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.\" mono manual page.
.\" Copyright 2003 Ximian, Inc.
.\" Copyright 2004-2009 Novell, Inc.
.\" Author:
.\" Miguel de Icaza (
.TH Mono "Mono 2.5"
mono \- Mono's ECMA-CLI native code generator (Just-in-Time and Ahead-of-Time)
.B mono [options] file [arguments...]
\fImono\fP is a runtime implementation of the ECMA Common Language
Infrastructure. This can be used to run ECMA and .NET applications.
The runtime contains a native code generator that transforms the
Common Intermediate Language into native code.
The code generator can operate in two modes: just in time compilation
(JIT) or ahead of time compilation (AOT). Since code can be
dynamically loaded, the runtime environment and the JIT are always
present, even if code is compiled ahead of time.
The runtime loads the specified
.I file
and optionally passes
.I arguments
to it. The
.I file
is an ECMA assembly. They typically have a .exe or .dll extension.
The runtime provides a number of configuration options for running
applications, for developing and debugging, and for testing and
debugging the runtime itself.
On Unix-based systems, Mono provides a mechanism to emulate the
Windows-style file access, this includes providing a case insensitive
view of the file system, directory separator mapping (from \\ to /) and
stripping the drive letters.
This functionality is enabled by setting the
environment variable to one of
.B all, drive
.B case.
See the description for
in the environment variables section for more details.
The following options are available:
\fB--aot\fR, \fB--aot[=options]\fR
This option is used to precompile the CIL code in the specified
assembly to native code. The generated code is stored in a file with
the extension .so. This file will be automatically picked up by the
runtime when the assembly is executed.
Ahead-of-Time compilation is most useful if you use it in combination
with the -O=all,-shared flag which enables all of the optimizations in
the code generator to be performed. Some of those optimizations are
not practical for Just-in-Time compilation since they might be very
time consuming.
Unlike the .NET Framework, Ahead-of-Time compilation will not generate
domain independent code: it generates the same code that the
Just-in-Time compiler would produce. Since most applications use a
single domain, this is fine. If you want to optimize the generated
code for use in multi-domain applications, consider using the
-O=shared flag.
This pre-compiles the methods, but the original assembly is still
required to execute as this one contains the metadata and exception
information which is not available on the generated file. When
precompiling code, you might want to compile with all optimizations
(-O=all). Pre-compiled code is position independent code.
Pre compilation is just a mechanism to reduce startup time, increase
code sharing across multiple mono processes and avoid just-in-time
compilation program startup costs. The original assembly must still
be present, as the metadata is contained there.
AOT code typically can not be moved from one computer to another
(CPU-specific optimizations that are detected at runtime) so you
should not try to move the pre-generated assemblies or package the
pre-generated assemblies for deployment.
A few options are available as a parameter to the
.B --aot
command line option. The options are separated by commas, and more
than one can be specified:
.ne 8
.I bind-to-runtime-version
If specified, forces the generated AOT files to be bound to the
runtime version of the compiling Mono. This will prevent the AOT
files from being consumed by a different Mono runtime.
.I full
This is currently an experimental feature as it is not complete.
This instructs Mono to precompile code that has historically not been
precompiled with AOT.
.I outfile=[filename]
Instructs the AOT compiler to save the output to the specified file.
.I write-symbols
Instructs the AOT compiler to emit debug symbol information.
.I save-temps,keep-temps
Instructs the AOT compiler to keep temporary files.
.I threads=[number]
This is an experimental option for the AOT compiler to use multiple threads
when compiling the methods.
.I nodebug
Instructs the AOT compiler to not output any debugging information.
.I ntrampolines=[number]
When compiling in full aot mode, the method trampolines must be precreated
in the AOT image. You can add additional method trampolines with this argument.
Defaults to 1024.
.I nrgctx-trampolines=[number]
When compiling in full aot mode, the generic sharing trampolines must be precreated
in the AOT image. You can add additional method trampolines with this argument.
Defaults to 1024.
.I nimt-trampolines=[number]
When compiling in full aot mode, the IMT trampolines must be precreated
in the AOT image. You can add additional method trampolines with this argument.
Defaults to 128.
.I print-skipped-methods
If the AOT compiler cannot compile a method for any reason, enabling this flag
will output the skipped methods to the console.
.I autoreg
The AOT compiler will emit a (ELF only) library initializer to automatically
register the aot compiled module with the runtime. This is only useful in static
.I asmonly
Instructs the AOT compiler to output assembly code instead of an object file.
.I soft-debug
This instructs the compiler to generate sequence point checks that
allow Mono's soft debugger to debug applications even on systems where
it is not possible to set breakpoints or to single step (certain
hardware configurations like the cell phones and video gaming
.I static
Create an ELF object file (.o) which can be statically linked into an executable
when embedding the mono runtime. When this option is used, the object file needs to
be registered with the embedded runtime using the mono_aot_register_module function
which takes as its argument the mono_aot_module_<ASSEMBLY NAME>_info global symbol
from the object file:
extern void *mono_aot_module_hello_info;
mono_aot_register_module (mono_aot_module_hello_info);
For more information about AOT, see:
Currently the only option supported by this command line argument is
\fBdisable\fR which disables the attach functionality.
This is an experimental flag that instructs the Mono runtime to not
generate any code at runtime and depend exclusively on the code
generated from using mono --aot=full previously. This is useful for
platforms that do not permit dynamic code generation.
Notice that this feature will abort execution at runtime if a codepath
in your program, or Mono's class libraries attempts to generate code
dynamically. You should test your software upfront and make sure that
you do not use any dynamic features.
\fB--config filename\fR
Load the specified configuration file instead of the default one(s).
