When build the libserial on a newly installed Linux server, Make tell me the Clock skew detected. Your build may be incomplete.

`make’ uses the last modification time on the files to
figure out what to build. For example, if the modification
time of a.c is later than the modification time of a.out,
then a.c needs to me recomplied to create a new a.out.

Sometimes the last modified time on the files is wrong:
because it is greater than the time of day clock. `make’
then issues the above message.

Given a standard make system, the quickest fix is:

cd directory
# Remove output files
make clean
# Put timestamps on all files equal to current time
find . -exec touch {} \;
# Rebuild all output files
make

You usually see these sort of problems in programming
enviroments that use NFS to share files but don’t sync
clocks using NTP.

Similarly, if you wind the clock back you will see these
messages. For that reason, when you wind back the clock
a moderate amount most UNIXen slow the clock ticks rather
than turn back time.