• Switching RVM to chruby

    I’ve found RVM’s gemsets are no longer useful to me. I used to make a separate gemset for each project by placing .ruby-version and .ruby-gemset file in each project directory. But whenever a Ruby release come out, I repeated uninstalling previous version and then clean installing new version. So I decided to move to chruby, smaller and simpler one.

    Goodbye, RVM

    rvm implode

    Also if you have additional script lines loading RVM, remove them. I left them to make it work only if RVM is installed.

    [[ -s "$HOME/.rvm/scripts/rvm/" ]] && source "$HOME/.rvm/scripts/rvm"

    Installing ruby-install

    ruby-install handles installations of various Rubies.

    If you’re on OS X:

    brew install ruby-install

    If you’re on Arch Linux:

    yaourt -S ruby-install


    wget -O ruby-install-0.6.0.tar.gz
    tar -xzvf ruby-install-0.6.0.tar.gz
    cd ruby-install-0.6.0/
    sudo make install

    Installing chruby

    If you’re on OS X:

    brew install chruby


    wget -O chruby-0.3.9.tar.gz
    tar -xzvf chruby-0.3.9.tar.gz
    cd chruby-0.3.9/
    sudo make install

    Then all I need to do is to load it from startup script, ~/.*shrc.

    if [ -e /usr/local/share/chruby/chruby.sh ]; then
      source /usr/local/share/chruby/chruby.sh
      source /usr/local/share/chruby/auto.sh

    The auto.sh is for auto-switching the current version of Ruby according to .ruby-version file of the current directory. This is optional.

    chruby provides ways to migrate Rubies from another Ruby manager, but I started from scratch, so installed latest Ruby using ruby-install.

    ruby-install ruby 2.3.0

    Then which ruby will points to some path under ~/.rubies directory.

    which ruby

    Now it’s possible to auto-switch the Ruby version with .ruby-version file or manually with chruby commands like chruby ruby-2.3.0 or chruby system, etc.

  • 32C3 CTF 2015: libdroid Write-up

    Reversing (150)

    Solves: 17

    Please install this on your new android phone, enter pass code and get the flag.


    • Updated the libdroid.apk, this one is now also able to run on a device. No changes to internal logic.

    If the above link doesn’t work, please use this link.

    Read on →

  • Moving Timezone to UTC in Jekyll

    At the very first, I haven’t think about the timezone of my blog. I had used to generate my blog on my local machine and deploy manually. At that time every content is released based on KST timezone, which is GMT+9.

    Right after that I tried to deploy my blog through Travis CI, I realized that something went wrong. Travis CI uses UTC by default, so the URL of every post between 0AM and 9AM was shifted by one day backward. I had to modify /etc/timezone or set environment variable TZ to restore the URLs.

    Yes, this can solve the problem I faced. But should I really use the KST for this whole blog? It’ll be nice if I can show the time based on timezone of each client, but I won’t be able to handle the date part of the post URL as well. So I decided to move the timezone of this site to UTC, global standard at least.

    Read on →

  • Revive the Tmux Sessions

    On the previous day, I accidently removed /tmp/tmux-1000/ directory. At first, there seems no problem with Tmux. But when I created another SSH connection, I saw this error message:

    $ tmux attach
    no sessions
    $ tmux list-sessions
    failed to connect to server

    But the Tmux prosesses were still there:

    $ ps -ef | grep tmux
    59277 16305  0 May06 pts/0    00:00:00 tmux attach

    Then I immediately noticed that the removing /tmp/tmux-1000/ things made the problem. And thankfully Tmux provides workaround. From the tmux manpage:

    -L socket-name

    tmux stores the server socket in a directory under /tmp (or TMPDIR if set); the default socket is named default. This option allows a different socket name to be specified, allowing several independent tmux servers to be run. Unlike -S a full path is not necessary: the sockets are all created in the same directory.

    If the socket is accidentally removed, the SIGUSR1 signal may be sent to the tmux server process to recreate it.

    Now we can revive our Tmux sessions by sending a signal to recreate sockets:

    killall -s SIGUSR1 tmux

    More simply, since the number of SIGUSR1 is 10:

    killall -10 tmux

    Then we can do tmux attach successfully. Yay!

  • Using Pinpoint with Docker


    Pinpoint is an open source APM (Application Performance Management) tool for large-scale distributed systems written in Java.


    In this post, our goal is to run a sample Pinpoint 1.6.x instance with QuickStart scripts. You can find them on GitHub. Also note that we’re going to use Docker.


    First things first, install Docker.

    wget -qO- https://get.docker.com/ | sh

    You can verify docker is installed correctly.

    sudo docker run hello-world

    For more details, see the installation guides of Docker.

    Look into the Dockerfile

    In fact, I already made a Dockerfile for Pinpoint. You can see on yous/pinpoint-docker. From now on, I’ll describe the Dockerfile line by line.

    Read on →