The default files are /etc/mono/config and ~/.mono/config or the file
specified in the MONO_CONFIG environment variable, if set. See the
mono-config(5) man page for details on the format of this file.
Configures the virtual machine to be better suited for desktop
applications. Currently this sets the GC system to avoid expanding
the heap as much as possible at the expense of slowing down garbage
collection a bit.
\fB--help\fR, \fB-h\fR
Displays usage instructions.
\fB--optimize=MODE\fR, \fB-O=MODE\fR
MODE is a comma separated list of optimizations. They also allow
optimizations to be turned off by prefixing the optimization name with
a minus sign.
In general, Mono has been tuned to use the default set of flags,
before using these flags for a deployment setting, you might want to
actually measure the benefits of using them.
The following optimizations are implemented:
all Turn on all optimizations
peephole Peephole postpass
branch Branch optimizations
inline Inline method calls
cfold Constant folding
consprop Constant propagation
copyprop Copy propagation
deadce Dead code elimination
linears Linear scan global reg allocation
cmov Conditional moves [arch-dependency]
shared Emit per-domain code
sched Instruction scheduling
intrins Intrinsic method implementations
tailc Tail recursion and tail calls
loop Loop related optimizations
fcmov Fast x86 FP compares [arch-dependency]
leaf Leaf procedures optimizations
aot Usage of Ahead Of Time compiled code
precomp Precompile all methods before executing Main
abcrem Array bound checks removal
ssapre SSA based Partial Redundancy Elimination
sse2 SSE2 instructions on x86 [arch-dependency]
gshared Enable generic code sharing.
For example, to enable all the optimization but dead code
elimination and inlining, you can use:
The flags that are flagged with [arch-dependency] indicate that the
given option if used in combination with Ahead of Time compilation
(--aot flag) would produce pre-compiled code that will depend on the
current CPU and might not be safely moved to another computer.
Mono supports different runtime versions. The version used depends on the program
that is being run or on its configuration file (named program.exe.config). This option
can be used to override such autodetection, by forcing a different runtime version
to be used. Note that this should only be used to select a later compatible runtime
version than the one the program was compiled against. A typical usage is for
running a 1.1 program on a 2.0 version:
mono --runtime=v2.0.50727 program.exe
\fB--security\fR, \fB--security=mode\fR
Activate the security manager, a currently experimental feature in
Mono and it is OFF by default. The new code verifier can be enabled
with this option as well.
.ne 8
Using security without parameters is equivalent as calling it with the
"cas" parameter.
The following modes are supported:
.I cas
This allows mono to support declarative security attributes,
e.g. execution of Code Access Security (CAS) or non-CAS demands.
.I core-clr
Enables the core-clr security system, typically used for
Moonlight/Silverlight applications. It provides a much simpler
security system than CAS, see
for more details and links to the descriptions of this new system.
.I validil
Enables the new verifier and performs basic verification for code
validity. In this mode, unsafe code and P/Invoke are allowed. This
mode provides a better safety guarantee but it is still possible
for managed code to crash Mono.
.I verifiable
Enables the new verifier and performs full verification of the code
being executed. It only allows verifiable code to be executed.
Unsafe code is not allowed but P/Invoke is. This mode should
not allow managed code to crash mono. The verification is not as
strict as ECMA 335 standard in order to stay compatible with the MS
The security system acts on user code: code contained in mscorlib or
the global assembly cache is always trusted.
Configures the virtual machine to be better suited for server
operations (currently, a no-op).
Verifies mscorlib and assemblies in the global
assembly cache for valid IL, and all user code for IL
This is different from \fB--security\fR's verifiable
or validil in that these options only check user code and skip
mscorlib and assemblies located on the global assembly cache.
\fB-V\fR, \fB--version\fR
Prints JIT version information (system configuration, release number
and branch names if available).
The following options are used to help when developing a JITed application.
\fB--debug\fR, \fB--debug=OPTIONS\fR
Turns on the debugging mode in the runtime. If an assembly was
compiled with debugging information, it will produce line number
information for stack traces.
.ne 8
The optional OPTIONS argument is a comma separated list of debugging
options. These options are turned off by default since they generate
much larger and slower code at runtime.
The following options are supported:
.I casts
Produces a detailed error when throwing a InvalidCastException. This
option needs to be enabled as this generates more verbose code at
execution time.
.I mdb-optimizations
Disable some JIT optimizations which are usually only disabled when
running inside the debugger. This can be helpful if you want to attach
to the running process with mdb.
.I gdb
Generate and register debugging information with gdb. This is only supported on some
platforms, and only when using gdb 7.0 or later.
Turns on profiling. For more information about profiling applications
and code coverage see the sections "PROFILING" and "CODE COVERAGE"
Shows method names as they are invoked. By default all methods are
The trace can be customized to include or exclude methods, classes or
assemblies. A trace expression is a comma separated list of targets,
each target can be prefixed with a minus sign to turn off a particular
target. The words `program', `all' and `disabled' have special
meaning. `program' refers to the main program being executed, and
`all' means all the method calls.
The `disabled' option is used to start up with tracing disabled. It
can be enabled at a later point in time in the program by sending the
SIGUSR2 signal to the runtime.
Assemblies are specified by their name, for example, to trace all
calls in the System assembly, use:
mono --trace=System app.exe
Classes are specified with the T: prefix. For example, to trace all
calls to the System.String class, use:
mono --trace=T:System.String app.exe
And individual methods are referenced with the M: prefix, and the
standard method notation:
mono --trace=M:System.Console:WriteLine app.exe
As previously noted, various rules can be specified at once:
mono --trace=T:System.String,T:System.Random app.exe
You can exclude pieces, the next example traces calls to
System.String except for the System.String:Concat method.
mono --trace=T:System.String,-M:System.String:Concat
Finally, namespaces can be specified using the N: prefix:
mono --trace=N:System.Xml
Don't align stack frames on the x86 architecture. By default, Mono
aligns stack frames to 16 bytes on x86, so that local floating point
and SIMD variables can be properly aligned. This option turns off the
alignment, which usually saves one intruction per call, but might
result in significantly lower floating point and SIMD performance.
