How to use the command faketime (with examples)

The faketime command is used to fake the system time for a specific command. It allows users to manipulate the time that certain commands or programs perceive, without actually affecting the system time.

Use case 1: Fake the time to this evening, before printing the result of date

Code:

faketime 'today 23:30' date

Motivation: This use case is helpful when you want to test how a command or program behaves at a specific time in the future without actually waiting for that time to come. By faking the system time, you can simulate future scenarios and observe the results.

Explanation:

• faketime: The command used to manipulate the system time for a given command.
• 'today 23:30': Specifies the desired fake time. In this case, it sets the time to 23:30 (11:30 PM) of the current day.
• date: The command that will be executed using the fake time set by faketime.

Example output: If the current real system time is 10:00 AM, running the above command will print the fake time as 23:30 (11:30 PM), even though the real system time remains unchanged.

Use case 2: Open a new bash shell, which uses yesterday as the current date

Code:

faketime 'yesterday' bash

Motivation: This use case is useful when you need to work within a specific date range for testing or debugging purposes. By faking the system time to the previous day, you can ensure that any commands or programs executed within the new shell will perceive the current date as the previous day.

Explanation:

• faketime: The command used to manipulate the system time for a given command.
• 'yesterday': Specifies the desired fake time. In this case, it sets the date to the previous day.
• bash: The command that will be executed using a new shell with the fake time set by faketime.

Example output: When running this command, a new bash shell will be opened. If today is July 20th, running the date command within the new shell will return the date as July 19th, simulating an environment that operates in the past.

Use case 3: Simulate how a program would act next Friday night

Code:

faketime 'next Friday 1 am' path/to/program

Motivation: This use case is helpful when you want to anticipate the behavior of a program at a specific time in the future. By faking the system time to a future date and time, you can observe how the program responds to different scenarios, such as running on a specific day or time of day.

Explanation:

• faketime: The command used to manipulate the system time for a given command.
• 'next Friday 1 am': Specifies the desired fake time. In this case, it sets the time to 1 am of the next upcoming Friday.
• path/to/program: The command or program that will be executed using the fake time set by faketime.

Example output: Running the above command on a Monday will simulate the program as if it were running on the following Friday at 1 am. This allows you to observe how the program behaves in a future scenario without having to wait until that specific time.

Conclusion:

The faketime command provides a convenient way to manipulate the system time for specific commands or programs. This can be useful for testing, debugging, or simulating future scenarios. By understanding how to use faketime and its various options, you can have more control over the perceived system time and observe the behavior of commands or programs in different time contexts.