CGAL - clock slew when making?

Question

I'm tired of manually executing one command after another just to compile a C++11 program that makes use of CGAL.

So I thought I'd create a small .sh file that would take care of it for me:

#!/bin/bash

cgal_create_cmake_script &&
cmake . &&
echo "set(CMAKE_CXX_FLAGS \"${CMAKE_CXX_FLAGS} -std=c++11\")" >> CMakeList.txt &&
make

I don't really know much about bash scripts, but this seems to work well enough. However, I'm constantly getting warnings that

make: Warning: File 'Makefile' has modification time 2.4 s in the future

make[1]: Warning: File 'CMakeFiles/Makefile2' has modification time 2.4 s in the future

make[2]: Warning: File 'CMakeFiles/my_dir.dir/progress.make' has modification time 2.4 s in the future

Now, as much as I'd like a computer capable of predicting the future, I'm not really happy about this. What am I doing wrong?

Sounds like you are using a remote file system (NFS?) and the clocks on your local machine and the server are out of sync. Either fix the clocks, or add `sleep 3` just before calling `make` to give your machine a chance to "catch up". — chepner, Oct 02 '15 at 13:21
@chepner: indeed, that seems to have been the issue. you want to elaborate so I can accept it as an answer? — User1291, Oct 02 '15 at 13:33
Because there are so many ways I just wanted to add a reference to [How to activate C++ 11 in CMake?](http://stackoverflow.com/questions/10851247/how-to-activate-c-11-in-cmake). — Florian, Oct 03 '15 at 15:24

score 3 · Accepted Answer · answered Oct 02 '15 at 13:36

Your Makefile is being created on a remote file system, so the timestamp is recorded using the server's clock, which appears to be fast (or your machine's clock is slow). make, however, is running on your local machine, so when it sees your Makefile, it appears to have been created in the future.

The right thing to do is to fix whichever clock is off. (Ideally, both machines should be using something like NTP to synchronize with a standard clock.)

A quick hack would be to add a sleep command to the list

cgal_create_cmake_script &&
cmake . &&
echo "set(CMAKE_CXX_FLAGS \"${CMAKE_CXX_FLAGS} -std=c++11\")" >> CMakeList.txt &&
sleep 3 &&
make

so that your local clock can "catch up" and make the remote file appear to have been created in the past instead of the future.

CGAL - clock slew when making?

1 Answers1