0-9][0-9].tar.gz'
|(head -n1 && tail -n1)|sed 's/.tar.gz//')

The results:

echo $zkver
zookeeper-3.4.10

How to test if a port is open and running

For the port which are not secured, do the following:

telnet www.somesite 80
GET /index.html HTTP/1.1
Host: www.somesite

For the ports which are secured, do the following:

openssl s_client -connect www.somesite:443 

For the server uses self-signed certificate and secured port, do the following:

openssl s_client -connect 12.34.56.78:443 -servername www.somesite

The servername should be the server name specified in the TLS certificate

Copy files with timestamp

rsync -t source_file_or_directory destination_file_or_directory