The man page of my linux (Ubuntu), does not mention the need of NULL as last parameter, the man page of a minix version execl mentions the need of NULL as last parameter. Yet, I had strange behavior while invoking modprobe that I solved putting NULL as last parameter.
The way that worked for me:
execl("/sbin/modprobe","modprobe","pl2303",NULL);
While if I do it this way:
execl("/sbin/modprobe","modprobe","pl2303")
I get an error no 14 (EFAULT).`
The man page on my Linux does say it explicitly:
The const char *arg and subsequent ellipses in the execl(), execlp(), and execle() functions can be thought of as arg0, arg1, ..., argn. [....]
The list of arguments must be terminated by a NULL pointer, and, since these are variadic functions, this pointer must be cast (char *) NULL.
With all due respect to Linux and Minix, the more authoritative page I think is the one from opengroup, which says:
The arguments represented by arg0,... are pointers to null-terminated character strings. These strings shall constitute the argument list available to the new process image. The list is terminated by a null pointer.
The first argument is the path of the executable and the following arguments are actually the argv of the executed program. The list of these arguments is terminated by a (char*)0
Citing from the man page:
The list of arguments must be terminated by a null pointer, and, since these are variadic functions, this pointer must be cast (char *) NULL.
Also references: https://stackoverflow.com/a/12677236/1938163 , http://man7.org/linux/man-pages/man3/exec.3.html
Yes, it does, the ISO C standard mandates for main that argv[argc] should be NULL to allow for programs to either use argc or a sentinel at the end, and the same reasoning applies to the exec-like calls.
The POSIX docs for this can be found at http://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html and they state:
The argv and environ arrays are each terminated by a null pointer. The null pointer terminating the argv array is not counted in argc.
