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on 14-Feb-2019 (Thu)

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Flashcard 3823615216908

Question
In linux, for debian distros (like ubuntu), the apt package management tool downloads packages from external repos that are defined in the file [...]
Answer

/etc/apt/sources.list

^^ note also that there are more repos listed in files under /etc/apt/sources.list.d


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Linux Package Management
software that is already installed. apt-get purge package-name(s) - Combines the functions of remove and clean for a specific package, as well as configuration files. apt-get update - Reads the <span>/etc/apt/sources.list file and updates the system’s database of packages available for installation. Run this after changing sources.list. apt-get upgrade - Upgrades all packages if there are updates availab







Flashcard 3823618362636

Question
In linux, for fedora/redhat distros, the yum package management tool downloads packages from external repos that are defined in files under the [...] directory
Answer

/etc/yum.repos.d

^^ the files have .repo files extenstions


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Linux Package Management
located at /etc/yum.conf provides system-wide configuration options for YUM, as well as information about repositories. Repository information may also be located in files ending in .repo under <span>/etc/yum.repos.d. The options in the [main] stanza don’t need modification, though you may set alternate logging and cache locations for the database by adding the following lines: /etc/yum.conf 1 2 log







Flashcard 3825323085068

Question
benefit of surprises is that they’re often a prod to action. It can gnaw at people to realize that the realities of the world don’t match their expectations for it. Some surprises help people see that the status quo needs to change. Some
Answer
Yes

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Unknown title
paigning for office on the other, 2018 felt to us like a series of surprises. The world looking backward from today is very different from what we pictured a couple years ago looking forward. A <span>benefit of surprises is that they’re often a prod to action. It can gnaw at people to realize that the realities of the world don’t match their expectations for it. Some surprises help people see that the status quo needs to change. Some surprises underscore that transformation is happening already. Twenty-five years ago, we read an article that said hundreds of thousands of kids in poor countries were dying from diarrh







Flashcard 3825327279372

Question
Benefits of electron microscopes
Answer
Electron microscopes have a much higher resolution than light microscopes.

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Unknown title
ge of visible objects. Definition Microscope resolution is the shortest distance between two separate points in a microscope’s field of view that can still be distinguished as distinct objects. <span>Electron microscopes have a much higher resolution than light microscopes. Add note The resolution of a light microscope is 200 nm compared to 0.1 nm for an electron microscope. This means that if two points are 100 nm apart, they will not be well-defined and







Flashcard 3825330949388

Question
What are limitations of light microscope?
Answer
The physical properties of light do not allow a greater magnification than 1000× and the smallest object that can be resolved (seen as a separate object) is 2 µm

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Unknown title
ntonie van Leeuwenhoek. Leeuwenhoek was one of the first to observe living microorganisms under a microscope. Credit: "Leeuwenhoek Microscope" by Jeroen Rouwkema is licensed under CC BY-SA 3.0 T<span>he physical properties of light do not allow a greater magnification than 1000× and the smallest object that can be resolved (seen as a separate object) is 2 µm Add note . The electron microscope, which uses a beam of electrons focused by magnets to produce a photographic image, came into general use in around 1940. It can differentiate objects







T he physical properties of light do not allow a greater magnification than 1000× and the smallest object that can be resolved (seen as a separate object) is 2 µm
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Unknown title
Antonie van Leeuwenhoek. Leeuwenhoek was one of the first to observe living microorganisms under a microscope. Credit: "Leeuwenhoek Microscope" by Jeroen Rouwkema is licensed under CC BY-SA 3.0 <span>The physical properties of light do not allow a greater magnification than 1000× and the smallest object that can be resolved (seen as a separate object) is 2 µm Add note . The electron microscope, which uses a beam of electrons focused by magnets to produce a photographic image, came into general use in around 1940. It can differentiate objects




T he physical properties of light do not allow a greater magnification than 1000× and the smallest object that can be resolved (seen as a separate object) is 2 µm

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T he physical properties of light do not allow a greater magnification than 1000× and the smallest object that can be resolved (seen as a separate object) is 2 µm

Original toplevel document

Unknown title
Antonie van Leeuwenhoek. Leeuwenhoek was one of the first to observe living microorganisms under a microscope. Credit: "Leeuwenhoek Microscope" by Jeroen Rouwkema is licensed under CC BY-SA 3.0 <span>The physical properties of light do not allow a greater magnification than 1000× and the smallest object that can be resolved (seen as a separate object) is 2 µm Add note . The electron microscope, which uses a beam of electrons focused by magnets to produce a photographic image, came into general use in around 1940. It can differentiate objects