The maintainer options are only used by those developing the runtime
itself, and not typically of interest to runtime users or developers.
\fB--break method\fR
Inserts a breakpoint before the method whose name is `method'
(namespace.class:methodname). Use `Main' as method name to insert a
breakpoint on the application's main method.
Inserts a breakpoint on exceptions. This allows you to debug your
application with a native debugger when an exception is thrown.
\fB--compile name\fR
This compiles a method (, this is used for
testing the compiler performance or to examine the output of the code
Compiles all the methods in an assembly. This is used to test the
compiler performance or to examine the output of the code generator
\fB--graph=TYPE METHOD\fR
This generates a postscript file with a graph with the details about
the specified method ( This requires `dot'
and ghostview to be installed (it expects Ghostview to be called
The following graphs are available:
cfg Control Flow Graph (CFG)
dtree Dominator Tree
code CFG showing code
ssa CFG showing code after SSA translation
optcode CFG showing code after IR optimizations
Some graphs will only be available if certain optimizations are turned
Instruct the runtime on the number of times that the method specified
by --compile (or all the methods if --compileall is used) to be
compiled. This is used for testing the code generator performance.
Displays information about the work done by the runtime during the
execution of an application.
Perform maintenance of the process shared data.
semdel will delete the global semaphore.
hps will list the currently used handles.
\fB-v\fR, \fB--verbose\fR
Increases the verbosity level, each time it is listed, increases the
verbosity level to include more information (including, for example,
a disassembly of the native code produced, code selector info etc.).
The Mono runtime allows external processes to attach to a running
process and load assemblies into the running program. To attach to
the process, a special protocol is implemented in the Mono.Management
With this support it is possible to load assemblies that have an entry
point (they are created with -target:exe or -target:winexe) to be
loaded and executed in the Mono process.
The code is loaded into the root domain, and it starts execution on
the special runtime attach thread. The attached program should
create its own threads and return after invocation.
This support allows for example debugging applications by having the
csharp shell attach to running processes.
The mono runtime includes a profiler that can be used to explore
various performance related problems in your application. The
profiler is activated by passing the --profile command line argument
to the Mono runtime, the format is:
Mono has a built-in profiler called 'default' (and is also the default
if no arguments are specified), but developers can write custom
profilers, see the section "CUSTOM PROFILERS" for more details.
If a
.I profiler
is not specified, the default profiler is used.
.I profiler_args
is a profiler-specific string of options for the profiler itself.
The default profiler accepts the following options 'alloc' to profile
memory consumption by the application; 'time' to profile the time
spent on each routine; 'jit' to collect time spent JIT-compiling methods
and 'stat' to perform sample statistical profiling.
If no options are provided the default is 'alloc,time,jit'.
By default the
profile data is printed to stdout: to change this, use the 'file=filename'
option to output the data to filename.
For example:
mono --profile program.exe
That will run the program with the default profiler and will do time
and allocation profiling.
mono --profile=default:stat,alloc,file=prof.out program.exe
Will do sample statistical profiling and allocation profiling on
program.exe. The profile data is put in prof.out.
Note that the statistical profiler has a very low overhead and should
be the preferred profiler to use (for better output use the full path
to the mono binary when running and make sure you have installed the
addr2line utility that comes from the binutils package).
.I logging profiler
is a general purpose profiler that can track many different kinds of
events and logs those into a file as the program executes. This is
different than previous profilers in Mono that kept the information in
memory and rendered a summary of the results when the program shut
Using the logging profiler means that useful information can be
gathered for long-running applications, applications that terminate
abormally (crashes, segfaults, complicated tear down processes) or
when no data about the shutdown is required.
The data collected by the running threads is kept independent of each
other to minimize the runtime overhead and the information dumped into
the log at regular intervals.
A sample use is very simple:
$ mono --profile=logging program.exe
$ mprof-decoder program.mprof
In the above example the logging profiler is used in its default mode
that merely records GC statistics for the execution of program.exe.
The profiling data collected is stored in the file program.mprof. The
mprof-decoder tool is then used to analyze the data.
You can instruct the logging profiler to record different one or more
sets of events. These are the modes supported:
.I Statistical Profiling (stat)
the program instruction pointer is periodically sampled to determine
where the program is spending most of its time. Statistical
profiling has a very low impact on a running application and it is
very useful to get a general picture of where time is being spent on a
If call chains are requested, for each sample the profiler gets a
partial stack trace (limited by the specified depth) so that
caller-callee information is available.
.I Instrumenting:
each method enter and exit is logged with a timestamp; further processing of
the data can show the methods that took the longer to execute, with complete
accounting for callers and callees. However, this way of profiling is rather
intrusive and slows down the application significantly.
.I Allocation:
each allocation is logged.
.I Allocation summary:
shows, for each collection, a summary of the heap contents broken down by
class (for each class the number of allocated and released objects is
given, together with their aggregated size in bytes).
.I Heap snapshot mode:
dumps the whole heap contents at every collection (or at user specified
collections). It is also possible to request a collection and snapshot dump
with a signal.
Moreover, other events can be logged and analyzed, like jit time for each
method, load and unload for assemblies, modules and and individual classes,
and appdomain and thread creation and destruction.
This profiler is activated passing the \fB--profile=logging\fR option to
the mono runtime, and is controlled attaching further options, like
\fB--profile=logging:statistical\fR for doing statistical profiling (multiple
options are separated by commas).
