Assembly: trying to write to file, but text is appending to filename - linux

Question

I'm trying to study assembly, while trying out the example in the tutorials I get stuck. I am compiling this using an ubuntu virtual machine.
Here is the code:
SYS_READ equ 3
SYS_WRITE equ 4
SYS_OPEN equ 5
SYS_CLOSE equ 6
SYS_CREATE equ 8
SYS_EXIT equ 1
section .text
global _start
_start:
mov eax, SYS_CREATE
mov ebx, filename
mov ecx, 0777
int 0x80
mov [fd_out],ebx
mov eax,SYS_WRITE
mov edx,len
mov ecx,msg
mov ebx,[fd_out]
int 0x80
mov eax,SYS_CLOSE
mov ebx,[fd_out]
int 80h
mov eax,SYS_OPEN
mov ebx,filename
mov ecx,0
mov edx,0777
int 0x80
mov [fd_in],eax
mov eax, SYS_READ
mov ebx,[fd_in]
mov ecx,info
mov edx,26
int 0x80
mov eax,SYS_WRITE
mov ebx,1
mov ecx,info
mov edx,26
int 0x80
mov eax,SYS_EXIT
mov ebx,0
int 0x80
section .data
filename db 'test.txt'
msg db 'Hello world file'
len equ $-msg
section .bss
fd_out resb 1
fd_in resb 1
info resb 26
after executing the compiled output, I get a file named test.txtHello world file.

Answer 1

While SYS_WRITE accepts the length of the information in EDX, the function SYS_CREATE needs a pointer to NULL terminated string for the filename.
Your filename, defined as
filename db 'test.txt'
is not NULL terminated and that is why it concatenates with the next string:
msg db 'Hello world file'
The terminating NULL in this case is the next defined:
fd_out resb 1
In order to fix it, simply define the filename with zero terminating byte:
filename db 'test.txt', 0