# Kernel Subsystem ## Overview The OpenHarmony kernel is a real-time OS kernel developed by Huawei for IoT devices. It is as lightweight as RTOS and as easy-to-use as Linux. The kernel repository is used to store the source code of the OpenHarmony kernel components, including process and thread scheduling, memory management, IPC mechanism, and timer management, as well as the version package compilation information. ## Directory Structure **Table 1** Directory structure of the OpenHarmony lightweight kernel source code

Directory	Description
apps	User-space init and shell application program
arch	System architecture, such as ARM
bsd	Code of the driver and adaptation layer module related to the FreeBSD, such as the USB module
compat	Compatibility with the kernel POSIX interfaces
fs	File system module, which mainly derives from the NuttX open-source project
kernel	Kernel modules including the process, memory, and IPC modules
lib	Kernel library
net	Network module, which mainly derives from the lwip open-source project
platform	Code for supporting different systems on a chip (SOCs), such as Hi3516DV300
security	Code related to security features, including process permission management and virtual ID mapping management
syscall	System calls
test	Kernel and user-space test cases
tools	Code related to compilation configuration and menuconfig

## Constraints By default, the JFFS2 file system is used during system startup. This file system is read-write. If other file systems need to be used, the configurations of the file systems must be added accordingly. ## Usage For details, see [en-us\_bookmap\_0000001050030794.md\#en-us\_topic\_0000001050032743](en-us_bookmap_0000001050030794.md#en-us_topic_0000001050032743). ## Repositories Involved drivers\_liteos kernel\_liteos\_a kernel\_liteos\_a\_huawei\_proprietary\_fs\_proc kernel\_liteos\_m