Startup in User Mode

Startup of the Root Process in User Mode

The root process is the first user-mode process in the system. The process ID is 1. The root process is the ancestor of all user-mode processes.

Figure 1 Process tree

Startup Process of the Root Process

Use the link script to place the following init startup code to the specified location in the system image.

#define LITE_USER_SEC_ENTRY   __attribute__((section(".user.entry")))
LITE_USER_SEC_ENTRY VOID OsUserInit(VOID *args)
{
#ifdef LOSCFG_KERNEL_DYNLOAD
    sys_call3(__NR_execve, (UINTPTR)g_initPath, 0, 0);
#endif
    while (true) {
    }
}

NOTE

The preceeding code is in kernel/liteos_a/kernel/user/src/los_user_init.c. The value of g_initPath can be /dev/shm/init or /bin/init, depending on the startup settings.

Use OsUserInitProcess to start the init process. The procedure is as follows:

  1. The kernel calls OsLoadUserInit to load the code for startup.

  2. A process space is created to start the /bin/init process.

Responsibilities of the Root Process

  • The root process starts key system programs or services, such as shell.

    NOTE In OpenHarmony, the init process reads /etc/init.cfg and runs commands or starts processes based on the configuration. For details, see init Configuration File.

  • The root process monitors the process for reclaiming the orphan process and clears the zombie processes in child processes.

Running Programs in User Mode

A user-mode program can be started in either of the following ways:

  • Using shell commands

    OHOS $ exec helloworld
OHOS $ ./helloworld
OHOS $ /bin/helloworld

  • Using POSIX APIs Use Fork() to create a process, and call exec() to execute a process.