Vsftpd + tcp_wrappers host and user access control

RHEL4 in vsftpd support at compile time has tcp_wrappers, so you can use tcp_wrappers to achieve the host access control.

Before the experiment, first said the implementation of the next order of tcp-wrappers:

First implementation of the hosts.allow, if hosts.allow inside the list, the list of the machine is allowed access; otherwise, then scroll down to hosts.deny, if the hosts.deny list inside, then refused to list the machine access, if also not (that is, which do not allow and deny list) is allowed access to the host.

Real life, host.allow can also set "Reject" feature, so generally only use / etc / hosts.allow for access control can host.

(A) of the host access control

The host (192.168.1.102) to configure vsftpd service, so in addition to 192.168.1.100 192.168.1.0/24 network segment other than to allow other hosts to access the FTP service.

Program very simple, edit / etc / hosts.allow

vsftpd: 192.168.1.100: DENY

vsftpd: 192.168.1.

Restart vsftpd, experimental purposes can be achieved, we can tcp_wrappers in the experiment will do more complex experiments.

(B) User Access Control

vsftpd flexible user access control. In the specific implementation, vsftpd user access control is divided into two categories: the first is the traditional list of users / etc / vsftpd / ftpusers, I understand it as the system list (that is, the system prohibited); second is to improve the user list file / etc / vsftpd / user_list, I understand it as they want to ban list

To realize the second list control must be inside vsftpd.conf

userlist_enable = YES

userlist_deny = YES / / This article is the system default exists, that is also unnecessary to add the system defaults to YES

userlist_file = / etc / vsftpd / usrer_list

The above simple experiment can be achieved vsftpd powerful control.







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Different CAD-output

Get rid of after the designers drawing board really do not have to "face the back overturned Sketchpad," to paint, but not only can not work out the plan less, with the three-dimensional CAD software features support for their demands instead of drawing more than ever, higher.

Harsh effects of the precision of photo

On the printed document or photo, you will try to use a ruler to the amount of text and images in which the specific size? Certainly not, if anyone do that, people would think he was crazy. However, the output of CAD drawings is entirely possible this situation: engineers, and finished drawings to tell you how big a part should be.

This is the CAD output on the printer's exact requirements, in particular, mainly in order to line the output of two-dimensional engineering drawings for each line length, width, there are stringent requirements, the so-called "by one point too long, minus one points are too short ", the drawings must be in accordance with the precise ratio of print.

For a variety of two-dimensional and three-dimensional renderings, engineering drawings, like the precision required is so high, but also color printing demands than the average much higher. For example, in architectural design, whether in color or line on, requires a more delicate and strict: Building on the transition to a different line of natural clear lines of coincidence between the cross should be clear, the performance of color to be nuanced, and in-kind exactly the same. The so-called "Shi Zhu is too red, the powder is Bai", only just right can truly embody the essence of the design.

This is the birth of the 20th century 80 plotter pen is obviously not very well qualified, therefore, the development so far, pen plotters basically no way out. Hewlett-Packard in 1991, the first of its thermal inkjet printing technology into large-format printer, introduced the world's first large format color inkjet printer HP DesignJet, a large-format printing in the most important milestone. Large format inkjet printers in terms of precision printing, print speed, machine performance, or from the printing cost, for both better meet customer needs. It works the same as ordinary inkjet printers with high resolution and multi-level color output capabilities. So far, apart from HP, Epson, Canon, Minolta, Xerox and other companies are able to provide various types of large format inkjet printers. However, in the field of large format printing, HP's market share in China reached 84%, while in the field of CAD output is as high as 91%.

Speed driving

Speed the development of printing technology has been the main driving factor. As the pen plotter in the course of their work there pen and paper contact will inevitably limit the pen speed, which is leading to the disappearance of one of the decisive factors.

