Persistent flag in memory

Good day,

May I ask you, gurus, whether it is possible to set a flag in PHP that
persists for the duration of the server being switched on?

If the server would be power cycled, the flag would be off. Similarly if
the web server would be restarted the flag would be off also.

I do realize that such a thing would be possible to be done in MySQL by
using a table with flags in memory: CREATE TABLE IF NOT EXISTS timer
(flag int) ENGINE = MEMORY;

But is this also possible in PHP?

Thanks for any help,

Teus Benschop