Additional Repositories for CentOS Linux

CentOS is a super solid Linux distro. However, its default repository’s packages are limited compared to Fedora. Even Fedora needs some additional repositories to have software packages for daily usage, such as MPlayer, ffmpeg. Fortunately, some community maintained repositories provides these software. In this post, we introduce theses additional common repositories and how to install them into CentOS. For the installation method, we use CentOS 7 as an example. » Read more

How to Change Systemd Boot Target on Linux

Many Linux distros, such as RHEL/CentOS 7, Fedora, Ubuntu 16, are now using systemd instead of init as the init system. It is common for Linux users to set Linux to boot to “GUI” or “Text” mode. The old way of changing ‘/etc/inittab’ for choosing Linux runlevels is not working for sytemd. This post will introduce the way for systemd systems to select the “runlevels”. » Read more

How to Set the Static IP Address Using CLI in Fedora/CentOS Linux

How to set the static IP address for CentOS 7/Fedora 22+ is introduced in this post. Here, we assume the Linux is using NetworkManager to manage the network. All steps are done as root. Find the interface you want to set the address ∞ Command ifconfig -a lists all interfaces. Find the interface name to set, such as enp2s0. datacenter-servers.jpg Edit the interface’s configuration file ∞ For interface NAME, the configuration file is stored in /etc/sysconfig/network-scripts/ifcfg-NAME. » Read more

Running a Command Upon Files or Directories Changes on Linux

Doing actions upon changes of files and directories is very useful. Examples like compiling a project after the source code files are changed, sending emails after important configuration files are modified, building the PDF after a TeX file is modified. On Linux, the inotify-tools provide good support for trigger actions after changes. In this post, I will introduce a small tool do-after-change.sh which continuously runs a command upon certain files and directories change. » Read more

How to Clean RAID Signatures on Linux

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 in use by the system” and refuses making a filesystem. » Read more

How to Regenerate Grub2 Config Files on Linux

Grub2 config file may need to be re-generated after changing Grub2 configurations such as configuration changes and setting default boot entries. The Grub2’s config file may be at different locations depending on your Linux distro and whether your Linux is booted in BIOS or UEFI mode. This makes regenerating Grub2 config file not easy for Linux users especially beginners. In this post, I will introduce a way that should be portable and easy to use. » Read more

What Is the Name of the Linux-based OS: A Survey

You may already well know “Linux” and may also use the “operating system based on the Linux kernel” directly or indirectly (you are indirectly using it now as this site is hosted on Linux). But how should we name the OS based on Linux? You may know there is GNU/Linux naming controversy. Different people have different opinions about this. Today, let’s see how do these widely used distributions call themselves by looking at their “about” web pages. » Read more

Making Chrome Accept Self-Signed Certificates on Linux

If your website uses a self-signed certificates, Chrome will show a warning every time and you need clicks to continue. In this post, I will introduce how to make Chrome accept self-signed certificates for sites on Linux. This post is made short on purpose and you need to search the Web and learn if you want to understand the stuff. self-signed-cert-chrome.png You will need libnss3-tools package on Debian/Ubuntu/Linux Mint or nss-tools on CentOS/Fedora/RHEL. » Read more

Creating Fedora 20 Domain-U on Fedora 20 Domain-0

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 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 be the amount of disk the virtual machine used. » Read more

Installing Xen on Fedora 20 as Domain-0

I ever introduced Installing Xen on Fedora as Domain-0 (Fedora 17) as the first try to use the xen package delivered from Fedora and get away from manually compiling Xen and patching the kernel. In this post, I introduce installing Xen Dom0 on Fedora 20. Installing Xen First, install the xen pacakges: # yum install xen The Linux kernel is already ready to run in Domain-0 with the pv_ops technology enabled. » Read more

Improving Fedora Font Rendering with Open Software and Fonts Only

It is continuously discussed that some Fedora users do not like the font rendering in Fedora Linux and there are solutions to improve the font rendering with potentially non-free or non-licensed software/fonts. However, with only the open source fonts and software and little tricks, the font rendering on Fedora can be quite good. In this post, I will introduce my method to improve Fedora’s font rendering with open software and fonts only. » Read more

How to Install, Run and Uninstall VMware Player and VirtualBox on Fedora Linux

VMware Player and VirtualBox are two cool and free full virtualization solutions and both can run on top of a Linux host. In this post, I introduce how to install, run, and uninstall VMware Player and VirtualBox on Fedora Linux. VMware Player ∞ Install VMware Player ∞ Download the installation bundle from VMware’s website. For example, the file we download is: VMware-Player-4.0.0-471780.x86_64.bundle . » Read more

Directly SSH to Hosts’ Internal IPs Through the Gateway

We have many hosts with internal/LAN IPs like 10.0.3.* behind a gateway and the hosts with LAN IPs can connect to the Internet through the gateway. We used iptables to forward port from the gateway to internal IPs so that users from hosts with Internet connections can SSH to the gateway’s forwarded port to log on the internal hosts. However, there should be rules added for these hosts and the users need to connect to these non-standard (not 22) ports of the gateway that may be blocked by firewalls of their network. » Read more

Improving ssh/scp Performance by Choosing Suitable Ciphers

Update on Oct. 9, 2014: You should be aware of the possible security problems of blowfish and it is suggested not to be used. Instead, you may consider ChaCha20 as suggested by Tony Arcieri. To use this with OpenSSH, you need to specify the Ciphers in your *.ssh/config* files as chacha20-poly1305@openssh.com possibly with another default one since only newer vesion of OpenSSH supports it. » Read more

Speeding Up WordPress with APC Object Cache and WP Super Cache

WordPress can be very fast after some (small) effort on performance optimization with the help from its plenty of plugins. Two of the directions are using cache to cut down the number of database queries and optimizing PHP’s performance with opcode cache. In this post, we introduce how to speed up WordPress with APC object cache and page cache with the two plugins “APC Object Cache Backed” and “WP Super Cache”. » Read more

Making Emacs Startup Faster

I use Emacs in terminals and start/close Emacs frequently as needed like in a file checking-editing-closing loop. However, Emacs seems take some time to start up especially some heavy modes are used. How to make Emacs start up faster? (If you just want the solution/script first, find the command in the summary section.) My solution is to make use of the server/client feature of Emacs ∞ This is how it works. » Read more

Customizing Fonts in Gnome 3

Gnome 3 is great and I can understand that it emphasizes on simplicity. However, the configuration settings for Gnome 3 does not provide tools for certain functions that I need. One of them is customizing the fonts. This post will summarize the tools/tips that I adopted to customize the fonts in Gnome 3. Usually, the settings will take effect after being changed. » Read more

Vim Howtos and Tips

Vim is a fast and handy editor on *nix systems. Like Emacs, Vim has a steep learning curve as you get constantly get new things. However, the effort deserves it as you efficiency is highly improved. Here, I summarize the tips and howtos I learned using Vim. Some previous posts on vim are tagged with vim.Table of Contents [hide]1 My .vimrc and .vim file1.1 How to use these files2 Previous posts tagged vim 3 Latex Writing in Vim with the Help of vim-latex3.1 master file 3.2 List references to sections, figure and tables to insert 3.3 List citations from the bibtex file to insertMy .vimrc and .vim file ∞ My .vimrc and .vim files: https://github.com/zma/vim-config How to use these files ∞ cd /path/to/vim-config/ git submodule update --init If you never configured Vim: cd ln -s /path/to/vim-config/.vimrc ./ ln -s /path/to/vim-config/.vim ./ If you ever configured your Vim, you may need to merge my configurations to yours. » Read more