Ubuntu Manpage: HylaFAX - introduction to HylaFAX server operation and file formats

Provided by: hylafax-server_6.0.7-7_amd64

NAME

       HylaFAX - introduction to HylaFAX server operation and file formats

DESCRIPTION

       HylaFAX  is  a  system  for  sending  and  receiving  facsimile.   It  supports  queued  transmission and
       asynchronous reception of facsimile.  Ancillary programs are invoked by the system  for  flexibility  and
       configurability.   HylaFAX  includes  client and server programs to support remote submission of jobs for
       transmission, remote removal of queued jobs, and  to  remotely  query  the  status  of  jobs  queued  for
       transmission.   This document describes the organization of the filesystem spooling area in which HylaFAX
       server and server-related processes operate, and introduces the various files that reside in the spooling
       area.

OVERVIEW

The spooling area is typically located under the directory /var/spool/hylafax. Ancillary command scripts
used by the server programs faxq(8), faxsend(8), pagesend(8), and faxgetty(8) are located in the bin
subdirectory. Configuration, access control, and accounting information are maintained in the etc and
config subdirectories. Outgoing jobs are described by files in the sendq subdirectory, while received
facsimile are deposited in the recvq subdirectory. The docq and temp subdirectories are also used in the
preparation of outbound jobs; the latter holds files that may be freely purged while the former holds
client files that may reside on the server independent of an associated job. The doneq subdirectory
holds jobs that have completed but have not yet been purged or archived. On systems with job archival
support, completed jobs that have been archived are placed in the archive subdirectory. The pollq
subdirectory holds documents that are available for polled retrieval from the server. The info
subdirectory contains files that describe the capabilities of facsimile machines that HylaFAX has
called-this information is used in preparing documents for transmission. The status subdirectory
contains files that server processes write their current status to. The log subdirectory contains
logging information about send and receive sessions. The client subdirectory contains FIFO special files
used for communication with faxq.

HylaFAX supports multiple modems on a host. A single process acts as central queueing agent for all
outbound jobs. Typically each modem also has a server process that monitors the modem status and handles
inbound phone calls. Per-modem server processes communicate with the central queueing agent using FIFO
special files; see mknod(2) or mkfifo(2). Any other synchronization between server processes is done
using file-level locking. The faxq process listens for commands written to the file named FIFO, while
each faxgetty process listens for commands written to a per-device file named FIFO.devid (where devid is
an identifier derived from the name of the device special file to which the modem is connected; e.g.
ttym2 for /dev/ttym2, term_10 for /dev/term/10.) To send a command to the queueing agent, one writes to
FIFO. This is useful, for example, for submitting a job for transmission. To send a command to a
specific faxgetty process, the FIFO.devid file is used.

Client applications interact with a HylaFAX server machine using a communications protocol implemented by
the hfaxd(8) program. The hfaxd program is typically started at system startup; it listens for client
requests for service and creates a process for each client. hfaxd supports the submission of outbound
jobs, querying the status of the send and receive queues, and altering parameters of previously submitted
jobs. The hfaxd processes communicate with the faxq process through FIFO special files. Commands sent
to faxq are sent to FIFO and responses are received on FIFO files that each hfaxd creates in the client
subdirectory.

SETUP

       Each  HylaFAX  server  machine  must  run  the  faxsetup(8)  command  prior to starting up HylaFAX server
       processes.  faxsetup verifies that the HylaFAX  software  has  been  installed  correctly  and  that  any
       parameters that were specified at the time the software was built are appropriate for the system.

SENDING

Each outgoing facsimile job has a job description file that is located in the sendq subdirectory. This
file contains all the information necessary to manage the transmission; c.f. sendq(5). The actual
documents that are to be sent are usually located in the docq subdirectory (though it is also possible to
reference documents from the recvq directory). HylaFAX accepts POSTSCRIPT, PDF, PCL, and TIFF documents
for transmission (support for PCL documents requires an external application). Documents are
automatically converted to TIFF/F documents prior to transmission according to the capabilities of the
remote facsimile machine: maximum page width and length, ability to handle 2D-encoded data, and ability
to handle high resolution (7 line/mm) data. This remote machine capability information is stored in
files in the info subdirectory. If a machine has not been called before, HylaFAX assumes the remote
machine has the requested capabilities. If a capabilities mismatch is detected while sending a facsimile
HylaFAX will disconnect and re-convert the submitted documents according to the newly discovered
capabilities. Users may also restrict the session parameters used to format documents on a per-job
basis.

