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_exit
__syscall
 
FreeBSD/Linux/UNIX General Commands Manual
Hypertext Man Pages
couriertcpd
 
COURIERTCPD(1)							COURIERTCPD(1)



NAME
       couriertcpd - Courier TCP server daemon

SYNOPSIS
       couriertcpd [ -pid=pidfile ] [ option ... ] list program arg ...


       couriertcpd -pid=pidfile -stop


       couriertcpd -pid=pidfile -restart


DESCRIPTION
       couriertcpd  accepts  incoming  network	connections,  and runs program
       after establishing each	network  connection.  The  program's  standard
       input and output are set to the network connection.

       list  is a comma-separated list of TCP port numbers where incoming con-
       nections are created.  program  is  the	program  to  run.  If  program
       requires  any  arguments, they are specified on the command line, after
       program itself.

       Before running program,	couriertcpd  initializes  several  environment
       variables  that describe the network connection. The environment inher-
       ited by program will be the environment inherited by couriertcpd,  plus
       any  additional environment variables initialized by couriertcpd. It is
       also possible to reject certain network	connections.  Several  options
       are available to specify which network connections will be rejected.

OPTIONS
       -access=filename
	      Specifies  an optional access file. The access file lists the IP
	      addresses from which connections should be accepted or rejected.
	      The access file is also used to initialize environment variables
	      based on the IP address of the connection. filename is a GDBM or
	      DB  database file that's usually created by a script from one or
	      more text files. See "ACCESS FILE" below for more information.

       -accesslocal
	      Lookup the local interface IP and port in the  access  file,  in
	      addition to looking up the remote IP. This gives a mechanism for
	      setting environment variables  depending	on  which  IP  address
	      and/or  port  the  client  connected  to.   In  the access file,
	      "1.2.3.4.25" matches connections to IP address 1.2.3.4 port  25;
	      "1.2.3.4" matches connections to IP address 1.2.3.4 on any port;
	      and "*.25" matches connections to port 25 on any IP address.

       -address=n.n.n.n
	      Accept network connections only to IP address  n.n.n.n.  If  not
	      specified,  couriertcpd  accepts	connections  to any IP address
	      that the system accepts connections on. If the system has multi-
	      ple  network  interfaces with separate IP addresses, this option
	      makes couriertcpd accept connections only  to  one  specific  IP
	      address.	Most  systems  have  multiple  network interfaces: the
	      loopback interface, plus the local network  interface,  so  that
	      -address=127.0.0.1  accepts connections only from the local sys-
	      tem. When multiple port numbers are specified, it is also possi-
	      ble to selectively bind different network addresses to each port
	      number when list specifies more than one port number. See  "Mul-
	      tiple port list" below for more information.

       -block=zone[,var[/n.n.n.n][,msg]]
	      Initialize the environment variable var if both of the following
	      conditions are true: var is not already  initialized;  the  con-
	      necting  IP  address  can  be found in a DNS-based list. See DNS
	      ACCESS LISTS, below.  Multiple -block options can be used.

       -denymsg=text
	      Specifies an optional message to be returned to  the  client  if
	      the -access option rejects them.	The default is to drop the TCP
	      connection without sending back any messages.

       -group=group
	      Set couriertcpd's its group ID. group may be  specified  numeri-
	      cally, or by its name. Only the superuser may use -group.

       -listen=n
	      Length  of  the  queue  which holds pending connections.	n is a
	      number. If not specified, the system default is used.

       -maxperc=n
	      Maximum number of connections accepted from the same  C  network
	      block.  Using  this  option  is  recommended, because connection
	      slots are limited. Without this option, the same C network block
	      can potentially use up all available connection slots.

       -maxperip=n
	      Maximum number of connections accepted from the same IP address.
	      Use both the -maxperc and -maxperip options to fine tune connec-
	      tion  limits.  For example, when couriertcpd is listening on the
	      SMTP port it makes sense to set an upper limit on the number  of
	      connections  from  the  same  C block. Domains that send a large
	      amount of mail often have multiple servers sending outbound mail
	      from  the same C block, so it makes sense to set limits on indi-
	      vidual C blocks. On the other hand, if couriertcpd is  listening
	      on the POP3 port it makes more sense to set limits on individual
	      IP addresses.  If a C block of addresses is assigned to a dialup
	      modem  pool,  it is certainly possible to have many IP addresses
	      within the same C block have connections to the POP3  server  at
	      the same time.

