After Windows 10 upgraded itself from 10.0 (Build 10240) to 1511
(Build 10586) shell scripts fail with fork errors.

This can be demonstrated from a Cygwin64 Terminal window by running a
trivial pair of commands. Create these two files in a folder:

1.  win1511.pl containing the three lines:
    my $subShell = "sh win1511.sh arg1 arg2";
    print "Running: $subShell\n";
    system("$subShell")

2.  win1511.sh containing the four lines:
    #!/bin/bash
    echo win1511.sh starts
    sh -c "echo FROM SUBSHELL"    # This fails under Windows (10) 1511
    echo win1511 all done

Then change to the folder and run: perl win1511.pl

On a Windows 10 (10240) this reports, as expected:

    Running: sh win1511.sh arg1 arg2
    win1511.sh starts
    FROM SUBSHELL
    win1511 all done

But on the "upgraded" Windows, it reports something like:

    Running: sh win1511.sh arg1 arg2
    win1511.sh starts
          0 [main] sh 7208 C:\cygwin\bin\sh.exe: *** fatal error in
forked process - fork: can't reserve memory for parent stack 0x600000
- 0x800000, (child has 0x400000 - 0x600000), Win32 error 487
        527 [main] sh 7208 cygwin_exception::open_stackdumpfile:
Dumping stack trace to sh.exe.stackdump
          0 [main] sh 1336 fork: child -1 - forked process 7208 died
unexpectedly, retry 0, exit code 0x100, errno 11
    win1511.sh: fork: retry: No child processes
    1011664 [main] sh 4084 C:\cygwin\bin\sh.exe: *** fatal error in
forked process - fork: can't reserve memory for parent stack 0x600000
- 0x800000, (child has 0x400000 - 0x600000), Win32 error 487
    1012796 [main] sh 4084 cygwin_exception::open_stackdumpfile:
Dumping stack trace to sh.exe.stackdump
    1055452 [main] sh 1336 fork: child -1 - forked process 4084 died
unexpectedly, retry 0, exit code 0x100, errno 11
    win1511.sh: fork: retry: No child processes
    3065101 [main] sh 1744 C:\cygwin\bin\sh.exe: *** fatal error in
forked process - fork: can't reserve memory for parent stack 0x600000
- 0x800000, (child has 0x400000 - 0x600000), Win32 error 487
    3066077 [main] sh 1744 cygwin_exception::open_stackdumpfile:
Dumping stack trace to sh.exe.stackdump
    3102454 [main] sh 1336 fork: child -1 - forked process 1744 died
unexpectedly, retry 0, exit code 0x100, errno 11
    win1511.sh: fork: retry: No child processes
    7111887 [main] sh 4100 C:\cygwin\bin\sh.exe: *** fatal error in
forked process - fork: can't reserve memory for parent stack 0x600000
- 0x800000, (child has 0x400000 - 0x600000), Win32 error 487
    7112715 [main] sh 4100 cygwin_exception::open_stackdumpfile:
Dumping stack trace to sh.exe.stackdump
    7152061 [main] sh 1336 fork: child -1 - forked process 4100 died
unexpectedly, retry 0, exit code 0x100, errno 11
    win1511.sh: fork: retry: No child processes
    15161677 [main] sh 1648 C:\cygwin\bin\sh.exe: *** fatal error in
forked process - fork: can't reserve memory for parent stack 0x600000
- 0x800000, (child has 0x400000 - 0x600000), Win32 error 487
    15162561 [main] sh 1648 cygwin_exception::open_stackdumpfile:
Dumping stack trace to sh.exe.stackdump
    15201626 [main] sh 1336 fork: child -1 - forked process 1648 died
unexpectedly, retry 0, exit code 0x100, errno 11
    win1511.sh: fork: Resource temporarily unavailable


I am running the latest version (which I downloaded after the problem
started in case there was a fix already). uname -a reports:

CYGWIN_NT-10.0 JCPR-Dell-3 2.3.1(0.291/5/3) 2015-11-14 12:44 x86_64 Cygwin


I attach a cygcheck.out