= Simultaneous-Use checking

There are a whole lot of pieces which have to work together for
`Simultaneous-Use` to work.  In this guide, we assume that user
sessions are stored in SQL.

For `Simultaneous-Use` to work. the server needs to know who is
online, which means that accounting must be configured and working.
Start off by checking the basics, independent of `Simultaneous-Use`.

As always, start off with reading the debug output, and use that
information to answer a few questions.

== Did the user get Access-Accept?

*No* - Fix that.  Make sure that the user can be authenticated!

*Yes* - FreeRADIUS told the NAS to allow the user online.  This usually
 works, but perhaps the NAS disagreed, and still dropped the user.  It happens.

The only way you know that a user is actually online is to check the
accounting data.  So we will do that next.

== Did the server then get an Accounting-Request for that user?

*No* - The NAS isn't sending accounting packets, Simultaneous-Use will never work.

Go fix the NAS so that it sends accounting packets.

*Yes* - The NAS is telling FreeRADIUS that it allowed the user online,
 and the user has an active session.  We now have to see where that data is stored.

== Did the accounting data go into the radacct table?

As always, Read the debug output.

*No* - There is nothing in the debug output about radacct?  Configure the server to write accounting data to SQL 

ou can use `radclient` to send fake accounting packets for testing.
Use a real accounting packet as a template for input to `radclient`,
but change the `User-Name` so that the tests don't affect real users.


*Yes* - You see successful `INSERT` or `UPDATE` lines in `radacct`.   That's good!

== One last check

Double-check the radacct database using an SQL client.  Just to be sure that the data is really there.

== It is now set up correctly to track user sessions

If all that works, then the server is set up correctly to authenticate
users, and to store their data in SQL.  This is the foundation for
`Simultaneous-Use`.

== Set Simultaneous-Use

Then, configure the server to set `Simultaneous-Use=1`.  That tells the server to enforce `Simultaneous-Use`.  That configuration can go into the `files` module, `sql`, or whereever else you want.

You will also need to configure the `default` virtual server to check session data in SQL.  Look for `Simultaneous-Use` in `sites-available/default`.  Uncomment the line containing `sql`

== Double check that a user can still log in!

Go through all of the above steps _again_, checking that the user can
log in, and that the server is receiving accounting packets.

This time, also look for the debug output to contain:

```
# Executing section session from file ...
session {
```

That shows it is checking the `session` database.  If all goes well, the next few lines after that should show that it is checking `sql`.

If the above text doesn't appear, then the server isn't getting told to set `Simultaneous-Use = 1`.  You will have to fix that before going to the next step.

If the user has not logged in yet, you will see an `Access-Accept`.  Otherwise, if the user already has an active session, the server should say that the user is being rejected due to multiple logins.