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  • Posted on Tuesday November 21, 2017
    What surprises are awaiting the tech world with .NET Core 2.1 Release in 2018? Technology is one of the most dynamic spheres these days. Every single year you will find a new version of an existing software and .NET Core is not an exception. The intentions of these upgradation is to make online activities seamless, daily work hassle free and to bring the world within our easy reach. » Read more Continue Reading »
  • Posted on Tuesday November 14, 2017
    Quick links to some useful software on Windows including Web browsers, Video/audio player and ssh/scpsftp/vnc tools for connecting to Linux.ssh/scp/sftp/vnc for connecting to Linux For Linux users, it is sometimes unavoidably to use Windows. With Windows, the Linux users will need to connect to Linux for some tasks. Some general software are needed. The most common ones may be ssh/scp/sftp/vnc. » Read more Continue Reading »
  • Posted on Thursday September 21, 2017
    Technology Hibernate Envers is the frameworks for auditing entities. As the name suggests Hibernate Envers is developed on top of Hibernate, it will on Hibernate and Hibernate implemented JPA. Hibernate Envers provides easy auditing, versioning solution for entity classes. Advantages of Hibernate Envers:Auditing of all mappings defined by JPA specification. Auditing Hibernate specific mappings which extends the JPA specification. Logging data for each revision using revision entity. » Read more Continue Reading »
  • Posted on Monday September 18, 2017
    Introduction In this tutorial, we will be learning as how to deploy .NET Core 2.0 MVC web application on Microsoft Public Cloud i.e. Microsoft Azure, using Microsoft Visual Studio 2017 v15.3 For novice Cloud developers, aspiring .NET / Cloud architects, and all other IT professionals associated with the .NET Core framework & Cloud computing, especially with Microsoft Azure, this tutorial will explain the importance and capabilities of newly released . » Read more Continue Reading »
  • Posted on Saturday September 09, 2017
    The encoding of x86 and x86-64 instructions is well documented in Intel or AMD’s manuals. However, they are not quite easy for beginners to start with to learn encoding of the x86-64 instructions. In this post, I will give a list of useful manuals for understanding and studying the x86-64 instruction encoding, a brief introduction and an example to help you get started with the formats and encodings of the x86-64 instructions. » Read more Continue Reading »
  • Posted on Saturday September 09, 2017
    The metadata checkpointing in HDFS is done by the Secondary NameNode to merge the fsimage and the edits log files periodically and keep edits log size within a limit. For various reasons, the checkpointing by the Secondary NameNode may fail. For one example, HDFS SecondaraNameNode log shows errors in its log as follows. 2017-08-06 10:54:14,488 ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode: Exception in doCheckpoint java.io.IOException: Inconsistent checkpoint fields. » Read more Continue Reading »
  • Posted on Sunday August 27, 2017
    Introduction In general, if we want to debug Linux Kernel, there are lots of tools such as Linux Perf, Kprobe, BCC, Ktap, etc, and we can also write kernel modules, proc subsystems or system calls for some specific debugging aims. However, if we have to instrument kernel to achieve our goals, usually we would not like to pay more efforts like above solutions since we’d like to achieve our aims quickly and easily. » Read more Continue Reading »
  • Posted on Saturday August 26, 2017
    Introduction As we know, network subsystems are important in computer systems since they are I/O systems and need to be optimized with many algorithms and skills. This article will introduce how QEMU/KVM [2] network part works. In order to put everything simple and easy to understand, we will begin with several examples and then understand how it works internally. Examples In this example, we will use TAP device [1] as QEMU/KVM host network device driver and VirtIO driver will be used to send/receive network packets/data between Host OS and Guest OS. » Read more Continue Reading »
  • Posted on Sunday August 20, 2017
    Abstract Most popular task monitor systems (such as top, iotop, proc, etc) can only get tasks’ disk I/O information like tasks’ I/O utilization percentage every seconds due to kernel timer/tick frequency and high time cost of system interfaces. This article presents I/O Microscopy, a new way to get tasks’ disk I/O information with high accuracy. Experiments show that I/O microscopy can filter out I/O intensive tasks effectively. » Read more Continue Reading »