As a quick primer, here are a few examples of the most common usage modes:
To perform statistical profiling:
mono --profile=logging:stat program.exe
To perform statistical profiling, inspecting call chains up to depth 8:
mono --profile=logging:stat=8 program.exe
To profile allocations (by default the call stack will be analized for
each allocation, producing detailed caller method attribution infornation):
mono --profile=logging:allocations program.exe
To profile garbage collection activity at a high level (collection time and objects freed
at each collection for each class are reported, but heap snapshots are not saved to disk):
mono --profile=logging:allocations-summary program.exe
To perform heap profiling taking heap snapshots:
mono --profile=logging:heap=all program.exe
To write the resulting data to a different file:
mono --profile=logging:output=mydata.mprof program.exe
Then you would need to invoke the decoder \fImprof-decoder(1)\fR
on the output file to see the profiling results, or to examine heap
snapshots and allocations in detail \fImprof-heap-viewer(1)\fR.
The operating modes described above are the default ones, and are sufficient
to use the profiler.
To further customize the profiler behavior there are more options, described
These options can be individually enabled and disabled prefixing them
with an (optional) '+' character or a '-' character. For instance,
the "allocations" option by default records also the full call stack
at each allocation. If only the caller is wanted, one should use
"allocations,-save-allocation-stack", or to disable call tracking
completely (making the profiler less intrusive)
"allocations,-save-allocation-caller,-save-allocation-stack". In
practice the "allocation" option by default behaves like
"allocations,save-allocation-caller,save-allocation-stack", but the
user can tune this to his needs.
These are all the available options, organized by category:
\fBExecution profiling modes\fR
.ne 8
\fIstatistical\fR, \fIstat\fR or \fIs\fR
Performs statistical profiling. This is a lightweight profiling
mechanism and it has a much lower overhead than the \fIenter-leave\fR
profiling as it works by sampling where the program is spending its
time by using a timer.
If specified with \fIs=<number>\fR, also inspect call chains up to level
\fIenter-leave\fR, \fIcalls\fR or \fIc\fR
Measure the time spent inside each method call, this is done by
logging the time when a method enters and when the method leaves.
This can be a time consuming operation.
\fIjit\fR, \fIj\fR
Collect information about time spent by the JIT engine compiling
\fBAllocation profiling modes\fR
.ne 8
\fIallocations\fR, \fIalloc\fR or \fIa\fR
Collect information about each allocation (object class and size).
By default this also implies "+save-allocation-caller" and
\fIsave-allocation-caller\fR, \fIsac\fR
Save the direct caller of each allocation. The profiler filters out wrapper
methods, and also recognizes if the allocation has been performed by the
runtime while jitting a method.
\fIsave-allocation-stack\fR, \fIsas\fR
Save the full managed execution stack at each allocation.
While the "sac" option saves the direct caller, this one records the whole
stack trace.
Note that in the call stack the wrapper methods are not filtered out.
Anyway the "sac" and "sas" options can be combined, and the decoder will
attribute the allocation to the correct method even if the wrapper is at the
top of the stack trace.
\fIallocations-summary\fR or \fIas\fR
At each collection dump a summary
of the heap contents (for each class, the number and collective size of all
live and freed heap objects). This very lightweight compared to full heap
\fIunreachable\fR, \fIfree\fR or \fIf\fR
Performs a lightweight profile of the garbage collector. On each
collection performed by the GC, the list of unreachable objects is
recorded, and for each object the class and size is provided. This
information can be used to compute the heap size broken down by class
(combined with "a" can give the same information of "as", but the log
file contains info about each individual object, while in "as" the
processing is done directly at runtime and the log file contains only
the summarized data broken down by class).
\fIgc\fR or \fIg\fR
Measure the time spent in each collection, and also trace heap resizes.
\fIheap-shot[=ARG]\fR, \fIheap[=ARG]\fR or \fIh[=ARH]\fR
Performs full heap profiling. In this case on each
collection a full heap snapshot is recorded to disk.
Inside the snapshots, each object reference is still represented so
that it's possible to investigate who is responsible for keeping objects
If the value of ARG is
.B all,
a heap snapshot is taken at each collection.
If the value is an integer
.B n,
a snapshot will be taken at the first
.B n
collections (like setting
.B gcd=n
If no additional argument is given to the heap option, the only way to take
heap snapshots is to requeste them using the runtime socket based command
interface described below (see "Profiler activity control").
Heap profiling also enables full allocation profiling (with call
stacks), and each allocation can be related to its corresponding
object in the snapshots, enabling investigations like "find all
objects of a given class allocated by a given method and still live at
a given collection, and then find all objects referencing them".
This kind of heap snapshot analysis is performed using the mprof-heap-viewer(1)
The number of heap snapshots taken (and the moment in which they are taken)
can be further customized with the following options:
\fIgc-dumps=N\fR, \fIgc-d=N\fR, \fIgcd=N\fR
states the number of snapshots that must be dumped (since the application
starts). Zero means no dumps at all, -1 means dump at all collections.
These options exist because it can happen that the user wants to investigate
what happens during collections but without forcing a collection using the
command interface, because forcing a collection alters the program behavior.
Of course it is possible to simply take a snapshot at every collection, but
in some workloads this is could not be feasible (too much data).
So we have this "garbage collection dumps" counter to control how many
snapshots to take.
\fBProfiler activity control\fR
.ne 8
\fIoutput=FILE\fR, \fIout=FILE\fR or \fIo=FILE\fR
Use this option to provide the output file name for the profile log.
If this option is not specified, it will default to "<program-name>.mprof".
