Saturday, October 23, 2010

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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Thursday, October 14, 2010

Quality control in the "Statistics" several concepts


1, "statistical methods" means
At present, some enterprises in the distribution functions, the use of statistical methods in the Finance department in charge of setting the ground that the whole plant accountants and statisticians in business leadership by the Finance Division. Some enterprises in the quality manual clearly writes: "Our" PRC Statistics Law "Application of statistical techniques ... ...." Obviously, not out to understand the meaning of statistical techniques. Statistical techniques (statistical methods) is the theoretical basis of probability theory a branch of applied mathematics. Random phenomena in the study to determine the mathematical laws of a mathematical discipline. Statistical techniques, including statistical inference and statistical control of two components.

Second, statistical inference and statistical control
Statistical inference is based on data collected (large samples or small samples) of analysis and statistical calculations are the eigenvalues of materials used to predict and infer technologies, such as the application of statistical sampling. Statistical control is based on data collected (large samples or small samples) of analysis and statistical computing eigenvalue obtained is used to predict and control things technical, such as the control diagram. Shows that the quality of statistical techniques in the production of the whole process of the formation and implementation, in every aspect will have its uses. In GB / T 19004.1-1994 idt ISO 9004-1:1994 standard, "20.1 Applications", he wrote: to identify and correct application of modern statistical methods to control every stage of the process of the organization an important factor. Shall establish and maintain a selection of statistical methods and their use for the following work documented procedures: a) market analysis; b) product design; c) credibility of the specification, the longevity and durability prediction; d) process control and process capability research; e) sampling program to determine the level of quality; f) data analysis, performance evaluation and failure analysis; g) process improvement; h) safety evaluation and risk analysis. Can be seen that any one organization does not exist the question whether the application of statistical techniques. Recognizing the importance of statistical techniques, the quality of rings can all be applied at any stage.

Third, statistical methods in the several concepts should be clear
1. Statistical method is the statistical rule, whether natural or social science, there are regular problems. Statistical techniques, is an important method of one of its laws. Broadly speaking, the experience of statistics, common sense is also the statistics, statistics is the law. It is said that some of the old craftsmen, there is no culture of the statistical methods do not know, but they can produce highly skilled crafts. In fact, this is the master of the law, but the results, but to master the process of the law to spend a lot of resources and energy to his life Besides not everyone can. However, if the real master of the statistical techniques, the use of statistical techniques to master the rules, you can learn in a short time, control of product quality. Therefore, application of statistical techniques to obtain better and more economical results. Application of statistical techniques can be better and more economical access to statistical laws. In process control, statistical techniques can be abnormal fluctuations in time to capture a precursor to the producers and managers to take prompt corrective measures to eliminate failure in the process, play a preventive role. Statistical techniques to capture an abnormal fluctuations in each sign, it allows us to eliminate an exception factor. Abnormal factors in the process is limited, so application of statistical techniques can make the process work to achieve the status of random factors only, namely, stability control. 2. Application of statistical methods to control the distribution theory of statistical methods to study random phenomena identified in the De mathematical laws of science, the mathematical laws that determine the quality of data reflected in the distribution. Many statistical methods of analysis and judgments are based on criteria established distribution theory. The most commonly used distribution is normal, there is binomial distribution, Poisson distribution. 3. Application of statistical methods to meet the law of large numbers of shows that only the average number of random phenomena only with a stable, that is law of large numbers. That is only a certain number of samples in the above results it is more accurate conclusions. Statistical law is built on the basis of large amounts of data can be obtained, such as throwing coins, words (or drawings) shows the probability of a large number of tests only to get close to 50%. 4. Application of the principle of small probability events.

Principles of small probability event, also known as small probability event does not occur principle. That "if the probability of event A occurs is small (eg 0.01), but once or less a number of test events A actually occurred, have reason to think that this is unusual and should not happen." Criterion of statistical methods is a small probability event under the principle of get. Therefore, the application of statistical methods necessary risks, "small probability" is to judge the degree of risk [recorded as a>, and its opposite is the confidence level [denoted b>, the relationship between the two is a + b = 1.

4, application of statistical methods have the basic conditions required
1. More solid foundation for enterprise management, a normal management order, the product quality with traceability; 2. Production process is stable, the five factors of human-computer method has been standardized materials, processes controlled in a stable state; 3. The workers, especially full-time quality management and technical personnel have received training in statistical methods, systems, application of statistical methods with flexible capacity; 4. Have the necessary technical, material conditions, such as: with a variety of goods, show the value of accurate measuring instruments, equipment and advanced testing methods, with the necessary computing equipment and record forms.






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Tuesday, October 5, 2010

Using Visual Basic's Timer control



Visual Basic provides a Timer control, which is essentially a set interval of time triggered procedures so that we can hide in the system to a time interval trigger procedures. The flexibility to use it can get very subtle effects.

Below, we give an example.

We can design the interface design of such an effect: a line of text in the form of gradually rolling from left to right, from the right "roll out" the form of text, then left to emerge. So the cycle continues. Information similar to the rolling television. This will allow you to design the software looked very lively and can easily cause the user's interest. In fact, the use of Visual Basic's Timer control can easily achieve it.

First, we set in the form of two Label controls Label1, Label2. Left control, in addition to the two properties, other properties set to the same. This is mainly to achieve the effect of rolling cycle. Their Caption property to display the text to scroll. Also re-adjust its font, size and color. In the Form-Load process set Label2. Left =- 6240 (Form width), Label1. Left = 0. This will ensure that La 顎?bel1 part of the "rolling" out of form, then part of the entry form Label2. Rolling circle formed in the form set? / FONT> Timer control. Timer control's Interval property determines the speed of rolling, in milliseconds.

For example, we set to 300, then roll once every 0.3 seconds.

Then, in the Timer1-Timer () process by adding the following procedures:

Private Sub Timer1-Timer ()
Label1. Left = Label1. Left +50
Label2. Left = Label2. Left +50
If Label1. Left> = 6240 Then
Label1. Left =- 6240
End If
If Label2. Left> = 6240 Then
Label2. Left = 6240
End If
End Sub

Rolling effect on the form, the interested reader can try. As long as the flexible use Timer control, we can design a more interesting effect. Timer control with control buttons, such as control of the Visible property to form a flashing button. Timer control with the control to display different images to form a simple animation.







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