At all levels of inkjet printers, HP DesignJet 430 A1 size prints black line graph takes about 90 seconds, the fastest; HP DesignJet 500/500ps A1 size printing Colour line takes about 90 seconds; the HP DesignJet 1050C + / 1055CM + Print A1 size of the color line drawings were not to 1 minute. Of course, the higher the image quality requirements for the printing needs of the time will take longer. However, the progress of speed, we can clearly feel the technology.

Simply from the speed, the ink-jet printers and laser printers are far more than a pen plotter, inkjet printer and laser printer inferior to superior, but so far, A3 format printers over inkjet printers is mainly Lord, according to the author knows, can provide more than A3 format laser printers few, Fuji Xerox DW2050EP is one of the best, it can output 5 per minute A1-format newspaper proofs.

Why are so few large format laser printer? Some experts predict that, due to high cost of large format laser printer, narrow range of applications, professional too, so the market demand is relatively small. In most applications, in order to speed inkjet printer fully capable of a variety of print job, demonstrate the advantages of its cost performance. Contrast, can provide the wide-format A3 color laser printer manufacturers a lot, especially in higher print quality image, its speed is better than inkjet printers.

Within the short term this situation may also persists, makers have vital interests also need to continue to maintain inkjet technology, Dan Suizhao laser technology progress and cost reductions Qingxing would change too knowing, Bi Jing laser is by far the the fastest printing technology.

Large format print market segments

In the general office printing, A4, A3 format is sufficient, and only print engineering drawings are required to use 1, 0, drawings, or even long-format printing. So, the large format printers are divided by format, but with the improvement of technologies, large-format printing technologies become more mature, more and more high print accuracy, faster and faster, more and more rich colors, ink quality increasingly The more quality, more and more ordinary supplies, the operation more convenient, more and more low cost, the needs of different users are increasingly divided, making printing more and more market segments. Manufacturers in different fields need to the specialized needs of different users, different users that met the characteristics of large format printers.

Large format printer products from HP, we can see quite a range of its product line. In the field of professional CAD, HP provides for the production output of the HP Designet 1050/1055CM large format inkjet printers and the upcoming HP DesignJet 5500 series; in individual areas of CAD output, Hewlett-Packard recently introduced the HP DesignJet 100. From the use of sub-scale, there are individuals and small working groups for the HP DesignJet 430 and HP DesignJet 500/500ps. If the medium of the Working Group, HP DesignJet 1000 series and 800 series is more appropriate. If it is a large working group, operating in large quantities, then HP DesignJet 5000 series is a good choice. Different emphasis depending on the application, designed specifically for HP also provides a wide format proofing the HP DesignJet 10ps/20ps/50ps "photo hand" series, if the image in the field of production proofing, you can use the HP DesignJet 5000 series, these two machines are suitable for process proofing.






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Easy to change driving

Imagine you are traveling at high speed on the road, changing lanes in preparation, the side of another car suddenly turned to you, seeing the car should hit with your car, even worse, the car also in your blind spot view. At this point, your car steering wheel automatically and quickly shake a bit and slow down, you go back to the right lane, you and your car safe.

The scenarios are not fantasy, this function has been obtained in a number of vehicles initially realized. Now almost every car manufacturer at least every family has a car model equipped with driving-related auxiliary equipment, such as automatic parking or adaptive cruise control device. In the automotive industry, these assistive devices are called advanced driver assistance systems (ADAS), such as the Cadillac STS, Buick Lucerne, Mercedes E-350, Ford Fusion, Mazda 3 and Infiniti (Infiniti) M are equipped with such devices to improve traffic safety, or at least allow the driver to make the moment more reasonable decisions.

In fact, these advanced driver assistance systems in some cars has become a major selling point, such as we see in television commercials: Audi A8 will automatically turn lights to illuminate the hidden corners of the road; Infiniti car will automatically brake to prevent the collision. But you know that these devices or systems is how the specific work to figure out what magical technology?

