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Kernel

The kernel is the core component of the OS. It:

  • Connects the HW/SW
  • Manages system resources (RAM/CPU)
  • Handles connected device drivers and makes devices available to OS.
  • Is responsible for system initialization and boot up.
  • Process scheduling.
  • Memory management.
  • Control access to HW.
  • I/O between applications and storage devices.
  • Implementation of local/network fs.
  • local and remove security control(e.g. fs permissions)
  • Networking control.

Boot​

Parameters are passed to the system at boot using the kernel command line. An example:

# root: root filesystem
# ro: mounts root device read-only on boot
# crashkernel: how much memory to set aside for kernel crashdumps

linux boot/vmlinuz-4.19.0 root=UUID=3829711-91487194-173541957 ro quiet crashkernel=384M-:128M

The parameters are key=value after boot/vmlinuz-4.19.0.

To see what command the system booted with:

cat /proc/cmdline

To view all possible parameters:

man bootparam

sysctl​

Interface that can be used to read and tune kernel parameters at runtime.

We can see all keys and values:

sudo systctl -a

abi.cp15_barrier = 2
...

Each key corresponds to an entry in /proc/sys/, i.e. /proc/sys/abi/cp15_barrier.

We can set a value:

# Either
sudo sh -c 'echo 1 > /proc/sys/abi/cp15_barrier'

# Or
sudo sysctl abi.cp15_barrier=1

Settings can be fixed at boot time by modifying:

sudo nano /etc/sysctl.conf

# makes change effective immediately
sudo sysctl -p