Makefile warning: Warning: File `main.cpp' has modification time 2.1e+04 s in the future

Question

I have a working Makefile, but there is a warning that I couldn't fix.

#Use the g++ compiler
CC = g++

# Compiler flags:
#   -Wall (most warnings enabled)
#   -g (for debugging with gdb)
CFLAGS = -Wall

# Executable name:
TARGET = deque_adt

all: main.o deque_adt.o deque_adt

$(TARGET): main.o deque_adt.o
    $(CC) $(CFLAGS) main.o deque_adt.o -o $(TARGET)

main.o: main.cpp deque_adt.h 
    $(CC) $(CFLAGS) main.cpp -c

deque_adt.o: deque_adt.cpp deque_adt.h
    $(CC)  $(CFLAGS) deque_adt.cpp -c

clean:
    rm *.o *~ $(TARGET)

error:

make: Warning: File `main.cpp' has modification time 2.1e+04 s in the future
g++ -Wall main.cpp -c
g++  -Wall deque_adt.cpp -c
g++ -Wall main.o deque_adt.o -o deque_adt
make: warning:  Clock skew detected.  Your build may be incomplete.

Can someone help me out to figure out the problem? I have tried to switch between the elements but it still gives the same warning.

Answer 1

To expand on Ben Voigt's answer:

find /your/dir -type f -exec touch {} +

will update the timestamp on all files in the directory. You can then make clean && make again.

Answer 2

That message is usually an indication that some of your files have modification times later than the current system time.

Chech if your system time is in the past. Example:

$ date

If so You have several ways to fix this. the easier one is to install an ntp server:

apt install ntp

Or

yum install ntp

Or ...

Regarding of your operating system (Ubuntu, Centos, ...etc)

Answer 3

check your computer time. I had the same problem and the root cause was my computer time was in the past - when I update it, it was work perfectly.