One auxiliary driving: lane departure reminded

In 2001, the devices first appeared on the Infiniti M. The results show that even relatively cheap device models (such as the Buick Lucerne) are also popular. In the process of moving, Lucerne will be displayed in the dashboard light green icon indicates that vehicles traveling in the right lane, and once deviated from the lane, the icon will become brown.

According to GM's global security manager John Capp introduced, Lucerne and several Cadillac models (such as equipment, luxury STS) in the rear view mirror next to the camera with black and white, with the help of these cameras, the system uses pattern recognition technology constantly scan the road. Color camera to search for the concentration of bright colors such as white line identification (or Yellow Line) and color differences between dark curbs.

Capp said that General Motors is to gradually improve the camera to enhance the availability of this feature. In Europe, the Opel Insignia will be scanning the road signs, measure out the car's current speed. If the car too fast, the system will remind drivers attention. In Germany and other European countries to help drivers identify road marking is necessary, because the driver may not notice the speed limit signs of these sparse. To achieve this functionality, GM of the Lucerne's lane departure warning (LDW) camera functions were expanded in order to correctly identify the Opel Insignia speed limit signs.

Lexus dealers dedicated to its advanced technical training manager Paul Williamson, said, in the Lexus car, Drive warning device comes with pre-scanning radar to observe the front there are no other vehicles, and to identify lane markings, and even identify a black shoulder, the car deviated from the lane to remind the drivers attention. The Lexus and other models can even automatically HS250h to cart back to the right Drive. Mercedes GL450 upcoming car will automatically adjust a driving route, let the car back to the right Drive.

In the future, this control device will be more powerful. For example, automobile manufacturers will be gradually improved lane departure reminded technology, with adaptive cruise control and lane keeping technology allows cars to drive, so that the control of vehicles in the absence of being able to open the road a long way, and ultimately automatic driving under no intervention.

The second driver assistance technologies: adaptive cruise control

Adaptive Cruise Control (Adaptive Cruise Control) and the front of the vehicle according to your preset between the conditions (such as intervals of 1.5 seconds or 3 seconds), automatic adjustment of speed. 2000 Lexus LS-430 the first use of this device, called dynamic laser cruise control system. Cadillac and Mercedes luxury cars equipped with the feature for some time.

Interestingly, although the device appears to be very complicated, in fact, it mainly relies on Doppler radar system (usually installed in the former grid) to scan the signal reflection. In some models, the windshield just above the camera is also equipped with a second.

Adaptive cruise is the Mercedes E350 cars such as the device one of the highest degree of automation. Start the system, if the vehicle in front, E350 will slow slow down, slow moving, with a few hundred feet in front of slow moving vehicles to maintain a certain distance. This technique, called limited distance control system enhancements (Distronic Plus), for setting, according to the distance with the front of the vehicle to determine when to start slowing the car.

Capp said: "GM currently mainly used to provide models to maintain continuous traffic on the highway, is being developed for the stop and go situations, such as encountered in front of a construction zone or traffic jams, car will automatically reduce speed. The principle of the system is obtained using the radar signal reflection, and combined with Doppler radar technology to detect vehicle speed and distance, and then the images, so you keep a safe distance with the front of the vehicle. "

It specializes in the production of sensors for automatic control and computer modules, Analog Devices, Test and Measurement director Rob O'Reilly describes this system in the object distance, and speed test has certain limits. In general, the car between 15 to 115 miles per hour driving the system can work, can be found as far 492 feet office and other vehicles.

He said: "The current number of actual systems in use, to measure the distance from the vehicle sensors working in the 60GHz to 80GHz most areas. These sensors send a signal, and then receiving the return signal, and the measured results to the host computer. the host computer is usually located under the dashboard, while the automatic steering module, speed brake assembly module and the location of the module closer to the engine.

Volvo XC60 used a program called City Safety System (City Safety) of the new technology for driving in city streets. National Automobile Dealers Association (NADA) Used Car Guide Magazine belongs to "NADA Guides" car expert Mike Caudill said: "If the road driver traveling at high road speed less than 10 miles, the brake system is available for work state, to prevent you hit the front of the vehicle. "He explained that under the adaptive cruise slow device helps to reduce collisions.

