IT 341: Introduction to System Administration
Definitions
(written by Glenn Hoffman for IT341)
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Z
- Absolute Path
- The list of directories, starting with the root, that leads to the directory holding a specific file.
- Absolute Pathname
- The absolute path to a file or directory, followed by a / and the
name of the file or directory.
- Absolute Address
- The absolute path of a file followed by the filename.
- Authoritative Name Server
- A single machine that is the original source of information about the range of IP
addresses associated with a domain.
- BIOS
- BIOS stands for Basic Input/Output System. It is firmware
that contains instructions to test the system and begin the boot process.
- Boot Process
- The series of steps by which a computer, when it is turned on, recognizes the hardware connected to it
and initializes all the services it provides.
- Boot Sector
- A sector on a hard drive that contains the as well
as software to start the boot process.
- Broadcast Address
- An IP address used to send messages to all machines on the network, for example
to broadcast the services the machine provides.
- Command Substitution
- A feature of Lunix/Unix that allows a command to be run in a sub-shell, with the output of that
command substituted for the command itself on the command line. The format for this feature is
$(COMMAND)
In bash you can also surround the command with backticks, ` ` .
- Daemon
- A background process that provides services. Daemons are often started when the system is booted.
- Delimiter
- A sequence of one or more characters used to mark the boundary between different parts of a string.
- DHCP
- The abbreviation for Dynamic Host Configuration Protocol.
- Dynamic Host Configuration Protocol
- A protocol that allows individual machines on a network to get their configuration
information from another machine. This other machine is the DHCP server.
- DNS Root Domain
- The top domain in the Domain Name System. This domain has no name are is represented by a
a single dot, . .
- Domain Name
- A string of characters that specifies either an IP address or a range of IP addresses.
A fully qualified domain name is
a unique string of characters which corresponds to a unique public IP address.
- DNS
- Abbreviation for the Domain Name System.
- DNS Name Resolution
- The process of providing an IP address for a domain name
- Domain Name System
- The system that translates a domain name into an IP address.
It is also the name of the protocol that makes this system work.
- Extended Partition
- A partition that is created in the
but only serves to hold the information pointing to logical partition
somewhere else on the physical hard drive.
- Firmware
- Code and data stored in hardware that does not need electric power to retains its contents, now usually flash memory.
- First-Stage Boot Loader
- The first software used in the process of loading the kernel.
The first-stage boot loader does not display a menu, so there is no way it can interact with the user.
The purpose of the first-stage bootloader is to find and run
the second-stage bootloader, which on
modern Linux systems is GRUB.
- Flat File
- A database architecture where all records are stored one right after the other, often in
a text file. Flat file databases become very slow when they contain large numbers of entries.
- Fully Qualified Domain Name
- A complete domain name of a machine on the Internet.
The first part of a fully qualified domain name identifies an individual machine.
This part of the domain name can be a hostname
though it does not have to be. The last part of a fully qualified domain
name is a top level domain name
A fully qualified domain name corresponds to a unique IP address.
- Gateway
- A router used to transfer traffic from a local network to the greater Internet.
- GRUB
- GRUB stands for Grand Unified Boot Loader.
It is the second-stage boot loader on
modern Linux systems.
- Global Variable
- A variable that is defined everywhere in a Perl program starting from the line on which it is defined.
- Hardware Virtualization
- A virtual machine that acts like a real computer with an operating system.
Software executed on these virtual machines is separated from the underlying hardware resources.
- Hexadecimal
- A base 16 number system where the digits after 9 are a, b, c, d, e and f.
- Host
- A machine on a network, often the machine you are using. It can be a physical or a virtual machine.
- Hostname
- The name by which a computer is known on the network.
- Kernel
- The part of the operating system that always remains in memory.
The kernel is the software that manages the hardware and creates running processes.
It handles all interactions between running programs and the hardware.
- Kernel Space
- The section of memory where the kernel, and processes it creates, run.
- Link
- A special file has no content, but points to another file or directory. A link
is like a shortcut on a PC, or an alias on a Mac.
- Logical Volume
- The volumes created by partitioning a disc.
Each logical volume acts as if it were a separate hard drive, though in
reality it is contained on a single physical volume with the other
logical volumes created by partitioning.
- Logical Volume Manager
- Software that manages disk drives and similar mass-storage devices.
- LVM
- The logical volume manager built into the Linux kernel
- Logical Partition
- A partition whose information is not contained directly in the
master boot record, but is stored elsewhere on
the physical disc. The information that lets the operating system find these
partitions is stored in an extended partition
which resides on the master boot record. Logical partitions have several advantages
over primary partitions.
- Loopback Interface
- A virtual network interface controller,
emulated in software, that sends any packets addressed to it back to the machine,
without traveling over the network.
- Master Boot Record
- Information stored on the boot sector
that contains information about each logical volume on the hard drive.
The MBR is located on the first sector of any bootable disk.
- MBR
- The abbreviation for the Master Boot Record.
The MBR contains the partition table and the
first-stage bootloader.