  • Posted on Saturday August 12, 2017
    With Google algorithm becoming more intelligent with each passing day, the margin for errors has significantly reduced over the past decade. Back in the day, you might get away with keyword stuffing but today, the same offense will strike off your website from Google search engine results. No one wants that, right. To save you from such a situation, here are ten common mistakes that most casual followers of the industry are making but should not. » Read more Continue Reading »
  • Posted on Tuesday July 25, 2017
    The word “viral” has received a lot of attention over the last few years and is applied to different types of content to describe how quickly it has spread and gained popularity. Many times, you’ll hear people speak about their idea and how fast it will spread while assuming that it will “go viral”, but they never seem to understand how they’re going to make it go viral. » Read more Continue Reading »
  • Posted on Friday May 12, 2017
    Call forwarding is useful if you are expected to be unavailable for receiving calls or lose cell phone coverage for some time. Call forwarding is not something that is "new" to modern phones. It is a feature which is invented in 1960s (the patent expired in 1980) of some telephone switching systems. But with iPhone/iOS, there is a convenient call forwarding feature in iOS for you to set up call forwarding to forward calls to a landline or other phone by its number or disable the call forwarding. » Read more Continue Reading »
  • Posted on Thursday April 20, 2017
    HTML supports many characters/symbols such as mathematical symbols, and currency symbols. They are not present on a normal keyboard. And some of these characters may have special meanings for formatting text. To add such characters / symbols to an HTML text, you can use an HTML entity name or an entity number in decimal or hexadecimal. This post list many special Characters in HTML as a friendly reference. » Read more Continue Reading »
  • Posted on Tuesday April 18, 2017
    From a small business owner, a blogger, a student or individual with a personal project, the need to create websites has never been more prominent. Having a basic understanding of HTML and canvas knowledge can be helpful, and it is simple to master. The thought of learning to code and programming may seem a long and daunting task, but some people may be surprised to know that it need not be as scary as it sounds. » Read more Continue Reading »
  • Posted on Saturday April 15, 2017
    This post introduces how to install a paravirtualized CentOS 7 DomU on Xen. The very common way of installing DomU does not work for CentOS 7. A little trick to set the repository and the network used by the VM should be used by adding a setting strings to the “extra=” field for this VM. Note that this tutorials was tested with CentOS 7.2 (1511). » Read more Continue Reading »
  • Posted on Sunday April 09, 2017
    The USB standards have evolved to 3.1 and the supported throughput have been increased too. On Linux, the support to USB standards are following the standards development. In this post, we will survey the standards that common hardware support and the support in Linux. USB standards USB 2.0: https://en.wikipedia.org/wiki/USB#USB_2.0Speed: » Read more Continue Reading »
  • Posted on Saturday March 18, 2017
    Building Linux kernel may sound a complex and geek-only thing. However, as Linux kernel itself has much less depended tools/packages compared to other software packages, it is quite easy to compile, build and install a Linux kernel from the source code in an existing Linux OS. Building Linux kernel is needed if you need to build a specific Linux kernel or update your drivers for a kernel by yourself. » Read more Continue Reading »
  • Posted on Friday February 24, 2017
    In today’s time, data visualization has become a significant part of the success story of an organization. With the help of right techniques, visualizing data can reveal insights which the management staff can use in their decision-making in order to make sound data-driven decisions. Mapping software is among the robust data visualization tools that you can avail today. With maps, you can find stories, trends, and insights that cannot be found in spreadsheets. » Read more Continue Reading »
  • Posted on Tuesday February 14, 2017
