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BRK(2)			    BSD	System Calls Manual			BRK(2)

NAME
     brk, sbrk -- change data segment size

SYNOPSIS
     #include <sys/types.h>

     int
     brk(const char *addr);

     char *
     sbrk(int incr);

DESCRIPTION
     The brk and sbrk functions	are historical curiosities left	over from ear-
     lier days before the advent of virtual memory management.	The brk()
     function sets the break or	lowest address of a process's data segment
     (unilitialized 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,	e.g.  "qetext +	rlp->rlim_max."	(see end(3) for	the definition
     of	etext).

RETURN VALUES
     Brk returns 0 if successful; -1 if	the process requests more memory than
     than allowed by the system	limit.	The sbrk function returns the old
     break value if successful,	otherwise a -1 is returned.

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

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.

HISTORY
     A brk function call appeared in Version 7 AT&T UNIX.

4th Berkeley Distribution	March 10, 1991	     4th Berkeley Distribution

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

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