faketime

Fake time to this evening

$ faketime '[today 23:30]' [date]

$ faketime '[yesterday]' [bash]

$ faketime '[next Friday 1 am]' [path/to/program]

faketime [options] timestamp command

faketime runs a command with a fake system time by intercepting time-related system calls. Useful for testing time-dependent software, debugging, and simulating future or past conditions.
Uses LD_PRELOAD to intercept calls without modifying the actual system time.

faketime runs a command with a fake system time by intercepting time-related system calls. It uses LDPRELOAD to wrap system calls like time(), gettimeofday(), and clockgettime(), returning user-specified times instead of actual system time.
This is useful for testing time-dependent software behavior, debugging date-related bugs, simulating future or past conditions, and testing expiration or scheduling logic. The tool accepts both absolute timestamps and relative offsets using natural language.
The freeze option (-f) prevents time from advancing, useful for testing code that expects a specific moment rather than progressing time.

timestamp

Time specification (natural language or specific date)

Command to run with faked time

Freeze time (don't advance)

Uses LD_PRELOAD so may not work with statically linked binaries or setuid programs. Time format is flexible and accepts natural language descriptions.

date(1), timedatectl(1)