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The explanation that New Jersey closed access lanes on the heavily traveled George Washington Bridge for a "traffic study" is a head scratcher for traffic engineers.
Engineers today use so-called microscopic traffic simulations to create virtual environments that can model driver behavior to road changes with exacting detail.
There's have plenty of data available for the simulations. One of the best sources are video camera systems that use software to count vehicles on roadways.
The simulation software can model the impact of road changes with precision and without any need to close lanes to test theories, according to several traffic engineers interviewed by Computerworld.
There is no evidence, in documents released late last week by investigators, that the Port Authority of New York and New Jersey considered computer models in lieu of a real world action. The Port Authority manages bridges and tunnels, airports, ports, and other critical systems in that region.
Instead, the Port Authority shut down two of the three access lanes for four days last September from Fort Lee to the George Washington Bridge without warning the public, citing a "traffic study."
After the lanes were closed, many people complained about it to the Port Authority, public officials and to local newspapers. The Port Authority was accused by one woman of "playing God with people's jobs" in a call to a Port Authority official, who made a note of it. It was among the documents released last week.
People weren't just late for work due to the disruption.
School buses and emergency vehicles were also delayed by an action that has led to multiple investigations of the administration of Republican Gov. Chris Christie. Some of the governor's top appointees orchestrated the lane closings, apparently as a type of retribution against Fort Lee's Democratic mayor, Mark Sokolich, documents have shown.
"Time for some traffic problems in Fort Lee," wrote Gov. Chris Christie aide Bridget Anne Kelly to David Wildstein, the Port Authority's director of interstate and capital project, who complied.
Real traffic engineering is a meticulous, safety-focused undertaking with some powerful software tools to work with.
"You certainly do not have to close lanes physically," said Joseph Hummer, chair of Civil and Environmental Engineering Dept. at Wayne State University. The impact of a lane closure can be modeled. Those models are accurate in the short-term, plus or minus a couple of percent, on measures such as travel time and delay, he said.
There is software available to project traffic changes 30 years out and give "good enough" answers for long-range planning purposes.
The most accurate tools, for microscopic analysis, includes equations for measuring the traffic flow of individual vehicles, which is something that gets to driver behavior, said Hummer.
A microscopic analysis can simulate when a driver changes lanes, speeds-up, slows down, how close do they follow the car in front of them, and the speed at which they follow, among other variables. It can update measurements every one-tenth of a second, said Hummer.
It is expensive software to run and is only used on big projects -- such as lane closures. The economic cost of the New Jersey lane closures more than justifies its use, Hummer says. | <urn:uuid:379819e9-6861-47fd-998e-b114ef3705e2> | CC-MAIN-2017-09 | http://www.computerworld.com/article/2487638/business-intelligence/a-new-jersey--traffic-study--wouldn-t-need-lane-closings.html | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501172902.42/warc/CC-MAIN-20170219104612-00042-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.954997 | 651 | 2.515625 | 3 |
In Linux, wc is a small command line utility that can be used to display details like number of words, newlines, bytes etc for a file. The wc command can display some extra information like length of the longest line in the file. In this article we will discuss the usage of this command through examples. Here is the basic syntax of wc command :
wc [OPTION]... [FILE]... As clear from the syntax, multiple files can be supplied as input to the Linux wc command.
Linux wc command examples The file input.txt will be used in the examples... [More] | <urn:uuid:eb879128-d794-42d5-ba61-ef800510b287> | CC-MAIN-2017-09 | https://www.ibm.com/developerworks/community/blogs/58e72888-6340-46ac-b488-d31aa4058e9c/tags/wc?lang=en | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501171162.4/warc/CC-MAIN-20170219104611-00034-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.810919 | 128 | 3.078125 | 3 |
Generic routing encapsulation (GRE) is a communication protocol used to establish a direct, point-to-point connection between network nodes. Being a simple and effective method of transporting data over a public network, such as the Internet, GRE lets two peers share data they wouldn’t be able to share over the public network itself.
GRE protocol offers a number of advantages, including:
- Use of multiple protocols over a single-protocol backbone
- Providing workarounds for networks with limited hops
- Connection of non-contiguous subnetworks
- Being less resource demanding than its alternatives (e.g. IPsec VPN)
Imperva Incapsula uses GRE to establish a direct connection to our clients’ servers, after virtually deploying our DDoS mitigation solution at the edge of their network.
Regardless of the DDoS attack type or target, this enables us to provide protection for every type of network infrastructure, across all communication protocols—because of GRE’s ability to transmit packets of all types.
In this post we shed some light on the GRE protocol: how it works, what it is capable of and how it can be effectively utilized.
Like Mailing a Package
Before diving into GRE, let’s discuss how Internet communication works in general. When one computer needs to send information to another over a network, the data is divided into a series of packets—small bits of the original data. Each packet contains both user data and control information.
User data, (a.k.a., the payload), is the actual content being sent. Control information, on the other hand, comprises instructions required for the content to reach its destination—including source and destination IP addresses, error codes, etc.
In this way, a network packet is similar to a package being delivered in the mail, with user data representing the content inside the package and control information as the delivery instructions found on it.
Network packets and mailed packages also resemble each other in the way they travel from their point of origin to their final destination.
When a package is sent, it makes several stops during the delivery process, passing through at least two post offices. The same goes for data packets, which need to journey between several ISP networks as they move across the globe.
Certain rules have to be observed in both cases. For example, your package must have the correct stamps and be of a certain size and weight. Similarly, data packets need to comply with the rules of a given network in which they are passing through, which may or may not support certain packet sizes and communication protocol types (e.g., AppleTalk).
If the rules aren’t observed, your packet can’t be delivered. This is where GRE is useful.
Repackaging Your T-Rex Replica
A GRE is similar to a multi-faceted delivery service that can handle any kind of package—from a nylon bag full of water to a life sized T-rex replica—transporting it from door-to-door. It simply takes whatever you give it, puts it in one of its own boxes, slaps an address label on it and gets it to where it needs to go.
GRE does essentially the same thing in a process called encapsulation, which takes a data packet being sent and “repackages” it. This is achieved by adding two additional headers, one identifying it as a GRE packet and the second to provide new source and destination IPs.
Transporting Data Through a GRE Tunnel
For an encapsulated packet to be transmitted, a GRE tunnel must be established. This is a virtual point-to-point connection between two networks—a safe passage that enables direct, “no-questions asked,” door-to-door delivery.
With a tunnel in place, a GRE packet can travel directly between its two endpoints. That the tunnel is virtual means that, even as the packet travels through other routers, there is no interaction with its payload. Instead, the packet is pushed forward until it reaches the tunnel’s endpoint, where the outer packet is de-encapsulated and the payload parsed.
GRE Tunnel Configuration
A GRE tunnel is established on a router level and differs depending on the hardware type or service you use. Typically you’ll be required to set up the tunnel interface IPs and provide public IP addresses for both ends of the GRE tunnel.
Here is an example of a tunnel set up between two Cisco routers:
|Router 1: R1||Router 2: R2|
|R1(config)# interface Tunnel1||R2(config)# interface Tunnel1|
|R1(config-if)# ip address
|R1(config-if)# ip mtu 1400||R2(config-if)# ip mtu 1400|
|R1(config-if)# ip tcp adjust-mss 1360||R2(config-if)# ip tcp adjust-mss 1360|
|R1(config-if)# tunnel source 220.127.116.11||R2(config-if)# tunnel source 18.104.22.168|
|R1(config-if)# tunnel destination 22.214.171.124||R2(config-if)# tunnel destination 126.96.36.199|
It is important to remember that you may have to whitelist source addresses in firewalls on both ends of the tunnel. However, it is best practice to terminate the tunnel ahead of your firewall so it can inspect inner packets.
Another item to note is the maximum transmission unit (MTU) you set for the tunnel. Ethernet MTU is generally 1500 bytes. When using GRE, however, the additional header has an overhead of another 24 bytes that needs to be taken into account.
Therefore, when establishing a GRE tunnel with a symmetric traffic flow, we recommend setting the MTU to 1400 bytes, as shown in the above example.
For more questions about GRE tunneling and to learn how it’s being implemented in Incapsula’s DDoS mitigation services, contact us here or simply leave a comment below.
Would you like to write for our blog? We welcome stories from our readers, customers and partners. Please send us your ideas: [email protected] | <urn:uuid:183c8843-b381-40cf-a790-8183df95c6db> | CC-MAIN-2017-09 | https://www.incapsula.com/blog/what-is-gre-tunnel.html | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501171162.4/warc/CC-MAIN-20170219104611-00034-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.902833 | 1,319 | 3.671875 | 4 |
While some processors still have the classic, four stage pipeline described above, most modern CPUs are more complicated. The G4e breaks the classic, four-stage pipeline into seven stages in order to allow it to run at increased clock speeds on the same manufacturing process. Less work is done in each of the G4e's shorter stages but each stage takes less time to complete. Since each stage always lasts exactly one clock cycle, shorter pipeline stages mean shorter clock cycles and higher clock frequencies. The P4, with a whopping 20 stages in its basic pipeline, takes this tactic to the extreme. Take a look at the following chart from Intel, which shows the relative clock frequencies of Intel's last six x86 designs. (This picture assumes the same manufacturing process for all six cores). The vertical axis shows the relative clock frequency, and the horizontal axis shows the various processors relative to each other.
Figure 2.1: I know it says "Figure 2," but ignore that.
Intel's explanation of this diagram and the history it illustrates is enlightening, as it shows where their design priorities were.
Figure 2 shows that the 286, Intel386 ?, Intel486 ? and Pentium ? (P5)processors had similar pipeline depths ? they would run at similar clock rates if they were all implemented on the same silicon process technology. They all have a similar number of gates of logic per clock cycle. The P6 microarchitecture lengthened the processor pipelines, allowing fewer gates of logic per pipeline stage, which delivered significantly higher frequency and performance. The P6 microarchitecture approximately doubled the number of pipeline stages compared to the earlier processors and was able to achieve about a 1.5 times higher frequency on the same process technology. The NetBurst microarchitecture was designed to have an even deeper pipeline (about two times the P6 microarchitecture) with even fewer gates of logic per clock cycle to allow an industry-leading clock rate. (The Microarchitecture of the Pentium 4 Processor, p. 3)
As we'll see, the Pentium 4 makes quite a few sacrifices for clock speed, and although Intel tries to spin it differently, an extraordinarily deep pipeline is one of those sacrifices. (For even more on the relationship between clock speed and pipeline depth, see my first K7 article.)