\fIoutput-suffix=SUFFIX\fR, \fIsuffix=SUFFIX\fR or \fIos=SUFFIX\fR: makes
the output file name equals to "<program-name>-SUFFIX.mprof".
\fIstart-enabled\fR or \fIse\fR: start with the profiler active
(which is the default).
\fIstart-disabled\fR or \fIsd\fR: start with the profiler inactive.
\fIforce-accurate-timer\fR (or \fIfac\fR): the profiler by default uses
rtdsc to acquire timestamps for frequent events, but this can be imprecise;
using this option you force the use of "gettimeofday" at every event, which
is more accurate but much slower.
\fIcommand-port=port\fR or \fIcp=port\fR (where port is an integer between
1024 nd 65535):
Choose a TCP port where the profiler will listen for user commands.
The protocol is ASCII based and line oriented (one line per command), and the
profiler answers with one line containing either "OK" or "ERROR" to each
received command.
The user can telnet to this port and give commands manually, or a GUI can
use this facility to control the profiler at runtime.
The available commands are:
\fIenable\fR: Enables the profiler.
\fIdisable\fR: Disables the profiler.
\fIheap-snapshot\fR: Takes a heap snapshot now (forces a full garbage collection).
\fIheap-snapshot-counter=arg\fR: Set the counter of the next heap snapshots
that must be taken, where arg can be "all" (take a snapshot at every
collection), "none" (do not take snapshots), or an integer "n" (take a heap
snapshot for the next "n" collections).
\fBInternal buffer sizes\fR
.ne 8
\fIper-thread-buffer-size=N\fR, \fItbs=N\fR
Use to specify the number of events that a thread buffer
can hold. When the thread buffer is full, a log block is
written to disk.
This defaults to tbs=10000.
\fIstatistical-thread-buffer-size=N\fR, \fIsbs=N\fR
The number of statistical samples that
are held in memory before they are dumped to disk (the system does
double-buffering and the statistical samples are written by a helper
thread, so the statistical profiler never stops and is able to profile
the profiler itself).
This defaults to sbs=10000.
\fIwrite-buffer-size\fR, \fIwbs\fR
Specifies the size in bytes of the internal write buffers.
This defaults to wbs=1024.
In its current state, this profiler can also perform heap analysis
like the HeapShot profiler, but there is no UI to process this
Another known issue is that if the timer is not strictly monotonic (like
rtdsc), differences between times can underflow (they are handled as
unsigned integers) and weird numbers can show up in the logs.
Finally, it can happen that when exceptions are thrown the profiler temporarily
loses track of the execution stack and misattributes the caller for a few
allocations (and method execution time).
The output file contains compressed events, to process the data you should
use tools like the "Mono.Profiler" tool provided on the Mono SVN
More explanations are provided here: "".
There are a number of external profilers that have been developed for
Mono, we will update this section to contain the profilers.
The heap Shot profiler can track all live objects, and references to
these objects, and includes a GUI tool, this is our recommended
To install you must download the profiler
from Mono's SVN:
svn co svn://
cd heap-shot
make install
See the included documentation for details on using it.
The Live Type profiler shows at every GC iteration all of the live
objects of a given type. To install you must download the profiler
from Mono's SVN:
svn co svn://
cd heap-prof
make install
To use the profiler, execute:
mono --profile=desc-heap program.exe
The output of this profiler looks like this:
Checkpoint at 102 for heap-resize
System.MonoType : 708
System.Threading.Thread : 352
System.String : 3230
System.String[] : 104
Gnome.ModuleInfo : 112
System.Object[] : 160
System.Collections.Hashtable : 96
System.Int32[] : 212
System.Collections.Hashtable+Slot[] : 296
System.Globalization.CultureInfo : 108
System.Globalization.NumberFormatInfo : 144
The first line describes the iteration number for the GC, in this case
checkpoint 102.
Then on each line the type is displayed as well as the number of bytes
that are being consumed by live instances of this object.
The AOT profiler is used to feed back information to the AOT compiler
about how to order code based on the access patterns for pages. To
use it, use:
mono --profile=aot program.exe
The output of this profile can be fed back into Mono's AOT compiler to
order the functions on the disk to produce precompiled images that
have methods in sequential pages.
Mono provides a mechanism for loading other profiling modules which in
the form of shared libraries. These profiling modules can hook up to
various parts of the Mono runtime to gather information about the code
being executed.
To use a third party profiler you must pass the name of the profiler
to Mono, like this:
mono --profile=custom program.exe
In the above sample Mono will load the user defined profiler from the
shared library `'. This profiler module must
be on your dynamic linker library path.
A list of other third party profilers is available from Mono's web
site (
Custom profiles are written as shared libraries. The shared library
must be called `' where `NAME' is the name of
your profiler.
For a sample of how to write your own custom profiler look in the
Mono source tree for in the samples/profiler.c.
Mono ships with a code coverage module. This module is activated by
using the Mono --profile=cov option. The format is:
\fB--profile=cov[:assembly-name[/namespace]] test-suite.exe\fR
By default code coverage will default to all the assemblies loaded,
you can limit this by specifying the assembly name, for example to
perform code coverage in the routines of your program use, for example
the following command line limits the code coverage to routines in the
"demo" assembly:
mono --profile=cov:demo demo.exe
Notice that the
.I assembly-name
does not include the extension.
You can further restrict the code coverage output by specifying a
mono --profile=cov:demo/My.Utilities demo.exe
Which will only perform code coverage in the given assembly and
Typical output looks like this:
Not covered: Class:.ctor ()
Not covered: Class:A ()
Not covered: Driver:.ctor ()
Not covered: Driver:method ()
Partial coverage: Driver:Main ()
offset 0x000a
The offsets displayed are IL offsets.
A more powerful coverage tool is available in the module `monocov'.