The actual transmission is handled by a faxsend(8) process that is initiated by the scheduler. This
program may be substituted for by specifying the FaxSendCmd configuration parameter in the faxq
configuration file.

While a job is being processed by a server process, its job description file is locked for exclusive use
with flock(2). The hfaxd(8) program uses this information to tell if a job is actively being processed.

If the SessionTracing parameter in a server's configuration file is non-zero, then tracing information
for an outgoing job will be logged in a file in the log subdirectory. Each destination machine has a
separate log file named by its canonical phone number.

The remote job submission facility includes host and user access control. The file etc/hosts.hfaxd must
be present and list those hosts and users that are permitted to queue jobs for transmission or do other
operations that alter the status of a job. Note that it is necessary to include the ``local host''
definition (usually 127.0.0.1) if local submission is to be permitted. For more information consult
hosts.hfaxd(5).

If an error is encountered during transmission and a subsequent retransmission would not include the
original cover page, then HylaFAX can be configured to generate a continuation cover page that is
prepended to the retransmitted pages. Such cover pages are usually generated by the bin/mkcover command;
though the exact command to use can be specified in the configuration file read by faxq.

HylaFAX can be configured to generate a line of status information across the top of each page of an
outbound facsimile. This information, termed a ``tagline'', typically includes the sender's identity
(i.e. phone number), the time and date of the transmission, and the page number. The exact format of the
tagline is configurable and applications can override the default configuration parameters on a per-job
basis. Note that in the United States the law requires that a tagline that identifies the sender's phone
number must appear on each transmitted page of facsimile.

Facsimile transmitted to receivers that accept variable-length pages may have short pages ``chopped''.
That is, if a page has a significant amount of trailing whitespace and the receiver accepts variable-
length pages then only the top part of the page will be transmitted. faxq can be configured so that only
the last page of each document is potentially chopped, all pages are potentially chopped, or chopping is
disabled. The minimum whitespace threshold is also configurable. Applications can override the default
configuration parameters on a per-job basis.

RECEIVING

faxgetty server processes can be configured to answer incoming phone calls and automatically receive
facsimile. Received documents are placed in the recvq subdirectory as TIFF Class F files. The faxgetty
processes can be configured to make these files publicly accessible, or they can be made private in which
case an administrator must manage their delivery and/or the assignment of ownership to particular users.
When a facsimile is received, the faxgetty process usually invokes the bin/faxrcvd command; though the
exact command to invoke can be specified in the per-modem configuration file. The default notify command
is a shell script that sends a mail message to a well known user, the FaxMaster, but one might also, for
example, automatically spool the document for printing.

HylaFAX supports a simple form of access control for receiving facsimile. Each faxgetty process may be
configured to check the Transmission Subscriber Identifiers (TSI) of the remote fax machine against an
access control list, typically etc/tsi. Only if the TSI is matched by a regular expression pattern in
the file, is the remote machine permitted to transmit a document. This mechanism can be used, for
example, to guard against junk fax.

HylaFAX can be configured to do copy quality checking on received facsimile data. When this feature is
enabled faxgetty decodes and analyzes the received facsimile data as it is received. If data is received
with too many errors, according to the setting of the MaxConsecutiveBadLines and PercentGoodLines
configuration parameters, then the sender will be told to retransmit the page. When copy quality
checking is enabled it is also possible to force received facsimile data to be saved with a different
compression scheme than was used for transmission. This function is known as transcoding and can
significantly reduce the space needed to store received facsimile.

POLLING

       HylaFAX  supports  the polled retrieval of facsimile documents.  Documents that are received because of a
       poll request are stored in the recvq subdirectory and also delivered directly to the requester using  the
       bin/pollrcvd  command;  though  the  exact  command  to  invoke  can  be  specified  with the PollRcvdCmd
       configuration parameter.  The pollrcvd script typically encodes the binary facsimile data and returns  it
       to the user via electronic mail.