Some might be tempted to attribute the vast differences in pipeline depth between the P4 and the G4e to the fact that modern x86 processors like the Athlon, PIII, and P4 need to break down large, complex x86 instructions into smaller, more easily scheduled operations. While such instruction translation does add pipeline stages to the P4, those stages aren't part of its basic, 20-stage pipeline. (Yes, the P4 still needs to translate x86 instructions into ?ops, but as we'll see later on the P4's trace cache takes the translation and decode steps out of the P4's "critical execution path.").
The drastic difference in pipeline depth between the G4e and the P4 actually reflects some very important differences in the design philosophies and goals of the two processors. Both processors want to run as many instructions as quickly as possible, but they attack this problem in two different ways. The G4e's approach can be summarized as "wide and shallow." Its designers added more functional units to its back end for executing instructions, and its front end tries to fill up all these units by issuing instructions to each functional unit in parallel. In order to extract the maximum amount of instruction-level parallelism (ILP) from the (linear) instruction stream the G4e's front end first moves a small batch of instructions onto the chip. Then, its out-of-order (OOO) execution logic examines them for interdependencies, spreads them out to execute in parallel, and then pushes them through the execution engine's nine functional units. Each of the G4e's functional units has a fairly short pipeline, so the instructions take very few cycles to move through and finish executing. Finally, in the last pipeline stages the instructions are put back in their original program order before the results are written back to memory.
At any given moment the G4e can have up to 16 instructions spread throughout the chip in various stages of execution simultaneously. As we'll see when we look at the P4, this instruction window is quite small. The end result is that the G4e focuses on getting a small number of instructions onto the chip at once, spreading them out widely to execute in parallel, and then getting them off the chip in as few cycles as possible.
Figure 2.2: The G4e's approach
The P4 takes a "narrow and deep" approach to moving through the instruction stream. It has fewer functional units, but each of these units has a deeper, faster pipeline. The fact that each functional unit has a very deep pipeline means that each unit has a large number of available execution slots and can thus work on quite a few instructions at once. So instead of having, say, three short FP units operating slowly in parallel, the P4 has one long FP unit that can hold and rapidly work on more instructions in different stages of execution at once.
It's important to note that in order to keep the P4's fast, deeply pipelined functional units full, the machine's front end needs deep buffers that can hold and schedule an enormous number of instructions. The P4 can have up to 126 instructions in various stages of execution simultaneously. This way, the processor can have many more instructions on-chip for the out-of-order execution logic to examine for dependencies and then rearrange to be rapidly fired to the execution units.
Figure 2.2: The P4's approach
It might help you to think about these two approaches in terms of a McDonald's analogy. At McDonald's, you can either walk in or drive through. If you walk in, there are five or six short lines that you can get in and wait to have your order processed by a single server in one, long step. If you choose to drive through, you'll wind up on a single, long line, but that line is geared to move faster because more servers process your order in more, quicker steps: a) you pull up to the speaker and tell them what you want; and b) you drive around and pick up your order. And since the drive-through approach splits the ordering process up into multiple, shorter stages, more customers can be waited on in a single line because there are more stages of the ordering process for different customers to find themselves in. So the G4e takes the multi-line, walk-in approach, while the P4 takes the single-line, drive-through approach. | <urn:uuid:95b0c1c8-7c3d-4a24-a56f-e0e5beda9691> | CC-MAIN-2017-09 | https://arstechnica.com/features/2001/05/p4andg4e/2/ | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501173866.98/warc/CC-MAIN-20170219104613-00086-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.949212 | 1,389 | 3.46875 | 3 |
Black Box Explains Industrial Networking
Industrial environments present much harsher conditions than are found in typical office environments. They not only often have extremes of temperatures, humidity, dirt, and corrosive materials, they may also contain devices such as motors and mechanical switches, which cause a large amount of electromagnetic interference (EMI)
The challenge with industrial controls as well as with other electronic devices intended for use in these environments is to have them function reliably in spite of adverse conditions. This may mean using a device that’s built to withstand harsh conditions, protecting the device in a specialized cabinet, or both.
Industrial networking solutions are suitable for use in:
• Military applications.
• Factory environments.
• Oil/gas drilling and mining.
• Public utilities.
• Traffic control
Extended temperature range
Many industrial devices are installed outdoors in unventilated sealed enclosures, which freeze in the winter and heat to extremely high temperatures in the summer. They and their power supplies are expected to perform over a wide temperature range. Typically they’re rated so you can select one appropriate to your environment.
Operating temperature tolerances are defined as:
• Standard: 0° to +40° C (32° to 104° F)
• Hardened: -25° to 60° C (-13° to +140° F)
• Extreme: -40° C to +75° C (-40° to +167° F)
Because industrial components are sealed against contaminants and also because they’re often installed inside enclosures, they rely on air convection rather than fans for cooling.
Components for office or data center use are usually either freestanding or mounted on 19" rails in a cabinet or rack. Industrial devices, on the other hand, are usually panel mounted by bolting them
to a flat surface, or they may be DIN rail mounted.
DIN rail is an industry-standard metal rail that is used both wallmounted or rackmounted. Industrial devices mount directly on the rail or may come with separate DIN rail brackets.
The power supplied to industrial sites can vary tremendously. AC power varies anywhere from 60 VAC to 960 VAC, and often only DC power is supplied, with 24 VDC or 48 VDC being common.
Industrial power may be three-phase power, which is used for power transmission across power grids and is favored for large motors and heavy loads at industrial sites. It’s also frequently
“dirty” power, subject to noise, voltage fluctuations, and spikes. This inconsistent power is hard on the electronic components in industrial devices and can cause equipment damage or data loss.
Because of this variability, industrial control devices are either sold entirely separately from their power supply or are available with a choice of power supplies. Unlike ordinary networking devices, industrial controls require you to choose the correct power supply for both device and application. Industrial power supplies must be matched to both the type of power input they’ll be receiving from the power grid and the power output they’ll be expected to provide to the industrial control device.
Industrial areas are also prone to electromagnetic interference (EMI) and radio-frequency interference (RFI). Interference and noise from EMI/RFI creates unwanted signals that may interfere with network performance. Devices for industrial applications are usually built to withstand higher EMI than those intended for office or data center use. Chassis are usually shielded, and EMI signals can be absorbed by using capacitor-based circuits or through special coatings as well.
Resistance to moisture and contaminants
Moisture is the enemy of electronic components, and industrial devices are often subject to water in all its forms, from high humidity and condensation to drips and splashes. Industrial devices are also often subject to dirt, dust, oil, salt spray, and chemicals when they’re installed outdoors or indoors in an environment such as a factory floor.
For these reasons, industrial components are usually housed in hardened metal cases that are sealed against contaminants, including particulates such as airborne dust, as well as moisture, and sometimes chemicals.
One way to protect industrial devices from their environment is with an enclosure designed to seal out contaminants such as dust and moisture. These enclosures are usually NEMA rated to describe the amount of protection they provide. | <urn:uuid:d4971901-b8b4-4348-b71f-3b5370478d18> | CC-MAIN-2017-09 | https://www.blackbox.com/en-us/products/black-box-explains/industrial-networking | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501170914.10/warc/CC-MAIN-20170219104610-00206-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.93644 | 891 | 3.125 | 3 |
Here's a short history on computer science student enrollments. Leading up to the dot-com bust, computer science enrollments soared to new highs, and then they plunged. Like a rock.
The number of computer science graduates at Ph.D.-granting institutions reached a low of 8,021 in 2007, down from 14,185 in the 2003-2004 academic year.
But it's been rising since. The number of new undergraduate computing majors at Ph.D.-granting U.S. universities rose by more than 13.4% in the 2012-13 academic year, according to the Computing Research Association's just-released annual report on computer science programs.
That was slightly lower than the increases of the previous few years, but it nonetheless represents the sixth straight year of enrollment gains. The dot-com crash of 2001 turned people away from computer science and sent enrollments falling until they bottomed out in 2007.
The number of bachelor's degrees awarded in computer science last year was up 3.7% overall from the previous year, reaching 12,503, according to the CRA, but the increase at schools that reported figures for both last year and the previous year was 9.4%.
The number of computer science graduates will continue to increase. Computer science enrollments rose by nearly 30% in the 2011-12 academic year, and they increased 23% the year before that.
The trend of enrollment increases since 2010 bodes well for a "future increase in undergraduate computing production," according to the report.
The recession that hit in 2008 sent IT unemployment soaring, but it may have done more damage to the finance sector, especially in terms of reputation. That prompted some educators at the time to predict that the recession might send math-inclined students from the world of hedge funds to computer science.
It's hard to draw a direct apples-to-apples comparison between computer science enrollments and enrollments in business-related disciplines, in part, because the number of students pursuing computer science degrees is much smaller and comparisons may not be fair. But still, according to government data, 327,500 business bachelor's degrees were awarded in 2006-07, and that figure rose 12% to 366,800 in 2011-12. Meanwhile, the number of bachelor's degrees awarded in computer science has increased by 55%, but over a slightly longer period.
There were 63,873 students enrolled in computer science programs last year, compared with 56,307 in 2012. That includes all the majors in computer science departments, such as computer engineering. The overall number doesn't include computer science schools that don't have Ph.D. programs.
Despite the slowdown in enrollments last year, the reality may be better than the data indicates. Among schools that submitted enrollment data to the CRA for its annual Taulbee Survey in two consecutive years, enrollments were up 22%.
