Microsoft Windows 10 Pro [Version 10.0.17134.228]
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"
++++++++++++++++++++++++++++++++++++++++
I encounter the same problem.

type the following COMMAND in bash:
mpirun -np 3 test_openmpi

WARNING: Linux kernel CMA support was requested via the
btl_vader_single_copy_mechanism MCA variable, but CMA support is
not available due to restrictive ptrace settings.

The vader shared memory BTL will fall back on another single-copy
mechanism if one is available. This may result in lower performance.

Local host: workstation

[workstation:04636] [[3228,0],0] ORTE_ERROR_LOG: Data unpack would read past end of buffer in file util/show_help.c at line 507
Hello: rank 1, world: 3
Hello: rank 0, world: 3
Hello: rank 2, world: 3
[workstation:04636] 1 more process has sent help message help-btl-vader.txt / cma-permission-denied
[workstation:04636] Set MCA parameter "orte_base_help_aggregate" to 0 to see all help / error messages

here is the file: test_openmpi.cpp
cat test_openmpi.cpp
/* Put this text inside hello.c file */
#include <mpi.h>
#include <stdio.h>

int main(int argc, char** argv) {
int rank;
int world;

MPI_Init(NULL, NULL);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &world);
printf("Hello: rank %d, world: %d\n",rank, world);
MPI_Finalize();
}

I have tested it using the OpenMPI-3.1.1 and OpenMPI-3.1.2 compiled by myself, the above problem always happens.

Of course I can use the following option to turn off this warning, but I do not sure whether it will affect the performance. Thus, I think it should be solved by a developer from either WSL or OpenMPI.

mpirun --mca btl_vader_single_copy_mechanism none -np 3 test_openmpi

+++++++++++++++++++++++++++++++++++++++++
In addition:
I agree the above author's suggestion, in fact we care more about the performance than the safety. So maybe if Win10 can give the more switches/options to tune the performance and turn off the safety options if they will influent the performance.

This link may be useful to someone.
open-mpi/ompi#4948

Thanks in advance.
QL

Same issue... Try the following:
https://groups.io/g/OpenHPC-users/topic/openmpi_and_shared_memory/16489081?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,16489081

$ echo 0 > /proc/sys/kernel/yama/ptrace_scope
or
$ sudo echo 0 > /proc/sys/kernel/yama/ptrace_scope
or
$ echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope

Yeah 1 appears to be the default on unadulterated Ubuntu. Maybe change the issue title to "change default ptrace_scope to 1 if that's really the concrete ask we're talking about here. [Someone will suggest making it a wsl.conf thing, and then I'll feel sad inside.]

If you'd like this setting to be persistent, then you need to edit the config file /etc/sysctl.d/10-ptrace.conf instead, e.g.

$ sudo vim /etc/sysctl.d/10-ptrace.conf

and edit the line that says

kernel.yama.ptrace_scope = 1

to

kernel.yama.ptrace_scope = 0

N.B. This was taken from this answer on Stack Overflow.

/etc/sysctl.d/10-ptrace.conf

Nothing reads that file on WSL (nothing starts systemd-sysctl.service), de-facto landing zone #994.

Ah I see. Right never mind then

Well, how to set kernel.yama.ptrace_scope to 0 permanently? There is no possibility to set kernel variable in wsl.conf (at least this is not documented) and WSL just ignores rc.local and /etc/sysctl.d files....

Test and set it in .bashrc or .profile is the de-facto standard operating procedure right now. Use sudoers to avoid the password prompt if you like.

Yeah 1 appears to be the default on unadulterated Ubuntu. Maybe change the issue title to "change default ptrace_scope to 1 if that's really the concrete ask we're talking about here. [Someone will suggest making it a wsl.conf thing, and then I'll feel sad inside.]

How did you change it? I have the same issue but I can't manage to figure out how to set it to 0

I will change it in wsl.conf to 0! That is what I need!!! Thank you!!! A value of 1 hurts OpenMPI performance
…
On Mon, Sep 3, 2018, 3:12 PM therealkenc @.***> wrote: Yeah 1 appears to be the default on unadulterated Ubuntu. Maybe change the issue title to "change default ptrace_scope to 1if that's really the concrete ask we're talking about here. [Someone will suggest making it awsl.conf` thing, and then I'll feel sad inside.] — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#3397 (comment)>, or mute the thread https://github.com/notifications/unsubscribe-auth/AdNyb267W1hMNBCcxFMpuuKbjtt_BFNJks5uXalYgaJpZM4VZwDE .

How did you change it? I have the same issue but I can't manage to figure out how to set it to 0