       -maxprocs=n
	      Maximum  number  of  connection  slots, or the maximum number of
	      processes started. This effectively specifies the maximum number
	      of connections accepted at the same time. After the maximum num-
	      ber of connections has been opened,  couriertcpd	waits  for  an
	      existing	connection to close, before accepting any more connec-
	      tions.

       -warn=n
	      Log a LOG_WARNING message to syslog when the  number  of	active
	      processes  exceeds  n.   The  default is 90% of maxprocs. couri-
	      ertcpd logs a LOG_ALERT syslog message when the number of active
	      processes reaches the maximum.

       -nodnslookup
	      Do  not  look  up  the  hostname	associated  with connecting IP
	      address and the local addres, do not initialize  the  TCPREMOTE-
	      HOST or TCPLOCALHOST environment variables (see below).

       -noidentlookup
	      Do not perform an ident lookup, and do not initialize the TCPRE-
	      MOTEINFO environment variable.

       -pid=filename
	      If given, couriertcpd puts itself into the background and  saves
	      its process ID in this file, usually somewhere in /var/run.

	      This  option  must  also	be present when using the -restart and
	      -stop options.

       -restart
	      Send a SIGHUP to an existing couriertcpd process.   Specify  the
	      same  -pid  argument  as	the  one that was used to start couri-
	      ertcpd. The process ID is read  from  the  -pid  file,  and  the
	      couriertcpd receives a SIGHUP signal.

       -stderr=socket
	      Set  program's  standard	error  to the network connection, just
	      like its standard input and output.

       -stderr=logfile
	      Set program's standard error to  the  specified  file,  logfile.
	      The file is created, if necessary, and is opened in append mode.

       -stderrlogger=logprogram
	      Set program's standard error to a pipe, which is read by logpro-
	      gram.   Only  one  instance of logger is started, which receives
	      standard error from every instance of  program.	The  specified
	      logger  is  executed with the output end of the stderr pipe con-
	      nected as standard input.  logprogram is executed with one argu-
	      ment - program's name.

       -stderrloggername=name
	      Use name as the argument to logprogram, instead of the program's
	      name.

       -stop  Stop (kill) an existing couriertcpd process.  Specify  the  same
	      -pid argument as the one that was used to start couriertcpd. The
	      process ID is read from  the  -pid  file,  and  the  couriertcpd
	      process  is  killed.  All  child	processes  of couriertcpd will
	      receive a SIGTERM signal.

       -user=user
	      Set couriertcpd's user ID. Also, the group  ID  is  set  to  the
	      user's  group  ID. Using both -group and -user is not necessary.
	      Only the superuser can specify -user.

MULTIPLE PORT LIST
       The list argument can be a comma-separated list of multiple  port  num-
       bers.  couriertcpd  will create network connections on any listed port.
       Each port number can be optionally  specified  as  "address.port",  for
       example:


       couriertcpd -pid=/var/run/smtp.pid 127.0.0.1.25,999 program

       This  instance  accepts	network  connections to either port 25 or port
       999, however connections on port 25 are created only on the IP  address
       127.0.0.1, the loopback interface.

       Whenever  an  IP  address  is  not  specified,  network connections are
       accepted to any IP address (called "wildcarding"). On IPv6-capable sys-
       tems,  couriertcpd  will attempt to create two incoming network connec-
       tion ports, if an IP address is not specified. After creating the first
       port  as  an IPv6 wildcard port, couriertcpd will then attept to create
       an IPv4 wildcard port, with the same port number. Some BSD-derived sys-
       tems  must use separate IPv6 and IPv4 wildcard ports to create incoming
       network connections.  Most other systems only need an IPv6 port to cre-
       ate  both  IPv6 and IPv4 incoming network connections. couriertcpd qui-
       etly ignores a failure to create an IPv4 wildcard port, as long	as  an
       IPv6 wildcard was succesfully created.

       The  -address  option  can be used to default a specific IP address for
       every listed port number.  For example:


       couriertcpd -pid=/var/run/smtp.pid 127.0.0.1.25,127.0.0.1.999 program

       and


       couriertcpd -pid=/var/run/smtp.pid -address=127.0.0.1 25,999 program

       will create network connections on ports 25 and 999 of the  IP  address
       127.0.0.1.