There are 266 Ph.D.-granting institutions, and 179 of those schools responded to the survey. The list of responding schools includes Harvard, Yale, Princeton, Georgia Tech, Purdue and several schools in the University of California system, including Berkeley UC Davis, as well as many of the country's other major state universities.
The data on computer science graduates reflects the fact that women are still under-underrepresented in the tech workforce. Women accounted for just 14.2% of the recipients of bachelor's degrees in computer science in the 2012-13 academic year. While low, that figure does represent a modest increase from 11.7% in 2010-11.
Meanwhile, just 13.9% of the students enrolled in computer science programs last year were women.
The number of Ph.D. degrees granted last year rose 3.2% to 1,991. Of those, 58% went to non-resident aliens.
Artificial intelligence, networking and software engineering, in that order, were the most popular areas of specialization for recipients of doctoral degrees, according to the report. The next two most popular disciplines were databases and theory and algorithms. These five areas "have been the most popular for the past few years," the report said.
The job prospects for Ph.D. grads are exceptional. Their unemployment rate is currently 0.8%, compared to 0.4% last year, and only 8% of them took jobs outside of North America, according to the report.
Patrick Thibodeau covers cloud computing and enterprise applications, outsourcing, government IT policies, data centers and IT workforce issues for Computerworld. Follow Patrick on Twitter at @DCgov, or subscribe to Patrick's RSS feed . His e-mail address is [email protected]. | <urn:uuid:fd882b16-ecbf-4ab5-86dd-e3a1ec2e49b9> | CC-MAIN-2017-09 | http://www.computerworld.com/article/2489255/it-careers/wall-street-s-collapse-was-computer-science-s-gain.html | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501170925.44/warc/CC-MAIN-20170219104610-00554-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.964896 | 954 | 2.625 | 3 |
Decene is an unsaturated aliphatic hydrocarbon and its isomerization depends largely on the position and geometry of the double bond. It is an alkene (C10H20), containing ten carbon atoms and a distinguishable double bond. The positional isomers 1-decene and 3-decene are known as decene, however, 1-decene is industrially important isomer.
1-Decene is produced by employing the industrial process of oligomerization of ethylene, using the Ziegler Process or by cracking of the petrochemical waxes. The production of 1-Decene may vary according to the customer’s requirements; it could be from few metric tons to hundred thousand metric tons.
This alpha-olefin is used as monomer in copolymers, and it is an intermediate in the production of epoxides, amines, oxo alcohols, synthetic lubricants, synthetic fatty acids and alkylated aromatics. Also, 1-decene is used as a feedstock for the production of surfactants (alkyl aromatics and detergent alcohols), and in the production of linear alkyl benzene sulfonates that are used in lube-oil additives, all purpose cleaners, dishwashing liquids and laundry detergents.
1-Decene is used in lubricants, detergent alcohols and oilfield chemicals, among others, however, under certain conditions (presence of various catalysts-acids), it may undergo exothermic addition polymerization reactions and attack some forms of plastic. If 1-decene is present in high concentration, its presence may cause irritation to the eyes and the respiratory track.
Alfa Olefins are sensitive to moisture and therefore contact with air or oxygen should be avoided, as auto-oxidation forms impurities, which gives rise to subsequent reactions. They should be kept in dry atmospheric conditions and handled under inert gas atmosphere. With all the hydrocarbons, alpha olefins can form explosive mixtures with oxygen or air in certain concentrations. Besides, 1-decene is stored under nitrogen blanket and is not corrosive to steel or aluminium.
In Western Europe, the surfactant consumption of linear alkylbenzene sulfonates, soaps and other surfactants is largely in the household sector (41%), followed by industrial sector (39%) and personal care (20%). Europe is expected to see a growth of 0.5–1.0%, for the forecast period (2012-18).
1-Decene is segmented into applications and companies. It is used in applications, such as alkylbenzenes, linear & branched, alpha olefin sulfonates (AOS), detergent alcohols, lubricant and oilfield chemicals. The different companies that are part of 1-decene are Dow Chemical Company, Evonik Industries AG, Exxon Mobil Corp, Godrej Industries Ltd., and Mitsubishi Chemical Corporation.
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Please visit http://www.micromarketmonitor.com/custom-research-services.html to specify your custom Research Requirement | <urn:uuid:f55e7d8b-5df4-4f7e-ac51-7d27ed9141ea> | CC-MAIN-2017-09 | http://www.micromarketmonitor.com/market/europe-1-decene-2523613387.html | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501170925.44/warc/CC-MAIN-20170219104610-00554-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.903103 | 667 | 3.4375 | 3 |
If you're a Windows user who wants to try Linux, and you are new to Linux, this tutorial is for you. We'll cover a few basic tasks that may be different from what you are used to. We'll cover these tasks:
- Logging in and understanding the Linux desktop
- Navigation and settings
- Tweaking settings to suit your personal needs
- Command line access
- When you really need to work at the command line
- Becoming superuser (or root)
- When ordinary user authority isn't enough
- Using a GUI application as another user
- Getting comfortable with multi-user system capabilities
- Removable devices
- Using removable media and making sure you don't lose data when you detach removable devices
- When you're done for a while or need a panel icon for logout or other applications
- Adding users and groups
- Adding more users or user groups to your system
These instructions and examples focus on three popular distributions and their default graphical desktops:
- Fedora 13 using a GNOME desktop
- OpenSUSE 11.3 using a KDE 4 desktop
- Ubuntu 10.10 using a GNOME desktop
Other distributions, desktops, and window managers are available, and we encourage you to explore further on your own. Even if some of the information here is specific to a particular distribution and even a particular version of a distribution, what you learn here should help you navigate a strange distribution. Because this tutorial simply aims to help you get started, you won't find information on more advanced tasks like recompiling your kernel or installing software. We recommend our no-charge Linux (LPI) certification self-study guides for deeper information.
At the time of writing, GNOME 3 is likely to be available soon. Expect changes in that user interface from what is described here.
Before using these instructions, install a Linux system and create at least one non-root user as part of your installation process.
Once you have installed your Linux distribution and booted your system, either you will be automatically logged in or you will see a login screen. The next section shows how to switch between these two startup methods and discusses the security implications of automatic login. For this section, we'll assume you are logging in. The three systems we consider in this tutorial implement login a little differently from each other, but all will prompt with the name of one or more users. Once a user is selected, you need to enter a password.
The login screen
The appearance of the screen varies according to your Linux distribution, and it will probably come as no surprise that you can customize it further, although we won't cover that in this short tutorial. A typical login screen for an Ubuntu 10.10 system is shown in Figure 1, and a typical one for Fedora 14 is shown in Figure 2. These both illustrate the default GNOME desktop used on these systems.
Figure 1. Ubuntu 10.10 login screen
Figure 2. Fedora 14 login screen
A typical login screen for an OpenSUSE 11.3 system with the default KDE 4 desktop is shown in Figure 3 or
Figure 3. OpenSUSE Linux 11.3 login screen
When you enter or select an id and press Enter, you will be prompted for your password. If a password field is showing on the login screen, as in the OpenSUSE example here, you can tab to the password field and enter your password. If there is no entry field for an id showing and you need to enter an id that is not in the list of available ids, you will usually find an entry for something like "other..." as shown in Figure 2. Select that and you should see an entry field for the id. We'll talk more about this in the section Becoming superuser (or root).
Login screens may have other items on them, including a clock, perhaps the name of the system, and icons or named menus that allow you to shut down or restart the system.
On the GNOME desktops is a small icon that looks something like a figure of a person inside a circle. Click this and you will see a dialog for accessibility options such as an on-screen keyboard or larger font. An example from our Fedora system is shown in Figure 4. We used the option to make text larger and easier to read for the login screen shown in Figure 2.
Figure 4. Fedora login accessibility options
The desktop screen
After you type in your password and press Enter again,
you should be logged in and see your desktop. Figure 5 shows what you might see as user
ian on an Ubuntu 10.10 system, with a
panel along the top and another along the bottom. To
explore the desktop, move your mouse over the icons or click on
Note: The next three images are intended to give you an impression of the way your desktop will look. Don't worry if you can't read the tiny print on them.
Figure 5. Sample initial window for Ubuntu 10 and GNOME desktop
Fedora 14 also uses a GNOME desktop. In Figure 6, we clicked the System icon on the left part of the top panel and then selected Preferences. As we hover over the Desktop Effects choice in the subsidiary menu, the hover help shows Select desktop effects. This is where you select desktop effects such as having your window edges wobble as you move them around the desktop. Note that this requires 3-D graphics capabilities and possibly a graphics driver that is not open source.
Figure 6. Sample initial window for Fedora 14 and GNOME desktop
Figure 7 shows what you might see with OpenSUSE and a KDE 4 desktop.
Figure 7. Sample initial window for SUSE Linux and KDE desktop
The relatively new KDE 4 desktop uses a different navigation metaphor, which we'll discuss more in the section Navigation and settings. Note that the window menu for Desktop folder slides out to the left or right of the window, rather than being fixed at the top.
Navigation and settings
Let's spend a moment exploring the Linux panels on the desktop and then look at navigation and an example of how you can customize your desktop by switching to left-handed mouse usage.
Panels give you a starting place for interacting with your desktop and provide information about your system. You will usually find one or two panels on your desktop. Typically these will default to being on the top, the bottom, or both the top and bottom edges of the screen. You can move them to the left or right edges if you wish, typically by right clicking and changing the properties.
Different distributions and different desktops often differ in panel layout, so expect differences here. Our Ubuntu GNOME panels are shown in Figure 8. We've shown the ends of the panels for clarity.
Figure 8. GNOME panel features on Ubuntu
- The left part of the top panel provides a launching place for accessing programs, folders (directories), or system settings and information.
- The right part of the top panel provides information such as time and date, along with several quick-access buttons for functions like setting volume control, opening chat windows, and logging out.
- The left part of the bottom panel has a button to hide all windows and show the desktop, along with buttons for active windows.
