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datefudge - Man Page

pretend the system time is different


datefudge [-s|--static] [-l|--add-ld-preload lib] at_date program [arguments ...]


datefudge is a small utility that pretends that the system time is different by pre-loading a small library which modifies the time(2), gettimeofday(2) and clock_gettime(2) system calls.

Date Format

The at_date argument can be given in any format accepted by the date(1) program, for example "2007-04-01 12:21" or "yesterday", or "next Friday".


--static,  -s

Mark the date as a `static' one.  The above mentioned system calls will always return the date given in the at_date argument, regardless of time passing.  Please note that sub-seconds part of the returned date is always set to 0. See Examples below.

--add-ld-preload lib, -l lib

Prepend lib to LD_PRELOAD environment variable before executing given program.  This option might be useful for example to inject sanitizer libraries (e.g. from Address Sanitizer) to the list of preloaded libraries before the internal datefudge's library.  See Examples below.

--help,  -h

Print short usage information and exit.

--version,  -v

Print version information and exit.


Basic examples

$ datefudge "2007-04-01 10:23" date -R
Sun, 01 Apr 2007 10:23:00 +0200

$ datefudge "1 May 2007" date -R
Tue, 01 May 2007 00:00:00 +0200

$ datefudge "2 weeks ago" date -R
Wed, 16 Jan 2008 13:32:12 +0100

Non-static vs. static example

$ datefudge "2007-04-01 10:23" sh -c "sleep 3; date -R"
Sun, 01 Apr 2007 10:23:03 +0200

$ datefudge --static "2007-04-01 10:23" sh -c "sleep 3; date -R"
Sun, 01 Apr 2007 10:23:00 +0200

Non-static with sub-seconds example

$ datefudge --static "2007-04-01 10:23:45.123456" date +"%F %T %N"
2007-04-01 10:23:45 000000000

Prepending LD_PRELOAD example

$ datefudge --add-ld-preload /path/to/libclang_rt.asan-x86_64.so "2007-04-01 10:23" command

If the command was compiled by 'clang -fsanitize=address -shared-libasan', then the above
command might display some errors, for example:

==7625==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000044 at pc ....

Without the --add-ld-preload argument, this would not work at all.


Written by Matthias Urlichs <smurf@noris.de>.  Modified by Robert Luberda <robert@debian.org>.


There is no attempt to make this change undetectable by the program. In particular, file modification times are not modified.  (Note that such a functionality might be provided by faketime(1) program available in libfaketime Debian package.)

On systems using 32-bit representation of time, datefudge is affected by the year 2038 problem, which might cause dates to be wrapped around, for instance:

$ TZ=UTC datefudge "2038-01-19 03:14:07" sh -c "sleep 1; date -R"
Fri Dec 13 20:45:53 UTC 1901

See Also

date(1), ld.so(1), time(2), gettimeofday(2), clock_gettime(2), faketime(1)


January 13th, 2024 datefudge 1.26 Debian