The HDFS has a configuration in hdfs-site.xml to set the global replication number of blocks with the “dfs.replication” property. However, there are some “hot” files that are access by many nodes. How to increase the number of blocks for these certain files in HDFS? You can the replication number of certain file to 10: hdfs…
How to run Chrome on remote host over a SSH tunnel? This way, I can access resource that can only be accessed inside the remote host’s network. Running Chrome over a SSH tunnel is much easier than running Firefox over SSH from a Linux host: First, ssh to the remote host with -X option: ssh…
What are all the bash supported comparison operators? The man 1 test contains all the operators supported in bash. An omitted EXPRESSION defaults to false. Otherwise, EXPRESSION is true or false and sets exit status. It is one of: ( EXPRESSION ) EXPRESSION is true ! EXPRESSION EXPRESSION is false EXPRESSION1 -a EXPRESSION2 both EXPRESSION1…
How to the number of files in a directory ls | wc -l works well for me. http://stackoverflow.com/questions/3702104/find-the-number-of-files-in-a-directory
On Linux, a default editor is used for text editing such as crontab -e or git commit. How to change it to the editor of my own choice? The default editor is indicated by the EDITOR environment variable. You can set this environment variable to set the default editor. For example, set it to emacs…
How to change the fonts of gnome-shell for gnome3? Like the system bar. The fonts of gnome-shell is described in its own theme. For the default gnome-shell, you need to edit the file as root: /usr/share/gnome-shell/theme/gnome-shell.css Right, it is a css file. Find the font-family keyword and change the corresponding fonts. Then you can restart…
How to tell whether the shell is run in screen? For example, I run screen and it starts a bash environment. How to tell in the bash, whether it is run by screen or it is a normal bash environment? It can be identified by checking the TERM environment variable: In a bash in screen:…
How to set an environment variable in bash? The syntax in bash for setting an environment variable is as follows. export VARIABLE=value Note that there is no space among the variable, the equals sign (“=”) and the value. If the value has spaces, the value should be put in quotes. To check it: echo $VARIABLE…
Which tools to mange OCaml packages in my system (Linux)? I use OPAM to manage OCaml packages: http://opam.ocamlpro.com/index.html To install it: $ wget https://raw.githubusercontent.com/ocaml/opam/master/shell/opam_installer.sh $ sh ./opam_installer.sh /usr/local/bin More options are available here. To make opam settings take effect, append this to ~/.bashrc: eval `opam config env` Some frequent usages: opam list # List all…
It is painful for a Linux user to use the OCaml toplevel without the readline features. Is there a method to enable/add these kinds of features in readline to the OCaml toplevel? I find 2 options that work very well for me: utop provides a beautiful interface and supports completion, colors, parenthesis matching, etc. It…
I miss Gnome 2. How to install the MATE fork of Gnome 2 on Fedora 17? MATE is already included into Fedora 17’s repository and is an official feature of Fedora 18. To install MATE on Fedora 17 # yum install @mate-desktop To install softwares usually needed: # yum install mate-media mate-screensaver mate-system-monitor mate-power-manager mate-utils…
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…
This post is about the Spring Shell technology and its use in java. Experts of java development India have shared their best knowledge in this post for Spring Shell with the community people. If you have anything to ask, do it at the end. Technology: It is command line tool for Java applications to interact…
Gnome Shell has a clean design. But many users want to get more from the desktop environment. Gnome 3’s extension system can help users customize the Gnome Shell’s look greatly. In this post, we summarize 6 extensions we considered essential to make Gnome Shell great. AlternateTab Make Alt-Tab “classic” instead of grouping windows by application….
Since version 7, RHEL has only x86-64 versions. The same thing happens to CentOS 7. In CentOS 7/EPEL, there is only package for Wine x86-64. However, many Windows .exe files are 32-bit. Even there are 64-bit versions for some software, their installation file is 32-bit. And for some certain software such as Office 2007, 32-bit…
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…
Linux may report “device is busy” when we try to umount a filesystem. This behavior is reasonable as it can help us avoid data loss by disallowing unmouting a filesystem when it is being used. But for situations when we are sure there is something wrong happened or we care not data lost such as…
Attaching a USB keyboard to a laptop is common when using a laptop because a normal keyboard may provide a more convenient typing experience. The laptop keyboard is not used in these situations. However, the laptop keyboard may still be touched by accident. In this post, we will discuss how to disable and enable the…
Bash script may need to get its own path. In normal Bash script, $0 is the path to the script. However, when a script is sourced, such as . a.sh, a.sh‘s $0 does not give a.sh while the caller’s name. How to reliably get a bash script’s own path no matter whether the Bash script…
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,…