sbrk(2) — Linux manual page


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

NAME         top

       brk, sbrk - change data segment size

SYNOPSIS         top

       #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         top

       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

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

RETURN VALUE         top

       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         top

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

NOTES         top

       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

       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         top

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

COLOPHON         top

       This page is part of release 5.09 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

Linux                            2016-03-15                           BRK(2)

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