How to compile asm to execute under Linux

Here is code snippet to show how to compile asm to execute under Linux:

shellx.asm:

section     .text
global      _start 
_start: 
    mov     edx,len   
    mov     ecx,msg   
    mov     ebx,1   
    mov     eax,4   
    int     0x80   
    mov     eax,1  
    int     0x80   
section     .data
msg     db  'Hello world',0xa  
len     equ $ - msg

let’s start

1. First step:

vagrant@kali:~/Desktop/cdasm$ nasm -f elf64 shellx.asm

2. Next step:

vagrant@kali:~/Desktop/cdasm$ ld -s -o shellx shellx.o

3. Execute :

vagrant@kali:~/Desktop/cdasm$ ./shellx 

then output :

Hello world