Linux Core Installation and Remastering for Output to Serial Port

Basically they are two methods how to install Linux Core. The first option is to use a Linux Core installation script that comes with tc-install extension. One should take this option as installation process is interactive and automated thanks to the installation script. The second method is manual installation of  Core Linux and will be described  in the tutorial.

The installation steps provided below have been tested for x86 and x86-64 Linux Core 6.x and they show step-by-step installation on Qemu virtual machine.

If you prefer automated Core Linux installation using an installation script, check this tutorial. Qemu installation on Fedora Linux is shown here.

Linux Core Live x86 and x86-64 ISO images can be downloaded from Tinycore webpage. I have created the script download_core64.sh  that downloads the latest CorePure64 ISO image. Afterwards it  creates a vmdk disk and starts the Qemu virtual machine with attached vmdk disk and CorePure ISO image.

1. Create Qemu Disk

x86
$ /usr/local/bin/qemu-img create -f qcow2  linux-core.img 200M

x86-64
$ /usr/local/bin/qemu-img create -f qcow2  corepure64.img 200M

2. Start Qemu Virtual Machine with Attached Live ISO Core Image 

x86
$ /usr/local/bin/qemu-system-i386 -boot d -cdrom Core.iso -hda linux-core.img

x86-64
$ /usr/local/bin/qemu-system-x86 -boot d -cdrom Core.iso -hda corepure64.img

3. Install Syslinux Extension

$ tce-load -wi syslinux

4. Create New Partition Ext4 Type

$ sudo fdisk /dev/sda

n Add new partition
p primary partition
Partition number (1-4): 1
First cylinder (1-25, default 1): ENTER
Last cylinder (1-25, default 25): ENTER
a toggle a bootable flag
Partition number (1-4): 1
w write table to the disk and exit

$ mkfs.ext4 /dev/sda1

5. Install Boot Sector

$ dd if=/usr/local/share/syslinux/mbr.bin of=/dev/sda

6. Rebuild /etc/fstab and Mount Partition /dev/sda1

$ sudo rebuildfstab
$ mount /mnt/sda1

7. Mount CDROM and Copy Files core.gz and vmlinuz to /mnt/sda1/boot

$ sudo mkdir -p /mnt/sda1/boot/extlinux

x86
$ mount /mnt/sr0
$ sudo cp -pr /mnt/sr0/boot/* /mnt/sda1/boot

x86-64
$ mount /mnt/sdb
$ sudo cp -pr /mnt/sdb/boot/* /mnt/sda1/boot

8. Install Boot Loader

$ sudo extlinux --install /mnt/sda1/boot/extlinux

9. Create Menu Config File

x86
$ sudo vi /mnt/sda1/boot/extlinux/extlinux.conf

DEFAULT core
LABEL core
KERNEL /boot/vmlinuz
APPEND initrd=/boot/core.gz quiet

x86-64
$ sudo vi /mnt/sda1/boot/extlinux/extlinux.conf

DEFAULT core64
LABEL core64
KERNEL /boot/vmlinuz64
APPEND initrd=/boot/corepure64.gz quiet

10. Create Directory for Storing Extension and Setup Proper Ownership

$ sudo mkdir /mnt/sda1/tce
$ sudo chown tc:staff /mnt/sda1/tce
$ touch /mnt/sda1/tce/mydata.tgz

11. Shutdown Core

Shutdown core and start it with the command below.

x86
$ /usr/local/bin/qemu-system-i386 -boot c -hda linux-core.img

x86-64
$ /usr/local/bin/qemu-system-x86_64 -boot c -hda CorePure64.img

Remastering Linux Core For Redirecting Output To Serial Port

This part discuss remastering of Linux Core for redirecting the CLI output to a serial port. Qemu can redirect a serial port of a guest virtual machine to the telnet server that it starts on the host machine. Thanks to it everyone can connect to a virtual machine even the virtual guest is not configured for accepting remote connection (ssh, telnet). This feature is very handy specially in a test environment where security is not an issue.

For example, the Qemu command -serial telnet:0.0.0.0:3000,server,nowait starts a telnet sever on a host machine and redirects a serial port of Qemu guest virtual machine to the server. The telnet server is listening for incoming connection to its IP address with destination TCP port 3000.

Note: Remastering is shown for 32 bit version of Core Linux. Remastering steps for 64 bit Core distribution are identical except that the core64 and vmlinux64 keywords must be used.

1. Edit Menu Config File

$ sudo vi /mnt/sda1/boot/extlinux/extlinux.conf

DEFAULT core
LABEL core
KERNEL /boot/vmlinuz console=ttyS0,38400n8
APPEND initrd=/boot/core.gz quiet

2. Extract File core.gz

$ mkdir -p /home/tc/temp/extract
$ sudo cp /mnt/sda1/boot/core.gz /home/tc/temp/
$ cd /home/tc/temp/extract/

$ zcat ../core.gz | sudo cpio -i -H newc -d

3. Disable Autologin for tty1 and add ttyS0

Autologin is useful when you do not want prompt user for login credentials. Unfortunately Core Linux hangs up after boot when autologin is in use and output is redirect to a serial port. For this reason we are going to disable autologin for tty1 and  ttyS0.

Picture 1 - Core Randomly Hangs Up when Autologin is Used

$ sudo vi ./etc/inittab

#tty1::respawn:/sbin/getty -nl /sbin/autologin 38400 tty1
tty1::respawn:/sbin/getty 38400 tty1
ttyS0::respawn:/sbin/getty 38400 ttyS0

4. Display Login Credentials

If you use Linux Core for testing it might by helpful to display login credentials when autologin is not used. Add the following lines to the file ./etc/issue.

$ sudo vi ./etc/issue

Login to Core Linux

Username "tc", password is not set

5. Edit /etc/securetty to Allow Root Login to Serial Port ttyS0

Uncomment line #ttyS0

$ sudo vi ./etc/securetty

ttyS0

6. Pack File core.gz

$ sudo su
$ cd /home/tc/temp/extract/

$ find | cpio -o -H newc | gzip -2 > /mnt/sda1/boot/core.gz

$ cd /home/tc
$ rm -rf /home/tc/temp

7. Test If Output Is Redirected to Serial Port

Shutdown Core Linux Qemu virtual machine.

$ sudo halt

$ /usr/local/bin/qemu-system-i386  -boot c  -hda linux-core.img -serial telnet:127.0.0.1:3000,server,nowait

Connect to serial port of  Core using a telnet command.

$ telnet 127.0.0.1 3000