diff --git a/www/index.html b/www/index.html new file mode 100644 index 000000000..972018ae5 --- /dev/null +++ b/www/index.html @@ -0,0 +1,260 @@ + + + + + + + + Minimal Linux Live + + + + + +
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+ Minimal Linux Live is a set of Linux shell scripts which automatically build minimal Live + Linux OS based on Linux kernel + and BusyBox. All necessary source codes are automatically + downloaded and all build operations are fully encapsulated in the scripts. +

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+ If you want to build your own Minimal Linux Live ISO image file, all you need to do is the following: +

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  • + Get the latest scripts from the download section. +
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  • + Extract the scripts to some folder. +
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  • + Make sure that all scripts are executable (chmod +x *.sh). +
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  • + Depending on which Linux OS you are using, there might be one or more (or none, or even more) build dependencies that you + need to resolve before you start the build process. If you work with Ubuntu, + the following commands should resolve all necessary build dependencies: +
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    • + sudo apt-get install wget +
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    • + sudo apt-get install make +
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    • + sudo apt-get install gcc +
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    • + sudo apt-get install bc +
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    • + sudo apt-get install syslinux +
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    • + sudo apt-get install genisoimage +
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  • + Execute the script build_minimal_linux_live.sh and wait. If you have resolved all build dependencies, the whole + process should take less than 30 minutes on a modern computer. If the build fails for some reason, most probably there + are unresolved build dependencies. Several users reported that the build-essential package resolves all unexpected + build dependencies for Ubuntu. If you are using Linux Mint try to + install the package g++ and if you still have troubles then try the build-essential package. On + Fedora you might need the static 'glibc' package glibc-static. +

    + Please have in mind that the build dependencies can vary a lot depending on the Linux OS which you use and the software + which you have already installed. +

    + If you still have troubles then examine the failure message and google it. If you are unable to find solution, then you + can ask someone more experienced Linux guru (if you know any) or as alternative you can contact me. Please, make sure that + you have researched your problem in advance before you send me your question. +

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  • + When the scripts finish their job you will find newly created minimal_linux_live.iso in the same folder where you + executed the scripts. You can burn the ISO image file on CD/DVD, install it on USB flash drive via + Universal USB Installer, + or run it directly via PC emulator like VirtualBox. +
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+ The produced ISO image file contains Linux kernel compiled with default options, BusyBox compiled with default options and very simple + initramfs. This means that you don't get Windows support out of the box, nor you get any fancy desktop environment. All you + get is a simple shell console which supports all BusyBox applets and... well, that's all. This is why it's called "minimal". +

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+ The good news is that even though the OS is small and simple, the build scripts are also very small and very simple. You can + quite easily learn from the scripts and later modify them to include more stuff (I encourage you to do so). After you learn + the basics you will have all the necessary tools and skills to create your own fully functional Linux based operating system! + Entirely from scratch! Isn't it great?! :) +

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+ The tutorial provides more details about the inner structure + of the scripts and the overall build process. I encourage you to go through this document when you have the time. +

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+ Below you can find several screenshots which show what the environment looks like when you boot your newly generated + Minimal Linux Live OS. +

