leaks(1) BSD General Commands Manual leaks(1)NAMEleaks — Search a process's memory for unreferenced malloc buffers
SYNOPSISleaks pid | partial-executable-name [-nocontext] [-nostacks]
[-exclude symbol] [-trace address]
DESCRIPTIONleaks identifies leaked memory -- memory that the application has allo‐
cated, but has been lost and cannot be freed. Specifically, leaks exam‐
ines a specified process's memory for values that may be pointers to mal‐
loc-allocated buffers. Any buffer reachable from a pointer in writable
global memory (e.g., __DATA segments), a register, or on the stack is
assumed to be memory in use. Any buffer reachable from a pointer in a
reachable malloc-allocated buffer is also assumed to be in use. The buf‐
fers which are not reachable are leaks; the buffers could never be freed
because no pointer exists in memory to the buffer, and thus free() could
never be called for these buffers. Such buffers waste memory; removing
them can reduce swapping and memory usage. Leaks are particularly dan‐
gerous for long-running programs, for eventually the leaks could fill
memory and cause the application to crash.
leaks requires one parameter -- either the process ID or executable name
of the process to examine. It also takes several arguments for modifying
For each leaked buffer that is found, leaks prints the address of the
leaked memory and its size. If leaks can determine that the object is an
instance of an Objective-C, CoreFoundation, or C++ class, or a CFType, it
also specifies the name and type of the class, and the binary image that
implements the class. It then prints a string or hexadecimal representa‐
tion of the contents of the memory, unless the -nocontext option was
If the MallocStackLogging environment variable was set when the applica‐
tion was launched, leaks also prints a stack trace describing where the
buffer was allocated.
OPTIONS-nocontext Do not print the string or hex representation of leaked
memory. Although that information can be useful for rec‐
ognizing the contents of the buffer and understanding why
it might be leaked, it can also provide overwhelming
detail, and could expose confidential information from
your process if you, for example, file bug reports with
that output included.
-nostacks Do not print backtraces of leaked blocks even if the tar‐
get process has the MallocStackLogging environment vari‐
Exclude leaked blocks whose backtraces include the speci‐
fied symbol. This option can be repeated for multiple
symbols. This allows ignoring leaks that, for example,
are allocated in libraries for which you do not have
Print chains of references from process 'roots' (e.g.,
global data, registers, or locations on stacks) to the
given block. This is useful for determining what is hold‐
ing onto a buffer such that it has not been freed.
The leaks command may detect more leaks if the target process is run with
the MallocScribble environment variable. If this variable is set then
when malloc blocks are deallocated they are filled with 0x55 bytes, thus
overwriting any "stale" data such as pointers remaining in those blocks.
This reduces the number of false pointers remaining in the process mem‐
The leaks command exits with one of the following values:
0 No leaks were detected.
1 One or more leaks were detected.
>1 An error occurred.
SEE ALSOmalloc(3), heap(1), malloc_history(1), stringdups(1), vmmap(1),
The Xcode developer tools also include Instruments, a graphical applica‐
tion that can give information similar to that provided by leaks. The
Allocations instrument graphically displays dynamic, real-time informa‐
tion about the object and memory use in an application, including back‐
traces of where the allocations occurred. The Leaks instrument performs
memory leak analysis.
BSD Mar. 16, 2013 BSD