title: Troubleshooting warning from "make -j N"
body: <p>When I issue a command like (for example) <code>make -j 4</code>, I get the following error:</p>
  
  <pre><code>warning: jobserver unavailable: using -j1.  Add `+' to parent make rule
  </code></pre>
  
  <p>I am using the developer toolkit from Scientific Linux 6 under RHEL6:</p>
  
  <pre><code>$ gcc -v
  Using built-in specs.
  COLLECT_GCC=gcc
  COLLECT_LTO_WRAPPER=/opt/rh/devtoolset-2/root/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper
  Target: x86_64-redhat-linux
  Configured with: ../configure --prefix=/opt/rh/devtoolset-2/root/usr --mandir=/opt/rh/devtoolset-2/root/usr/share/man --infodir=/opt/rh/devtoolset-2/root/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --enable-languages=c,c++,fortran,lto --enable-plugin --with-linker-hash-style=gnu --enable-initfini-array --disable-libgcj --with-isl=/builddir/build/BUILD/gcc-4.8.2-20140120/obj-x86_64-redhat-linux/isl-install --with-cloog=/builddir/build/BUILD/gcc-4.8.2-20140120/obj-x86_64-redhat-linux/cloog-install --with-mpc=/builddir/build/BUILD/gcc-4.8.2-20140120/obj-x86_64-redhat-linux/mpc-install --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
  Thread model: posix
  gcc version 4.8.2 20140120 (Red Hat 4.8.2-15) (GCC)
  </code></pre>
  
  <p>I have <code>libmpc</code> 0.8.3 installed:</p>
  
  <pre><code>$ rpm -qa | grep mpc
  libmpcdec-1.2.6-6.1.el6.x86_64
  libmpc-0.8-3.el6.x86_64
  </code></pre>
  
  <p>Is there a way to troubleshoot my project's makefile or gcc to determine what is causing the warning and fix it? I do not seem to need the <code>+</code> symbol added to rules when building from OS X via Clang/LLVM. Google searches on the warning text are not returning much information that is apparently useful.</p>