- The right part of the bottom panel contains a trash bin and four rectangles that allow you to navigate between your virtual desktops. Most Linux systems set up multiple distinct desktops, so you can keep your email and web browsing on one desktop, while doing program development on another and testing on yet another, for example. You switch between them by clicking the appropriate smaller square or by using a key combination. For GNOME, Ctrl-Alt-left arrow or Ctrl-Alt-right arrow usually cycles through them in the same way that Alt-tab will cycle through application windows on a given desktop. For OpenSUSE, ctrl-F1 through ctrl-F4 will directly select desktops 1 through 4. When exploring, make sure you log in as a non-root user to avoid accidents; such mistakes may be more serious when you have unlimited authority.
The panels for our Fedora system are shown in Figure 9. The System item in the upper left is selected as we used the image from Figure 6 to create this image. Notice that we do not have quick access to the logout function in the upper right, the hide all windows function in the lower left, or the trash icon that we saw in the lower right of the Ubuntu panels. Otherwise, the panel layout is reasonably similar.
Figure 9. GNOME panel features on Fedora
The OpenSUSE system has a panel across the bottom only, as shown in Figure 10. Access to programs as well as folders and system functions starts with the large button at the far left, which we will refer to as the Start button. Also on the left are quick-access buttons to a browser and desktop navigator, followed by buttons for each of the five virtual desktops. On the right end of the panel, you find a clock and several convenience buttons similar to those at the right end of the upper Ubuntu GNOME panel.
Figure 10. KDE 4 panel features on OpenSUSE
The GNOME 2.3x desktop uses the cascading menus that have now become familiar. Figure 11 illustrates how to access the mouse settings from the Fedora System icon. Different distributions may arrange these menus differently. For example, you will find the mouse settings on Ubuntu in the same location, but if you are looking for the Desktop Effects preferences, which you find under System->Preferences->Desktop Effects on our Fedora system, you find it as the Visual Effects tab under System->Preferences->Appearance. Exploring graphical applications is often like turning over different rocks to see what is hiding underneath them.
Figure 11. Accessing mouse settings in Fedora
In contrast, the KDE 4 desktop uses a different metaphor for the Start menu. Menu panels replace each other, and you navigate by clicking on items in the menu or by mousing over the icons at the bottom of the menu. Figure 12 illustrates the Favorites and Applications menus.
Figure 12. Changing KDE 4 menus by mousing over icons
When submenus are selected, such as from Start->Applications->Utilities, a back button opens along the left of the menu so you can return to the previous menu level. Figure 12 illustrates this.
Figure 13. KDE 4 menu back button
Some Start menu items on OpenSUSE open a dialog box, possibly containing further selections. An example is the Start->Applications->Configure Desktop menu, which opens a window like that in Figure 14, where we show the hover help for the Keyboard & Mouse settings menu item.
Figure 14. KDE 4 Configure Desktop menu
Switching to left-handed mouse usage
A right-handed user is generally assumed, but you can change your mouse configuration for left-handed use, along with many other desktop settings. Refer back to Figure 11 or Figure 14 to navigate to the mouse settings dialog.
On an Ubuntu system, you should see a window similar to Figure 15 where you can change your mouse settings. In addition to basic left-handed or right-handed use, there are several other settings you can change and a tab of additional settings for accessibility. Settings take effect immediately, so once you click the left-handed choice, your mouse is set for left-handed use and you'll have to use the right mouse button as button 1 to close the dialog. The dialog on a Fedora system is similar.
Figure 15. GNOME dialog to change mouse settings
On an OpenSUSE system with KDE, you should see a window similar to Figure 16 where you can change your mouse settings. Note the mouse image in the dialog. If you switch to left-handed use, the right button in the mouse illustration will be highlighted to indicate that it is your primary selection button. Switch back to right-handed use, and the left button will be highlighted. As with the Ubuntu dialog, there are several other options that you can set. Unlike the Ubuntu dialog, the changes only take effect when you click the Apply button.
Figure 16. KDE dialog to change mouse settings
Command line access
Sometimes on a Linux system you need to enter Linux commands rather than using a GUI. A Linux Terminal window is similar to a DOS command prompt under Windows. On our KDE desktop, you can reach a list of available terminal programs using Start->Applications->System->Terminal as shown in Figure 17.
Figure 17. Opening a terminal on OpenSUSE with KDE 4
On the Ubuntu system, you can find a terminal window either under Applications->Accessories->Terminal as shown in Figure 18 or under Applications->System->Terminal. On Fedora systems, look under Applications->System Tools->Terminal.
Note: If you right-click (or use the appropriate button if you reconfigured your mouse) the terminal menu choice, you will usually see an option to add this icon to your panel or desktop. Adding it to your panel gives you quick access to a terminal without going through the menus.
Figure 18. KDE shell icon
On the OpenSUSE system, select the Terminal (konsole) choice and you will get a terminal window something like Figure 19. In both Figure 19 and Figure 20, we've included some commands and their output that we'll discuss below.
Figure 19. KDE shell icon
The Ubuntu terminal window will look something like Figure 20.
Figure 20. KDE shell icon
The default appearance of your shell window depends on your
distribution and your choice of desktop. To resize it, you can use the
left mouse button to drag the corners or sides of the window. To
scroll back through the most recent history, you can use the scroll
bar. The command prompt typically ends with a $ character for users
root. Usually the command prompt
will end with a
# character indicating that
the user of this shell is user
root or has
root authority. You can use the up arrow to recall previous commands
and modify them if necessary. You will usually find a Settings or
Terminal menu where you change things like window colors and
Figure 19 and Figure 20 show a few commands and their output:
- Shows who is using this terminal window,
ianin this case.
- Prints the full name of the current working directory, which is
/home/ianin this case. Note that the tilde (~) before the $ in the command prompt shows that the user is currently in his or her home directory.
- Changes the current or working directory. We illustrate changing
to the / (or root) directory and then to the /tmp directory, which
is usually used for storing temporary files. Note that / is the
root of the whole file system, and /root is the home directory of
cdwithout any directory name returns the user to the home directory, and using
cd -returns you to the last directory you were in before the current one. Users other than root will normally have a home directory under /home. For example, /home/ian is my home directory on a system where my id is
ian. Remember that tilde (~) is shorthand for the home directory of the current user. Add the name of a specific user to reference that user's home directory. For example, the home directory for user
iancan also be referenced as
- Without parameters, shows the name of the operating system: Linux.
-aparameter, displays additional information about your system.
- Scans the directories in your
PATHenvironment variable, and shows the full path to an executable program that would be executed if you typed the command at the shell prompt. In this case, we see that the
xclockprogram would be run from /usr/bin/xclock. Note: This application is not always installed in a default Linux installation. It is usually part of a package with a name like xorg-x11-apps, so you may have to find and install the appropriate package to use it.
- Launches a new window on your desktop with a clock. Note the
trailing & on the command, which indicates that the command
processor should return control to the terminal window rather than
wait for the command to finish. Note also that this is the first
such process spawned by this terminal window, and it has a process
PID) of 1774.
- With the
-Toption, displays all processes started by this terminal. On some systems, the default display from the
pscommand includes a process status. See the man pages for details on all possible options and output columns. If the status were displayed in this example, you would see the
bashshell program waiting for input (status
Sfor sleeping) as would be the
pscommand is running and would have status
The output from these commands is shown in the two terminal windows above. A text form from the Ubuntu system is shown in Listing 1.
Listing 1. Ubuntu output from some basic commands
ian@pinguino:~$ whoami ian ian@pinguino:~$ pwd /home/ian ian@pinguino:~$ cd / ian@pinguino:/$ cd /tmp ian@pinguino:/tmp$ uname Linux ian@pinguino:/tmp$ uname -a Linux pinguino 2.6.35-27-generic #48-Ubuntu SMP Tue Feb 22 20:25:29 UTC 2011 i686 GNU/Linux ian@pinguino:/tmp$ which xclock /usr/bin/xclock ian@pinguino:/tmp$ xclock& 2072 ian@pinguino:/tmp$ ps -T PID SPID TTY TIME CMD 2049 2049 pts/1 00:00:00 bash 2072 2072 pts/1 00:00:00 xclock 2073 2073 pts/1 00:00:00 ps ian@pinguino:/tmp$
Some other commands that you might find useful include:
- Displays information about the command named cmd_name.
info infoto find out about the info documentation system.
- Is an interface to the online manual (man) pages about the command
named cmd_name. Some information is in info format, while
some is available only in man page format. Try
man manto find out more about manual pages.
Becoming superuser (or root)
For many tasks on Linux, you need root or
superuser authority. The root user, sometimes
called the superuser, is the user that is normally used for
administrative tasks like configuring the system or installing
root only when you
need to do administrative tasks; avoid using
root for your normal work. The
root user can do anything, including accidentally destroying your
system, which is usually not a good thing. Normal users have fewer
privileges, and the system is much more protected from being
inadvertently damaged by normal users.
Most administrative applications that have a graphical interface now ask for the root password before allowing non-root users access to the function. When you need to run commands from a terminal window as root, this doesn't help.
Your first thought may be to switch to another userid by logging out of
the current userid and logging in as the new userid. But what if you
only need to run a couple of quick commands as another user? Linux has
a solution for you: The
(substitute user) and
sudo commands allow
you to temporarily run one or more commands as another user.
This is often used for tasks that require root access. Indeed, if you
connect in remotely to a system using a terminal program such as
ssh (or the very insecure
telnet), then many Linux distributions will
prevent you from signing in as root. This is a good security practice,
and we encourage you to not try to circumvent it. Rather, you should
sign in as a non-privileged user and then use the
command to do the work you need to do with root authority.
To summarize, there are two main ways to run an arbitrary command with root authority.
- Use the
sucommand, usually with the
-option to become root.
- Use the
sudocommand to execute a single command with root authority.
On systems such as Fedora or OpenSUSE, both methods are available,
su is perhaps more common.
