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

NAME
     brk, sbrk -- change data segment size

SYNOPSIS
     #include <unistd.h>

     char *
     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
     (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
     Brk() returns 0 if	successful; otherwise -1 with errno set	to indicate
     why the allocation	failed.	 The sbrk() function returns a pointer to the
     base of the new storage if	successful; otherwise -1 with errno set	to in-
     dicate why	the allocation failed.

ERRORS
     Brk() or 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 ex-
	       pansion.

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

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

4th Berkeley Distribution	  May 1, 1995	     4th Berkeley Distribution

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

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