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+ Minimal Linux Live +

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+ Minimal Linux Live +

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+ + + diff --git a/www/style.css b/www/style.css new file mode 100644 index 000000000..52e746637 --- /dev/null +++ b/www/style.css @@ -0,0 +1,139 @@ +html { +overflow: -moz-scrollbars-vertical; +overflow-y: scroll; +} + +body { +background: #f0f0f0; +margin: 0; +} + +#container { +width: 780px; +margin: 0 auto; +} + +#header { +padding: 5px 0px 0px 0px; +text-align: center; +background: #3b7687; +} + +#header a { +color: #fefefe; +text-decoration: none; +font-size: 25px; +font-family: "Verdana"; +} + +#menu { +background-color: #3b7687; +padding: 5px 0px 5px 0px; +text-align: center; +} + +#menu a { +color: #d5e6eb; +text-decoration: none; +font-size: 12px; +font-family: "Verdana"; +} + +#menu a:hover { +color: #ecf2f3; +} + +#sidebar { +float: right; +width: 160px; +padding: 20px 10px 40px 10px; +margin: 0; +color: #444444; +text-align: left; +background: #e6e6e6; +} + +#sidebar a { +text-decoration: none; +color: #262626; +font-family: "Verdana"; +font-size: 12px; +} + +#sidebar a:hover { + color: #666666; +} + +h1 { +margin: 0px; +color: #869843; +font-size:24px; +font-family: "Verdana"; +font-weight: normal; +} + +h2 { + color: #3b7687; + font-size: 14px; + font-family: "Verdana"; + margin: 0px; +} + +ul { + margin: 10px 0px 0px 0px; + line-height: 16px; +} + +#main { + background-color: #fefefe; +} + +#text { + margin: 0px 0px 0px 0px; + padding: 20px 20px 20px 20px; + color: #444444; + font-family: "Verdana"; + font-size: 12px; + line-height: 16px; + text-align: justify; +} + +#text a { +color: #3b7687; +text-decoration: underline; +} + +#text a:hover { +color: #444444; +} + +#footer { +padding: 10px 0px 5px 0px; +background: #d6d6d6; +font-family: "Verdana"; +color: #444444; +font-size: 11px; +text-align: center; +} + +#footer a { +text-decoration: none; +color: #262626; +} + +#footer a:hover { +color: #666666; +} + +.separator { +font-size:11px; +color:#FFFFFF; +} + +.center { + text-align: center; +} + +.clear { +clear:both; +} \ No newline at end of file diff --git a/www/the_dao_of_minimal_linux_live.txt b/www/the_dao_of_minimal_linux_live.txt new file mode 100644 index 000000000..512864abd --- /dev/null +++ b/www/the_dao_of_minimal_linux_live.txt @@ -0,0 +1,678 @@ + + The Dao of Minimal Linux Live (31-Jul-2014) + + Author: Ivan Davidov + Website: http://minimal.linux-bg.org + Email: davidov (dot) i {at} gmail [dot] com + + Redistributed by: + + ### ### ### + + Contents + + 1. Preface + 2. Boot Process + 3. Inside The Shell Scripts + 4. Possible Improvements + 5. Epilogue + + ### ### ### + + 1. Preface + + Please feel free to redistribute this document in any form you see fit. I only ask you to + respect my efforts and keep me as the original author. That's all I ask. + + Note that the explanations regarding the script details are based on the "28-Jul-2014" + version of "Minimal Linux Live". Future versions of the scripts may already include some + of the stuff discussed in the section "Possible Improvements". + + ### ### ### + + 2. Boot Process + + The overall boot process is quite complex but we need to know these details since we are + talking about operating systems and to be more precise - Linux based operating systems. + + You can find some general information here: + + http://en.wikipedia.org/wiki/Linux_startup_process + + When we talk about live Linux OS, the overall boot process is the following: + + 1) BIOS gives the execution control to the boot loader present on the boot media such + as CD, DVD, USB flash or something else. + 2) In most cases the boot loader is based on Syslinux. On our boot media we should have + two special files - the kernel file and the initramfs file. + 3) The boot media also contains a special configuration file which points to the location + of the kernel/initramfs files. + 4) Now that Syslinux knows where the kernel file is, it loads it in the RAM and passes + the execution control to it. + 5) The kernel detects the available hardware, loads necessary drivers and then it passes + the execution control to the initramfs. + 6) The initramfs file is an archive which is unpacked automatically by the kernel in the + RAM. The actual execution control is passed to the shell script file /init which must + be present in the initramfs file. + 7) Since we are talking about minimal live CD, in theory /init is not supposed to do much. + All we need form /init is to prepare the environment and provide the user with shell. + In most live Linux distributions the /init script is supposed to do much more work + but in our case for now it is