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  • Handling Sparse Files on Linux
    Posted on Thursday April 05, 2018
    Sparse files are common in Linux/Unix and are also supported by Windows (e.g. NTFS) and macOSes (e.g. HFS+). Sparse files uses storage efficiently when the files have a lot of holes (contiguous ranges of bytes having the value of zero) by storing only metadata for the holes instead of using real disk blocks. They are […] The post Handling Sparse Files on Linux appeared first on SysTutorials. Continue Reading »
  • How to Add a File Based Swap for Linux
    Posted on Tuesday April 03, 2018
    We may want to add some swap space for a Linux box while only find that all disk space is partitioned and mounted. Some partition has large available free space. For such cases, we may not want to change the partition allocation. The solution may be to add a file based swap for Linux as […] The post How to Add a File Based Swap for Linux appeared first on SysTutorials. Continue Reading »
  • How to resize a virtual disk of KVM
    Posted on Saturday March 24, 2018
    I test it for qcow2 format. Other formats are TBA. qemu-img resize kvm1.qcow2 +20G cp kvm1.qcow2 kvm1-orig.qcow2 virt-resize --expand /dev/sda1 kvm1-orig.qcow2 kvm1.qcow2 Reference: https://fatmin.com/2016/12/20/how-to-resize-a-qcow2-image-and-filesystem-with-virt-resize/ I test it for qcow2 format. Other formats are TBA. qemu-img resize kvm1.qcow2 +20G cp kvm1.qcow2 kvm1-orig.qcow2 virt-resize --expand /dev/sda1 kvm1-orig.qcow2 kvm1.qcow2 Reference: https://fatmin.com/2016/12/20/how-to-resize-a-qcow2-image-and-filesystem-with-virt-resize/ Answered by harryxiyou. The post How to resize a virtual disk of KVM appeared first on SysTutorials. Continue Reading »
  • How to not use concrete types in lambda function parameters in C++11?
    Posted on Saturday March 24, 2018
    C++11 requires that lambda function parameters be declared with concrete types. This is sometimes annoying. auto is really nice, especially when the type is complex like std::vector<std::string>::iterator is quite long to type. I know C++14 allows auto in lambda functions. But how to not use concrete types in lambda function parameters in C++11? In C++11, […] The post How to not use concrete types in lambda function parameters in C++11? appeared first on SysTutorials. Continue Reading »
  • How to operator[] access element in a const map in C++?
    Posted on Saturday March 24, 2018
    How to operator[] access element in a const map in C++? For example, the compiler will report error on this piece of code: #include <iostream> #include <string> #include <map> std::int64_t count(const std::map<std::string, std::int64_t>& map) { return map["one"] + map["two"]; } int main () { std::map<std::string, std::int64_t> map = { {"one", 1}, {"two", 2} }; std::cout […] The post How to operator[] access element in a const map in C++? appeared first on SysTutorials. Continue Reading »
  • How to hide my private IP in Email header in Thunderbird?
    Posted on Saturday March 24, 2018
    It seems Thunderbird sends out my private/lan IP to the SMTP server. For example, in an Email sent out by Thunderbird, the header contains Received: from [192.168.1.2] (example.com [1.2.3.4]) by mail.example.com (Postfix) with ESMTPSA id 92CD297DEA; It is fine that the SMTP server records the public IP (1.2.3.4) as it is what it sees. But […] The post How to hide my private IP in Email header in Thunderbird? appeared first on SysTutorials. Continue Reading »
  • How to make Vim indent C++11 lambdas correctly?
    Posted on Saturday March 24, 2018
    Vim seems not indent C++11 lambas very well. How to make Vim indent C++11 lambdas correctly? For this following program, Vim indents it as #include <iostream> #include <string> #include <vector> #include <algorithm> int main () { std::vector<std::string> strs({"one", "two"}); std::vector<std::string> newstrs; std::transform(strs.begin(), strs.end(), std::back_inserter(newstrs), [](const std::string& s) -> std::string { if (s == "one") { […] The post How to make Vim indent C++11 lambdas correctly? appeared first on SysTutorials. Continue Reading »
  • How to list start and end sectors of a partition by parted in Linux?
    Posted on Saturday March 24, 2018
    How to list start and end of a partition by the sectors in parted on Linux? The default behavior seems be listing the start and end by bytes in parted. # parted /dev/sdc print Model: Innostor IS888 ext. HDD (scsi) Disk /dev/sdc: 2000GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End […] The post How to list start and end sectors of a partition by parted in Linux? appeared first on SysTutorials. Continue Reading »
  • How to enable Email address auto completion in Evolution?
    Posted on Saturday March 24, 2018
    Does Evolution support automatic email address filling/completing in the “To” or “CC” fields which is commonly seen in other Email clients such as Thunderbird. Is is possible and how to enable Email address auto completion in Evolution? Evolution supports the contact autocompletion. To enable it, do as follows in Evolution. In Evolution Preferences dialog, in […] The post How to enable Email address auto completion in Evolution? appeared first on SysTutorials. Continue Reading »
  • How to make Evolution not wrap lines in composed Emails?