ACCESS FILE
       The  access  file  lists  IP  addresses that couriertcpd will accept or
       reject connections from. An access file is optional. Without an	access
       file couriertcpd accepts a connection from any IP address.

       Both  IPv4  and	IPv6  addresses  can  be specified, if IPv6 support is
       available. A non-standard syntax is  currently  used  to  specify  IPv6
       addresses.   This is subject to change in the near future. IPv6 support
       is currently considered to be experimental.

       The access file is a binary database file that's usually created  by  a
       script,	such  as makesmtpaccess(8), from one or more plain text files.
       Blank lines in the text file are ignored. Lines that start with	the  #
       character are also ignored.

   REJECTING AND ACCEPTING CONNECTIONS BY IP ADDRESS
       The following line instructs couriertcpd to reject all connections from
       an IP address range:


       netblockdeny

       netblock is an IP address, such as 192.68.0.2.  is the  ASCII  tab
       character. There MUST be exactly one tab character after the IP address
       and the word "deny".

       You can also block connections from an entire network C block:


       192.68.0deny

       This  blocks  connections  from	 IP   addresses   192.68.0.0   through
       192.68.0.255.  Blocking connections from an entire B or A network block
       works the same way.

       Use the word "allow" instead of "deny" to explicitly allow  connections
       from that IP address or netblock. For example:


       192.68.0deny
       192.68.0.10allow

       This  blocks all connections from 192.68.0.0 to 192.68.0.255 except for
       192.68.0.10.  These two lines  can  occur  in  any  order.  couriertcpd
       always uses the line with the most specific IP address.

       If the IP address of the connection is not found in the access file the
       connection is accepted by default. The following line  causes  unlisted
       connections to be rejected:


       *deny

   IPV6 ADDRESSES
	      Note:  IPv6  support  in the access file is experimental, and is
	      subject to change in a future release.  The following syntax  is
	      subject to change at any time.

       The  access  file  can  also specify IPv6 addresses, if IPv6 support is
       available.  The existing IPv4 address format is	used  for  IPv6-mapped
       IPv4  addresses,  and  no  changes  are	required.   For all other IPv6
       addresses use the following format:


       :hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhhaction

       The IPv6 address must begin with :. The	initial  :  character  is  not
       really  a  part	of the IPv6 address, it is only used to designate this
       record as an IPv6 address, allowing an access file to contain a mixture
       of  IPv4  and  IPv6  addresses.	The IPv6 address follows the initial :
       character, and it must be spelled out using zero-padded lowercase hexa-
       decimal digits.	For example:


       :0000:0000:0000:0000:0000:f643:00a2:9354deny

       Netblocks must be specified using even-word boundaries only:


       :0000:0000:0000:e240deny

       This puts the entire ::e240/32 IPv6 CIDR into the access file.

   SETTING ENVIRONMENT VARIABLES
       allow  can  be  optionally  followed  by a list of environment variable
       assignments, separated by commas. The  environment  variables  are  set
       before  executing  program  or  checking  access lists (see below). For
       example:


       192.68.0allow,RELAYCLIENT
       192.68.0.10allow,RELAYCLIENT,SIZELIMIT=1000000

       This sets RELAYCLIENT environment variable  for	connections  from  the
       192.68.0 block. In addition to that, the SIZELIMIT environment variable
       is set  to  1000000  if	the  connection  comes	from  the  IP  address
       192.68.0.10.

       Note  that  RELAYCLIENT must be explicitly specified for the IP address
       192.68.0.10. The first line is NOT used for connections	from  this  IP
       address.  couriertcpd  only  reads  one entry from the access file, the
       entry for the most specific IP address.

   DNS ACCESS LISTS
       An alternative to listing banned IP addresses is  to  use  an  external
       DNS-based IP access list.

       There  is  no  provision  to support IPv6-based lists, because none yet
       exist. IPv6-based access list support will be added in the future.

       couriertcpd does not  automatically  reject  connections  from  any  IP
       address	listed	on  a  DNS-based list. If the connecting IP address is
       listed couriertcpd simply sets an environment variable. It's up to  the
       program,  run  by  couriertcpd,	to  read  the environment variable and
       choose what to do if the environment variable is set.

       Please note that if the environment variable  is  already  set,	couri-
       ertcpd  will  NOT  search the access list. This can be used to override
       the access list where program only recognizes the access  list  if  the
       environment  variable is not empty. By setting the environment variable
       to an empty string in the access file (see  above),  you  can  override
       access lists for selected IP addresses.

