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terms.md

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  • Command prompt - the brief text automatically provided by the shell at the left hand side of each line in a console or terminal window.

  • Shell - is a program that provides the traditional, text-only user interface for Unix-like operating systems. Its primary function is to read commands that are typed into a console or terminal window and then execute them, i.e. tell the operating system what to do. Examples of shells: zsh, bash, sh.

  • Environmental variables are a class of variables that tell the shell how to behave as a user works at the command line or in shell scripts. They can be, and often are, set differently for each user.

  • Process is a running instance of a program. Processes are managed by the kernel and each process has an ID associated with it called the process ID (PID). This PID is assigned in the order that processes are created.

  • System log files - automatically updated files that contain records of events that have occurred on a system.

  • Data packet is an all-encompassing term that represents any single set of binary data being sent across a network link. This term is not tied to any specific layer of a networking model or technology. It just represents a concept of one set of data to be sent form point A to point B. So when speaking about the layer of networking models, it's safe to say, for example, that data packets at the data link layer are called frames.

  • Hash is a short unique identifier for a much bigger set of data. Often used as mechanism to verify the integrity of the data as the result of the trasmission on the network.

  • A nameserver is a computer that answers questions about domain names, such as "what is the IP addresses of this domain name?".

  • A crash is the situation in which a program, either a user application or a part of the operating system, stops performing its expected function(s) and responding to other parts of the system. The program might appear to the user to freeze.

  • An assembly language is a human-readable notation for the machine language that a specific type of processor (also called a central processing unit or CPU) uses. Machine language, also referred to as machine code, is a pattern of bits (i.e., zeros and ones) that is directly readable by a processor.

  • A register is a very small amount of high speed memory inside of the CPU.

  • An interrupt is a signal to the kernel (i.e., the core of the operating system) that an event has occurred, and it results in a change in the sequence of instructions that is executed by the CPU. In the case of a hardware interrupt, the signal originates from a hardware device such as a keyboard (i.e., when a user presses a key), mouse or system clock (a circuit that generates pulses at precise intervals that are used to coordinate the computer's activities). A software interrupt is an interrupt that originates in software, and it is usually triggered by a program in user mode. For example, the standard procedure to change from user mode to kernel mode is to call the software interrupt 0x80.