Timeshift
=========

From time to time it is useful to test an existing binary program with an
altered system clock, without changing the clock and messing up the rest of the
machine. Timeshift is a small shared object which can be used to accomplish
this via the /etc/ld.so.preload or LD_PRELOAD mechanism.

Installation
------------

Type make. Type make test. Verify that it's behaving sensibly. Put timeshift.so
somewhere. Tested only on Linux -- sorry.

Use
---

    LD_PRELOAD=/path/to/timeshift.so TIMESHIFT=start:end /path/to/program

(Note that the linker ignores LD_PRELOAD for setuid programs. Instead, you
can use the /etc/ld.so.preload mechanism. If you do this, be careful: the
setting applies to the whole system, and if you make a mistake, you could be
unable to run any dynamically linked program. Keeping a statically-linked shell
running is a wise precaution.)

The two colon-separated elements of TIMESHIFT should be epoch time expressed in
decimal. You can convert human-readable to epoch time using GNU date(1):

    date +%s -d 'yyyy-mm-dd hh:mm:ss'

The time reported to the program will wrap around inside the window from start
to end, advancing by one second per real second. The formula used is

    reported_time = start + ((real_time - start) % (end - start))

Note that this means the time will sometimes go backwards. You can alter the
function shift() in timeshift.c to implement a more sophisticated behaviour.


-- Chris Lightfoot <chris@ex-parrot.com>
   http://ex-parrot.com/~chris/
   http://ex-parrot.com/~chris/software.html#timeshift

   Redistribute freely.

$Id: README,v 1.4 2003/05/21 11:47:52 chris Exp $