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Working with data streams on the Linux command line | myboat345 boatplans
Out of complete curiosity I would like to check the speed between the two boxes. I am not having any problems with speed or anything, it really is just the geek in me that is curious. Plus maybe the results will let me know if there is room for improvement, or that I have something configured wrongly. So how do you properly test the network speed between Ubuntu boxes?� If you want to test your Ethernet LAN at a lower level you can use Etherate which is a free Linux CLI Ethernet testing tool: myboat345 boatplans Throwing it in the mix as tools like iPerf (which are very good!) operate over IP and TCP or UDP. Brief: In this article, we list some open source utilities to monitor the network traffic, bandwidth and internet speed in Linux. Monitoring internet speed can be a crucial step in understanding your connection and it can help you find possible problems. It will also help you troubleshoot any connectivity problems you might have and find possible bottlenecks.� It has client and server functionality, and can create data streams to measure bandwidth, loss and other parameters between the two ends in one or both directions. There are two implementations: the original iPerf (iPerf2) and a non-backwards compatible implementation iPerf3. The easiest way to install (or remove) iPerf or iPerf3 is using the package manager. For example, in Ubuntu. If you think streams and pipes make a Linux expert sound like a plumber, here's your chance to learn about them and how to redirect and split them. You even learn how to turn a stream into command arguments. You can use the material in this tutorial to study for the LPI exam for Linux system administrator certification, or just to learn for fun.� Streams are accessed using file IO techniques, whether or not the actual stream of characters comes from or goes to a file, a keyboard, a window on a display, or some other IO device. Linux shells use three standard I/O streams, each of which is associated with a well-known file descriptor: About this series. This series of tutorials helps you learn Linux system administration tasks.

Jump to navigation. Modified by Opensource. Data streams are the raw materials upon which the GNU Utilities , the Linux core utilities, and many other command-line tools perform their work. This chapter introduces the use of pipes to connect streams of data from one utility program to another using STDIO. You will learn that the function of these programs is to transform the data in some manner. You will also learn about the use of redirection to redirect the data to a file.

By definition, a filter is a device or a tool that removes something, such as an air filter removes airborne contaminants so that the internal combustion engine of your automobile does not grind itself to death on those particulates.

In my high school and college chemistry classes, filter paper was used to remove particulates from a liquid. They can add data to a stream, modify the data in some amazing ways, sort it, rearrange the data in each line, perform operations based on the contents of the data stream, and so much more. Feel free to use whichever term you prefer, but I prefer transformers. I expect that I am alone in this.

Data streams can be manipulated by inserting transformers into the stream using pipes. Each transformer program is used by the sysadmin to perform some operation on the data in the stream, thus changing its contents in some manner.

Redirection can then be used at the end of the pipeline to direct the data stream to a file. As mentioned, that file could be an actual data file on the hard drive, or a device file such as a drive partition, a printer, a terminal, a pseudo-terminal, or any other device connected to a computer. The ability to manipulate these data streams using these small yet powerful transformer programs is central to the power of the Linux command-line interface.

In the Unix and Linux worlds, a stream is a flow of text data that originates at some source; the stream may flow to one or more programs that transform it in some way, and then it may be stored in a file or displayed in a terminal session. As a sysadmin, your job is intimately associated with manipulating the creation and flow of these data streams.

Write programs to work together. Write programs to handle text streams, because that is a universal interface. Programs that implement STDIO use standardized file handles for input and output rather than files that are stored on a disk or other recording media.

STDIO is best described as a buffered data stream, and its primary function is to stream data from the output of one program, file, or device to the input of another program, file, or device. Each STDIO data stream is associated with a file handle, which is just a set of metadata that describes the attributes of the file. STDIN can be redirected from any file, including device files, instead of the keyboard. This ensures that when the data stream itself is not displayed on the terminal, that STDERR is, thus ensuring that the user will see any errors resulting from execution of the program.

STDERR can also be redirected to the same or passed on to the next transformer program in a pipeline. Enter and run the following command line program to create some files with content on the drive. We use the dmesg command simply to provide data for the files to contain.

We have generated data streams using the dmesg command, which was redirected to a series of files. Most of the core utilities use STDIO as their output stream and those that generate data streams, rather than acting to transform the data stream in some way, can be used to create the data streams that we will use for our experiments. Data streams can be as short as one line or even a single character, and as long as needed.

It is now time to do a little exploring. In this experiment, we will look at some of the filesystem structures. You should be at least somewhat familiar with the dd command.

Many of us have inadvertently destroyed the contents of an entire hard drive or partition using the dd command. Despite its reputation, dd can be quite useful in exploring various types of storage media, hard drives, and partitions.

We will also use it as a tool to explore other aspects of Linux. Log into a terminal session as root if you are not already. We first need to determine the device special file for your hard drive using the lsblk command.