See the monocov(1) man page for details.
To debug managed applications, you can use the
.B mdb
command, a command line debugger.
It is possible to obtain a stack trace of all the active threads in
Mono by sending the QUIT signal to Mono, you can do this from the
command line, like this:
kill -QUIT pid
Where pid is the Process ID of the Mono process you want to examine.
The process will continue running afterwards, but its state is not
.B Important:
this is a last-resort mechanism for debugging applications and should
not be used to monitor or probe a production application. The
integrity of the runtime after sending this signal is not guaranteed
and the application might crash or terminate at any given point
The \fB--debug=casts\fR option can be used to get more detailed
information for Invalid Cast operations, it will provide information
about the types involved.
You can use the MONO_LOG_LEVEL and MONO_LOG_MASK environment variables
to get verbose debugging output about the execution of your
application within Mono.
environment variable if set, the logging level is changed to the set
value. Possible values are "error", "critical", "warning", "message",
"info", "debug". The default value is "error". Messages with a logging
level greater then or equal to the log level will be printed to
Use "info" to track the dynamic loading of assemblies.
Use the
environment variable to limit the extent of the messages you get:
If set, the log mask is changed to the set value. Possible values are
"asm" (assembly loader), "type", "dll" (native library loader), "gc"
(garbage collector), "cfg" (config file loader), "aot" (precompiler) and "all".
The default value is "all". Changing the mask value allows you to display only
messages for a certain component. You can use multiple masks by comma
separating them. For example to see config file messages and assembly loader
messages set you mask to "asm,cfg".
The following is a common use to track down problems with P/Invoke:
$ MONO_LOG_LEVEL="debug" MONO_LOG_MASK="dll" mono glue.exe
Mono's XML serialization engine by default will use a reflection-based
approach to serialize which might be slow for continuous processing
(web service applications). The serialization engine will determine
when a class must use a hand-tuned serializer based on a few
parameters and if needed it will produce a customized C# serializer
for your types at runtime. This customized serializer then gets
dynamically loaded into your application.
You can control this with the MONO_XMLSERIALIZER_THS environment
The possible values are
.B `no'
to disable the use of a C# customized
serializer, or an integer that is the minimum number of uses before
the runtime will produce a custom serializer (0 will produce a
custom serializer on the first access, 50 will produce a serializer on
the 50th use). Mono will fallback to an interpreted serializer if the
serializer generation somehow fails. This behavior can be disabled
by setting the option
.B `nofallback'
(for example: MONO_XMLSERIALIZER_THS=0,nofallback).
Turns off the garbage collection in Mono. This should be only used
for debugging purposes
When Mono is compiled with LLVM support, this instructs the runtime to
stop using LLVM after the specified number of methods are JITed.
This is a tool used in diagnostics to help isolate problems in the
code generation backend. For example \fBLLVM_COUNT=10\fR would only
compile 10 methods with LLVM and then switch to the Mono JIT engine.
\fBLLVM_COUNT=0\fR would disable the LLVM engine altogether.
If set, this variable will instruct Mono to ahead-of-time compile new
assemblies on demand and store the result into a cache in
If set, this variable overrides the default system configuration directory
($PREFIX/etc). It's used to locate machine.config file.
Sets the style of COM interop. If the value of this variable is "MS"
Mono will use string marhsalling routines from the liboleaut32 for the
BSTR type library, any other values will use the mono-builtin BSTR
string marshalling.
If set, this variable overrides the default runtime configuration file
($PREFIX/etc/mono/config). The --config command line options overrides the
environment variable.
If set, enables some features of the runtime useful for debugging.
This variable should contain a comma separated list of debugging options.
Currently, the following options are supported:
.ne 8
If this variable is set, when the Mono VM runs into a verification
problem, instead of throwing an exception it will break into the
debugger. This is useful when debugging verifier problems
Collects information about pagefaults. This is used internally to
track the number of page faults produced to load metadata. To display
this information you must use this option with "--stats" command line
This is an Optimization for multi-AppDomain applications (most
commonly ASP.NET applications). Due to internal limitations Mono,
Mono by default does not use typed allocations on multi-appDomain
applications as they could leak memory when a domain is unloaded.
Although this is a fine default, for applications that use more than
on AppDomain heavily (for example, ASP.NET applications) it is worth
trading off the small leaks for the increased performance
(additionally, since ASP.NET applications are not likely going to
unload the application domains on production systems, it is worth
using this feature).
Captures the interrupt signal (Control-C) and displays a stack trace
when pressed. Useful to find out where the program is executing at a
given point. This only displays the stack trace of a single thread.
This option will leak delegate trampolines that are no longer
referenced as to present the user with more information about a
delegate misuse. Basically a delegate instance might be created,
passed to unmanaged code, and no references kept in managed code,
which will garbage collect the code. With this option it is possible
to track down the source of the problems.
This option will disable the GDB backtrace emitted by the runtime
after a SIGSEGV or SIGABRT in unmanaged code.
This option will suspend the program when a native SIGSEGV is received.
This is useful for debugging crashes which do not happen under gdb,
since a live process contains more information than a core file.
If set, tells mono NOT to attempt using native asynchronous I/O services. In
that case, a default select/poll implementation is used. Currently only epoll()
is supported.
If this environment variable is `yes', the runtime uses unmanaged
collation (which actually means no culture-sensitive collation). It
internally disables managed collation functionality invoked via the
members of System.Globalization.CompareInfo class. Collation is
enabled by default.
For platforms that do not otherwise have a way of obtaining random bytes
this can be set to the name of a file system socket on which an egd or
prngd daemon is listening.
Sets the type of event log provider to use (for System.Diagnostics.EventLog).
