Monday, 27 June 2011

Ubuntu 11.04 - Device management (4/6)

General Information
This is the result of personal research through community and official documentation about GNU/Linux and Ubuntu. References used are provided also. It will be presented in 6 posts as listed below:

UBUNTU has support for all types of hardware built into the kernel. (Ubuntu pocket guide and reference, p.19). To the extent possible, all device drivers appear as normal files. Devices are separated in three classes:
  • block devices
Here belong all the devices that allow random access to completely independent, ficed-size blocks of data, such as HDDs, floppy disks, CD-ROMs, flash memory. They are accessed randomly.
  • character devices
In this category belong most other devices, most of which are pointing devices such as keyboards, mice etc. They are accessed serially.
  • network devices
Here we find the network devices that users cannot communicate directly. Their transfer data by opening connection with the kernel's network subsystem. (Operating System Concepts, p.835)
A fundamental difference in Ubuntu 11.04, based on their kernel version, 2.6.38 is the use of deadline I/O shceduler in order address the starvation issue. The deadline for read request is 0,5 second and for write requests is 5 seconds. It maintains a sorted queue, a read and a write queue. (Operating System Concepts, p.836)
Four are the key folders for devices in UBUNTU, show in the table below:
/dev Virtual files representing hardware devices
/media Contains folder where storage devices can be mounted
/proc Virtual folder containing file representing stats and settings
/etc System (global) configuration files
(Ubuntu pocket guide and reference, p.53)
UBUNTU does not have a “Computer” view like windows. Storage devices are mounted in folders inside the /media folder. Moreover, for HDDs Master Boot record is important, because bootloader (GRUB 2.0) cannot be after the 1024th cyclinder, since it may cause system to halt at boot.
Through kernel updates the drivers are updated and more are included. However, it is possible to compile drivers in kernel. However, it is addressed to advanced users only. The administration of the devices using graphical tools is limited, compared to the tools available in terminal. The utilities can be found in the System settings → “Hardware” and “System” section.
Additionally the gnome-device-manager package can be installed through the synaptic manager or through terminal,
$sudo apt-get install gnome-device-manager
in order to graphically list all the available connected devices. “Connected” devices does not mean “operational” too.
System administrator must count in terminal to list and compare values from the /proc folder and /dev for the problematic device, so as to verify the amount of interrupts, mapping, memory allocation addresses, pages etc to figure out where the problem is located.
  1. Ubuntu pocket guide and reference, Keir Thomas, MacFreda publishing, 2009
  2. Operating System Concepts, 8th Edition, Abraham Silberschatz, Peter B. Galvin, Greg Gange, 2010, Jonh Wiley and Sons

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