Re: exit(), _exit() and sys_exit()

[Bernhard Walle <bernhard.walle@xxxxxx>]

Rajaram Suryanarayanan <rajaram_linux@xxxxxxxxx> [2006-03-04]:
> Hi,
>    
>   What is the difference between exit and _exit() ?

man _exit:

The  function _exit() is like exit(), but does not call any
functions registered with atexit() or on_exit().  Whether it flushes
standard I/O buffers and removes temporary files  created  with
tmpfile(3)  is  implementation  dependent.   On the other hand, _exit()
does close open file descriptors, and this may cause an unknown delay,
wait- ing for pending output to finish. If the delay is undesired, it
may be useful to call functions like tcflush() before calling _exit().
Whether any  pending  I/O  is  can- celled, and which pending I/O may
be cancelled upon _exit(), is implementation-depen- dent.


>   I studied in some google links that exit() is a C library wrapper and _exit() is the system call. Then what is sys_exit() ? The system calls should begin with "sys_" as per convention. Am I right ?

sys_exit should be the system call in the kernel. The exit() or _exit() 
library functions do a syscall (software interrupt 70 on i386 and place
the syscall number in %eax) and the kernel has a syscall table where it
searches for the sycall number. 

So the name is irrelevant, only the number is important. By convention,
sysalls in the kernel begin with sys_, right.


Regards,
  Bernhard

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