Possible values are:
.I "local[:path]"
Persists event logs and entries to the local file system.
The directory in which to persist the event logs, event sources and entries
can be specified as part of the value.
If the path is not explicitly set, it defaults to "/var/lib/mono/eventlog"
on unix and "%APPDATA%\mono\eventlog" on Windows.
.I "win32"
Uses the native win32 API to write events and registers event logs and
event sources in the registry. This is only available on Windows.
On Unix, the directory permission for individual event log and event source
directories is set to 777 (with +t bit) allowing everyone to read and write
event log entries while only allowing entries to be deleted by the user(s)
that created them.
.I "null"
Silently discards any events.
The default is "null" on Unix (and versions of Windows before NT), and
"win32" on Windows NT (and higher).
If set, contains a colon-separated list of text encodings to try when
turning externally-generated text (e.g. command-line arguments or
filenames) into Unicode. The encoding names come from the list
provided by iconv, and the special case "default_locale" which refers
to the current locale's default encoding.
When reading externally-generated text strings UTF-8 is tried first,
and then this list is tried in order with the first successful
conversion ending the search. When writing external text (e.g. new
filenames or arguments to new processes) the first item in this list
is used, or UTF-8 if the environment variable is not set.
The problem with using MONO_EXTERNAL_ENCODINGS to process your
files is that it results in a problem: although its possible to get
the right file name it is not necessarily possible to open the file.
In general if you have problems with encodings in your filenames you
should use the "convmv" program.
Provides a prefix the runtime uses to look for Global Assembly Caches.
Directories are separated by the platform path separator (colons on
unix). MONO_GAC_PREFIX should point to the top directory of a prefixed
install. Or to the directory provided in the gacutil /gacdir command. Example:
.B /home/username/.mono:/usr/local/mono/
Enables some filename rewriting support to assist badly-written
applications that hard-code Windows paths. Set to a colon-separated
list of "drive" to strip drive letters, or "case" to do
case-insensitive file matching in every directory in a path. "all"
enables all rewriting methods. (Backslashes are always mapped to
slashes if this variable is set to a valid option.)
For example, this would work from the shell:
If you are using mod_mono to host your web applications, you can use
directive instead, like this:
MonoIOMAP <appalias> all
See mod_mono(8) for more details.
If set to "disabled", System.IO.FileSystemWatcher will use a file watcher
implementation which silently ignores all the watching requests.
If set to any other value, System.IO.FileSystemWatcher will use the default
managed implementation (slow). If unset, mono will try to use inotify, FAM,
Gamin, kevent under Unix systems and native API calls on Windows, falling
back to the managed implementation on error.
If set causes the mono process to be bound to a single processor. This may be
useful when debugging or working around race conditions.
Provides a search path to the runtime where to look for library
files. This is a tool convenient for debugging applications, but
should not be used by deployed applications as it breaks the assembly
loader in subtle ways.
Directories are separated by the platform path separator (colons on unix). Example:
.B /home/username/lib:/usr/local/mono/lib
Alternative solutions to MONO_PATH include: installing libraries into
the Global Assembly Cache (see gacutil(1)) or having the dependent
libraries side-by-side with the main executable.
For a complete description of recommended practices for application
deployment, see
Experimental RTC support in the statistical profiler: if the user has
the permission, more accurate statistics are gathered. The MONO_RTC
value must be restricted to what the Linux rtc allows: power of two
from 64 to 8192 Hz. To enable higher frequencies like 4096 Hz, run as root:
echo 4096 > /proc/sys/dev/rtc/max-user-freq
For example:
MONO_RTC=4096 mono --profiler=default:stat program.exe
Disable inlining of thread local accesses. Try setting this if you get a segfault
early on in the execution of mono.
If set its the directory where the ".wapi" handle state is stored.
This is the directory where the Windows I/O Emulation layer stores its
shared state data (files, events, mutexes, pipes). By default Mono
will store the ".wapi" directory in the users's home directory.
Uses the string value of this variable as a replacement for the host name when
creating file names in the ".wapi" directory. This helps if the host name of
your machine is likely to be changed when a mono application is running or if
you have a .wapi directory shared among several different computers.
Mono typically uses the hostname to create the files that are used to
share state across multiple Mono processes. This is done to support
home directories that might be shared over the network.
If set, extra checks are made during IO operations. Currently, this
includes only advisory locks around file writes.
If set, disables the shared memory files used for cross-process
handles: process have only private handles. This means that process
and thread handles are not available to other processes, and named
mutexes, named events and named semaphores are not visible between
This is can also be enabled by default by passing the
"--disable-shared-handles" option to configure.
The name of the theme to be used by Windows.Forms. Available themes today
include "clearlooks", "nice" and "win32".
The default is "win32".
The time, in seconds, that the SSL/TLS session cache will keep it's entry to
avoid a new negotiation between the client and a server. Negotiation are very
CPU intensive so an application-specific custom value may prove useful for
small embedded systems.
The default is 180 seconds.
The maximum number of threads in the general threadpool will be
20 + (MONO_THREADS_PER_CPU * number of CPUs). The default value for this
variable is 10.
Controls the threshold for the XmlSerializer to produce a custom
serializer for a given class instead of using the Reflection-based
interpreter. The possible values are `no' to disable the use of a
custom serializer or a number to indicate when the XmlSerializer
should start serializing. The default value is 50, which means that
the a custom serializer will be produced on the 50th use.
Set this value to 1 to prevent the serializer from removing the
temporary files that are created for fast serialization; This might
be useful when debugging.
Mono contains a feature which allows modifying settings in the .config files shipped
with Mono by using config section mappers. The mappers and the mapping rules are
defined in the $prefix/etc/mono/2.0/ file and, optionally, in the file found in the top-level directory of your ASP.NET application.
