Adam Williamson from happyassasin.net has a nice article titled Some comparisons between Fedora 13, 15, 17, 19 and 20. Adam works for Red Hat as Fedora QA Community Manager, meaning he knows what he’s taking about:
We can see that the memory used when you simply boot to a console and log in has changed very little all the way back to Fedora 13, released 2010-05-25. We’re doing a fairly good job of keeping our base system from bloating excessively. 19 and 20 are both 30MB worse than 17, but then, 17 was 25MB better than 15.
The same certainly doesn’t hold true for the graphical desktop, though. Just sitting at a mostly-idle desktop with a terminal open, our memory usage has gone from 275MB under the ancien GNOME 2 regime to 300MB with GNOME 3′s ‘fallback mode’ (which was more or less GNOME 2), then rocketed to nearly 400MB, 535MB, and nearly 700MB in subsequent releases. I haven’t yet looked in detail at the changes, but I did take screenshots of ‘top’ ordered by memory usage for each install.
The measurements are done using free command in a gnome-terminal immediately after bootup. GNOME runs in a virtual machine without hardware acceleration, and it ends up using Mesa llvmpipe driver. These are the graphs based on Adam’s measurements:
Fedora server memory (MB)
Fedora GNOME Desktop memory (MB)
Ethernet networks can be partitioned into multiple distinct broadcast domains using VLANs. VLAN domains are mutually isolated. Whenever a hosts in one VLAN domain needs to communicate with a hosts in another VLAN domain, the traffic must be routed between the two domains. This is known as inter-VLAN routing.
This document provides a VLAN configuration example for a small network split into two separate VLAN domains: SALES and ENGINEERING. The backbone consists of two VLAN bridges connected by a VLAN trunk. I will use a Linux-based router, RCPlive, connected to the trunk to provide routing between the two VLAN domains and the outside world. On the router I will also enable a number of services such as DHCP and stateful firewall.
Virtualization refers to the creation of virtual machines that acts like real computers with an operating system. Software executed on these virtual machines is separated from the underlying hardware resources.
This article discusses LXC, a lightweight virtualization technology built into Linux kernel. The user space LXC tool is distributed with a number of templates that allow the creation of different Linux distro filesystems, usually one template for each major Linux distribution. The problem with these templates is they never work, or they stop working with every new release of LXC tool or of the particular Linux distribution. This is the case with all Linux distributions, and Debian is no exception. Currently, the Debian template is borken under “wheezy”. The relevant Debian bug is here, and history shows that as soon such a bug gets fixed, lxc user space driver changes again and breaks it. It could be worse, in Fedora LXC was broken in Fedora 15 and it was never fixed.
The simple way to handle the problem is to forget all about the template mechanism and roll your own containers. In Debian you can build the container filesystem using the standard debootstrap, or mount read-only the host filesystem, and then use lxc-execute to start a simple bash session inside the container. In this session you can than start all the programs you need to run in the container. It is an application container, very similar to the containers created using the official ssh template distributed with LXC.
The virtual machine I will describe in this article uses a root filesystem build using debootstrap (apt-get install debootstrap). The procedure is simple and it should work on any Debian machine. It will probably work also on any other distro based on Debian, such as Ubuntu, Mint etc.
Hundreds of new open source software projects are published on Internet each day. The vast majority are built by private individuals in their spare time, or at least this is how the projects are starting. The usefulness of these projects is secondary in nature, most of the time the goal is learning and personal development, or how somebody else put it, scratching one developer’s personal itch.
This blog post is about how to package and publish an open-source project. I have this source code just sitting there on my hard drive, I wrote it some time ago, other people might find it interesting. Let’s start with the itch.
Many people are very surprised when they find out telnet protocol requires more than a TCP socket connection between a client and a server. There are two tty terminals involved, one on the server side, and one on the client side. These terminals are synchronized by special messages sent over the socket connection, mangled with the session data.
To figure it out, I can start by reading a long list of RFCs, or I can take a shortcut and try to lift it from a wireshark trace:
An SNMP MIB browser is an indispensable tool for engineers and system administrators to manage SNMP enabled network devices such as routers, switches, servers and workstations. The information provided by SNMP includes uptime, interface traffic data, routing information, TCP and UDP connection information, installed software, and much more.
In this tutorial, I introduce qtmib, an easy-to-use SNMP browser available for Linux and published under GPLv2 license. The program is build as a front-end for net-snmp tools using QT4 library.
qtmib browser window
A live CD or live DVD is a complete bootable Linux operating system loaded from a CD or DVD. Although there are a lots of live Linux CDs, for seemingly every taste and purpose, it might still be useful on occasion to build your own. This guide details the steps to build a bootable live CD/DVD based on Debian “wheezy”.
