Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

An ordinary stable 3* kernel is about 70 mb now. But there are little linux distributions of 30-10 mb with software and other stuff running out of the box.

How can the linux kernel be so small in these distros? Can stripping down only unneeded modules and drivers dramatically reduce the size? What else is done to reduce the kernel size?

share|improve this question
2  
Another option is to use size optimizations when compiling, but I'm not sure how big impact can that make. –  AndrejaKo Dec 22 '11 at 10:12
2  
"Linus calls Linux 'bloated and huge'" theregister.co.uk/2009/09/22/linus_torvalds_linux_bloated_huge –  Aki Dec 22 '11 at 10:22
    
@AndrejaKo - A lot. (If you go for small size.) –  Shiki Dec 22 '11 at 10:24
8  
70 MB is the size of the source. A standard compiled and compressed kernel is around 2 MB, modules like 10 MB. –  ott-- Dec 22 '11 at 11:42
    
yes, indeed, its 3.6 mb while initramfs is 21mb in my distro. –  puzzled tux Dec 22 '11 at 12:15
show 2 more comments

5 Answers

up vote 20 down vote accepted

Yes. If you strip them down (compile/make modules only things that you need), compress the kernel (optimize for size)... it'll result in such a small kernel. You can make an even smaller ones, for targeted system. Like I know my PC, I know my stuff. So I'll just compile what I need. Like my own SATA drivers, driver for USB, etc. Nothing else. No webcam, no old IDE drives, nothing.

Also: The bigger ones you encounter are the WHOLE kernel (which one never needs to use). Even the desktop ones contains (most of the times, as modules) a LOT OF unneeded stuff. But newbies expect that every kind of hardware they plug-in will just work.

(Note that, the modules won't get loaded until they are needed. There are 3 states:
[ ] - Won't get compiled, won't be part of your kernel.
[M] - Will be compiled as a module.
(You can modprobe it, or your system will auto-load it when it's needed.
Depends on the system, userland.)
[X] - It'll be compiled into the kernel AND will be present - always.

Distros with small kernel:

share|improve this answer
    
thank you for answers –  puzzled tux Dec 22 '11 at 12:15
    
Just a small addition - [X] means it'll be compiled into the kernel, hence the reason why it's always loaded. –  Lawrence Jan 10 at 12:02
add comment

Early Linux distributions such as Tom's Root-Boot, MuLinux, Diet-router, (the now defunct) LOAF and many others now departed, all fitted a working Linux system on to one or two 1.44 MB diskettes.

The Linux kernel has grown but don't forget it is modular, kernel modules are loaded as needed. Thus it is still possible to produce a Linux distribution with a very small footprint.

See: Kernel Size Tuning Guide - eLinux.org

If you read Linux_tiny.pdf you will see this

  • historic 0.99pl15 kernel: Slackware 1.1.2, 1994 301K
  • Fedora Core 2 1.2M
  • SuSE 9.1 1.5M
  • 2.6.5-tiny1 test config: IDE, ext2, TCP, NIC 363K
share|improve this answer
    
yes, thanks again –  puzzled tux Dec 22 '11 at 12:18
add comment

Most major distros configure their kernels with maximum hardware support so it will work out of the box with most computers and anything you plug in later on. They also use an initrd system which is not needed in most cases. There are also options in the kernel configuration that make the build process optimize for size, and a better (though slower) compression method can be selected as well. Lastly, if you are looking at the size of the kernel source code, keep in mind that it also includes support for several architectures beyond x86/amd64, network protocols, file systems, and other features that you'll probably never use and that can be disabled.

share|improve this answer
add comment

The default kernel configuration is configured to support as many hardware as possible. A non-stripped kernel with default configuration resulted in a size of 1897996 kB (including kernel + modules). When stripping many unnecessary drivers and options (why would I need a HP module if I own a Clevo notebook), it resulted in a size of 892892 kB which is a size reduction of 53% compared to the stock kernel.

When installing the kernel modules, append the INSTALL_MOD_STRIP=1 option. This will strip all debugging symbols and reduced the size by 92% for me (from 892892 kB to 69356 kB). Note this will only affects modules to be installed and not the kernel (vmlinuz) itself:

make INSTALL_MOD_STRIP=1 modules_install

From Documentation/kbuild/kbuild.txt:

INSTALL_MOD_STRIP
--------------------------------------------------
INSTALL_MOD_STRIP, if defined, will cause modules to be
stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
the default option --strip-debug will be used.  Otherwise,
INSTALL_MOD_STRIP value will be used as the options to the strip command.
share|improve this answer
    
wow, 1897996 kB is almost 2GB! –  netvope Oct 23 '13 at 2:18
add comment

It is quite simple, a minimal system just need bootloader + kernel though it is almost useless. Most of commands used everyday, are optional binary for the system, like sh, ls, etc. If you are interested in internals, Linux From Scratch! is a good start point.

share|improve this answer
    
Note that Busybox takes care of most of the "everyday" stuff. –  new123456 Dec 22 '11 at 15:25
    
No, busybox just combined them together. It is popular in small and embedded system, but not the case for desktop system. –  pinxue Dec 22 '11 at 17:48
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.