INBOUND CALL HANDLING

       In environments where Caller-ID information is available, HylaFAX also supports a call screening facility
       similar to the TSI access control facility.  faxgetty can be configured to check the phone number of each
       caller  against  an  access  control list, typically etc/cid.  Only if the number is matched by a regular
       expression pattern in the file is the call answered.  All Caller ID information is  logged,  irregardless
       of whether or not it is used to screen incoming calls.

       faxgetty  is  also  capable  of using distinctive ring information to identify whether an inbound call is
       voice, data, or fax.  Consult the RingData, RingFax, and RingVoice parameters in hylafax-config(5) for  a
       description of this facility.

DATA CALLS

       Most fax modems also support non-facsimile communication.  HylaFAX uses the locking mechanism employed by
       uucp(1C),  cu(1C), slip(8), and ppp(8).  Any faxgetty processes will transparently ``get out of the way''
       when an application wants to use a modem for an outgoing call.  In addition, HylaFAX can be configured to
       deduce whether an incoming call is for facsimile or data use.  If a call from a data modem is  recognized
       and  the  GettyArgs  parameter  is specified in the configuration file, faxgetty will invoke the getty(8)
       program so that caller may login to the system.  Similar functionality is also available for  invoking  a
       ``voice getty'' process, though auto-detection of inbound voice calls is less extensive.

STATUS

HylaFAX maintains status information in several forms. General status information for each server
process is maintained in the status subdirectory and returned to users by the faxstat(1) program. The
syslog(3) facility is used by all server processed for logging status and error diagnostics. The server
processes may also be configured to log various kinds of debugging and tracing information; c.f. the
ServerTracing parameter description in hylafax-config(5).

Any problems encountered when transmitting a facsimile are described in messages returned to the user by
electronic mail. A user may also request notification by mail when a job is requeued; for example,
because a call failed. Notification by electronic mail is implemented by the bin/notify command script;
though the name of the script may be overridden with the NotifyCmd configuration parameter.

The faxstat utility provides (remote) status of jobs queued for transmission, jobs received, and the
general status of server processes.

The file etc/xferfaxlog contains status information about all facsimile sent and received on a machine.
This file is in a simple ASCII format that is easy to manipulate with programs such as awk(1), to
generate accounting information. See xferfaxlog(5) for information about the format. See
xferfaxstats(8) and recvstats(8) for example scripts that print summarized accounting information.

Finally, the hfaxd process supports a event monitoring facility that can be access via the faxwatch(8)
program. This facility permits clients to register interest in various events and receive ``realtime
notification'' when such events occur on the server. Using this facility it is/should-be simple to
construct applications that do things like monitor modem status and use.

MODEM STATE CHANGES

       In  normal operation each modem is managed by a HylaFAX server process such as faxgetty.  These processes
       communicate with the central scheduler process to notify it when a modem  is  ready  for  use,  busy  for
       outbound  use, or possibly in an unusable state (either purposely marked unavailable or potentially found
       to be wedged).  Modem usage can be explicitly controlled with the faxstate(8) program.  The  faxconfig(8)
       program  can  also be used to dynamically make changes to configuration parameters that may cause a modem
       to be treated differently (e.g.  setting RingsBeforeAnswer to zero will  cause  faxgetty  to  not  answer
       incoming calls).

       When  HylaFAX is used in a send-only configuration there are no faxgetty processes and communication must
       be done directly with the faxq process.  The faxstate program can still be used to manipulate  modem  use
       for outbound jobs but the faxconfig program is not frequently needed.

JOB SCHEDULING

       Outbound jobs are scheduled by a single process.  Jobs have a ``scheduling priority'' that is assigned at
       the  time  the  job is submitted.  This priority can be changed at any time the job is not actively being
       processed using the faxalter(8) program.  A job's scheduling priority may also  be  altered  by  faxq  in
       response to certain scheduling events (e.g. after a failed attempt to send).