Notice that we are not looking at the first block of the partition, we are looking at the very first block of the hard drive. In this case, there is information about the filesystem and, although it is unreadable because it is stored in binary format, the partition table.

If this were a bootable device, stage 1 of GRUB or some other boot loader would be located in this sector. The last three lines contain data about the number of records and bytes processed. The command is similar to the previous one, except that we have specified a few more blocks of data to view. Remember, we are doing all of this as root user because non-root users do not have the required permissions.

Enter the same command as you did in the previous experiment, but increase the block count to be displayed to , as shown below, in order to show more data. Now try this command. Use Ctrl-C to break out and stop the stream of data.

This data could be redirected to a file for use as a complete backup from which a bare metal recovery can be performed. It could also be sent directly to another hard drive to clone the first.

But do not perform this particular experiment. You can see that the dd command can be very useful for exploring the structures of various types of filesystems, locating data on a defective storage device, and much more. It also produces a stream of data on which we can use the transformer utilities in order to modify or view.

The real point here is that dd , like so many Linux commands, produces a stream of data as its output. That data stream can be searched and manipulated in many ways using other tools. It can even be used for ghost-like backups or disk duplication.

There are a number of reasons that sysadmins might want to generate a stream of random data. Perform this experiment as a non-root user. You may need to use Ctrl-C multiple times. Random data is also used as the input seed to programs that generate random passwords and random data and numbers for use in scientific and statistical calculations. I will cover randomness and other interesting data sources in a bit more detail in Chapter Everything is a file.

Pipes are critical to our ability to do the amazing things on the command line, so much so that I think it is important to recognize that they were invented by Douglas McIlroy during the early days of Unix thanks, Doug! The Princeton University website has a fragment of an interview with McIlroy in which he discusses the creation of the pipe and the beginnings of the Unix philosophy.

Notice the use of pipes in the simple command-line program shown next, which lists each logged-in user a single time, no matter how many logins they have active.

Perform this experiment as the student user. Enter the command shown below:. The results from this command produce two lines of data that show that the user's root and student are both logged in. It does not show how many times each user is logged in. Your results will almost certainly differ from mine. This is not always desirable, but it does offer flexibility in the ability to record the STDERR data stream for the purposes of problem determination.

Think about how this program would have to work if we could not pipe the data stream from one command to the next. The first command would perform its task on the data and then the output from that command would need to be saved in a file. The next command would have to read the stream of data from the intermediate file and perform its modification of the data stream, sending its own output to a new, temporary data file.

The third command would have to take its data from the second temporary data file and perform its own manipulation of the data stream and then store the resulting data stream in yet another temporary file.

At each step, the data file names would have to be transferred from one command to the next in some way. When I am doing something new, solving a new problem, I usually do not just type in a complete Bash command pipeline from scratch off the top of my head.

I usually start with just one or two commands in the pipeline and build from there by adding more commands to further process the data stream. This allows me to view the state of the data stream after each of the commands in the pipeline and make corrections as they are needed.

It is possible to build up very complex pipelines that can transform the data stream using many different utilities that work with STDIO. Redirection is the capability to redirect the STDOUT data stream of a program to a file instead of to the default target of the display. There is no output to the terminal from this command unless there is an error. You can view the contents of the file you just created using this next command:. If it does exist, the contents are overwritten by the data stream from the command.

Although input sources can be redirected to STDIN, such as a file that is used as input to grep, it is generally not necessary as grep also takes a filename as an argument to specify the input source.

Most other commands also take a filename as an argument for their input source. The grep command is used to select lines that match a specified pattern from a stream of data.

The grep command is one of the few that can correctly be called a filter because it does filter out all the lines of the data stream that you do not want; it leaves only the lines that you do want in the remaining data stream.

In this case, we want somewhat less random data that would be limited to printable characters. A good password generator program can do this. The following program you may have to install pwgen if it is not already creates a file that contains 50, passwords that are 80 characters long using every printable character. Try it without redirecting to the random.

Considering that there are so many passwords, it is very likely that some character strings in them are the same. First, cat the random. Short strings of two to four characters work best. It is the use of pipes and redirection that allows many of the amazing and powerful tasks that can be performed with data streams on the Linux command line.

The ability to pipe streams of data through one or more transformer programs supports powerful and flexible manipulation of data in those streams. Each of the programs in the pipelines demonstrated in the experiments is small, and each does one thing well. They are also transformers; that is, they take Standard Input, process it in some way, and then send the result to Standard Output.

Implementation of Minimum Speed Of Streaming Chair these programs as transformers to send processed data streams from their own Standard Output to the Standard Input of the other programs is complementary to, and necessary for, the implementation of pipes as a Linux tool.

Main points:

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