1.1. Android Filesystem

1.1.1. How it is different from general GNU/linux filesystem ?

Android is based on linux kernel, but its filesystem hirarchy differs from conventional linux filesystem. Most of the filesystem fall under /system. Also this is the main OS system. User’s data is stored under /data directory. The /cache partition is mostly used by Android’s Dalvik virtual machine. default.prop contains default system property setting which are restored at every bootup. /etc is symlink to /system/etc. /dev/ contains all device files. /proc Filesystem acts same as in linux. /sdcard is external SD-card directory.

Android filesystem

/
| -> acct/
| -> cache/
| -> config/
| -> d/
| -> data/
          | -> local/
| -> default.prop
| -> dev/
         | -> alarm
         | -> android_adb
         | -> ashmem
         | -> aw_i2c_ts1
         | -> binder
         | -> block
         .
         .
         .
| -> etc/
         | -> apns-conf.xml
         | -> audio_effects.conf
         | -> bluetooth
         | -> camera.cfg
         | -> dbus.conf
         | -> dhcpcd
         .
         .
         .
| -> init
| -> init.goldfish.rc
| -> init.rc
| -> init.sun5i.rc
| -> init.sun5i.usb.rc
| -> initlogo.rle
| -> mnt/
| -> oem/
| -> proc/
| -> root/
| -> sbin
| -> sdcard/
| -> sys/
| -> system/
            | -> app
            | -> bin/
                     | -> preinstall
            | -> build.prop
            | -> etc/
            | -> fonts/
            | -> framework/
            | -> lib/
            | -> media/
            | -> preinstall/
| -> ueventd.goldfish.rc
| -> ueventd.rc
| -> ueventd.sun5i.rc
| -> vendor

1.1.2. Introduction to chroot

code

example of chroot

SYNTAX : chroot <chroot-dir> <shell>

chroot /linux /bin/bash

running Xvfb

nohup Xvfb :1 -screen 0 640x480x24 -ac < /dev/null > Xvfb.out 2>
Xvfb.err &

Aakash Programming Language(APL) is a web based front end to four programming languages C, C++, Python and Scilab. In the backend, we run a webserver in a chroot'd environment. The chroot environment is a custom made GNU/Linux distribution without any ‘X-server’. Instead of having a ‘X-server’ which is high on both CPU and memory, we use a X virtual framebuffer called Xvfb. Xvfb is low on both CPU and memory and requires no dedicated display hardware for graphical display. All display of graphs(plots) in APL is done using Xvfb.

As the name says, CHROOT stands for change root which means, user can decide the root or / directory for its environment. For more information on chroot, Visit its man page. Chroot as its own advantage, apart from what we have used in APL. For developer’s, it can be a good development environment to test their new software as it is totally isolated from host machine.