How to trap Ctrl-C in a Bash script? The piece of code: # trap ctrl-c and call ctrl_c() trap ctrl_c INT function ctrl_c() { echo echo “Ctrl-C by user” # do the jobs exit }
Tag: How to
How to choose the number of mappers and reducers in Hadoop
Posted onHow to choose the number of mappers and reducers in Hadoop to get good job performance? The Hadoop Wiki gives a discussion on this: http://wiki.apache.org/hadoop/HowManyMapsAndReduces Some valuable points: About the number of Maps: The number of maps is usually driven by the number of DFS blocks in the input files. Although that causes people to
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Specifying –no-print-directory within the Makefile
Posted onThe –no-print-directory option of make tells make not to print the message about entering and leaving the working directory. However, how to specify the –no-print-directory inside the Makefile itself? Add this line to the Makefile: MAKEFLAGS += –no-print-directory You can also set MAKEFLAGS in a makefile, to specify additional flags that should also be in
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How to spawn a background process in a bash script
Posted onFor example, I want to spawn many ssh background processes in one bash script: for i in `cat ./all-hosts` do ssh $i “ifconfig | grep Link” done Simply adding a & to the ssh commands does not work. Here is the script that works: for i in `cat ./all-hosts` do ssh $i “ifconfig | grep
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Force Linux to reboot
Posted onHow to force Linux to reboot when the reboot command does not work. Enable the use of the magic SysRq option: # echo 1 > /proc/sys/kernel/sysrq Reboot the machine: # echo b > /proc/sysrq-trigger Even if you could not log on the system but sshd is working, you can force the Linux to reboot by:
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How to force Chrome on iPhone refresh pages and invalidate the caches
Posted onI find Chrome on my iPhone caches pages/css/js files. That makes browsing faster. However, under some situation, I’d like to force it refresh the pages/css/js and give me the latest one. How to force Chrome on iPhone refresh pages and invalidate the caches? The only method as far as I can find is to clear
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How to install Scala on Fedora Linux
Posted onThis tutorial introduces how to install Scala 2.9.2 on 64-bit Fedora Linux 17. There are some changes needed to make scala work on Fedora Linux 17. Please check it out in the answer. Install Java Scala depends on Java, so please install Java first. In this tutorial, we installed JDK to: /usr/java/jdk1.6.0_24/lib/. Install Scala from
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How to exclude certain repositories in yum?
Posted onThis tutorial introduces how to exclude certain repositories in yum. Excluding certain repositories is needed usually. One example may be when you have several repositories that have the same package and you only want the one from a certain repository. For my situation, I choose to exclude the google-chrome and other repositories from Google when
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How to install Scala from the official Scala distribution
Posted onHow to install Scala from the official Scala distribution? This is needed on a Linux release with older version of Scala in the repository, e.g. Fedora 12. Use the install-scala.sh script: # wget https://raw2.github.com/zma/usefulscripts/master/script/install-scala.sh # sh ./install-scala.sh VER where VER is the scala version that you want to install. First step, install and configure the
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How to get the assembly code for OCaml code generated by ocamlopt?
Posted onHow to get the native assembly code (e.g. x86-64 asm) for OCaml code generated by the native ocamlopt compiler? To get the assembly code for an OCaml program, add these parameters to ocamlopt: -S -inline 20 -nodynlink An example is as follows. The OCaml program: $ cat not.ml let not x = ((x – 1)
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How to delete all topics and posts from a user/spammer in myBB?
Posted onThis is a tutorial on “how to delete all topics and posts from a user/spammer in myBB”. Please check out the answer. I use the Goodbye Spammer plugin for MyBB. First, install it after downloading the plugin form its homepage: Upload ./inc/plugins/goodbyespammer.php to ./inc/plugins/ Upload ./inc/languages/english/goodbyespammer.lang.php to ./inc/languages/english/ Go to ACP > Plugins > Activate
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How to repair a MySQL table?
Posted onAfter a server crash and restarting, MyBB reports a SQL Error as follows: MyBB SQL Error MyBB has experienced an internal SQL error and cannot continue. SQL Error: 145 – Table ‘./mybb/mybb_sessions’ is marked as crashed and should be repaired Query: SELECT * FROM mybb_sessions WHERE sid=’40021925bd0494ea31…’ AND ip=’x.x.x.x’ LIMIT 1 The dababase is MySQL.
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How to save a Word as a PDF in Office 2007
Posted onHow to save a Word document to be a PDF in Office 2007? I find this add-on for Office 2007 from Microsoft: 2007 Microsoft Office Add-in: Microsoft Save as PDF or XPS. It works very well for me. After installing this plugin, I can open a Word document and save it as a PDF file.
How to use OCaml as a script language?
Posted onHow to use OCaml as a script language like bash and python? It will be good that I can write a script in OCaml and directly invoke it. For example, I write a script named “script.ml” and then I can invoke it directly by $ ./script.ml Thanks! Three helloworld scripts: script3.ml #! /usr/bin/env ocaml print_string
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How to list a git repository’s all branches on the remote server?
Posted onI can list all local branches by git branch How to list a git repository’s all branches on the remote server? You need the -r option: git branch -r From the man page of git-branch. -r List or delete (if used with -d) the remote-tracking branches.
How to change the position of y-axis label in Gnuplot
Posted onAfter setting the font sizes for Gnuplot, they fonts look good. However, the y labels is too far away from the y-axis. How to change the position of y-axis label in Gnuplot? You can make use of the {offset <offset>} option. For example: set ylabel “Y Label” offset 3,0,0 which moves the ylabel 3 characters
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Where are the backup files of my iPhone by iTune and how to get the real files from them?
Posted onI backup my iPhone with iTune to my local computer. Where can I find out the backup files of my iPhone by iTune? And how to get the real files (like songs, notes, etc.) from the backup files? The location of the backup files from iTune It depends on the computer’s operating system: Mac: ~/Library/Application
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How to print the text in a web page?
Posted onHow to efficiently print a webpage? E.g. I want to only print the text for some pages but with figures for some other pages. I tried to copy the webpage to a document, but the format turns to be just terrible. One good tool that I use is PrinterFriendly which can convert a webpage to
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How to change the font sizes in Gnuplot
Posted onHow to change the font sizes of labels (x and y axis) and keys for Gnuplot? The default fonts turn to be too small when I shrink the images in my paper. Several methods are available for Gnuplot: Set the global fonts size for the terminal: set terminal enhanced font ‘Verdana,10’ Here, 10 is the
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Grub2: How to boot Fedora to an old kernel?
Posted onGrub2: How to boot Fedora to an old kernel? The old kernel is a submenu under “Advanced options for Fedora”. It is not shown if I follow the instruction that # grep menuentry /boot/grub2/grub.cfg | cut -d “‘” -f2. The old kernel in grub2 is in a submenu entry in a menu. The key is
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