On Debian-based systems such as Ubuntu, the security model prevents
root login, so you can neither log in as root nor use
su to become root, so you must use
Suppose you are logged in and looking at a terminal window, and you are
not the root user but need to run a command, such as
fdisk, which requires root authority. You
switch to root using the
su command alone,
or, more commonly, add the
su command without the
- option simply switches you to become
root, but does not change your environment variables, including your
- option, which may also be typed
if you really like typing extra letters, allows the login startup
files for the substitute user to be read, thus setting things such as
the path, environment, and prompt to those of the target user. Listing 2 shows examples of these two
forms on our Fedora system. We've used the
pwd (print working directory) command to
show the current working directory in each case. Note how the prompts
differ. If you'd like to understand more about how to customize your
own prompts or what makes these prompts appear as they do, check out
the "Prompt magic" tip on developerWorks.
Listing 2. Switching to the root user
[ian@echidna ~]$ su Password: [root@echidna ian]# pwd /home/ian [root@echidna ian]# su - [root@echidna ~]# pwd /root
You will notice, not surprisingly, that you had to provide a password
to switch to root. Once you have root authority, you can use
to switch to another user or to switch to root with the login option.
If you want to switch to a non-root user, just add the id. As before,
you can use the
- option or not, according
to your needs. For example:
su - db2inst1
To return to the previous id, press
exit and press
Enter if you are using the bash shell, which is
the default on most Linux systems.
Now that we've learned how to use
put it into practice with the
Listing 3. Running the fdisk command with su
[ian@echidna ~]$ fdisk /dev/sda Unable to open /dev/sda [ian@echidna ~]$ su - Password: [root@echidna ~]# fdisk /dev/sda Command (m for help): m Command action a toggle a bootable flag b edit bsd disklabel c toggle the dos compatibility flag d delete a partition l list known partition types m print this menu n add a new partition o create a new empty DOS partition table p print the partition table q quit without saving changes s create a new empty Sun disklabel t change a partition's system id u change display/entry units v verify the partition table w write table to disk and exit x extra functionality (experts only) Command (m for help): q [root@echidna ~]# exit logout [ian@echidna ~]$
su command, the
sudo command allows you to run commands
with the authority of another user. The commands that a given user or
class of users may execute are listed in the /etc/sudoers file. In
contrast to the
su command, you do
not need to know the password of the root, or
other user, although you will need to provide your own password. The
/etc/sudoers file is maintained by root and can be edited using the
Usually, if you are executing multiple
commands in rapid succession, you will not need to reenter your
password for each one. An alternative is to run
sudo with the
option, which runs a shell for you, from which you can run many
commands as the target user until you close the shell.
Listing 4 illustrates
both of these methods.
Listing 4. Using the sudo command on Ubuntu
ian@pinguino:~$ fdisk /dev/sda Unable to open /dev/sda ian@pinguino:~$ sudo fdisk /dev/sda [sudo] password for ian: WARNING: DOS-compatible mode is deprecated. It's strongly recommended to switch off the mode (command 'c') and change display units to sectors (command 'u'). Command (m for help): p Disk /dev/sda: 120.0 GB, 120034123776 bytes 255 heads, 63 sectors/track, 14593 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x54085408 Device Boot Start End Blocks Id System /dev/sda1 * 1 2611 20972826 7 HPFS/NTFS /dev/sda2 2612 2624 104422+ 83 Linux /dev/sda3 2625 14593 96140962 5 Extended /dev/sda5 2625 2689 522081 82 Linux swap / Solaris /dev/sda6 2690 5180 20008926 83 Linux /dev/sda7 5181 9341 33423201 83 Linux /dev/sda8 9342 14593 42186658+ 83 Linux Command (m for help): q ian@pinguino:~$ sudo -s root@pinguino:~# fdisk /dev/sda WARNING: DOS-compatible mode is deprecated. It's strongly recommended to switch off the mode (command 'c') and change display units to sectors (command 'u'). Command (m for help): q root@pinguino:~# exit ian@pinguino:~$
If you are not authorized in the sudoers file, you will receive an error message similar to that in Listing 5.
Listing 5. Attempting to use sudo without authority
[ian@echidna ~]$ sudo fdisk /dev/sda [sudo] password for ian: ian is not in the sudoers file. This incident will be reported.
Using a GUI application as another user
You may have noticed in the discussion of the
su command in the previous
section that we ran only commands that displayed output in the
terminal window. Usually you will be able to run GUI commands too. For
example, some installation programs require you to have root authority
to install a program and have a GUI installer. If you find you cannot
start GUI applications as another user, then read on, as you may have
to take additional steps on some distributions in order to run GUI
applications as another user.
Note: Recent distributions often let you have multiple desktops open at once and switch between them using a key sequence such as Ctrl-Alt-F7 or Ctrl-Alt-F8. Depending on what you need to do, this may be another alternative. See the section on Logout for details on this menu option.
GUI applications on Linux use the X Window System, a client-server system designed to allow multiple users to access a computer across a network using windowed applications. An X display is known by a name of the form hostname:displaynumber.screennumber. For Linux running on a workstation such as a PC, there is typically only one display with a single screen. In this case, the displayname may be, and usually is, omitted so the display is known as :0.0, or sometimes just :0.
The X Window System server needs to know the display and also whether you are authorized to connect to the server. Authorization is most commonly done using the MIT-MAGIC-COOKIE-1, which is a long random string that is regenerated whenever the server is reset. So that applications can pass this information to the X server, you will have DISPLAY and XAUTHORITY variables set in your environment. The XAUTHORITY variable will point to a file that is usually only able to be read or written by the owning user as a security precaution. We assume you are using a graphical login if you are reading this, so your startup should have already set these for you. The example in Listing 6 is from our Ubuntu system and shows the values of the DISPLAY and XAUTHORITY variables as well as the ownership for the file pointed to by the XAUTHORITY variable.
Listing 6. DISPLAY and XAUTHORITY
ian@pinguino:~$ echo $DISPLAY :0.0 ian@pinguino:~$ echo $XAUTHORITY /var/run/gdm/auth-for-ian-WoeKHn/database ian@pinguino:~$ ls -l $XAUTHORITY -rw------- 1 ian ian 53 2011-04-01 16:24 /var/run/gdm/auth-for-ian-WoeKHn/database
Now we attempt to use
sudo to run the
xclock command as user
editor, again on our Ubuntu system. As
Listing 7 shows, the
values for DISPLAY and XAUTHORITY variables are the same as for user
ian, but the
xclock command fails.
Listing 7. DISPLAY and XAUTHORITY with sudo
ian@pinguino:~$ sudo -u editor echo $DISPLAY [sudo] password for ian: :0.0 ian@pinguino:~$ sudo -u editor echo $XAUTHORITY /var/run/gdm/auth-for-ian-WoeKHn/database ian@pinguino:~$ sudo -u editor xclock No protocol specified Error: Can't open display: :0.0
In this case, user
editor has the XAUTHORITY
variable set to /var/run/gdm/auth-for-ian-WoeKHn/database, but we
already saw that the permissions on that file only allow user
ian to read or write it. The variable may
as well not be set if user
read the file it points to. Before we look at how to address this
issue, let's look at what happens if we unset either the DISPLAY or
XAUTHORITY variables for user
do this by running the
xclock command with
an environment variable modified using the
-u option to unset an environment
variable before running
xclock. Our results
are in Listing 8.
Listing 8. Unsetting DISPLAY and XAUTHORITY
ian@pinguino:~$ env -u DISPLAY xclock Error: Can't open display: ian@pinguino:~$ env -u XAUTHORITY xclock
You may be surprised to see that the
command runs, even though we unset the XAUTHORITY environment
So far, we have mentioned the MIT-MAGIC-COOKIE-1 security method. If
the token is not provided, the X server will also check a list of
authorized hosts. Use the
xhost command to
display or update the list. Use the
option to add entries and the
- option to
remove entries. Use the special family entry
local: (note the ':') to allow access to
the display by any local user on the system. Since you are a single
user system, this means that you can su to an arbitrary non-root user
and can now launch
xclock or other X
applications. We illustrate the use of the
xhost command in Listing 9.
Listing 9. Using xhost
ian@pinguino:~$ xhost access control enabled, only authorized clients can connect SI:localuser:ian ian@pinguino:~$ xhost +local: non-network local connections being added to access control list ian@pinguino:~$ xhost access control enabled, only authorized clients can connect LOCAL: SI:localuser:ian ian@pinguino:~$ sudo -u editor xclock ian@pinguino:~$ # Close the xclock window to return here ian@pinguino:~$ xhost -local: non-network local connections being removed from access control list ian@pinguino:~$ xhost access control enabled, only authorized clients can connect SI:localuser:ian
On a single user system, enabling the display for use by all local
users is usually a reasonable and simple solution. If you need to be
more restrictive, use the
xauth to extract
the cookie from your XAUTHORITY file and give it to the user who needs
access to the display. In Listing 10 we perform the following tasks:
ianto display the cookie in a format that can be emailed or otherwise sent to the desired other user.
sudo -sand switch to user
editorto run several commands.
xauthto create a new authorization file. Note that we used
echoto pipe the data to stdin while splitting the command over several lines by using a trailing backslash (\).
- We export a new value for the XAUTHORITY variable so it now points to our newly created authorization file.
- Finally, we run the xclock command using a trailing ampersand (&) to run it in the background and retain control of our terminal window.
Listing 10. Using xauth
ian@pinguino:~$ xauth -f $XAUTHORITY nextract - :0 0100 0008 70696e6775696e6f 0001 30 0012 4d49542d4d414749432d434f4f4b49452d31 0010 3c4bc87 c2ce4ce5e97f8199c213b4ec9 ian@pinguino:~$ sudo -s -u editor editor@pinguino:~$ echo "0100 0008 70696e6775696e6f 0001 30 0012"\ > " 4d49542d4d414749432d434f4f4b49452d31"\ > " 0010 3c4bc87c2ce4ce5e97f8199c213b4ec9" | > xauth -f ~editor/temp-xauth nmerge - xauth: creating new authority file /home/editor/temp-xauth editor@pinguino:~$ export XAUTHORITY=~editor/temp-xauth editor@pinguino:~$ xclock& 4827
This brief introduction will probably get you started with running X
applications as another user. Although we have used Ubuntu as an
example, the basic principles we have demonstrated here apply to all
distributions. For more details on using the
commands, you can use any of these commands as appropriate to view the
online manual pages:
On Linux and UNIX® systems, all files are accessed as part of a single large tree that is rooted at /. To access the files on a CD-ROM, you need to mount the CD-ROM device at some mount point in the file tree. On current distributions, this is usually automated for you; you need only insert the disc and it will be recognized and mounted. Once mounted, it is important to properly unmount the device to avoid data loss.