    Motivation Recently, I find it is hard to know the percentage of time that one process uses to wait for synchronous I/O (eg, read, etc). One way is to use the taskstats API provided by Linux Kernel [1]. However, for this way, the precision may be one problem. With this problem, I dig into Linux Kernel source codes to see how “blkio_delay_total” (Delay time waiting for synchronous block I/O to complete) is calculated. » Read more Continue Reading »
  • Posted on Monday February 06, 2017
    Making a career choice is difficult. And, if you have decided on becoming a programmer, the difficulty is just beginning. The most important thing is to first decide the language that you want to learn and this is often the most difficult decision. The good part is that you know you need to focus on learning programming and the bad part is that you might still be thinking which programming language should you begin to learn. » Read more Continue Reading »

Latest QA answers

  • Posted on Thursday November 23, 2017
    In a Symmetric Multiprocessor, the architectural “distance” to any memory location is the same for all processors, i.e. “symmetric”. In a NonUniform Memory Access machine, each processor is “closer” to some memory locations than others; i.e. memory is partitioned among them Asymmetrically. From my understanding, most of current architectures are SMP+UNMA if we consider cache is also part of memory hierarchy. Part of above answers are copied from https://www.quora.com/What-is-the-difference-between-SMP-and-NUMA-architectures Continue Reading »
  • Posted on Tuesday November 21, 2017
    Tested on Linux Ubuntu 14.04 Trusty > sudo apt-get install dmidecode > sudo dmidecode -s system-serial-number Continue Reading »
  • Posted on Sunday November 19, 2017
    login without PWD: add PC A's public key to PC B's authorized keys. > a@A:~> cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys' > b@B's password:Run command remotely ssh root@MachineB "ls"NOTE: running commands remotely is dangerous since there might be some ENVIRONMENT conflicts. Continue Reading »
  • Posted on Saturday November 18, 2017
    Copied from https://tex.stackexchange.com/questions/53235/why-does-latex-bibtex-need-three-passes-to-clear-up-all-warnings. The reason is as follows: 1, At the first latex run, all \cite{...} arguments are written in the file document.aux. 2, At the bibtex run, this information is taken by bibtex and the relevant entries are put into the .bbl file, sorted either alphabetically or by citation order (sometimes called "unsorted") and formatted according to the instructions provided by the bibliography style that's in use. 3, At the next run of latex, the .bbl file is included at the point the \bibliography instructions, and the correct labels for \cite{...} Continue Reading »
  • Posted on Friday November 17, 2017
    I would recommend meld for Windows users. Meld is a visual diff and merge tool open source software.meld is available on Linux, Windows and Mac OS X. Continue Reading »
  • Posted on Wednesday November 15, 2017
    In a work-conserving mode, the scheduler must choose one of the pending requests, if any, to dispatch, even if the pending requests are far away from the current disk head position. The rationale for non-work-conserving schedulers, such as the anticipatory scheduler (AS) and Completely Fair Queuing (CFQ), is that a request that is soon to arrive might be much closer to the disk head than the currently pending requests, in which case it may be worthwhile to wait for the future request. In my point view, non-work conserving keeps the locality of synchronous I/O requests so that the system Continue Reading »
  • Posted on Tuesday November 14, 2017
    For example, to change date to 14 Nov 2017 11:57:00, the command would be, $ sudo date --set "14 Nov 2017 11:57:00" Tue Nov 14 11:57:00 HKT 2017 Continue Reading »
  • Posted on Tuesday November 07, 2017
    Your permission bits may be turned off by umask. Try to make umask 000 first: import os# make dirs with mode def mkdir_with_mode(directory, mode): if not os.path.isdir(directory): oldmask = os.umask(000) os.makedirs(directory, 0777) os.umask(oldmask)It will clear the umask first so that the mode provided takes full effect. Continue Reading »
  • Posted on Wednesday October 18, 2017
    alien is already in EPEL and it makes it quite easy to install it in CentOS 7. First, enable EPEL following this tutorials. Then, install alien by # yum install alienThen alien should be ready: # yum info alien Installed Packages Name : alien Arch : noarch Version : 8.95 Release : 3.el7 Size : 223 k Repo : installed From repo : epel Summary : Converter between the rpm, dpkg, stampede slp, and Slackware tgz file formats URL : https://sourceforge.net/projects/alien-pkg-convert/ License : GPLv2+ Description : Alien is a program that converts between the Continue Reading »
