Handbook:Advanced Server Configuration:UUCP Lock Files
HylaFAX implements shared inbound/outbound modem usage using UUCP lock files. In normal operation each modem has a faxgetty process listening for data from the modem. When an inbound call is received the modem emits a RING status message that wakes up the appropriate faxgetty process. faxgetty then checks the UUCP lock file for the port to make sure the port is not busy for outbound use. If the port is busy (i.e. a UUCP lock file is present), then faxgetty will stop listening on the port and wait for the outbound use to terminate. If the port is not busy, then faxgetty will answer the call according to the parameters specified in the configuration file.
For this scheme to work outbound callers must install a UUCP lock file before using a modem. This lock file must be created using the same conventions understood by HylaFAX. In particular the lock file name must be consistent and the file contents must include the process ID of the lock file owner written either as a binary or ascii value according to the system-specific conventions.
HylaFAX supports several schemes found on different systems. The appropriate scheme is normally setup according to the target system at the time that HylaFAX is configured for building. It is possible, however, to override these parameters through the runtime configuration files; consult the hylafax-config(4F) manual page for information about the UUCPLockType configuration parameter. In addition to the lock type there are configuration parameters that control the protection mode of the lock file (UUCPLockMode), the directory in which lock files are created (UUCPLockDir), and a timeout parameter used to purge stale lock files. Again, consult hylafax-config(4F) for a full description of these parameters.