Mounting removable devices
When you insert a CD or DVD disc into a SUSE 11.3 system, or attach a USB drive, you will see a pop-up window similar to Figure 21. If you miss the pop-up before it closes, you can use the panel icon that we've shown in the top left of the figure to open it again. Hovering over the icon shows the tooltip indicating that the device is not yet mounted.
Figure 21. Pop-up when CD or DVD loaded on SUSE system
Hovering over the plug icon to the right of the image reveals a tooltip saying "Click to access this device from other applications". Clicking over the text "4 actions for this device" expands the image to look like Figure 22. The available actions may differ on your system if you have installed different software packages.
Figure 22. Available actions for CD or DVD
If you click the "Open with File Manager" selection, you will see a window something like Figure 23. From this window you can navigate around the DVD, open files, or run applications. Hover over an item to see a description in the right part of the window.
Figure 23. SUSE File Manager
On Ubuntu and Fedora systems, the default action on inserting a disc is slightly different. Usually, an icon similar to that shown in Figure 24 will appear on your desktop. The file manager (Nautilus) may also open automatically. If it does not, you can double-click the icon to open the file manager. Depending on your system, you may also be prompted as to whether to run the autorun file in the root of the disc or not.
Figure 24. Inserted CD on Ubuntu
If you clicked to access the device from other applications (OpenSUSE),
or opened it with File Manager or another application on any
distribution, then the device will have been mounted for you. It will
usually be mounted in the /media directory and will probably use the
disc label as a mount point. You can verify by opening a terminal
window and running the
mount command as
shown for our OpenSUSE system in Listing 11. Other systems are very similar,
although the mount options may differ slightly.
Listing 11. Using the mount command
ian@lyrebird:~> mount /dev/sdb12 on / type ext4 (rw,acl,user_xattr) proc on /proc type proc (rw) sysfs on /sys type sysfs (rw) ... /dev/sr0 on /media/openSUSE-DVD-x86_64.0702..001 type iso9660 (ro,nosuid,nodev,uid=1000, utf8)
In this case our disc is mounted at /media/openSUSE-DVD-x86_64.0702..001 and you can explore it or change to a directory on the disc from the terminal window. Note that the CD/DVD device is /dev/sr0. Devices on a Linux system also appear in the filesystem tree. To put this another way, the filesystem that is on the media in the device /dev/sr0 is accessible to applications starting at the mount point /media/openSUSE-DVD-x86_64.0702..001. If you'd like to learn more about how devices are mounted, see our article Learn Linux, 101: Control mounting and unmounting of filesystems.
Safely removing devices
Once a DVD or CD is mounted, you can use the files on the disk as they are now part of your file system. While a CD-ROM is mounted, Linux will lock the CD so that it cannot be ejected with the Eject button. Of course, this doesn't stop you from unplugging an external CD or USB drive, pulling a USB stick out of the USB socket, or ejecting a floppy disk. To avoid potential data loss, you should always remove the device safely by first unmounting it.
You can unmount devices from the graphical desktop, or from the command
umount command (note umount
without an 'n') unmounts a device, and the
eject command first unmounts a device and then
tries to eject it, for example by opening a CD drawer. Traditionally,
mounting and unmounting devices required root authority. Nowadays, it
is common to allow user mounting, so that a non-root user is
able to mount and unmount devices. You may have noticed back in Listing 11 the option
uid=1000. The uid of 1000 corresponds to
user ian on this system as shown in Listing 12.
Listing 12. Using the id command for the current user
iian@lyrebird:~> id uid=1000(ian) gid=100(users) groups=33(video),100(users)
If you use the graphical desktop tools to unmount the device, you may only need to worry about ids if you have logged out and then back in as a different user. So let's look at the graphical tools, then the command line ones.
On Ubuntu or Fedora, if you right click on the icon for the removable media you will see a context menu similar to that in Figure 25. You will have an option to either unmount or eject the device. Select the eject option for a CD or DVD and the device will be unmounted, the icon will disappear from your desktop, and your drawer will open. For a USB drive, the option may be unmount rather than eject, and you can safely unplug the device after it is unmounted. If you use an external hard drive with multiple partitions, you need to make sure that all partitions are unmounted before removing or powering off the drive.
Figure 25. SUSE File Manager
In Figure 26 we show our OpenSUSE system with an attached USB drive as well as the DVD we had used earlier. The DVD and one partition of the hard drive are mounted. OpenSUSE distinguishes the mounted from the unmounted by changing the plug icon (when a device is not mounted) to an eject button (when it is mounted). You will also note that the small square at the bottom left of the device icon also changes from having a diagonal line to having an asterisk. Note that for writeable media, such as our hard drive, the available space is also displayed.
Figure 26. OpenSUSE File Manager
To unmount or eject a mounted drive, simply click the eject button (shown above for the 2006R1 partition). If you eject a device such as a CD or DVD where a drawer opens or some other similar physical disconnection takes place, then the device will be removed from your list of plugged devices.
Safe removal from the command line
We mentioned the
eject commands earlier. Let's now look at
how to use them and the
lsof that you may
also want to know about. You will find some differences between
systems in this area, so be prepared for things not to be exactly as
we illustrate here.
To begin, we'll look at using the
command to unmount the CD on our Ubuntu system as shown in Listing 13. We first use
grep to filter out the entries from the
mount to show only those entries
that contain 'media', the usual mount point for removable media. We
umount to unmount the device using
its mount point (/media/Ubuntu 10.10 i386). Finally, we
repeat the mount + grep filter to confirm that the device is no longer
mounted. Note that you can use either the mount point or the device
name (/dev/sr0 in this case) as the argument to
Listing 13. Unmounting a CD on Ubuntu from the command line
ian@pinguino:~$ mount | grep media /dev/sr0 on /media/Ubuntu 10.10 i386 type iso9660 (ro,nosuid,nodev,uhelper=udisks, uid=1000,gid=1000,iocharset=utf8,mode=0400,dmode=0500) ian@pinguino:~$ umount /media/Ubuntu\ 10.10\ i386 ian@pinguino:~$ mount | grep media
As you can see, Ubuntu allows you to use the command line to unmount a drive that was automatically mounted. Repeating the above scenario on OpenSUSE 11.3 is likely to result in something like Listing 14.
Listing 14. Unmounting a CD on OpenSUSE from the command line (1)
ian@lyrebird:~> mount | grep media /dev/sr0 on /media/openSUSE-DVD-x86_64.0702..001 type iso9660 (ro,nosuid,nodev,uid=1000, utf8) /dev/sdc6 on /media/2006R1 type ext3 (rw,nosuid,nodev) ian@lyrebird:~> umount /media/openSUSE-DVD-x86_64.0702..001/ umount: /media/openSUSE-DVD-x86_64.0702..001 is not in the fstab (and you are not root) ian@lyrebird:~> umount /dev/sr0 umount: /dev/sr0 is not in the fstab (and you are not root)
Sometimes you will find a disconnect between what you can do
graphically and what you might expect to do at a command line. As
Linux matures, such disconnects become less frequent, but you will
sometimes find them as we have done here. The obvious solution, given
what you have already learned in this tutorial, is to use
run the required command with root privileges. So let's try it using
su as shown in Listing 15.
Listing 15. Unmounting a CD on OpenSUSE from the command line (2)
ian@lyrebird:~> su - Password: lyrebird:~ # mount | grep media /dev/sr0 on /media/openSUSE-DVD-x86_64.0702..001 type iso9660 (ro,nosuid,nodev,uid=1000, utf8) /dev/sdc6 on /media/2006R1 type ext3 (rw,nosuid,nodev) lyrebird:~ # umount /dev/sdc6 lyrebird:~ # umount /media/openSUSE-DVD-x86_64.0702..001/ umount: /media/openSUSE-DVD-x86_64.0702..001: device is busy. (In some cases useful info about processes that use the device is found by lsof(8) or fuser(1))
We were able to unmount /dev/sdc6 successfully, but were unable to
unmount /media/openSUSE-DVD-x86_64.0702..001 because Linux claimed it
was busy. We would get a similar error message if we tried to use the
eject command. Remember that we said that
Linux will lock a CD or DVD closed while it is in use. More generally,
you cannot unmount a filesystem if it is in use by some other user. As
suggested in the error message above, you can use the
command to find which user is causing your unmount problem. Typical usage
is illustrated in Listing 16.
Listing 16. Using lsof and fuser (as root)
lyrebird:~ # lsof /media/openSUSE-DVD-x86_64.0702..001/ COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME bash 3824 ian cwd DIR 11,0 2048 2048 /media/openSUSE-DVD-x86_64.0702..001/ boot lyrebird:~ # fuser -um /media/openSUSE-DVD-x86_64.0702..001/ /media/openSUSE-DVD-x86_64.0702..001: 3824c(ian)
lsof command shows the actual file or
directory (/media/openSUSE-DVD-x86_64.0702..001/boot in this case)
that is open as well as the process id (3824) and user id (ian) using
the file or directory. The
shows the user and process id using the
/media/openSUSE-DVD-x86_64.0702..001 filesystem, but not the specific
open file or directory.
Normally you would use this information to cleanly close the open
process or window using the filesystem. On some Linux systems there is
-L option to
umount that allows a lazy unmount
where the filesystem is detached from the filesystem hierarchy
immediately, and all references to the filesystem are cleaned up when
the filesystem is no longer busy. On OpenSUSE 11.3 this option is not
available, so you need to clean up the filesystem references, either
by terminating the offending processes or by ensuring they are no longer
using affected resources, before unmounting.
