leaks(1)

NAME
leaks - Search a process's memory for unreferenced malloc buffers

SYNOPSIS
leaks pid | partial-executable-name | memory-graph-file [-nocontext] [-nostacks] [-quiet] [-exclude symbol] [-trace address] [-outputGraph path] [-fullContent]

DESCRIPTION
leaks identifies leaked memory -- memory that the application has allocated, but has been lost and cannot be freed. Specifically, leaks examines a specified process's memory for values that may be pointers to malloc-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 buffers 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 dangerous for long-running programs, for eventually the leaks could fill memory and cause the application to crash.

leaks requires one argument -- either the process ID or the full or partial executable name of the process to examine, or the pathname of a memory graph file generated by leaks or the Xcode Memory Graph Debugger.

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 representation of the contents of the memory, unless the -nocontext option was specified.

If the MallocStackLogging environment variable was set when the application was launched, leaks also prints a stack trace describing where the buffer was allocated.

MEMORY GRAPH FILES
A memory graph file archives the memory state of a process for further analysis at a later time, on a different machine, or by other people. It includes information about all VM and malloc nodes in the process, and the references between them. Memory graph files can be generated by leaks using the -outputGraph option (and the -fullContent option if desired), or by examining a live process with the Xcode Memory Graph Debugger then using the Export Memory Graph menu item from the File menu. The standard filename suffix for memory graph files is ".memgraph". These files can be used as input to various commands including leaks, heap, stringdups, vmmap, and the Xcode Memory Graph Debugger.

OPTIONS

-nocontext
    Do not print the string or hex representation of leaked memory. Although that information can be useful for recognizing 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 target process has the MallocStackLogging environment variable set.

-quiet
    Do not print process description header or binary image list.

-exclude symbol
    Exclude leaked blocks whose backtraces include the specified 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 source code.

-trace address
    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 holding onto a buffer such that it has not been freed.

-outputGraph path
    Generate a memory graph file containing information about all VM and malloc nodes, and the references between them. path can be a path to a file, or just a directory name; in the latter case a filename with the ".memgraph" suffix will be generated.

-fullContent
    When generating a memory graph file, include descriptions of the content of various objects, as would be shown by "heap <pid> -addresses all", and as needed by "stringdups <pid>".

ENVIRONMENT
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 memory.

EXIT STATUS
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 ALSO
malloc(3), heap(1), malloc_history(1), stringdups(1), vmmap(1), DevToolsSecurity(1)

The Xcode Memory Graph Debuggger graphically shows malloc blocks and VM regions (both leaked and non-leaked), and the references between them.

The Xcode developer tools also include Instruments, a graphical application that can give information similar to that provided by leaks. The Allocations instrument graphically displays dynamic, real-time information about the object and memory use in an application, including backtraces of where the allocations occurred. The Leaks instrument performs memory leak analysis.