Comment 3 for bug 1283326

When running u-s-c by hand:
root@ubuntu-phablet:~# strace unity-system-compositor --file /tmp/mir_socket
execve("/usr/sbin/unity-system-compositor", ["unity-system-compositor", "--file", "/tmp/mir_socket"], [/* 34 vars */]) = 0
brk(0) = 0x1560000
uname({sys="Linux", node="ubuntu-phablet", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb6fec000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
...
open("/root/.config/unity-system-compositor.conf", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
open("/etc/xdg/unity-system-compositor.conf", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
eventfd2(0, O_NONBLOCK|O_CLOEXEC) = 3
epoll_create1(EPOLL_CLOEXEC) = 4
timerfd(1, 0x80000 /* CLOCK_??? */, TFD_TIMER_ABSTIME|0xfffffffe, NULL) = 5
epoll_ctl(4, EPOLL_CTL_ADD, 3, {EPOLLIN|EPOLLERR|EPOLLET, {u32=22461928, u64=22461928}}) = 0
write(3, "\1\0\0\0\0\0\0\0", 8) = 8
epoll_ctl(4, EPOLL_CTL_ADD, 5, {EPOLLIN|EPOLLERR, {u32=22461940, u64=22461940}}) = 0
epoll_ctl(4, EPOLL_CTL_ADD, -1, {EPOLLIN|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET, {u32=22461992, u64=22461992}}) = -1 EBADF (Bad file descriptor)
close(4) = 0
close(5) = 0
close(3) = 0
write(2, "ERROR: ", 7ERROR: ) = 7
write(2, "Throw location unknown (consider"..., 248Throw location unknown (consider using BOOST_THROW_EXCEPTION)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::system::system_error> >
std::exception::what: assign: Bad file descriptor
) = 248
write(2, "\n", 1
) = 1
futex(0xb6fbd824, FUTEX_WAKE_PRIVATE, 2147483647) = 0
futex(0xb6dc8f6c, FUTEX_WAKE_PRIVATE, 2147483647) = 0
futex(0xb68e62c8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
exit_group(1) = ?
+++ exited with 1 +++

Also what is available in /var/log/lightdm/unity-system-compositor.log:
ERROR: /build/buildd/mir-0.1.5+14.04.20140212/src/platform/graphics/android/android_alloc_adaptor.cpp(68): Throw in function virtual std::shared_ptr<mir::graphics::NativeBuffer> mir::graphics::android::AndroidAllocAdaptor::alloc_buffer(mir::geometry::Size, MirPixelFormat, mir::graphics::android::BufferUsage)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error> >
std::exception::what: buffer allocation failed