Hans and Zacharias Jansen are largely acknowledged as the inventors of the light microscope but similar efforts were occurring in many other countries. Almost 20 years later, Galileo was informed of their work and immediately built a microscope of his own design, despite not having seen their original.
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Unknown title
ficiency of aerobic respiration. Figure 3. A modern electron microscope. Credit: by James Gathany (CC0) International Mindedness Modern technology allows faster rates of communication of ideas. <span>Hans and Zacharias Jansen are largely acknowledged as the inventors of the light microscope but similar efforts were occurring in many other countries. Almost 20 years later, Galileo was informed of their work and immediately built a microscope of his own design, despite not having seen their original. Add note Modern day communication means that inventions and innovations can very quickly be shared and developed. Section questions You have not completed this section. You have complet




Flashcard 3825839508748

Question
In linux, data is transmitted between different machines (or specifically between network cards on different machines), over the internet, in what are called [...]
Answer

packets


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25. Introduction to IP
eroute 25.10.3 tcpdump 25. Introduction to IP IP stands for Internet Protocol. It is the method by which data is transmitted over the Internet. 25.1 Internet Communication At a hardware level, n<span>etwork cards are capable of transmitting packets (also called datagrams) of data between one another. A packet contains a small block of, say, 1 kilobyte of data (in contrast to serial lines, which transmit continuously). All Internet communication occurs through transmission of packet







Flashcard 3825846324492

Question
In linux, for networking (i.e. for sending and receiving packets), each machine has a unique ip v4 address, such as 152.2.254.81, which can be represented by a [...] bit binary number.
Answer

32

^^ note that each dot devided segment is an 8 bit number. 4*8 = 32

^^^each dot deviced segment can have a value between 0 to 255, since 255 in binary is 11111111


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25. Introduction to IP
ill reconstruct a packet from all the smaller subpackets that have the same Identification field. The convention for writing an IP address in human readable form is dotted decimal notation like <span>152.2.254.81 , where each number is a byte and is hence in the range of 0 to 255. Hence the entire address space is in the range of 0.0.0.0 to 255.255.255.255 . To further organize the assignment of addresses, each 32-bit address is divided into two parts, a network and a host part of the address, as shown in Figure 25.1. Figure 25.1: IP address classes The network part of the address designates the LAN, and the







Flashcard 3825850256652

Question
In linux, in networking, class A addresses, have their first [...] bit segment represent the LAN, and the next [...] bits represent the host machine
Answer

8, 24

^^ normally class A is not too often used

^^^ Class A addresses are identified by 0 being the first bit (from left), so they are all 0.x.x.x to 127.x.x.x range


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25. Introduction to IP
machine on the LAN. Now, because it was unknown at the time of specification whether there would one day be more LANs or more machines per LAN, three different classes of address were created. <span>Class A addresses begin with the first bit of the network part set to 0 (hence, a Class A address always has the first dotted decimal number less than 128 ). The next 7 bits give the identity of the LAN, and the remaining 24 bits give the identity of an actual machine on that LAN. A Class B address begins with a 1 and then a 0 (first decima







Flashcard 3825852615948

Question
In linux, in networking, [...] addresses, have their first 16 bit segment represent the LAN, and the next 16 bits represent the host machine.
Answer

class B

^^ normally class B is used within large organizations with lots of machines, as it can support 2^16 (i.e. 65536) unique machines

^^^ Class B addresses are identified by 10 being the first 2 bits (from left), so they are of 128.x.x.x to 191.x.x.x range


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25. Introduction to IP
address always has the first dotted decimal number less than 128 ). The next 7 bits give the identity of the LAN, and the remaining 24 bits give the identity of an actual machine on that LAN. A <span>Class B address begins with a 1 and then a 0 (first decimal number is 128 through 191 ). The next 14 bits give the LAN, and the remaining 16 bits give the machine. Most universities, like the a







Flashcard 3825855761676

Question
In linux, in networking, class C addresses, have their first [...] bit segment represent the LAN, and the next [...] bits represent the host machine
Answer

24, 8

^^ normally class C addresses are used by small organizations (as it only supports 2^8, i.e. 256 unique machines)

^^^ Class C addresses are identified by 11 being the first two bit (from left), so they are all 192.x.x.x and above


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25. Introduction to IP
(first decimal number is 128 through 191 ). The next 14 bits give the LAN, and the remaining 16 bits give the machine. Most universities, like the address above, are Class B addresses. Lastly, <span>Class C addresses start with a 1 1 0 (first decimal number is 192 through 223 ), and the next 21 bits and then the next 8 bits are the LAN and machine, respectively. Small companies tend use Cl







Flashcard 3825858907404

Tags
#has-images
Question
In linux, for IP v4 addresses (e.g. 191.2.13.250), three are 3 different classes of address, class A, class B, class C. What is the difference between them?


