libfaketimefs
This is a FUSE filesystem that provides a dynamic faketimerc file for libfaketime. The primary use case it to allow consistent fast forward behaviour across multiple processes. This is intended for testing environments only and should not be used in a production system.
Usage
Install and start libfaketimefs in the foreground:
# Install libfaketimefs
pip install libfaketimefs
# Create a mount point
mkdir -p /run/libfaketimefs
# Run libfaketimefs using the mount point
libfaketimefs /run/libfaketimefs
Use libfaketime and libfaketimefs to fast forward at 60 seconds per second:
# Build and send a fast forward command (see the File API documentation)
NOW=$(date +%s)
TOMORROW=$(date -d tomorrow +%s)
RATE=180
echo "$NOW $NOW $TOMORROW $RATE" > /run/libfaketimefs/control
# Enable libfaketime and configure it to use libfaketimefs
export LD_PRELOAD=libfaketime.so.1
export FAKETIME_TIMESTAMP_FILE=/run/libfaketimefs/faketimerc
export FAKETIME_NO_CACHE=1
# Watch the result
watch -n 1 date
File API: /control
This file controls the dynamic value of faketimerc using a specific command format.
Format:
REF TIME1 TIME2 RATE
| Parameter | Type | Description |
|---|---|---|
REF |
integer (unix timestamp) | When the command was issued (real time) |
TIME1 |
integer (unix timestamp) | The starting fake time |
TIME2 |
integer (unix timestamp) | The ending fake time |
RATE |
integer (seconds per second) | The rate to move between TIME1 and TIME2
|
When a valid command is written to /control, the value of /faketimerc will be dynamically generated to output an offset according to the command. When the fake time has reached TIME2 then it will continue at normal speed.
To jump to a specific time, and not fast forward between two times, use the same value for TIME1 and TIME2.
The fake time is calculated as though it has been fast forwarding since the REF time, which may or may not be the same as when the command is received. This helps when running libfaketimefs across multiple machines that may receive the command at different times. For example, one machine may boot up while other machines have been fast forwarding. Given the same command as the other machines, and synchonised system times via NTP, all machines will have the same fast forwarded fake time.
File API: /faketimerc
This file contains a dynamically generated offset according to the /control command. If no command has been written to /control then it will contain +0 which is the same as the real time. libfaketime should be configured to use this file with FAKETIME_TIMESTAMP_FILE and FAKETIME_NO_CACHE should be used to avoid libfaketime's cache behaviour.
File API: /realtime
This file contains the real system time formatted as a unix timestamp floating point number. This is an escape hatch for programs under the effects of libfaketime to access the real time.
File API: /status
This file contains the current status of libfaketimefs. While fast forwarding, the value is MOVING. Otherwise, the value is IDLE.
