Maximum number of Bash arguments != max num cp arguments?

Question

I have recently been copying and moving a large number of files (~400,000). I know that there are limitations on the number of arguments that can be expanded on the Bash com

Answer 1

ARG_MAX is the maximum length of the arguments to the exec(3) functions. A shell is not required to support passing this length of arguments from its command line.

Answer 2

As Ignacio said, ARG_MAX is the maximum length of the buffer of arguments passed to exec(), not the maximum number of files (this page has a very in-depth explanation). Specifically, it lists fs/exec.c as checking the following condition:

PAGE_SIZE*MAX_ARG_PAGES-sizeof(void *) / sizeof(void *)

And, it seems, you have some additional limitations:

On a 32-bit Linux, this is ARGMAX/4-1 (32767). This becomes relevant if the average length of arguments is smaller than 4. Since Linux 2.6.23, this function tests if the number exceeds MAX_ARG_STRINGS in <linux/binfmts.h> (2^32-1 = 4294967296-1). And as additional limit, one argument must not be longer than MAX_ARG_STRLEN (131072).