Ubuntu Manpage: faketime - manipulate the system time for a given command

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 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
       http://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.

       -f     use the advanced timestamp specification format.

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 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)

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
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 "+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 timestamps 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
       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.

AUTHOR

       Please see the README and NEWS files for contributers.

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 executed 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 programs 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

COPYRIGHT

       Copyright © 2003-2013 by the libfaketime authors.

       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.