System Call in Operating System | OS Tutorials

In the Operating System, a system call is the service provided by the Linux kernel. In C programming, it often uses functions defined in libc, which provides a wrapper for many system calls.

Linux System Call

• To get an overview, use “man 2 intro” in a command shell.
• It is also possible to invoke the syscall() function directly.
• Each system call has a function number defined in <syscall.h> or <unistd.h>.
• Internally, a system call is invoked by software interrupt 0x80 to transfer control to the kernel. System call table is defined in the Linux kernel source file “arch/i386/kernel/entry.S”.

Here are some Linux system calls used by an operating system, given in the tables.

#include <syscall.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>

int main(void){
    long ID1, ID2;
    
    ID1 = syscall(SYS_getpid);
    printf("syscall (SYS_getpid) = %ld\n",ID1);
    
    ID2 = getpid();
    printf("getpid() = %ld\n",ID2);
    return(0);
}

#include <syscall.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>

int main(void){
    long ID1, ID2;
    
    ID1 = syscall(SYS_getpid);
    printf("syscall (SYS_getpid) = %ld\n",ID1);
    
    ID2 = getpid();
    printf("getpid() = %ld\n",ID2);
    return(0);
}

Output

syscall (SYS_getpid) = 3
getpid() = 3