As noted above, the Security() function has the ability to kill all existing clients when setting a logon block. SEC_BLOCK_KILL acts like SEC_BLOCK_NONSUP by blocking logins by any user other than ADMIN, but also kills any clients already logged in.
Only ADMIN can make this call, and only ADMIN can resume logins with mode SEC_BLOCK_OFF. The internal threads that might open files are also suspended:
The COMPATIBILITY NO_BLOCK_KILL FairCom Server configuration keyword removes this capability. When COMPATIBILITY NO_BLOCK_KILL is in the configuration file, a call by ADMIN with mode SEC_BLOCK_KILL fails with NSUP_ERR (454).
The ability to suspend the Server gives remote ADMIN clients an added dimension. As an example, say a remote administrator needs to perform some type of operation in which it might be desirable to shut down the FairCom Server. An ADMIN client program can be authored to stop the Server, however restarting the server in a “non-telnet” type of environment might be impossible. By giving the administrator the ability to block new logins and kill existing clients (suspending the server) and then re-allow logins (like a restart) provides a solution to this problem.