Running a Unix command every few seconds is not something Vixie cron can deal with natively because its smallest level of granularity is the minute. It can easily run a script every minute. But to run a cron job every second, or every 5 seconds, or even every 30 seconds, takes a few more shell commands.
As mentioned, a command can be run every minute with the crontab time signature of
* * * * * (5 stars) followed by the command.
Had we wanted to run the command every 5 minutes, we can do that with
/5 on the minute field:
*/5 * * * *....