We mentioned back in Listing 14 that the OpenSUSE system does not
support command line use of
for a device that was mounted from
the desktop, so we attacked the problem by using root authority. There
is another approach using the
command to unmount the device. HAL is a Hardware Abstraction
Layer, which provides a consistent application interface to various
hardware devices. If you use
will still be unable to unmount a busy device. Listing 17 shows how to use
halmount and then switch to
root to forcibly terminate the process that
is keeping the disc busy. Note that killing the process in this way
may cause data loss, so we do not recommend it unless you are sure you
will not lose data. We then switch back to normal user mode and use
halmount to unmount the filesystem that is
no longer busy. Finally we use
open the drawer and eject the DVD.
Listing 17. Using halmount, kill, and eject
ian@lyrebird:~> halmount -u /dev/sr0 /dev/sr0: org.freedesktop.Hal.Device.Volume.Busy: umount: /media/openSUSE-DVD-x86_64.0702 ..001: device is busy. ian@lyrebird:~> lsof /dev/sr0 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME bash 3824 ian cwd DIR 11,0 2048 2048 /media/openSUSE-DVD-x86_64.0702..001/ boot ian@lyrebird:~> su - Password: lyrebird:~ # kill -9 3824 lyrebird:~ # ps -ef | grep 3824 root 5542 5507 0 22:47 pts/2 00:00:00 grep 3824 lyrebird:~ # logout ian@lyrebird:~> halmount -u /dev/sr0 ian@lyrebird:~> eject /dev/sr0
We hope this brief introduction to removable media use on Linux will help you enjoy your removable media files and avoid data loss.
The tasks of logging out, locking your screen, shutting down, and restarting the system are usually related in the sense that they are accessed from the same or similar menus. Frequently your distribution will add a quick launch button to access these tasks. If not, you can add one yourself.
To log out, click Start and then Leave. You will see a menu like Figure 27 with options for logging out, locking the screen, and shutting down or restarting the system. Click the appropriate selection.
Figure 27. Adding a logout button with Red Hat enterprise Linux 3
You will also see icons for leave and lock at the bottom right of the OpenSUSE panel. Click the Leave icon on the right, and you will see a dialog box like Figure 28. Again, make your selection.
Figure 28. Using the OpenSUSE panel logout icon
You access Ubuntu logout and restart functions from a panel icon at the right end of the top Ubuntu panel. This icon is similar to the Leave icon on OpenSUSE. Click it to reveal a dialog similar to Figure 29 where you can make your choice.
Figure 29. Using the Ubuntu panel logout icon
Access the Fedora logout and restart functions from the System menu on the top panel as shown in Figure 30. Your choices are similar to the OpenSUSE and Ubuntu choices that you have seen above.
Figure 30. Logging out of the Fedora GNOME desktop
Adding a logout button to your panel
Fedora does not install a panel icon for logout or screen lock similar to those on OpenSUSE or Ubuntu. However, you can add your own quite easily.
Start by right-clicking a blank part of the panel. From the context menu, select Add to Panel..., and you will see a selection of items that you may add. Scroll down to the Log Out selection and click on it to add it to your panel. You can add the Lock Screen icon in the same manner.
Figure 31. Adding a logout button to the Fedora GNOME desktop
A logout icon will be added to your panel.
If an application is not in the list, and you can start it from the Applications menu or you can open the menu to the point where you would start the application, then right-click to open a context menu that includes choices to add a launcher to the panel or to your desktop.
Adding users and groups
Sometimes you will need to define new users of your system and new groups for those users. For example, you may need to define a user called mqm and a group also called mqm (as well as another group called mqbrkrs when installing the embedded messaging component in WebSphere Application Server), or you may need to create users to administer databases.
If you do not specify a user number, graphical tools will usually assign the next available user number. For Fedora and Red Hat systems, user numbers start at 500, so the user you created when you installed your system is probably user 500. For OpenSUSE and Ubuntu, the numbers start at 1000. If you use the same id on several systems as I do, you will probably find it convenient to use the same id and group numbers on each system too.
For the purpose of this section, we will add a user called
testuser with id 2000 and group 2000.
Usually you will define the group first and then define the users who
will use the group, so that's what we will do here. You can either use
the graphical tools for user administration or enter commands in a
terminal window. We'll give an overview of the graphical process here
using OpenSUSE's system administration tools. Then
we'll tell you where to find the corresponding tools
on a Fedora or Ubuntu system. Finally we'll give you the commands if you really want to do it from the
Adding users and groups to your OpenSUSE system
On an OpenSUSE system with KDE, you access the YaST (Yet Another System Tool) control center using Start->Applications, then select System and scroll down to Administrator Settings as shown in Figure 32.
Figure 32. YaST2 Control Center
Open this application and click Security and users in the left panel to view the tasks shown in the main panel of Figure 33.
Figure 33. YaST2 Control Center
Select User and Group Management. If you have not recently received root authority, you will be prompted for the root password. On the next screen, you will see any existing users. Select the Groups tab, and you will see something like Figure 34.
Figure 34. Group list in YaST2 Control Center
Click the Add button to add a new group. You will see something like Figure 35. Note that there are a number of groups that were created when you installed your system. Enter 'testuser' for the Group Name and '2000' for the Group ID. Click OK to return to the group list display and see the new group listed. At this point your group has not yet been saved to the system, so it will be lost if you cancel.
Figure 35. Adding a group in YaST2 Control Center
Click the Users tab to return to the user display, then click Add to add a new user. Enter 'Test User' for the User's Full Name, 'testuser' for the User Name, then type and retype an initial password for the user. See Figure 36.
Figure 36. Adding a user in YaST2 Control Center
Click on the Details tab and enter '2000' for the User ID (uid), and select 'testuser' from the Default Group drop-down menu. This panel is where you can change the default home directory and default login shell, among other items. You can also select additional groups that this user will be a member of. When you have finished, click OK to return to the list of users where you will see your new user. Click OK, and YaST will process all your changes and save them to the system.
Figure 37. User details in YaST2 Control Center
Adding users and groups to your Fedora or Ubuntu system
On GNOME systems, such as our Fedora and Ubuntu systems, you start user management from the System->Administration->Users and Groups menu as shown in Figure 38.
Figure 38. Starting user and group management on GNOME
However, Fedora and Ubuntu have different dialogs once you open the
User and Group management. Fedora starts the
system-config-users application, while
Ubuntu starts the
We'll illustrate the Fedora usage here and then summarize the
differences for Ubuntu.
If you are not logged in or recently authenticated as root, you will need to provide the root password when prompted. You will then see the User Manager screen, opened at the Users tab as in Figure 39. By default, only normal users and groups are shown. To view system users and groups, uncheck the Hide system users and groups checkbox under Edit->Preferences.
Figure 39. Fedora User Manager
We could do as we did above for the OpenSUSE system and define our
groups first. However, the Red Hat User Manager has a convenient feature that
lets you create a private group for a
user with the group name being the same as the user name. So
click the Add User button and fill in the details
testuser user as for
OpenSUSE above. However, this time, check the Specify user
ID manually and Specify group ID
manually check boxes and fill in 2000 for each of these
values. Our screen now looks like Figure 40.
Figure 40. Adding a user in Fedora
After you click OK, you will return to the User Manager. Your new user will already be added to the system, unlike the case for OpenSUSE. Click Add Group to add any additional groups you may need. To make users members of additional groups, you can either select a group and use its properties to add users or select a user and use the properties to add groups. When you are done with properties, click OK to return to User Manager and then File->Quit to close the User Manager.
Ubuntu user manager
Now that you are familiar with adding users on both OpenSUSE and
Fedora, you will be able to manage the Ubuntu process. In general,
Ubuntu will lead you through the process of adding a user and set up
the user with a default id and group. Once you have added
testuser in this way, you should see a
screen like Figure 41.
Figure 41. User management in Ubuntu
At this point you will need to use the
Manage Groups button to add the new group
(or you could add it before you add the user). Once you have added the
testuser group, you will need to come back
to the screen of Figure 41, select
testuser id, and click the
Advanced button to change both the id number and
primary group for the user.
Adding users and groups using the command line
You can add or change users and groups from the command line. These tasks require root authority.
Information on groups is stored as a flat file in /etc/group. You may
groupadd command to add a new
group. This is fairly simple. Adding a new user is a little more
complex as there are more parameters, and you will need the numerical
number of the user's group. Let's use the
groupadd command to add our
testuser group, with group id 2000, and
then use the
grep command to search
/etc/group and verify the settings. Note: If you do not provide a
group id, the system will assign the next one that is higher than any
existing group id.
root@pinguino:~# groupadd -g 2000 testuser root@pinguino:~# grep testuser /etc/group testuser:x:2000:
As you see, the
testuser group is 2000. Now
let's use the
useradd command to add the
testuser user. The
-c option allows us to specify a comment
that is usually a user's real name. The
option allows us to specify the numerical id (2000) for the user. The
-d option allows us to specify the home
directory for the user. The
specifies the user's primary group. Here we use 2000, which is the
testuser group we just created. The last
option we use is the
-G option to specify
additional groups for this user. Here we can use the group name. In
this case, we'll add
testuser to the group
Once you have added the user, you can
grep command again, and you will see
testuser has been added to the
groups. At this point you have created a new user, but the user does
not have a password and cannot log on to the system. Some users do not
need to log on, so that would be alright for those users. The root
user has the authority to set (or reset) passwords for other users. To
do this, you use the
passwd command and
give the username as a parameter. You will be prompted for the new
password, and then you will be prompted to retype it for
root@pinguino:~# useradd -c"Test User" -u 2000 -d/home/testuser -g 2000 -G ian \ > testuser root@pinguino:~# grep testuser /etc/group ian:x:1000:testuser testuser:x:2000: root@pinguino:~# passwd testuser Enter new UNIX password: Retype new UNIX password: passwd: password updated successfully
Finally, you may need to add users to an existing group. You can use
usermod command to do this, but you
need the list of existing groups for the user as you will replace
the list of additional groups. It is often easier to edit /etc/group
directly. Make a backup copy first, just in case you make a mistake.