In the Cadillac STS and other GM models on the application of the adaptive cruise, in the long term effect will help reduce consumption of gasoline cars to save fuel costs. Because the traditional standard cruise control device that is to ask the driver brakes or release the brakes to start the system or turn off the system. "At any time, as long as a step on the brake, cruise control devices will be out of engagement." Caudill explained that "adaptive cruise control device for a smooth running car, in order to minimize the brakes or brake smoothly. Because after the cruise in the brake system will make the car faster speed to the pre-set speed, while the adaptive cruise control in front of the vehicle according to driving speed of the car remain in the driver settings from within, regardless of the speed of the front car is fast or slow. This helps to save fuel. "

Auxiliary driving three: auxiliary parking

Lexus and Toyota is the leader in auxiliary parking areas of technology. Assist the driver to drive the truck into the parking space is, the car can automatically assist the driver to park in place. This automated technology is important, because the parking needs of highly skilled, very difficult for many drivers, some novice or simply not be completed.

Lexus of Williamson said the auto parking is very complex calculations involved, including the calculation of the distance and has been parked vehicles, wheel position and current speed.

Williamson said: "First of all, when you are approaching the empty car parking spaces, the ultrasonic sensor detects the edge of each side of car parking spaces, to determine whether it can only put the car parking spaces. Next, the car will call the rear view camera video screen capture, so the driver stopped at what position to confirm the selection. in the driver options with your fingers clicking and dragging the location, the car automatically into the specified location. "

He explained that the car every corner of the sensor will send a radio signal, through the collection of objects rebound next to the signal to detect whether the obstacle. Concern is the 2010 Lexus LS 600h out of the wheel speed indicator, and also use wireless sensors to collect more data when the car decelerating. For example, Lexus know you are ready to slow down, "parking", and therefore more carefully scanning obstacles to get more data.

Such as in the Ford Flex and Taurus Sho board, adaptive parking assist device also incorporates automatic technology and driver assistance technologies. For example, the Ford Flex will be able to scan to find the space, suggesting that drivers slow down, stop and reverse. In this system, with the help of the car quickly in place, stopping at designated parking spaces. Currently, Flex vehicle into space, the pilot use statistics brake; and then the car forward, had to use the brakes. Luther Auto Group, said account manager Jerry Krauth, Ford also needed to use these automated technologies involved in control of the driver, not fully automated. The future, the company will gradually use more artificial intelligence control device.

It is worth mentioning that, at present, not a car maker said it planned to provide a full automatic device for re-training, the United States did not automatically parking and other devices for the certification process. As vehicles become a kind of automation standards, the auto makers may pinpointing these advanced driving device for additional courses, the Government has Bi Yao Ye Gong Zuo promote this area.

Auxiliary driving four: area to remind

Including the Buick Lucerne and Ford Fusion, including several of the latest models use a sensor to detect a vehicle close to the car, that is "blind to remind." According to GM Capp introduced, most of the blind spot to remind the device is not used to audible buzzer, as it would distract drivers, but in the side mirror next to the display lights, the driver will be from time to time to see side-looking mirror. He said this will help avoid crashes caused by driver distraction.

Blind spot sensor scan is usually about six feet from the vehicle objects. Analog Devices Inc. O'Reilly said that the car is equipped with blind reminder to use cameras to detect most of reflection, or, as the Mercedes E350 as working in the 20kHz band using ultrasonic sensors to detect moving objects. CPU sensor and connect the car can be the direction of the sensor data and comparing the information obtained to detect the speed and steering angle, the same time, they also detect the steering wheel rotation speed (slow, fast or not moving) gyroscope connected.

In the Acura (Acura) ZDX, the blind spot sensor with two 24GHz radar installations send short radio signal, and then use multiple antennas to receive the car back to the signal. If the system returns the signal measured within a certain distance from another vehicle, it will appear in the side mirror blind spot warning signals.