Step 1 – Installing the necessary software
These are the software packages you need to install on your Debian system:
# apt-get install xorriso live-build syslinux squashfs-tools
Step 2 – Create a basic filesystem
Start by creating a new work directory, and bring in a basic Debian filesystem using debootstrap. Depending on your network connection, it will take some time downloading all the necessary packages:
# mkdir ~/livework && cd ~/livework
# debootstrap --arch=amd64 wheezy chroot
The new filesystem was created in ~/livework/chroot directory. It is time to chroot into the new filesystem and finish the installation.
Virtualization allows the creation of multiple virtual machines (VM) on top of an existing computer, each VM configured in a very specific way. All virtual machines run in parallel alongside the regular host applications, without affecting the host system. The type of virtualization I am currently using is Linux containers (LXC), a lightweight virtualization technology built into Linux kernel.
This is my third Debian virtualization article. In the first article, I’ve described the steps to create and run a basic virtual machine using LXC. In the second article I’ve isolated the VM on its own network segment, with its own TCP/IP networking stack. Both articles were dealing with server VMs, I’ve used Lighttpd as an example throughout my articles.
I will describe now how to run desktop applications such as Mozilla Firefox and LibreOffice in a virtual machine. I will use virtenv to build and run the VM. virtenv is a QT4 application released under GPLv2 license. It is basically a configuration wizard that allows you to configure and start the LXC-based virtual machines. Once the VM is started, you get a regular controlling terminal (xterm) and a desktop window running the lightweight Openbox window manager. In this window you can run your GUI applications, very similar to VMware Workstation or Oracle’s VirtualBox.
virtenv desktop and controlling terminal
Linux containers (LXC) is a lightweight virtualization technology built into Linux kernel. In my previous article, Debian Virtualization: LXC Application Containers, I have detailed the steps to configure and run a simple application container using LXC. LXC application containers are very lean and consume strictly the resources the application requires. This is in sharp contrast with other virtualization technologies which are running a full Linux distribution in VM.
The container uses its own file system, built by mounting read-only the relevant directories from the host file system. The host is an older computer running Debian 7 “wheezy”. The virtual machine is controlled through GNU screen if the VM was started automatically at boot time, or through a regular xterm.
One thing I left out was the networking stack. In my Lighttpd web server example, the VM uses the same networking stack as the host. This could become a problem if someone manages to compromise the web server: the intruder could then probe the networks connected to our host, in search for the next victim.
In this article I’ll modify the VM to run on a separate networking stack. I will place the VM on its own network segment, connected to the host through a Linux bridge interface. I will then go and set up the host firewall using iptables. This effectively isolates the VM and limits the potential damage that could be inflicted on the larger network. The final setup looks like this:
Linux containers (LXC) is a lightweight virtualization technology built into Linux kernel. Unlike other similar technologies, the virtual machines (VM) are driven without any overhead by the kernel already running on the computer. In VM you run only the processes you need, most of the time without even going through the regular SysV or Linux init. This means that memory is used very conservatively. These lightweight containers are sometimes called application containers, as opposed to distribution containers where you run a full distro starting with SysV/Linux init.
In this article I’ll take a look at installing and building a small web server application container using LXC on a Debian 7 workstation. Debian is a popular distribution for personal use among software developers, and the amount of software packaged far exceeds any other Linux disto out there. It also encourages tinkering, experimenting, and in a more general sense, learning about Linux and Free/Open Source Software.
The computer I am using is an old amd64 dual-core computer with a minimal LXDE desktop manager installed. For those of you interested, I have detailed the installation steps in my Lightweight Debian: LXDE Desktop From Scratch article. Since we are dealing with kernel utilities, all the commands in this article are specified as user root.
Home, Trash and Web icons used to be enabled by default on most Linux desktops – not anymore! I am often asked to add them back when I install Linux for some other people. They are part of the workflow, and I am not interested in changing workflows. I am simply interested in moving the user from Windows to Linux. This article describes how I do it for various Linux desktops.
To create the icons in LXDE, right-click on the desktop and select Create New/Blank File. Name the file Home.desktop. Right-click on the file and open it in Leafpad. Copy the following text in the file:
Similarly, create a new Trash.desktop file with the following content:
/usr/share/applications stores desktop files for all installed GUI applications. Copy firefox.desktop file in ~/Desktop folder. If you want to change the name appearing under the icon, edit Name= line in the file.
$ cp /usr/share/applications/firefox.desktop ~/Desktop/.