    Posted on Saturday March 24, 2018
    Evolution seems wrap long lines automatically in “Plain Text” mode. How to make Evolution not wrap lines in composed Emails? Evolution does not have (so far) “Flowing Text” mode where “the text is soft broken at the composer edge, but those soft breaks aren’t translated to hard breaks when the mail is sent” ( Reference: […] The post How to make Evolution not wrap lines in composed Emails? appeared first on SysTutorials. Continue Reading »
  • Why I cannot login remote server with its root
    Posted on Saturday March 24, 2018
    # ssh root@192.168.122.96 root@192.168.122.96's password: Permission denied, please try again. Do according to [1]. NOTE: on Ubuntu, remember to restart ssh service like this “sudo restart ssh”. [1] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/v2v_guide/preparation_before_the_p2v_migration-enable_root_login_over_ssh Answered by harryxiyou. The post Why I cannot login remote server with its root appeared first on SysTutorials. Continue Reading »
  • How to apply the Email sort order to all folders in Evolution?
    Posted on Saturday March 24, 2018
    Evolution’s default Email sort order is not very convenient, at least to me. How to apply the settings of sort order for a folder to all folders in Evolution? Manually setting the email sort order for each dir is tedious. Evolution has a function to “apply the same view settings to all folder” so that […] The post How to apply the Email sort order to all folders in Evolution? appeared first on SysTutorials. Continue Reading »
  • How to search history commands very effectively in bash shell command line?
    Posted on Saturday March 24, 2018
    How to search history commands very effectively in bash shell command line? Just enter CTRL+r The function of above is: (reverse-i-search)`’: It is very fast and efficient. Answered by harryxiyou. The post How to search history commands very effectively in bash shell command line? appeared first on SysTutorials. Continue Reading »
  • How to check CPU working frequency in iOS on iPhone?
    Posted on Saturday March 24, 2018
    How to check CPU working frequency in iOS on iPhone, such as my iPhone 6? The Litum Info Lite free app (Litum Info full version app) can show you the info of CPU including its frequency. The CPU frequency: You can find the CPU info page from the menu: Answered by Eric Z Ma. The post How to check CPU working frequency in iOS on iPhone? appeared first on SysTutorials. Continue Reading »
  • How to remove newline characters from a string in C++?
    Posted on Saturday March 24, 2018
    How to remove newline characters from a string in C++? For example, a string like line 1 line 3 line 4 should be converted to line 1line 3line 4 In short, use this code snippet: input.erase(std::remove(input.begin(), input.end(), 'n'), input.end()); std::remove() shifts all elements that are equal to the value n by moving the elements in […] The post How to remove newline characters from a string in C++? appeared first on SysTutorials. Continue Reading »
  • How to change the default target of `make`?
    Posted on Saturday March 24, 2018
    The default target of make is the first target. But can I change the default target in Makefile and how to change the default target of make? The default goal of make is the first target whose name does not start with ‘.’ if .DEFAULT_GOAL is not set. Ref: make manual. To set the default […] The post How to change the default target of `make`? appeared first on SysTutorials. Continue Reading »
  • What are the differences between BIOS and UEFI?
    Posted on Saturday March 24, 2018
    BIOS: Basic Input Output Systems UEFI: Unified Extensible Firmware Interface UEFI is the advanced BIOS, which solves some limitations in BIOS such as 1, 16-bit processor mode; 2, 1 MB addressable space and PC AT hardware. References: https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface Answered by harryxiyou. The post What are the differences between BIOS and UEFI? appeared first on SysTutorials. Continue Reading »
  • how to list and delete shared memory in linux?
    Posted on Saturday March 24, 2018
    how to list and delete shared memory in linux? List all shared memories in your Linux Systems > $ ipcs -m Delete specific one > $ ipcrm -M 0x0001869c Answered by harryxiyou. The post how to list and delete shared memory in linux? appeared first on SysTutorials. Continue Reading »
  • How to get one process’s port number?
    Posted on Saturday March 24, 2018
    If we want to check one program on one remote server, we need to know this server’s IP and port number. How to get this program’s port number in the remote server? # netstat -tulpn Remember to run this program with root permission since some programs can only be accessed by root. Answered by harryxiyou. The post How to get one process’s port number? appeared first on SysTutorials. Continue Reading »
  • What are the differences between NUMA architecture and SMP architecture?
    Posted on Saturday March 24, 2018
    NUMA Architecture: Non-Uniform Memory Access architecture. SMP: Symmetric Multiprocessing architecture. 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, […] The post What are the differences between NUMA architecture and SMP architecture? appeared first on SysTutorials. Continue Reading »
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