Answer
Look at answer photo, which shows: class A has first 8 bits rep. network, next 24 rep. host; class B has first 16 for network, next 16 for host; class C has first 24 rep network, last 8 rep. host

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25. Introduction to IP
ignates the LAN, and the host part the particular machine on the LAN. Now, because it was unknown at the time of specification whether there would one day be more LANs or more machines per LAN, <span>three different classes of address were created. Class A addresses begin with the first bit of the network part set to 0 (hence, a Class A address always has the first dotted decimal number less than 128 ). The next 7 bits give the i







Flashcard 3825868606732

Question
In linux, for IP v4 addresses, class A addresses start with [...] , class B start with [...] , class C start with [...] (i.e. by start, meaning left most digits).
Answer
0, 10, 11

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25. Introduction to IP
y, Class C addresses start with a 1 1 0 (first decimal number is 192 through 223 ), and the next 21 bits and then the next 8 bits are the LAN and machine, respectively. Small companies tend use <span>Class C addresses. In practice, few organizations require Class A addresses. A university or large company might use a Class B address but then would have its own further subdivisions, like u







Flashcard 3825871752460

Question
In linux, large organizations use class B IP v4 addresses and use the third dotted decimal (e.g. 162.246.X.28) as a department and the last dotted decimal (e.g. 162.246.216.X) as the machine within that department. Here, the LAN (the first two dotted decimals: i.e. 162.246) is called a network and the various departments are each called a [...]
Answer
subnet

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25. Introduction to IP
next 8 bits are the LAN and machine, respectively. Small companies tend use Class C addresses. In practice, few organizations require Class A addresses. A university or large company might use <span>a Class B address but then would have its own further subdivisions, like using the third dotted decimal as a department (bits 16 through 23) and the last dotted decimal (bits 24 through 31) as the machine within that department. In this way the LAN becomes a micro-Internet in itself. Here, the LAN is called a network and the various departments are each called a subnet. 25.2 Special IP Addresses Some special-purposes IP addresses are never used on the open Internet. 192.168.0.0 through 192.168.255.255 are private addresses perhaps used inside a local L







Flashcard 3825874898188

Question
In linux, for IP v4 Class B addresses, the third dotted decimal number (i.e. the X in 162.246.X.280) can often represent the [...]
Answer

subnet

^^ note that the subnet is just a grouping of machines within a network LAN. So in class B IP 162.246.216.28, 162.246 represents the LAN, while the 216 represents the subnet, and the 28 is the actual machine.


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25. Introduction to IP
its 24 through 31) as the machine within that department. In this way the LAN becomes a micro-Internet in itself. Here, the LAN is called a network and the various departments are each called a <span>subnet. 25.2 Special IP Addresses Some special-purposes IP addresses are never used on the open Internet. 192.168.0.0 through 192.168.255.255 are private addresses perhaps used inside a local L







Psoriasis is a common inflammatory skin disorder characterized by erythematous, well-defined plaques covered by thick silvery scales
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pdf

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Flashcard 3825887481100

Question
Psoriasis is a common inflammatory skin disorder characterized by erythematous, well-defined plaques covered by thick silvery [...]
Answer
scales

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Parent (intermediate) annotation

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Psoriasis is a common inflammatory skin disorder characterized by erythematous, well-defined plaques covered by thick silvery scales

Original toplevel document (pdf)

cannot see any pdfs







Flashcard 3825889316108

Question
In linux, in networking, [...] [...] is a number that defines a range of IP addresses
Answer

network mask or subnet mask

^^ the mask is given as a dot seperated 32 bit decimal number (e.g. 255.255.255.0)


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25. Introduction to IP
machine itself. Further, 172.16.0.0 through 172.31.255.255 are additional private addresses for very large internal networks, and 10.0.0.0 through 10.255.255.255 are for even larger ones. 25.3 <span>Network Masks and Addresses Consider again the example of a university with a Class B address. It might have an IP address range of 137.158.0.0 through 137.158.255.255 . Assume it was decided that th







