i forget my password os X server

There is no way to recover a lost password, and I'm going to assume you have no other adminstrative user that can reset the password.

Given you're using OS X Server, I'm also going to assume that this is the Open Directory domain administrator password that's been lost.

Here's the sequence for resetting the OS X Server domain administrator password, using Workgroup Manager tool (HT1194).

If you're not using OS X Server or if it's not the domain administrator password, the details of the reset sequence vary by the underlying OS X client version. Here's that password reset sequence. (HT1274)

We are not Apple. We are just other users like yourself. Contact Apple at the email addresses or phone numbers given.