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FAKETIME(1) wolfcw FAKETIME(1)

NAME
faketime - manipulate the system time for a given command

SYNOPSIS
faketime [options] timestamp program [arguments...]

DESCRIPTION
The given command will be tricked into believing that the current sys-
tem time is the one specified in the timestamp. Filesystem timestamps
will also be reported relative to this timestamp. The wall clock will
continue to run from this date and time unless specified otherwise (see
advanced options). Actually, faketime is a simple wrapper for libfake-
time, which uses the LD_PRELOAD mechanism to load a small library which
intercepts system calls to functions such as time(2) and fstat(2).
This wrapper exposes only a subset of libfaketime's functionality;
please refer to the README file that came with faketime for more de-
tails and advanced options, or have a look at
https://github.com/wolfcw/libfaketime

OPTIONS
--help show usage information and quit.

--version
show version information and quit.

-m use the multi-threading variant of libfaketime.

-p <PID>
pretend that the program's process ID is PID. (only available if
built with FAKE_PID)

-f use the advanced timestamp specification format.

--exclude-monotonic
Do not fake time when the program makes a call to clock_gettime
with a CLOCK_MONOTONIC clock.

--disable-shm
Disable use of shared memory by libfaketime.

--date-prog <PATH>
Use a specific GNU-date compatible implementation of the helper
used to transform "timestamp format" strings into programmati-
cally usable dates, instead of a compile-time default guess for
the generic target platform.

EXAMPLES
faketime 'last Friday 5 pm' /bin/date
faketime '2008-12-24 08:15:42' /bin/date
faketime -f '+2,5y x10,0' /bin/bash -c 'date; while true; do echo $SECONDS ; sleep 1 ; done'
faketime -f '+2,5y x0,50' /bin/bash -c 'date; while true; do echo $SECONDS ; sleep 1 ; done'
faketime -f '+2,5y i2,0' /bin/bash -c 'while true; do date ; sleep 1 ; done'
In this single case all spawned processes will use the same global clock without restarting it at the start of each process.

(Please note that it depends on your locale settings whether . or , has to be used for fractional offsets)

ADVANCED TIMESTAMP FORMAT
The simple timestamp format used by default applies the /bin/date -d
command to parse user-friendly specifications such as 'last friday'.
When using the faketime option -f, the timestamp specified on the com-
mand line is directly passed to libfaketime, which enables a couple of
additional features such as speeding the clock up or slowing it down
for the target program. It is strongly recommended that you have a
look at the libfaketime documentation. Summary:

Freeze clock at absolute timestamp: "YYYY-MM-DD hh:mm:ss"
If you want to specify an absolute point in time, exactly this
format must be used. Please note that freezing the clock is
usually not what you want and may break the application. Only
use if you know what you're doing!

Relative time offset: "[+/-]123[m/h/d/y]", e.g., "+60m", "+2y"
This is the most often used format and specifies the faked time
relatively to the current real time. The first character of the
format string must be a + or a -. The numeric value by default
represents seconds, but the modifiers m, h, d, and y can be used
to specify minutes, hours, days, or years, respectively. For
example, "-2y" means "two years ago". Fractional time offsets
can be used, e.g., "+2,5y", which means "two and a half years in
the future". Please note that the fraction delimiter depends on
your locale settings, so if "+2,5y" does not work, you might
want to try "+2.5y".

Start-at timestamps: "@YYYY-MM-DD hh:mm:ss"
The wall clock will start counting at the given timestamp for
the program. This can be used for specifying absolute time-
stamps without freezing the clock.

ADVANCED USAGE
When using relative time offsets or start-at timestamps (see ADVANCED
TIMESTAMP FORMAT above and option -f), the clock speed can be adjusted,
i.e., time may run faster or slower for the executed program. For ex-
ample, "+5y x10" will set the faked time 5 years into the future and
make the time pass 10 times as fast (one real second equals 10 seconds
measured by the program). Similarly, the flow of time can be slowed,
e.g., using "-7d x0,2", which will set the faked time 7 days in the
past and set the clock speed to 20 percent, i.e., it takes five real
world seconds for one second measured by the program. Again, depending
on your locale, either "x2.0" or "x2,0" may be required regarding the
delimiter. You can also make faketime to advance the reported time by
a preset interval upon each time() call independently from the system's
time using "-7d i2,0", where "i" is followed by the increase interval
in seconds.

Faking times for multiple programs or even system-wide can be simpli-
fied by using ~/.faketimerc files and /etc/faketimerc. Please refer to
the README that came with faketime for warnings and details.

Faking of filesystem timestamps may be disabled by setting the
NO_FAKE_STAT environment variable to a non-empty value.

AUTHOR
Please see the README and NEWS files for contributors.

BUGS
Due to limitations of the LD_PRELOAD mechanism, faketime will not work
with suidroot and statically linked programs. While timestamps and
time offsets will work for child processes, speeding the clock up or
slowing it down might not work for child processes spawned by the exe-
cuted program as expected; a new instance of libfaketime is used for
each child process, which means that the libfaketime start time, which
is used in speed adjustments, will also be re-initialized. Some pro-
grams may dynamically load system libraries, such as librt, at run-time
and therefore bypass libfaketime. You may report programs that do not
work with libfaketime, but only if they are available as open source.

REPORTING BUGS
Please use https://github.com/wolfcw/libfaketime/issues

There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. You may redistribute copies of faketime under the
terms of the GNU General Public License.
For more information about these matters, see the file named COPYING.

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