Linux system generator

linsygen is a shell script which creates an image file of a Linux system from scratch. The image can be used later to run a virtual machine or can be written to a real HDD drive.

There is a few variations of the same script - for each Linux distro because there is some essential differences between them (package manager, config locations etc.).

The generation takes near a minute to generate a brand new HDD image of a Linux system, but the time spent can be much more when your Internet connection is slow because the most of time is spent by the package manager to fetch the packages from the network and install them into the image.

Supported Linux distros

• Debian;
• OpenSuse;
• CentOS.

Common algorithm:

• create a file for the image;
• connect the file as a block device to the host system;
• create a partition table at the block device;
• create a primary partition at the block device;
• create an ext3 filesystem on the partition;
• mount the filesystem;
• install all packages listed in a configuration file to the mounted filesystem;
• make a primary Linux system configuration (fstab, network etc.);
• install a SSH public key into the filesystem's /root/.ssh/authorized_keys;
• configure and install a boot loader into the block device;
• unmount the filesystem;
• disconnect the block device.

Network configuration note: the target system will try to configure the network interface with DHCP.

How to generate

To create an image of the Debian system, cd into a debian subdir, check contents of a wheezy.conf configuration file.

The configuration file is self-documented. You can define:

• release name (so, you can create squeeze system from a wheezy system);
• DEB-repository mirror to use;
• a target disk size;
• password for the root user;
• a hostname for the target;
• list a DEB packages to install into the target;
• list of tarballs to extract into the target's root FS.

When configuration is ready, type:

$ sudo ./generate.sh wheezy.conf

The script execution needs superuser privileges because of playing with devices, mounting/unmounting etc.

If everything is OK, you will see Done in the stdout and the script will finish with 0 exit code.

A results of the generation you'll find in a tmp subdir:

• image.raw - HDD image file in raw format;
• initrd - initial RAM disk;
• vmlinuz - linux kernel.

Note that the initrd and the vmlinuz files are essential only in rare cases. For the simplest case the image.raw file is all you need.

You'll find SSH identity key in a .ssh/id_rsa file. The identity can be used to access the generated system via SSH into a root user.

How to use with QEMU

As optional step you can convert the image into QEMU-known qcow2 format which consumes less disk space than raw HDD image:

$ qemu-img convert -O qcow2 tmp/image.raw tmp/image.qcow2

QEMU understands both image formats.

To start a QEMU virtual machine, type:

$ kvm -hda tmp/image.raw

or

$ kvm -hda tmp/image.qcow2