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Comment by zoobab | Hacker News Reader

If you compile a minimal linux kernel without a tcp/ip stack -> 400KB. If you add a tcp/ip stack -> 800KB.

For a project where I should just send the temperature, I just made a small C program in userspace that sent the value over a crafted UDP message, saved a lot of space (and complexity) :-).

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Wow that’s crazy!

As someone who knows nothing about anything: that doesn’t mean the tcp/ip stuff is half the source code of the whole kernel, does it?

The majority of the Linux kernel's source code is device drivers. The overwhelming majority of that is not included in the kernel image by default, but instead made available as kernel modules you can enable as needed. E.g., your thermostat probably doesn't need support for an obscure game controller, so doesn't have those drivers, but it could if you were so inclined.

Curiosly, why is the IP stack so large? 400kbytes of binary is a lot of code. Is it highly optimised for large server use case?

Modern TCP/IP stacks have a lot of extra code, including for anti-spoofing, performance enhancements (eg zero-copy integration with hardware network cards), various attack prevention measures (SYN floods, randomization of sequence numbers, etc) support for various hardware offloading (including many network cards that will do checksum offloading, etc), IPv6 (that also originally mandated IPSec integration), support for lower layer 2 protocols (mostly just ARP for Ethernet, but there are still others around).

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