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.