enough to know that the point at which we take the control + is exactly the /init script. + + ### ### ### + + 3. Inside The Shell Scripts + + So far we learned that we need several pieces in order to build a live Linux OS: + + 1) boot loader - to make our media bootable. + 2) kernel file - to take care of the initial system bootstrap process. + 3) initramfs file - to prepare the necessary environment for the user. + + This document focuses on parts (2) and (3). The reason we won't discuss (1) in details is + because the build process that we are going to rely on later, takes care of the boot loader + part automatically. + + The ZIP which you have downloaded contains the following files: + + .config + 0_prepare.sh + 1_get_kernel.sh + 2_build_kernel.sh + 3_get_busybox.sh + 4_build_busybox.sh + 5_generate_rootfs.sh + 6_pack_rootfs.sh + 7_generate_iso.sh + build_minimal_linux_live.sh + + If you have followed the explanation posted on http://minimal.linux-bg.org then you already + know that you need to execute the script "build_minimal_linux_live.sh". If you open this + file with text editor you will find out that all this script does is to execute all other + scripts one by one. + + From this point onwards, I encourage you to execute the script files one by one. We will + start with "0_prepare.sh". If you take a look at the script's contents, you will find out that + all the script does is to create an empty folder named "work". We will store our temporary + work files there. + + OK, let's continue with the kernel. Somehow we need to end up with fully functional kernel which + is able to do the system initialization for us. We need to download the kernel sources, compile + these sources and finally pack the kernel. + + The script "1_get_kernel.sh" downloads the kernel sources and unpacks them. Here is the full + source code of the script: + + #/bin/sh + + DOWNLOAD_URL=$(grep -i KERNEL_SOURCE_URL .config | cut -f2 -d'=') + ARCHIVE_FILE=${DOWNLOAD_URL##*/} + + cd work + rm -f $ARCHIVE_FILE + wget $DOWNLOAD_URL + rm -rf kernel + mkdir kernel + tar -xvf $ARCHIVE_FILE -C kernel + cd .. + + First we read the ".config" file to find the URL for the kernel sources. The URL is stored in + the variable "DOWNLOAD_URL". Then we get the actual name of the archive file and we store the + name in the variable "ARCHIVE_FILE". + + The important part of the script is the line where we get the kernel sources: + + wget $DOWNLOAD_URL + + The next important part of the script is the line where we unpack the kernel sources: + + tar -xvf $ARCHIVE_FILE -C kernel + + At this point we have downloaded and unpacked the kernel sources. So far so good. Now we need + to compile them. We move to the next script in the chain called "2_build_kernel.sh". Here is + the full source code that we are going to analyse: + + #/bin/sh + + cd work/kernel + cd $(ls -d *) + make clean + make defconfig + sed -i "s/.*CONFIG_DEFAULT_HOSTNAME.*/CONFIG_DEFAULT_HOSTNAME=\"minimal-linux-live\"/" .config + make vmlinux + cd ../../.. + + First we navigate to the kernel source folder. Then we execute the following commands: + + make clean + + The above command cleans the output from our previous kernel builds. Obviously, if this is the + first time we go through the build process, we have nothing to clean. + + make defconfig + + The above command creates new ".config" file in the current folder which contains all default + configuration parameters that we need in order to build our new kernel. Note that the defaults + will be either 32 or 64 bit specific, depending on your Linux environment. + + sed -i "s/.*CONFIG_DEFAULT_HOSTNAME.*/CONFIG_DEFAULT_HOSTNAME=\"minimal-linux-live\"/" .config + + The above command searches for a specific line in the ".config" file which contains the string + "CONFIG_DEFAULT_HOSTNAME" and replaces the whole line with the following text: + + CONFIG_DEFAULT_HOSTNAME="minimal-linux-live" + + Later, when you boot up your live Linux OS you can execute the command "uname -a" and you will + see the string "minimal-linux-live" in the output. All we did was to replace the default value + "(none)" with our custom value. + + Now you have a sample command which you can use to search for specific configurations in the + file ".config" and replace these configurations with your own. Obviously, you can skip this + replacement and everything will work just fine. Like I said, the only difference will be that + the default host name will be "minimal-linux-live" instead of "(none)". + + Now we come to the most important and also the slowest part in the whole process. We need to + actually create the kernel. + + make vmlinux + + The above command will compile the Linux kernel. This takes a lot of time, so I guess it's + high time for a short break. The final kernel file is located here: + + arch/x86/boot/bzImage + + OK, at this point we should have a kernel file compiled with default options, where we have + changed the default host name with some other value of our own. Now we move to the next + part. + + The kernel itself is far from enough - we also need some kind of environment with basic + command line tools like ls, cat, mkdir, etc. This environment is called "initramfs" which + stands for "initial RAM file system". This is what we are going to do: + + 1) We are going to download & compile BusyBox. This will give us the basic command line + tools that we need for normal work in console mode. + 2) We will use BusyBox to provide us with some default directory/file structure which + we will modify into our own initramfs file. + + One by one - we need to download and unpack the BusyBox sources. Let's take a look at the + script file "3_get_busybox.sh": + + #/bin/sh + + DOWNLOAD_URL=$(grep -i BUSYBOX_SOURCE_URL .config | cut -f2 -d'=') + ARCHIVE_FILE=${DOWNLOAD_URL##*/} + + cd work + rm -f $ARCHIVE_FILE + wget $DOWNLOAD_URL + rm -rf busybox + mkdir busybox + tar -xvf $ARCHIVE_FILE -C busybox + cd .. + + The contents is almost identical to the one in "1_get_kernel.sh" which we have already + explained above. Long story short - we get the source archive with "wget" and then we + unpack the sources with "tar". That's it. Nothing complex at all. + + Now that we have BusyBox sources we need to compile them. Let's take a look at the next + script "4_build_busybox.sh" which we need to execute: + + #/bin/sh + + cd work/busybox + cd $(ls -d *) + make clean + make defconfig + sed -i "s/.*CONFIG_STATIC.*/CONFIG_STATIC=y/" .config + make busybox + make install + cd ../../.. + + You have probably already noticed it - we are going to execute several "make" commands + and meanwhile we are going to change one property in the ".config" file. Let's go + through all of these commands: + + make clean + + The above command ensures that we will get rid of all build artefacts, assuming this + is not the first time we go through the BusyBox build process. + + make defconfig + + The above command creates new ".config" file which contains the defaults for proper + BusyBox build process. Again, nothing extraordinary here. + + sed -i "s/.*CONFIG_STATIC.*/CONFIG_STATIC=y/" .config + + The above command is very important because we inform the build process to build + static version of BusyBox, which means that the BusyBox executable file will not + be dependent on any external library. We cannot skip this, otherwise our OS will + fail with "kernel panic" when we try to boot. + + make busybox + + The above command compiles BusyBox. Nothing interesting here. The build should be + significantly faster compared to the kernel build. + + make install + + The above command creates new "_install" folder and installs BusyBox in it. We + will use this folder as a base for our new initramfs file. + + At this point we should have kernel compiled with default settings (yes, we changed + one setting but it's not a big deal) and we should also have BusyBox compiled with + static option enabled and all other default settings. + + Now we come to the part where we create our own initramfs folder which later on we + will pack into a file. The steps that we are going to follow is this: + + 1) Use the already created "_install" folder as base for initramfs. + 2) Create some new folders in the initramfs folder. + 3) Create some configuration files in the initramfs folder. + + Now we come to the script "5_generate_rootfs.sh" which is responsible to generate + proper initramfs folder with all necessary files and sub-folders in it. + + #/bin/sh + + cd work + rm -rf rootfs + cd busybox + cd $(ls -d *) + cp -R _install ../../rootfs + cd ../../rootfs + rm -f linuxrc + mkdir dev + mkdir etc + mkdir proc + mkdir src + mkdir sys + mkdir tmp + cd etc + touch welcome.txt + echo >> welcome.txt + echo ' #####################################' >> welcome.txt + echo ' # #' >> welcome.txt + echo ' # Welcome to "Minimal Linux Live" #' >> welcome.txt + echo ' # #' >> welcome.txt + echo ' #####################################' >> welcome.txt + echo >> welcome.txt + cd .. + touch init + echo '#!