At present, this function is relatively mature, such as the Buick Lucerne's blind spot indicator was more precise: as long as a car around, and immediately sent in the side mirror on the warning signals, embankment, fence or building will not trigger alerts.

The five auxiliary driving: crash warning

Collision detection and prevention systems are also a number of high-end models selling point. Market has several cars equipped with anti-collision detection and prevention systems. For example, the Audi A8 car if it detects that there is another vehicle in front will slowly brake gently, seeing if we should hit, it will be the emergency brake. O'Reilly explained that the direction of this brake system uses sensors (and Apple iPhone, not very different from the direction of the sensor), can detect rapid changes in throttle angle. If you normally drive, suddenly release the throttle, cars will make use of pressurized brake fluid to the braking system to ensure smooth braking.

Edmunds.com automotive Web site, according to a senior evaluation engineer Albert Austria introduction, Mercedes and Audi models the most advanced collision detection system uses sensors to detect vehicles in front of the rear lights. He said the sensors can distinguish a movement in the truck and a tree, but most of the collision detection system does not recognize the car completely stopped, because the sensor will scan moving objects. Collision detection works similar to the blind spot warning and lane departure warning system.

Austria said: "sensors detect the need to pay attention to the object, put the information sent to the electronic control unit sets the car (ECU), many of these devices inside the microprocessor. ECU using complex algorithms, according to a number of input information to measure traffic intervention and driving directions. such as speed, throttle position, close to the object's distance, the use of brakes, yaw (side to move), so shaking (rotation along the line) and around the bumps (upper and lower vibration) and other input information. "

In the Acura ZDX, the collision detection system uses millimeter-wave radio signals front - this is the highest power radio frequency band, scan in front of about 300 feet of the object. Concern is that the collision mitigation brake system, called the device under the driver's response to determine how to brake. It is the first real-time tracking obstacles, then alerts the driver through the picture and sound, waiting for a response, and then gently brake, and show more warning information, the last hard braking, and automatically tighten seat belts.

Other auxiliary driving

In addition to these technical means other than some cars also use other techniques to help the driver safety and convenience to drivers. A Mazda 3, the latest example (that is, advanced technology and equipment Grand Touring models), you drive around the road bend, it's headlights will automatically turn, rather than straight to shine in the dark; if you go back box installed many things, the weight sensor will automatically adjust headlights to headlight according to the correct angle and direction; rain, you do not even open the rain-sensing wipers, it will automatically work.

Headlights turn on the principle that the direction of the sensor to read through the steering wheel position, speed and slope of the car on the road. According to the weight of goods to adjust headlight height, the car use the car to the right of the direction sensor determines the current slope, but also view the current speed and road surface (based on body height) into account. As for the rain sensor, their work mainly by an infrared sensor, it will light projected onto the windshield, if the windshield blurred or scattered rain, wiper will automatically start working.

Of course, the car driver assistance technology is still progressing into the future there will be the introduction of new technologies, these advanced technologies including the ability to recognize facial, monitoring the health status of the driver. Capp says that GM has already tested these types of devices. One of the latest sensor to monitor the oxygen content of the driver and respiration. "It will also monitor the driver's head is not due to fatigue and begin to hang."

Edmunds.com automotive Web site of Austria also said the global positioning system (GPS) technology is expected to bring more help to the driver. For example, a car may be the light of the future GPS data, combined with the car's driver assistance systems to adapt to changing road surface shape (such as corners and ramps). One possible application is to a car according to the received GPS satellite from the detailed map data on the road driving assessment, if the judge in front of the radius is too small, and the speed too fast, it will take the initiative to provide braking assistance, such as reducing the throttle input will also strengthen the yaw control.

"Ultimately, through the integrated application of all these techniques not only improves the vehicle's handling, to prevent accidents, drivers will improve our way." Caudill said, "technology helps prevent accidents, even if the accident occurred, also help save lives.







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