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BRK(2)			  FreeBSD System Calls Manual			BRK(2)

NAME
     brk, sbrk -- change data segment size

SYNOPSIS
     #include <unistd.h>

     int
     brk(void *addr);

     void *
     sbrk(int incr);

DESCRIPTION
     The brk() and sbrk() functions are	historical curiosities left over from
     earlier days before the advent of virtual memory management.  The brk()
     function sets the break or	lowest address of a process's data segment
     (uninitialized data) to addr (immediately above bss).  Data addressing is
     restricted	between	addr and the lowest stack pointer to the stack seg-
     ment.  Memory is allocated	by brk() in page size pieces; if addr is not
     evenly divisible by the system page size, it is increased to the next
     page boundary.

     The current value of the program break is reliably	returned by "sbrk(0)"
     (see also end(3)).	 The getrlimit(2) system call may be used to determine
     the maximum permissible size of the data segment; it will not be possible
     to	set the	break beyond the rlim_max value	returned from a	call to
     getrlimit(2), e.g., `etext	+ rlp->rlim_max' (see end(3) for the defini-
     tion of etext).

RETURN VALUES
     The brk() function	returns	the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

     The sbrk()	function returns a pointer to the base of the new storage if
     successful; otherwise -1 with errno set to	indicate why the allocation
     failed.

ERRORS
     sbrk() will fail and no additional	memory will be allocated if one	of the
     following are true:

     [ENOMEM]		The limit, as set by setrlimit(2), was exceeded.

     [ENOMEM]		The maximum possible size of a data segment (compiled
			into the system) was exceeded.

     [ENOMEM]		Insufficient space existed in the swap area to support
			the expansion.

SEE ALSO
     execve(2),	getrlimit(2), mmap(2), end(3), malloc(3)

HISTORY
     A predecessor break() appeared in Version 1 AT&T UNIX.  The sbrk()	func-
     tion call first appeared in Version 4 AT&T	UNIX and brk() in Version 6
     AT&T UNIX.

BUGS
     Setting the break may fail	due to a temporary lack	of swap	space.	It is
     not possible to distinguish this from a failure caused by exceeding the
     maximum size of the data segment without consulting getrlimit(2).

FreeBSD	13.0		       September 8, 2019		  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY | BUGS

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