/bin/sh' >> init + echo 'dmesg -n 1' >> init + echo 'mount -t devtmpfs none /dev' >> init + echo 'mount -t proc none /proc' >> init + echo 'mount -t sysfs none /sys' >> init + echo 'cat /etc/welcome.txt' >> init + echo 'while true' >> init + echo 'do' >> init + echo ' setsid cttyhack /bin/sh' >> init + echo 'done' >> init + echo >> init + chmod +x init + cp ../../*.sh src + cp ../../.config src + cd ../.. + + As you see, this script is much longer than the others. Let's take a look at the + important parts one by one. + + cd work + rm -rf rootfs + cd busybox + cd $(ls -d *) + cp -R _install ../../rootfs + cd ../../rootfs + + The above code snippet removes the old initramfs folder called "rootfs" and then + copies the "_install" folder (the one created by BusyBox) with new name "rootfs". + This folder is going to be our new initramfs focal point. + + rm -f linuxrc + + The folder "rootfs" contains file "linuxrc" which we don't need since we are going + to use initramfs boot scheme. Take a look at the following Wikipedia article for + more details: + + http://en.wikipedia.org/wiki/Initrd + + OK, lets go on. + + mkdir dev + mkdir etc + mkdir proc + mkdir src + mkdir sys + mkdir tmp + + The above code snippet creates some basic folders which we are going to use later. + + cd etc + touch welcome.txt + echo >> welcome.txt + echo ' #####################################' >> welcome.txt + echo ' # #' >> welcome.txt + echo ' # Welcome to "Minimal Linux Live" #' >> welcome.txt + echo ' # #' >> welcome.txt + echo ' #####################################' >> welcome.txt + echo >> welcome.txt + cd .. + + The above code snippet creates the file "/etc/welcome.txt" and fills it with the message + which will be displayed every time we boot up the system. + + touch init + echo '#!/bin/sh' >> init + echo 'dmesg -n 1' >> init + echo 'mount -t devtmpfs none /dev' >> init + echo 'mount -t proc none /proc' >> init + echo 'mount -t sysfs none /sys' >> init + echo 'cat /etc/welcome.txt' >> init + echo 'while true' >> init + echo 'do' >> init + echo ' setsid cttyhack /bin/sh' >> init + echo 'done' >> init + echo >> init + + The above code snippet creates the file "/init" which is going to be invoked by our kernel + when we boot up the system. In fact we create new shell script file. This is what our new + "/init" script does: + + dmesg -n 1 - We hide all kernel messages. We don't want them in our + console. Only kernel panic messages will be displayed. + mount -t devtmpfs none /dev - With this command we politely ask the kernel to + populate the /dev folder with all necessary system + devices like "console", "tty", etc. We also have nice + names for the hardware devices like "sr0", "sda", etc. + mount -t proc none /proc - The kernel populates the /proc folder. + mount -t sysfs none /sys - The kernel populates the /sys folder. + cat /etc/welcome.txt - Now we display the welcome message. + while true - This code snippet starts shell on "tty" device and + setsid cttyhack /bin/sh we rest assured that when we execute the "exit" + done command new shell will be started automatically. + + As you see, the "/init" script file doesn't do much but what it does is really essential. + We have only one more bit of code relevant to the "/init" file: + + chmod +x init + + The above command ensures that our "/init" script is executable. + + cp ../../*.sh src + cp ../../.config src + + The last thing we do is to copy all "Minimal Linux Live" shell scripts (including the + configuration file) in the "/src" folder. The scripts won't do anything there. This step + simply ensures that the live Linux ISO file which we are going to create later contains + the build sources, just for reference. + + OK, at this point we have "rootfs" folder which contains all necessary files and + configurations for our initramfs file. The next step is to pack the "rootfs" folder + into an actual initramfs file. Let's take a look at "6_pack_rootfs.sh": + + #!/bin/sh + + cd work + rm -f rootfs.cpio.gz + cd rootfs + find . | cpio -H newc -o | gzip > ../rootfs.cpio.gz + cd ../.. + + The above script removes the already existing initramfs file called "rootfs.cpio.gz" + and then creates a new file called "rootfs.cpio.gz" based on the contents of the + "rootfs" folder. + + We are almost finished. At this point we have already compiled the Linux kernel and we + have also created initramfs file based on BusyBox and our own set of configurations. + The last thing to do is to generate bootable ISO file. Let's take a look at the last + script "7_generate_iso.sh": + + #/bin/sh + + rm -f minimal_linux_live.iso + cd work/kernel + cd $(ls -d *) + make isoimage FDINITRD=../../rootfs.cpio.gz + cp arch/x86/boot/image.iso ../../../minimal_linux_live.iso + cd ../../.. + + As usual, we first remove the already generated ISO file, assuming this is not the first + time we go through this process. Then we navigate to the kernel's source folder and + we execute the following command: + + make isoimage FDINITRD=../../rootfs.cpio.gz + + The above command generates bootable ISO based on the already compiled Linux kernel and + it uses the initramfs file which we pass to the "make" command as additional parameter. + The