  • Posted on Wednesday October 18, 2017
    I don't think GNOME 3 or GNOME 3 classic has this function available or there any plugins that supports so. If you need this function that the panel can hide automatically, you may consider another desktop environment, such as MATE, that supports so. This may not solve your problem. But it's just an alternative way to support the need. Continue Reading »
  • Posted on Thursday September 14, 2017
    2 possible ways: /forcefsck way for / # touch /forcefsckand reboot. Next time the / will be fsck'ed . systemd way Add these 2 kernel boot parameters: fsck.mode=force fsck.repair=yesWhat these 2 kernel parameters do: KERNEL COMMAND LINEsystemd-fsck understands one kernel command line parameter:fsck.mode=One of "auto", "force", "skip". Controls the mode of operation. The default is "auto", and ensures that file system checks are done when the file system checker deems them necessary. "force" unconditionally results in full file system checks. "skip" skips any file system checks.fsck.repair=One of "preen", "yes" Continue Reading »
  • Posted on Tuesday September 12, 2017
    On CentOS 7 Linux it is usually by default /var/lib/mysqlBut here I give you another "hacky" way to find it out. The method is to find out the mysql daemon mysqld' opened files and the paths because it must open the files to read/write data. First, find out the process ID of the mysqld process: # ps aux | grep mysqldmysql 25403 1.0 17.2 1322220 174948 ? Ssl Aug31 178:10 /usr/sbin/mysqldSecond, go to the mysqld process' dir under /proc/. For the above example, # cd /proc/25403/Check the opened files under the directory Continue Reading »
  • Posted on Tuesday September 12, 2017
    You can check this tutorial for how to force a checkpointing of metadata in HDFS: How to force a metadata checkpointing in HDFS Continue Reading »
  • Posted on Thursday September 07, 2017
    Try gore https://github.com/motemen/gore Get gore $ go get -u github.com/motemen/goreAn example $ gore gore version 0.2.6 :help for help gore> :import fmt gore> fmt.Println("hello world!") hello world! 13 nilgore> Continue Reading »
  • Posted on Thursday September 07, 2017
    In PHP, to disable the short open tags, you can set the variable short_open_tags = FALSE;in your php.ini. Reference: short_open_tags in php.ini Continue Reading »
  • Posted on Thursday September 07, 2017
    This feature of {} without the position argument specifier is only available after at least 3.1 for Python 3, or 2.7 for Python 2. On CentOS 6, the default Python version is 2.6: $ python --version Python 2.6.6So you need to add the position argument specifiers: print '== {0} SPF'.format(d) Continue Reading »
  • Posted on Thursday September 07, 2017
    For a domain with email and SMTP hosted by DreamHost, you can set its SPF record to v=spf1 include:netblocks.dreamhost.comReference: What SPF records do I use? - DreamHost Continue Reading »
  • Posted on Thursday September 07, 2017
    Please run command: # cat /proc/interrupts or you can execute $ watch -n1 "cat /proc/interrupts" to watch interrupts every 1 second. See [1] [2] for more details. References: [1] https://stackoverflow.com/questions/28301875/how-to-observe-interrupts-in-windows-or-linux-ubuntu-14-04 [2] http://www.linuxjournal.com/content/watch-live-interrupts Continue Reading »
  • Posted on Thursday September 07, 2017
    gfortran on CentOS 7 is provided in the gcc-gfortran package. You may install it to install gfortran. # yum install gcc-gfortran Loaded plugins: fastestmirror, langpacks Loading mirror speeds from cached hostfile * base: ftp.cuhk.edu.hk * epel: ftp.cuhk.edu.hk * extras: centos.01link.hk * nux-dextop: li.nux.ro * updates: ftp.cuhk.edu.hk Resolving Dependencies --> Running transaction check ---> Package gcc-gfortran.x86_64 0:4.8.5-11.el7 will be installed --> Finished Dependency ResolutionDependencies Resolved================================================================================ Package Arch Version Repository Size ================================================================================ Installing: gcc-gfortran x86_64 4.8.5-11.el7 base 6.6 Continue Reading »
  • Posted on Thursday September 07, 2017
    1, Get this task's ID # taskset -pc PID2, Set this task's CPU affinity # taskset -c affinity ./task Continue Reading »

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