- Module
- A file that contains subroutines that can be used by scripts.
- Mount Point
- A directory where shared directories for other machines will appear as if part
of the local filesystem. Directories used as mount points should empty.
- NAT
- The abbreviation for Network Address Translation
- Network Address Translation
- A service that rewrites packets from private IP address to public IP address and
packets from public IP addresses to private IP addresses. NAT allows machines
with private IP addresses to communicate with the public Internet.
- Network Interface Controller
- A hardware component the connects a computer to a network.
- NIC
- The abbreviation for a network interface controller.
- Non-volatile Memory
- Memory that keeps its contents once the power has been turned off, unlike RAM which only keeps its data
while it has power.
- Octal
- A base 8 number system, where digits range from 0 to 7.
- Octet
- One for the four numbers that form an IPv4 address.
Each octet has a value that ranges from 0 to 255.
- Packet
- A packet is a chunk of information, sent out over a network, that allows two computers to communicate.
- Partition
- A section of a physical drive that acts as if it were a separate physical hard drive
and has its own file system.
- Partitioning
- Dividing a single physical hard drive into more than one virtual hard drives,
each of which has its own file system and acts as if it were a separate physical disk.
- Partition Table
- The section of the MBR that contains data on the various
partitions to be found on that disk.
- Package Manager
- A package manager is a collection of software tools to automate the process of installing,
upgrading, configuring, and removing software packages for a computer's operating system
in a consistent manner.
- Path
- The location of a file, specified by the list of the directories that you must go through to get to the file.
- Pathname
- The path to a file followed by the name of the file. The pathname uniquely specifies a file.
- Primary Partition
- A partition whose information resides in the master boot record.
There can only be 4 primary partitions on a disc and it is very hard to change their sizes.
- Port
- A communication channel associated with a specific IP address. Two computers communicate
by exchanging packets addressed to a specific port at a specific IP address.
Ports allow computers to have multiple conversations with many other machines at the same time.
The server communicates on a well-known port, while the client
picks a random port for the communication.
- POST
- See Power On Self Test.
- Power On Self Test
- A test performed when the machine is first turned on that checks the memory and hardware.
- Private IP Address
- A private IP address is an address which cannot be used on the Internet. Both IPv4 and IPv6 set aside
blocks of IP addresses which a system administrator is free to assign to any computer on the network.
These addresses can only be used inside a local network and are not routable on the Internet. Computers
assigned private IP addresses can only communicate to computers on the Internet through another computer
providing Network Address Translation.
- Process
- A running program. Processes have resources, like memory and access to files.
- Program Number
- A unique number assigned to a specific daemon which allows a remote machine
to contact this daemon using a remote procedure call.
- Relative Path
- The list of directories, starting with the current directory, that leads to the directory holding a specific file.
- Remote Procedure Call
- A Unix technology that allows a user on one machine to run a program on another machine.
- Root Account
- The first account automatically created when Unix or Linux is installed.
This account can do anything on the machine and is used for system administration and configuration.
- Router
- A hardware device that forwards data packets from one network to another.
- Runlevel
- A concept from the init program from the original Unix, SystemVinit.
Startup was viewed as a sequential process with different stages, each one of which had to finish
before the next could begin. There were 7 runlevels used in booting up and shutting down.
Each runlevel has access to different system processes.
- Sand-boxing
- The idea that a program should have its own area of memory that no other program can access without permission.
- Second-stage Bootloader
- The second software used in the process of loading the kernel.
The second-stage bootloader displays a menu to the user, which allows the user
to customize the following stages of the boot process.
GRUB is the second-stage bootloader used in modern Linux systems.
- Secondary Prompt
- The shell prompt you get when you continue a command onto another line. By default the secondary prompt is
> , but you can change this using the keyword shell
variable PS2.
- Socket
- The combination of an IP address, a port and a packet protocol,
such as TCP or UDP, is called a socket.
- Standard Input
- In Unix or Linux, where input for a command comes from, if not otherwise specified. By default, Standard Input
comes from the keyboard, but you can change it using redirection.
- TCP
- See Transmission Control Protocol.
- Transmission Control Protocol
- The protocol that manages a connection between computers over the Internet. TCP makes
sure that all bytes sent by one machine are received by the other machine and that
they are sent in the correct order.
- Top Level Domain Name
- Names at the second level in the hierarchy of the Domain Name System, directly under the
DNS Root Domain. Some examples are
- User Space
-
A section of the computer's memory reserved for processes started by some uesr
with an account on the system.
- Virtual Machine
- A software configuration that, when run inside hardware virtualization sofware.
- Virtualization
- Virtualization is simulating a hardware platform, operating system (OS),
storage device, or network resources.
- VMWare
- A commercial package that performs hardware virtualization software we'll be using in this course.
- Well-known Ports
- The port numbers in the range from 0 to 1023. They are used by system processes that provide
idely used types of network services. A process must execute with root privileges to be able
communicate with one of the well-known ports.
Z
- Zone
- The network for which an individual DNS server is responsible for providing IP addresses.
The zone may include subnetworks