To add the editor user to both the ian and testuser groups, edit
/etc/group and update the lines for ian and testuser so they look as
You will find much of the user information is stored in /etc/passwd,
but you should not edit this file yourself. Use the
userdel commands instead. If you are
not a full time system administrator, you will probably find it easier
to do occasional manipulation of users and groups through the
- For help with more advanced Linux development tasks, take a look at the developerWorks roadmap for LPIC-1. The roadmap leads to many developerWorks articles to help you study for LPIC-1 certification based on the April 2009 objectives.
- Customize your own prompts with "Prompt magic" (developerWorks, September 2000).
- In the developerWorks Linux zone, find hundreds of how-to articles and tutorials, as well as downloads, discussion forums, and a wealth of other resources for Linux developers and administrators.
- Stay current with developerWorks technical events and webcasts focused on a variety of IBM products and IT industry topics.
- Attend a free developerWorks Live! briefing to get up-to-speed quickly on IBM products and tools, as well as IT industry trends.
- Watch developerWorks on-demand demos ranging from product installation and setup demos for beginners, to advanced functionality for experienced developers.
- Follow developerWorks on Twitter, or subscribe to a feed of Linux tweets on developerWorks.
Get products and technologies
- Evaluate IBM products in the way that suits you best: Download a product trial, try a product online, use a product in a cloud environment, or spend a few hours in the SOA Sandbox learning how to implement Service Oriented Architecture efficiently.
- Get involved in the My developerWorks community. Connect with other developerWorks users while exploring the developer-driven blogs, forums, groups, and wikis. | <urn:uuid:5ea878b5-b4e2-4f95-a885-259bd8e6520a> | CC-MAIN-2017-09 | http://www.ibm.com/developerworks/linux/library/l-basics/index.html?ca=drs- | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501171171.24/warc/CC-MAIN-20170219104611-00078-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.851537 | 13,758 | 2.9375 | 3 |
If you've been on the internet today, you probably know by now that it's International Women's Day. To celebrate, we decided to blog about some of the women throughout history who have made outstanding contributions to the fields of Science, Technology, Engineering, and Math (STEM).
She was the lead software designer for NASA's Apollo Program and SKYLAB, which took tons of astronauts to space and back again safely. It doesn't get much more badass than that. Hamilton and her team wrote so much code for the space program that it filled a stack of books taller than she was.
Grace Murray Hopper
Modern computer science owes a lot to "Amazing Grace" Hopper. She was instrumental in developing and popularizing machine-independent programming languages, and is widely credited with the development of COBOL, one of the first high-level programming languages. As if that didn't already make her a superstar, she was also one of the first programmers on the Harvard Mark I computer, worked on the development of the UNIVAC I commercial computer, and is credited with inventing the first compiler for a computer programming language. Oh, and did we mention she was a Rear Admiral in the United States Navy?
Born March 23, 1882 in Erlangen, Germany, Noether was a brilliant mathematician. Her contributions to the field include an algebraic theorem that united two fundamental laws of physics, an effort that many consider to be as important as her contemporary Albert Einstein's theory of relativity. Her prolific and groundbreaking work in abstract algebra and ring theory undergirds many of the most important advances in modern physics, including the work around Higgs Boson. Learn more about Noether in this excellent piece from The New York Times.
When Sally Ride launched into space in 1983 aboard the Space Shuttle Challenger, she also launched the dreams of thousands of little girls across the world who saw a whole new universe of possibility open up to them. Ride was not only the first American woman in space, at age 32 she was also the youngest American in space. She followed up her historic Challenger voyage with a second mission aboard the same shuttle in 1984. She continued to work closely with NASA until her death in 2012.
Computer programmers owe their careers to Ada Lovelace, the woman who wrote what is commonly recognized as the first algorithm that could be processed by a machine. Her work with Charles Babbage on his mechanical general-purpose computer is at the foundation of all modern computer science. But while Babbage saw the future of computing as focused solely on calculation, Lovelace believed that computing had far more potential. Her notes and writings prove that she was far ahead of her time.
No conversation about women in STEM would be complete without a mention of Marie Curie, whose research led to the isolation of polonium, named after the country of Marie's birth, and radium. Curie spent her early career researching alongside her husband, Pierre Curie, a professor in the school of physics at the Sorbonne in Paris. After herself graduating from the Sorbonne, she succeeded her husband as Head of the Physics Laboratory. Upon his untimely death in 1906, she also took his place as the Professor of General Physics in the Faculty of Sciences, the first woman to hold this position.
Women of ExtraHop, Making A Mark in STEM
ExtraHop is also home to some women who are making a big mark in STEM. Palvi Mehta, ExtraHop's CFO, is one of those women. In addition to her work at ExtraHop, she is on the board of Code.org, for which she serves as treasurer. Her deep experience in the technology industry working with companies like RadioFrame Networks, and NewPath Networks, also makes her a key strategic advisor to Code.org as it works to advance its mission to make computer sciences education available to the masses. Palvi was also recently recognized as Seattle's mid-size company CFO of the year by The Puget Sound Business Journal.
To meet some of the other outstanding women at ExtraHop making their mark in STEM, check out the videos below: | <urn:uuid:bfd8ac69-9f29-4b8b-a24d-3aeb07f58a42> | CC-MAIN-2017-09 | https://www.extrahop.com/company/blog/2016/great-women-in-stem/ | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501171171.24/warc/CC-MAIN-20170219104611-00078-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.973713 | 840 | 3.609375 | 4 |
The "learn to code" movement is picking up momentum as organizations like Code.org press for computer science to be taught in schools. But there's a big difference between just learning to code and learning actual computer science.
Terence Eden's blog on the matter puts it pretty clearly. When asked to sort a set of numbers, all sorts of discussion can arise: Which way to sort (high to low or low to high)? What are we going to do with the sorted numbers? What are the potential "gotchas" (e.g., if two numbers are the same)? Thinking through this is exploring computer science.
Learning to code, however, or just learning code (like "sort([7, 8, 1, 3, 2, 7, 6]);") might only teach syntax.
Many of today's free online programming sources throw you into the code immediately, so you can play around and learn by doing. Maybe the fundamentals of thinking logically and reasoning through a problem, however, would serve students better.
Code.org's "unplugged" computer science classes are an excellent example of this. You don't need a device or internet connection, yet the tutorials teach what computer science is all about. Similarly, I'm a big fan of Harvard's CS50 course (the free version is on edX), because it not only teaches programming languages, but, more importantly, how to think algorithmically and solve problems.
As someone who has taken CS50, taught both children and adults, and majored in literature, I agree with Eden when he says:
Learning to code is merely teaching people to spell.
Computer Science is about what makes a poem beautiful, why alliteration is alluring, how iambic pentameter unlocks the secrets of Shakespeare.
That is what I think we need to be teaching.
Read more of Melanie Pinola's Tech IT Out blog and follow the latest IT news at ITworld. Follow Melanie on Twitter at @melaniepinola. For the latest IT news, analysis and how-tos, follow ITworld on Twitter and Facebook. | <urn:uuid:27c0d78d-3dcd-4a94-b591-c75e3dd2b24c> | CC-MAIN-2017-09 | http://www.itworld.com/article/2700153/consumerization/the-difference-between-learning-to-code-and-learning-computer-science.html | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501174135.70/warc/CC-MAIN-20170219104614-00130-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.937572 | 433 | 3.09375 | 3 |
GCN LAB IMPRESSIONS
IBM claims breakthrough with 'liquified' memory
- By Greg Crowe
- Jun 30, 2011
IBM already has pretty good memory for a hundred-year-old, but now it has gotten even better. The company’s research division in Zurich, Switzerland, just announced a breakthrough that will enable manufacturers to use a type of memory that was previously deemed too unreliable for widespread usage.
Researchers said their tests of a new approach to phase-change memory showed it performed 100 times faster than the most advanced flash memory, and that was in a worst-case scenario. PCM also can last for at least 10 million write cycles, compared with 30,000 cycles for enterprise-class Flash and 3,000 cycles for consumer flash drives, IBM said.
PCM was initially developed in the 1960s. Developed as solid-state alternative to dynamic random-access memory (DRAM), PCM uses an electrical charge to change a piece of chalcogenide glass — some forms of which exist in CD-RWs — from a crystalline state to a more amorphous one.
Does that seem like sci-fi? Sure, but the difference in the resistances of the two states gives you your ones and zeros. Although its performance was comparable to DRAM, it was considered too much of a power hog and its materials too expensive to be put in mainstream devices. So PCM was essentially the Betamax of computer memory.
Twice Betamax actually, because when flash, another, different type of solid-state memory, was developed, PCM was again overlooked. This was in spite of the vastly superior speed that PCM was capable of over flash. It was simply too expensive to put in a drive that people could wear on their key chains.
But now, as the need for further miniaturization of memory chips continues, we will shortly run up against a wall with both DRAM and flash memory. So researchers have been working for the past several years on making PCM more affordable and stable.
First, they found a way to put two logical bits in each physical cell, thus cutting material costs nearly in half. But this created some problems with the resistance levels shifting more, which would make read errors more likely. The breakthrough that the IBM scientists have announced involves some modulation coding techniques to help allay this problem. So now nothing stands in the way of developing this technology for consumer use.
It’s like some kind of Betamax Phoenix. Hmm, I like that. Hands off, it’s my copyright now!
So when can we expect computers or portable drives to come out with this new memory? Well, IBM expects it to be ready by 2016. So don’t throw your flash drives away yet.
Greg Crowe is a former GCN staff writer who covered mobile technology. | <urn:uuid:a467262c-e5e7-4e7d-bdaa-6b3df65b619b> | CC-MAIN-2017-09 | https://gcn.com/articles/2011/06/30/ibm-breakthough-phase-change-memory.aspx | null | s3://commoncrawl/crawl-data/CC-MAIN-2017-09/segments/1487501171629.92/warc/CC-MAIN-20170219104611-00602-ip-10-171-10-108.ec2.internal.warc.gz | en | 0.969185 | 596 | 2.921875 | 3 |
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