Kernel

Useful tools

elixir

Writing modules

preparing kernel source:

git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git checkout <version>
git checkout -b <your-branch>

preparing menuconfig:

# e.g. drivers/hid/Kconfig

config YOUR_STRING
tristate "Summary text"
depends on SOME_OTHER_MODULES
default n|y|m
---help---
your additional info
in multiple lines

preparing Makefile:

# e.g. drivers/hid/Makeconfig

obj-$(CONFIG_YOUR_STRING)       += your-cfile.o

Beating the kernel

Magic sysrq's

Press Alt+SysRq

SysRq is often located at Print

space = print summary of available SysRq keys
m = print the current memory information to the console

Unbind/Bind hardware to/from modules

echo -n "xxxx:yyyy:zzzz.aaaa" > /sys/bus/hid/drivers/generic-usb/unbind
echo -n "xxxx:yyyy:zzzz.aaaa" > /sys/bus/hid/drivers/hid-foo/bind

Coredumps

cat /proc/sys/kernel/core_pattern
|/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %e

command/location to store coredump files

Suspend to ram

echo mem > /sys/power/state

Networking

Dealing with the limits of too much concurrent connections.

Outgoing

# gather port range for local/dynamic sockets.
sysctl net.ipv4.ip_local_port_range
# gather tcp connection timeout. socket is in TIME_WAIT.
sysctl net.ipv4.tcp_fin_timeout

ip_local_port_range / tcp_fin_timeout = sockets_per_second

Incoming

# gather the maximum number of requests queued to a listen socket.
sysctl net.core.somaxconn