generated ISO file is then copied to the folder where we are executing our scripts. + + ### ### ### + + 4. Possible Improvements + + Now that you have played around with your shiny new live Linux OS, you have probably + noticed that you are logged in automatically and you have no restrictions. However, + it only looks like you are automatically logged in. Yes, you get shell console and + this console allows you to perform "root" operations, but this doesn't mean that you + are logged in as "root" or any other user. In fact there are no users and groups in + the system. + + I'll show you the proper way to add some users and groups from within your system + while it is still running. You can examine the final result for yourself and modify + the "5_generate_rootfs.sh" script according to your needs. + + OK, let's go with the "root" account! + + touch /etc/group + + The above command will create empty file "/etc/group" where we store the information + for all groups. + + addgroup -g 0 root + + The above command will create a group "root" with group identification number "0". + It is important to provide 0 (zero) as group identifier (gid) because this is the + expected gid for "root". + + touch /etc/passwd + + The above command will create empty file "/etc/passwd" where we store the login + information for our users. + + adduser -h /root -G root -u 0 root + + The above command will create user "root" with home folder "/root", assign the new + user to the "root" group and set user identifier (uid) "0". It is important to + provide 0 (zero) as uid because this is the expected uid for the "root" user. Add + whatever password you want when asked. Try to remember it. + + login + + The above command will initiate the login process. Now you should be able to log in + as "root" with the password which you have provided. + + --- --- --- + + Another possible improvement is to set appropriate "global" rights (including the 't' + sticky flag) for the /tmp folder. You can do that by executing the following command: + + chmod 1777 /tmp + + The reason I haven't included this in the /init script is because in this particular + situation it doesn't really matter. By default we get uid=0 shell console and we have + full and unrestricted access to the /tmp folder. However, if you decide to add more + users to the system (not just the "root" user), you may also include the above command + in the /init script file. + + --- --- --- + + Probably the easiest update you can do is to re-compile the kernel with other than + default options. This is how we do it for the kernel. First of all we need to know + what possible options we have. Navigate to the kernel's source folder and execute the + following command: + + make help + + We have several options for interactive ".config" generation. Let's go with this one: + + make menuconfig + + You might need to resolve one more dependency ("ncurses") if you want the above command + to work. Once you do that you can choose any kernel configuration options you like. The + provided menu is quite complex but we are not in hurry. Take your time and enable or + disable any options you want. Don't forget to save your configuration. Now all we need + is to compile the new kernel. + + make vmlinux + + Depending on your configuration this time the build might take longer. Obviously if + you decide to go through manual kernel ".config" configuration you can no longer use + the script "2_build_kernel.sh" because it will override your new configuration with + the default configuration. + + --- --- --- + + Even though we haven't discussed this topic, you might have already noticed that the + file ".config" which comes along with the other build scripts contains the URL + locations for the kernel sources and the BusyBox sources. You can easily build live + Linux OS based on different kernel/BusyBox versions if you provide different + URLs in the ".config" file. Here is the content of the default ".config" file: + + # You can find the latest Linux kernel source bundles here: + # + # http://kernel.org + # + KERNEL_SOURCE_URL=https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.15.6.tar.xz + + # You can find the latest BusyBox source bundles here: + # + # http://busybox.net + # + BUSYBOX_SOURCE_URL=http://busybox.net/downloads/busybox-1.22.1.tar.bz2 + + Of course, once you do that you also need to go through the scripts "1_get_kernel.sh" + and "3_get_busybox.sh" or execute the relevant commands from these scripts manually. + + --- --- --- + + Another very interesting improvement is to execute /sbin/init and rely on further + configuration provided in /etc/inittab. Here is the modified version of the shell + script "5_generate_rootfs.sh": + + #/bin/sh + + cd work + rm -rf rootfs + cd busybox + cd $(ls -d *) + cp -R _install ../../rootfs + cd ../../rootfs + rm -f linuxrc + mkdir dev + mkdir etc + mkdir proc + mkdir src + mkdir sys + mkdir tmp + cd etc + touch bootscript.sh + echo '#!