       The  -block  option  queries a DNS list for each connecting IP address.
       The only required argument to -block is the DNS zone that  is  used  to
       publish	thelist.  The name of the zone can optionally be followed by a
       comma and the name of the environment variable to set if the  DNS  list
       includes  the  IP  address.   couriertcpd sets the environment variable
       BLOCK if you do not specify the name yourself.

       The name of the environment variable can be optionally  followed  by  a
       slash  and  an  IP  address.  Normally couriertcpd sets the environment
       variable if the access list includes any A record entry for the	speci-
       fied  IP address. Some access lists may offer additional information by
       returning one of several possible A records. If the name of  the  envi-
       ronment variable is followed by a slash and an IP address, the environ-
       ment variable will be initialized only if the access list includes an A
       record containing the indicated IP address.

       The  contents  of  the environment variable will be the contents of any
       TXT record for the listed IP address. var[/n.n.n.n] can	be  optionally
       followed  by  a comma and a text message, which will be used instead of
       the TXT record. The text message may include a single @ character some-
       where in it, which will be replaced by the listed IP address.

   MULTIPLE DNS LISTS
       Multiple  -block options can be used. The connecting IP address will be
       looked up in multiple access lists. This is implemented as follows.

       couriertcpd processes all -block options one at a time.	If  the  indi-
       cated  environment  variable  is already set, couriertcpd skips the DNS
       list lookup (this is also true if only one -block option is specified).
       Therefore,  if  multiple  -block options are used, and an IP address is
       found in the first access list, the remaininglists that	use  the  same
       environment  variable  will  not be checked. But other lists that use a
       different environment variable WILL be checked.

       The same zone can be specified more than once, with different  environ-
       ment variables and different IP addresses. For example:


       couriertcpd -block=block.example.org,BLOCK1/127.0.0.2 \
		   -block=block.example.org,BLOCK2/127.0.0.3

       If  the	specified  access  list  contains  an  A record for the listed
       address, and the A record contains the  IP  address  127.0.0.2,	couri-
       ertcpd  initializes  the  BLOCK1  environment variable. If the A record
       contains the IP address 127.0.0.3, couriertcpd initializes  BLOCK2.  If
       both records are present, both variables are initialized.

       couriertcpd  uses  the  following  logic  to determine what kind of DNS
       query to issue:

       If neither the IP address, nor msg is specified, couriertcpd will query
       for existence of TXT records, for the IP address.

       If  only  msg  is  specified,  couriertcpd  looks up the existence of A
       records, for the IP address.

       If /n.n.n.n is used, and msg is not specified for at least  one	-block
       option  for this same zone, couriertcpd will query for existence of ANY
       records, which should return both TXT and all the A records for this IP
       address.

       If  /n.n.n.n  is used, and msg is specified for every -block option for
       this same zone, couriertcpd will query for existence of A records only.

ENVIRONMENT VARIABLES
       couriertcpd  also initializes the following environment variables prior
       to running program:

       TCPLOCALHOST
	      The name of the host on the local end of the network connection,
	      looked up in DNS. TCPLOCALHOST will not be set if the IP address
	      of the network connection's local end cannot be found in DNS, or
	      if  -nodnslookup	option is specified.  TCPLOCALHOST will be set
	      to the string softdnserr if the DNS lookup fails with  a	tempo-
	      rary  error  (so	you  cannot tell if the IP address has a valid
	      host name associated with it), or if the reverse and forward DNS
	      lookups  do  not	match.	 TCPLOCALHOST  will  not be set if the
	      reverse DNS lookup fails completely.

       TCPLOCALIP
	      The IP address of the local end of the network connection.

       TCPLOCALPORT
	      Rhe number of the port of the local end of the  network  connec-
	      tion.

       TCPREMOTEHOST
	      The  hostname of the connecting host. Like TCPLOCALHOST, but for
	      the connecting IP address.

       TCPREMOTEIP
	      Connecting IP address.

       TCPREMOTEINFO
	      Identification string received from  the	IDENT  server  on  the
	      remote  IP  address.  Not  set  if  the IDENT server returned an
	      error, or if the -noidentlookup option was specified.

       TCPREMOTEPORT
	      TCP port of the remote end of the network connection.

SEE ALSO
       courier(8).



Double Precision, Inc.		 02 July 2005			COURIERTCPD(1)
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