Flashcard 3825892986124

Question
In linux, in networking, what is the subnet/network mask if you want to have 512 IP addresses in your network, ranging from e.g. 137.158.26.0 through 137.158.27.255? (when giving answer give the logic of why the answer is so)
Answer

255.255.254.0

^^note that for 255.255.254.0, the first two number sets. i.e 255.255, each 255=11111111, the third number set 254=11111110, while 0=00000000

^^^ so final binary is 11111111.11111111.11111110.00000000, so there are 9 open 0s on right, and 2^9 = 512, so there are a range of 512 IPs available


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25. Introduction to IP
ain the example of a university with a Class B address. It might have an IP address range of 137.158.0.0 through 137.158.255.255 . Assume it was decided that the astronomy department should get <span>512 of its own IP addresses, 137.158.26.0 through 137.158.27.255 . We say that astronomy has a network address of 137.158.26.0 . The machines there all have a network mask of 255.255.254.0 . A particular machine in astronomy may have an IP address of







Flashcard 3825896918284

Question
In linux machines, the network card has a physical address of 48 bits (represented in hex) that uniquely identifies the card, this is called the [...] address
Answer

MAC

^^ MAC stands for Media Access Control

^^^e.g. MAC address is 08:00:27:7a:ab:12, each 2-digit hex chunck is 8 bits, so 6x8=48. The reason for each 2 digit chunch being 8 bits is, think FF = 11111111


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25. Introduction to IP
ts to transmit a frame while another card is in the process of transmitting a frame, then a clash is said to have occurred, and the card waits a random amount of time and then tries again. Each <span>network card has a physical address of 48 bits called the hardware address (which is inserted at the time of its manufacture and has nothing to do with IP addresses). Each frame has a destination address in its header that tells what network card it is destine







Flashcard 3825900064012

Question
In linux, transmittion of data frames within a LAN network is governed by network cards, therefore MAC addresses are used and translation has to be done between MAC and IP. You can use the command [...] to get a list of hardware address (aka MAC address) to IP mappings.
Answer

arp

^^^ arp stands for Address Resolution Protocal

^^^^ the result from running "arp" gives you all the MAC address to IP translations that your machine has from sending frames to neighbouring machines in the LAN.

^^^^^the way things work is your network card sends a frame by destination IP, and the destination machine, reconizes its own IP and responds with the MAC address, which your machine keeps the mapping for future reference. arp just prints out those stored mappings


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25. Introduction to IP
erence. Of course, if you suddenly switch network cards, then other machines on the LAN will have the wrong information, so ARP has time-outs and re-requests built into the protocol. Try typing <span>the command arp to get a list of hardware address to IP mappings. 25.5 Configuring Interfaces Most distributions have a generic way to configure your interfaces. Here, however, we first look at a complete network configuration using only raw networkin







Flashcard 3825903209740

Question
In linux, in networking, data sent between machines over the internet is called packets but data send between machines in a LAN is called [...]
Answer

frames

^^^ NOTE: frames are a wrapper around packets (meaning a frame has within it a packet, or a part of a packet, if the packet is too big for the frame size)


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25. Introduction to IP
y) called Local Area Networks, or LANs. These are all connected to each other by lower-speed long distance links. On a LAN, the raw medium of transmission is not a packet but an Ethernet frame. <span>Frames are analogous to packets (having both a header and a data portion) but are sized to be efficient with particular hardware. IP packets are encapsulated within frames, where the IP packet fits within the Data par







Flashcard 3825907141900

Question
In linux, the [...] command is used to configure network interfaces (network cards, etc) and to also list out all the configured network interfaces (and their info like IPs, MAC/HW address, etc).
Answer

ifconfig

^^ note the if in ifconfig stands for interface

^^^ the interfaces listed when you run ifconfig include eth0 (and other network cards if you have more than 1), as well as lo (the loopback network interface to refer to the machine itself).


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25. Introduction to IP
an imaginary network card that is used to communicate with the machine itself; for instance, if you are telnet ing to the local machine, you are actually connecting via the loopback device. The <span>ifconfig ( i nter f ace config ure) command is used to do anything with interfaces. First, run /sbin/ifconfig lo down /sbin/ifconfig eth0 down to delete any existing interfaces, then run /sbin/i