Change system time for UNIX process?
Well, I found the answer by myself.
In unix shell there is an environmental variable TZ which is the timezone and it is used by all C/C++ time functions.
This variable can be manipulated to set time in current unix shell to any arbitrary time (limited to number of seconds, not milliseconds) and even change date.
Examples:
export TZ=A-02:10:20(shifts time by 2 hours 10 minutes and 20 seconds from now forward).
export TZ=A+02:10:20(the same shift backwards)
If you want to change the date, you can use large number of hours, for example:
export TZ=A-72:10:20Unfortunately it does not let you change date too much, from my experiments it is up to several days back/forward. So for changing month/year this does not work.
(use 'date' command to check current date/time after setting TZ variable).
To cancel all changes use
export TZ=