/bin/sh' >> bootscript.sh + echo 'dmesg -n 1' >> bootscript.sh + echo 'mount -t devtmpfs none /dev' >> bootscript.sh + echo 'mount -t proc none /proc' >> bootscript.sh + echo 'mount -t sysfs none /sys' >> bootscript.sh + echo >> bootscript.sh + chmod +x bootscript.sh + touch welcome.txt + echo >> welcome.txt + echo ' #####################################' >> welcome.txt + echo ' # #' >> welcome.txt + echo ' # Welcome to "Minimal Linux Live" #' >> welcome.txt + echo ' # #' >> welcome.txt + echo ' #####################################' >> welcome.txt + echo >> welcome.txt + touch inittab + echo '::sysinit:/etc/bootscript.sh' >> inittab + echo '::restart:/sbin/init' >> inittab + echo '::ctrlaltdel:/sbin/reboot' >> inittab + echo '::once:cat /etc/welcome.txt' >> inittab + echo '::respawn:/bin/cttyhack /bin/sh' >> inittab + echo 'tty2::once:cat /etc/welcome.txt' >> inittab + echo 'tty2::respawn:/bin/sh' >> inittab + echo 'tty3::once:cat /etc/welcome.txt' >> inittab + echo 'tty3::respawn:/bin/sh' >> inittab + echo 'tty4::once:cat /etc/welcome.txt' >> inittab + echo 'tty4::respawn:/bin/sh' >> inittab + echo >> inittab + cd .. + touch init + echo '#!/bin/sh' >> init + echo 'exec /sbin/init' >> init + echo >> init + chmod +x init + cp ../../*.sh src + cp ../../.config src + cd ../.. + + The above script creates very minimal /init which executes /sbin/init. Then the + new init process (that is /sbin/init with PID 1) reads the file /etc/inittab and + executes all commands provided there. The script /etc/bootscript.sh takes care of + the initial "mount" stuff. We also have 4 terminals (you can switch between them + with "Alt + F1" to "Alt + F4") and the contents of the file /etc/welcome.txt is + displayed before we access the shell for each of these terminals. + + You can find more information about the supported /etc/inittab commands here: + + http://git.busybox.net/busybox/tree/examples/inittab + + Note that the above details are specific for BusyBox. Usually the "init" process + supports runlevels but that's not the case with BusyBox. + + --- --- --- + + Most probably you use normal user (i.e. not "root") when you execute the scripts. + One side effect is that the generated initrtamfs will keep the original ownership + of all files and folders. However, this leads to some interesting discrepancies + when you run the system. Some of the files/folders will have "root" ownership + (uid=0, gid=0) but most of the files/folders will have the same uid/gid as the + user which you used in order to build the system. This has no implications at all + since we have unrestricted shell console but if you'd like to "fix" this you will + have to either execute "5_generate_rootfs.sh" as "root" or manually change the + ownership of the initramfs folder (i.e. "work/rootfs") before you execute the + script "6_pack_rootfs.sh" with this command: + + chown -R root:root work/rootfs + + Note that the above command requires "root" permissions, so there is no way to + escape from the above described discrepancies if you don't have "root" access. + + Also note that you may need to take care of the permissions for the script files + in the "work/rootfs/src" folder. Either delete the "src" folder before you run + "6_pack_rootfs.sh" or make sure that all files have global "read" permissions. + + ### ### ### + + 5. Epilogue + + That's all folks! I hope you find this tutorial useful. And remember, we are talking + about very minimal live Linux OS here. If you want to create something bigger, I + suggest you take a look at "Linux From Scratch" (google it, you'll find it). + + At some point you may also find it useful to play around with other live Linux + distributions. Don't forget that the initramfs file is compressed and in order to + get to the actual /init script you will need to uncompress it. Then you can see + the actual file structure of the initial root file system and examine the /init + script file. This will give you more insight on the boot process for the + particular live Linux distributions that you are learning from. + + One interesting live Linux distribution is "Slax". Just download it and take a + look at the /init script file (remember, you can uncompress the initramfs file). + There is also a very good document which explains the internal root file system + and the OS boot process for Slax: + + http://slax.org/en/documentation.php#internals + + The above URL may have changed but it is valid at the time I write this document. + \ No newline at end of file