BRK(2)                                                       Linux Programmer's Manual                                                      BRK(2)

NAME

       brk, sbrk - change data segment size

SYNOPSIS

       #include <unistd.h>

       int brk(void *addr);

       void *sbrk(intptr_t increment);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       brk(), sbrk():
           Since glibc 2.19:
               _DEFAULT_SOURCE ||
                   (_XOPEN_SOURCE >= 500) &&
                   ! (_POSIX_C_SOURCE >= 200112L)
           From glibc 2.12 to 2.19:
               _BSD_SOURCE || _SVID_SOURCE ||
                   (_XOPEN_SOURCE >= 500) &&
                   ! (_POSIX_C_SOURCE >= 200112L)
           Before glibc 2.12:
               _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION

       brk()  and sbrk() change the location of the program break, which defines the end of the process's data segment (i.e., the program break is
       the first location after the end of the uninitialized data segment).  Increasing the program break has the effect of allocating  memory  to
       the process; decreasing the break deallocates memory.

       brk() sets the end of the data segment to the value specified by addr, when that value is reasonable, the system has enough memory, and the
       process does not exceed its maximum data size (see setrlimit(2)).

       sbrk() increments the program's data space by increment bytes.  Calling sbrk() with an increment of 0 can be used to find the current loca-
       tion of the program break.

RETURN VALUE

       On success, brk() returns zero.  On error, -1 is returned, and errno is set to ENOMEM.

       On success, sbrk() returns the previous program break.  (If the break was increased, then this value is a pointer to the start of the newly
       allocated memory).  On error, (void *) -1 is returned, and errno is set to ENOMEM.

CONFORMING TO

       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.

NOTES

       Avoid using brk() and sbrk(): the malloc(3) memory allocation package is the portable and comfortable way of allocating memory.

       Various systems use various types for the argument of sbrk().  Common are int, ssize_t, ptrdiff_t, intptr_t.

   C library/kernel differences
       The return value described above for brk() is the behavior provided by the glibc wrapper function for the Linux  brk()  system  call.   (On
       most  other  implementations, the return value from brk() is the same; this return value was also specified in SUSv2.)  However, the actual
       Linux system call returns the new program break on success.  On failure, the system call returns the  current  break.   The  glibc  wrapper
       function does some work (i.e., checks whether the new break is less than addr) to provide the 0 and -1 return values described above.

       On  Linux,  sbrk()  is implemented as a library function that uses the brk() system call, and does some internal bookkeeping so that it can
       return the old break value.

SEE ALSO

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

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux                                                               2016-03-15                                                              BRK(2)