This experiment shows how it is possible to virtualize the perception of the time in VUOS.
We need a clock application. The command date works is not very convenient for this
example. I should be executed repeatedly to see how the time flows.
Our suggestion is to use xclock.
If it not installed in your system it can be easily added, it is included in the Debian
package x11-apps.
Run:
# apt-get install x11-apps
Start a clock from a non-VUOS shell:
$ xclock -update 1
Note: if you are using the virtual machine image as described here,
from a terminal window of the hosting system run
ssh -X -p 2222 user@localhost xclock -update 1.
Now start a VUOS session and run:
$$ xclock -update 1 &
$$ vu_insmod vumisc
$$ vumount -t vumisctime none /mnt
$$ ls /mnt
base frequency offset
$$
These commands start a second xclock, load the ummisc module and activate
the vumisctime submodule.
The file system that vumount makes accessible on /mnt consists of
three virtual files:
- offset: difference in seconds between the real and virtual time
- frequency: the pace of a virtual second with respect to a real second
- base: base time for the frequency change.
Note: for the interested readers the formula of the virtual time is
Virt-time = ((real-time - base) * frequency) + base + offset
Now the two xclocks are synchronized. The first one launched shown the time as seek by the Linux kernel, the second is showing the virtual time.
This command:
$$ echo 3600 > /mnt/offset
adds an hour of the virtual time, The hour arm of the virtual xclock moves
correspondingly.
Warning: xclock has not been designed to go backwards. So if virtual time
is decreased the xclock must be closed and restarted.
Now let us stop the flowing of the virtual time:
$$ echo 0 > /mnt/frequency
The second harm stops.
The frequency can be modified: the virtual time can go fast:
$$ echo 2 > /mnt/frequency
or slow:
$$ echo 0.5 > /mnt/frequency
If frequency is set to a negative number: the virtual time flows backwards.
xclock is not able to show this. it can be shown using the command date.
$$ echo -1 > /mnt/frequency
$$ date
Thu 13 Aug 2020 07:25:55 PM CEST
$$ date
Thu 13 Aug 2020 07:25:53 PM CEST
$$ date
Thu 13 Aug 2020 07:25:52 PM CEST
$$ date
Thu 13 Aug 2020 07:25:51 PM CEST
$$ date
Thu 13 Aug 2020 07:25:50 PM CEST
$$ date
Thu 13 Aug 2020 07:25:49 PM CEST
$$ date
Thu 13 Aug 2020 07:25:48 PM CEST
renzo@eipi[305642]:~$