       Modems  are  assigned  to  outbound  jobs  if  they are deemed ready for use.  Modem readiness is usually
       communicated to faxq by per-modem faxgetty processes.  In a send-only environment  however  this  is  not
       possible; instead modems configured for use with faxmodem are considered always ready for use unless they
       are  presently  assigned  to an outbound job or their state is explicitly changed through the faxstate(8)
       program (faxstate can also be used in a send-recv environment).

       Each modem has a ``modem priority'' in the range [0..255].  Modems  with  a  lower  priority  number  are
       assigned  to  outbound  jobs first.  Modem priority is statically configured through configuration files,
       the faxmodem program, and the faxconfig program.  If multiple modems share the same priority value,  then
       faxq(8) will allocate jobs to them in a round-robin fashion.

JOB MANAGEMENT

Outbound jobs are considered to be in one of several states that reflect their treatment by the central
scheduling process. Jobs are initially created in a suspended state, and may be returned to this state
at any time that they are not actively being processed (e.g. a faxsend program is running to process the
job). Jobs that are suspended are not processed by the scheduler; and their internal state may be safely
altered by the owner or a system administrator. Suspending and then releasing a job has the effect of
requeueing the job, meaning that it will end up at the bottom of queue for that job's priority. Jobs
that are ready for processing by the scheduler are ``submitted'' and their state is changed to be either
pending (delayed waiting for a future time to send), sleeping (delayed waiting for a scheduled timeout),
blocked (delayed by concurrent activity to the same destination), or ready (ready for transmission,
waiting only for available resources). When a job is actively processed by the faxsend program its state
is marked active. Jobs that have completed, either successfully or unsuccessfully are placed in a done
state and their job description files are moved to the doneq subdirectory. Clients may still access the
state of jobs that are done; until a ``cleaner process'' either purges them from the system or archives
their state. This delayed removal of a completed job's state permits clients to resubmit failed jobs
using previously transmitted documents and other job state information. The exact mechanics of how and
when done jobs are processed is system-dependent; for example, how long a job is left in the done queue
before being purged, and whether job archival support is present.

CONFIGURATION

       HylaFAX  server  programs  read  configuration information from a configuration file.  Multiple files are
       used, one for the faxq program and one for each modem.  Long-running server  programs  all  automatically
       re-read  their configuration file if it is modified.  Typically this re-reading is done frequently enough
       that administrators do not need to be aware of exactly when it takes place.   However  in  some  esoteric
       cases  the  file may not be read when expected (the one important case is that the faxgetty process reads
       its configuration file only when answering a call or when resetting a modem; this means that it will  not
       recognize changes when the modem is idle).

       In  addition  to  the  static  configuration files, HylaFAX server programs accept commands on their FIFO
       special files to alter configuration parameters in the running executable (the faxconfig(8)  program  can
       be  used  to  dynamically change configuration parameters).  Values set in this way however are lost when
       the process exits or if the configuration file is re-read.

NOTES

       Automatic routing of incoming facsimile is desirable.

FILES

       FIFO                  fifo for job submission
       FIFO.<devid>          fifo for communicating with a faxgetty process
       /usr/sbin/faxinfo     command that prints information about received facsimile
       /usr/sbin/faxquit     command to force server to quit
       bin/faxrcvd           faxd command for handling newly received facsimile
       bin/mkcover           faxd command for generating continuation cover pages
       bin/notify            faxd command for doing user notification
       bin/pollrcvd          faxd command for delivering facsimile received by poll
       bin/ps2fax            faxd command for converting POSTSCRIPT to TIFF
       docq/doc*             documents available for transmission
       etc/setup.cache       server setup file created by faxsetup
       etc/cid               caller id access control list
       etc/config.<devid>    configuration data for <devid>
       etc/hosts.hfaxd       hosts that may submit jobs for transmission
       etc/tsi               fax machine receive access control list
       etc/xferfaxlog        log of facsimile sent and received
       info/*                data base of remote fax machine capabilities
       client/*              FIFO special files created by client processes
       config/*              prototype configuration files used by faxaddmodem
       log/*                 session logging records
       recvq/fax*            received facsimile
       sendq/q*              descriptions of jobs queued for transmission
       doneq/q*              descriptions of jobs that are done
       status/*              server status information
       tmp/*                 temporary files created when submitting a job
       archive/*             database of archived jobs