Both files are read by System.Web on application startup, if they are found at the
above locations. If you don't want the mapping to be performed you can set this
variable in your environment before starting the application and no action will
be taken.
Mono supports a plugin model for its implementation of System.Messaging making
it possible to support a variety of messaging implementations (e.g. AMQP, ActiveMQ).
To specify which messaging implementation is to be used the evironement variable
needs to be set to the full class name for the provider. E.g. to use the RabbitMQ based
AMQP implementation the variable should be set to:
If set to any value, temporary source files generated by ASP.NET support
classes will not be removed. They will be kept in the user's temporary
The logging level, possible values are `error', `critical', `warning',
`message', `info' and `debug'. See the DEBUGGING section for more
Controls the domain of the Mono runtime that logging will apply to.
If set, the log mask is changed to the set value. Possible values are
"asm" (assembly loader), "type", "dll" (native library loader), "gc"
(garbage collector), "cfg" (config file loader), "aot" (precompiler) and "all".
The default value is "all". Changing the mask value allows you to display only
messages for a certain component. You can use multiple masks by comma
separating them. For example to see config file messages and assembly loader
messages set you mask to "asm,cfg".
Used for runtime tracing of method calls. The format of the comma separated
trace options is:
[-]M:method name
[-]T:class name
disabled Trace output off upon start.
You can toggle trace output on/off sending a SIGUSR2 signal to the program.
If set, enables the System.Diagnostics.DefaultTraceListener, which will
print the output of the System.Diagnostics Trace and Debug classes.
It can be set to a filename, and to Console.Out or Console.Error to display
output to standard output or standard error, respectively. If it's set to
Console.Out or Console.Error you can append an optional prefix that will
be used when writing messages like this: Console.Error:MyProgramName.
See the System.Diagnostics.DefaultTraceListener documentation for more
This throws an exception when a X11 error is encountered; by default a
message is displayed but execution continues
This is used in the System.Windows.Forms implementation when running
with the X11 backend. This is used to debug problems in Windows.Forms
as it forces all of the commands send to X11 server to be done
synchronously. The default mode of operation is asynchronous which
makes it hard to isolate the root of certain problems.
This environment variable controls the kind of generic sharing used.
This variable is used by internal JIT developers and should not be
changed in production. Do not use it.
The variable controls which classes will have generic code sharing
Permissible values are:
.I "all"
All generated code can be shared.
.I "collections"
Only the classes in System.Collections.Generic will have its code
shared (this is the default value).
.I "corlib"
Only code in corlib will have its code shared.
.I "none"
No generic code sharing will be performed.
Generic code sharing by default only applies to collections. The
Mono JIT by default turns this on.
When the the MONO_XDEBUG env var is set, debugging info for JITted
code is emitted into a shared library, loadable into gdb. This enables,
for example, to see managed frame names on gdb backtraces.
Enables the maximum JIT verbosity for the specified method. This is
very helpfull to diagnose a miscompilation problems of a specific
If you want to use Valgrind, you will find the file `mono.supp'
useful, it contains the suppressions for the GC which trigger
incorrect warnings. Use it like this:
valgrind --suppressions=mono.supp mono ...
On some platforms, Mono can expose a set of DTrace probes (also known
as user-land statically defined, USDT Probes).
They are defined in the file `mono.d'.
.B ves-init-begin, ves-init-end
Begin and end of runtime initialization.
.B method-compile-begin, method-compile-end
Begin and end of method compilation.
The probe arguments are class name, method name and signature,
and in case of method-compile-end success or failure of compilation.
.B gc-begin, gc-end
Begin and end of Garbage Collection.
To verify the availability of the probes, run:
dtrace -P mono'$target' -l -c mono
On Unix assemblies are loaded from the installation lib directory. If you set
`prefix' to /usr, the assemblies will be located in /usr/lib. On
Windows, the assemblies are loaded from the directory where mono and
mint live.
.B ~/.mono/aot-cache
The directory for the ahead-of-time compiler demand creation
assemblies are located.
.B /etc/mono/config, ~/.mono/config
Mono runtime configuration file. See the mono-config(5) manual page
for more information.
.B ~/.config/.mono/certs, /usr/share/.mono/certs
Contains Mono certificate stores for users / machine. See the certmgr(1)
manual page for more information on managing certificate stores and
the mozroots(1) page for information on how to import the Mozilla root
certificates into the Mono certificate store.
.B ~/.mono/assemblies/ASSEMBLY/ASSEMBLY.config
Files in this directory allow a user to customize the configuration
for a given system assembly, the format is the one described in the
mono-config(5) page.
.B ~/.config/.mono/keypairs, /usr/share/.mono/keypairs
Contains Mono cryptographic keypairs for users / machine. They can be
accessed by using a CspParameters object with DSACryptoServiceProvider
and RSACryptoServiceProvider classes.
.B ~/.config/.isolatedstorage, ~/.local/share/.isolatedstorage, /usr/share/.isolatedstorage
Contains Mono isolated storage for non-roaming users, roaming users and
local machine. Isolated storage can be accessed using the classes from
the System.IO.IsolatedStorage namespace.
.B <assembly>.config
Configuration information for individual assemblies is loaded by the
runtime from side-by-side files with the .config files, see the for more information.
.B Web.config, web.config
ASP.NET applications are configured through these files, the
configuration is done on a per-directory basis. For more information
on this subject see the
Mailing lists are listed at the
certmgr(1), csharp(1), mcs(1), mdb(1), monocov(1), monodis(1),
mono-config(5), mozroots(1), pdb2mdb(1), xsp(1), mod_mono(8).
For more information on AOT:
For ASP.NET-related documentation, see the xsp(1) manual page
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