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faketime - manipulate the system time for a given command


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


The given command will be tricked into believing that the current system time is the one
specified in the 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 libfaketime, 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 details and advanced options, or have a look at


--help show usage information and quit.

show version information and quit.

-m use the multi-threading variant of libfaketime.

-f use the advanced timestamp specification format.


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 restaring 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)


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 command 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

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 timestamps without freezing the clock.


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 example, "+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 simplified by using
~/.faketimerc files and /etc/faketimerc. Please refer to the README that came with
faketime for warnings and details.

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