Release Notes For Linux v0.95

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This is the release notes for linux release v0.95 (source code: linux-0.95.tar.gz) with format adjusted by removing/replacing tabs/spaces/new lines. This notes document can give us an understanding of the early development of the Linux kernel. The original ASCII formatted version is at the end of this post. RELEASE NOTES FOR LINUX v0.95 Linus Torvalds, March
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Handling Sparse Files on Linux

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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
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How to Add a File Based Swap for Linux

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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
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How to get the IP addresses of VMs in KVM with virsh

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When we create VMs in KVM, we may don’t know the IP addresses because they are automatically assigned by DHCP. So we want to get them in VMM so that can login by SSH. Do the commands as follows. $ virsh domiflist hvm1 Interface Type Source Model MAC ——————————————————- vnet0 network default virtio 52:54:00:1c:36:cd $
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‘dd’ command cannot support calculation for its parameters

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$ dd if=/dev/zero of=./4Ktest100M bs=4KB count=25000*9 dd: invalid number `25000*9′ I think ‘dd’ should support calculation for its parameters like ‘bs’, ‘count’ and so on. You can get the effect by using some other tools/commands, like dd if=/dev/zero of=./4Ktest100M bs=4KB count=$((25000*9)) or dd if=/dev/zero of=./4Ktest100M bs=4KB count=$(bc <<< 25000*9) I think it makes sense. Thank
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How to make dd faster on Linux?

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dd seems slow when I use command like # dd if=/dev/sda2 of=./sda2.bak How to make it faster? You can make dd faster by specifying a good bs like # dd if=/dev/sda2 of=./sda2.bak bs=8192 8192 is a magic number. There are may be other good sizes for bs for different systems. But 8192 works pretty well
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SEEK_HOLE and SEEK_DATA: efficiently archive/copy large sparse files

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How to efficiently archive a very large sparse file, say 1TB? The sparse file may contains a small amount of data, say 32MB. SEEK_HOLE and SEEK_DATA The SEEK_HOLE/SEEK_DATA functionalities play the trick and makes `tar` and `cp` handle the large sparse file very efficiently. `lseek` with `SEEK_HOLE` returns the offset of the start of the
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I/O Microscopy: Tasks’ Disk I/O Information with High Accuracy

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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.
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How to Install Paravirtualized CentOS 7 DomU on Xen

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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.
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Vim Tutorial for Beginners: vimtutor

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There are many Vim tutorials and Vim tips on the Web. However, I find the vimtutor provides the best tutorial among those so far as I found on the Web while the vimtutor seems usually reachable from a terminal which is not obviously known to Vim beginners who are usually Linux beginners too. This page
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Which Checksum Tool on Linux is Faster?

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It is common practice to calculate the checksums for files to check its integrity. For large files, the checksum computation is slow. Now I am wondering why it is so slow and whether choosing another tool will be better. In this post, I try three common tools md5sum, sha1sum and crc32 to compute checksums on
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How to Clean RAID Signatures on Linux

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RAID systems such as MegaRAID add signatures to disks to maintain the infomration on these didks. When we simply remove these disks and install them to another server, Linux on the new server may detect these RAID signature infomration and refuses to continue write to the disk. Here is one example that mkfs reports “apparently
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How to Get Available Filesystem Space on Linux: a C Function with a C++ Example

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It is common for programs to write to files in filesystems on disks. However, what if the disk was almost full when your program writes to the filesystem on a disk? For systems software and mission critical programs, it is a better or must-to-do practice to check the available filesystem space before actually writing to
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SSD Enabled For DreamHost Shared Hosting: Simple Performance Measurement

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SSD is common for VPS and PaaS virtual machines for higher I/O performance. Now, it is coming to shared hosting too. DreamHost states that “Now with solid state drives (SSDs), our standard web hosting loads pages 200% faster”. We ourselves are happy to know this performance improvement with the price kept the same. Good work,
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How to Create Fedora 20 Domain-U on Fedora 20 Domain-0

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In this post, creating a file-backed virtual block device (VBD) and installing Fedora 20 in the Xen DomU via internet will be introduced. This domain is created on a Fedora 20 Dom0 as introduced in https://www.systutorials.com/installing-xen-on-fedora-20-as-domain-0/. For better performance, you may consider using LVM backed VM. Create file-backed VBD The actual space of VBD will
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Duplicating and Backing Up LVM Backed Xen DomU from a Remote Server

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LVM’s snapshot feature enables us to duplicate an LVM backed Xen DomU in seconds inside of the same volume group. When we want to duplicate LVM backed Xen DomU from a remote server, we need to make use of LVM’s snapshot function and tools like scp and dd. Backing up the DomU is only part
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How to Create Fedora Live USB Media

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How to create a Fedora live USB media is introduced in this post. We can boot to Fedora operating system environment through a live USB system in the USB flash media on a USB-bootable computer without writing the computer’s hard disk. We can also install Fedora operating system from the live system environment. Remember to
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