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

NAME

     brk, sbrk -- change data segment size

SYNOPSIS

     #include <unistd.h>

     void *
     brk(const 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 segment.  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 a pointer to the new end of memory 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 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), malloc(3), mmap(2), 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					 December 11, 1993					 4th Berkeley Distribution