Set the time backward or forward for a process by intercepting the relevant system calls using
LD_PRELOAD to have the run time loader preload this library.
A small shared library that intercepts the three system calls that Linux processes use to get the current time viz
time_t time (time_t* t); -- time(2)
int gettimeofday (struct timeval* tv, struct timezone* tz); -- gettimeofday(2)
int clock_gettime (clockid_t clk_id, struct timespec* ts); -- clock_gettime(2)
The offset in seconds from the current time is passed via the environment variable HACK_CLOCK_SHIFT. Note: the apparent time still increases monotonically at a constant offset from the real time.
Examples
# date uses clock_gettime(2)
/bin/date
Mon Apr 8 21:02:35 EST 2013
LD_PRELOAD=`pwd`/libclockhack.so HACK_CLOCK_SHIFT=-100000000 /bin/date
Sat Feb 6 11:16:25 EST 2010
BUGS
Should be able to fiddle it to work on most unix systems.
If RTLD_NEXT isn't supported then accessing the real system calls using the syscall(2)
interface is another option.
NetBSD seems to rename gettimeofday to gettimeofday50 and has a slightly different prototype
but did work after making this change.
Obviously doesn't work for statically linked executables such as /bin/date on OpenBSD.
LICENSE Creative Commons CC0 (http://creativecommons.org/publicdomain/zero/1.0/legalcode)
AUTHOR James Sainsbury