The update daemon flushes the filesystem buffers at a regular interval. It has two modes of operation. By default it will wake up every 5 seconds and flush some dirty buffers. Newer kernels do not need a user space update daemon. This is automatically detected by update which will simply exit. The traditional behavior of waking up every 30 seconds to call sync(2) can be forced with an option if it is deemed necessary.
The following options are accepted by update:
Use the traditional behavior of calling sync(2).
-s, --sync-interval secs
If using sync, wake up and call it every secs seconds. The default is every 30 seconds.
-f, --flush-interval secs
Unless using sync, wake up and flush some buffers every secs seconds. The default is every 5 seconds.
Print a usage message on standard output and exit successfully.
Print version information on standard output then exit successfully.