cdcc(8) Distributed Checksum Clearinghouse cdcc(8)NAMEcdcc — Control Distributed Checksum Clearinghouse
SYNOPSIScdcc [-VBdq] [-h homedir] [-c ids] [op1 op2 ... [-]]
DESCRIPTION
Cdcc is used to clear, control, and query the control file used by Dis‐
tributed Checksum Clearinghouse clients such as dccm(8). The host names,
UDP port numbers, IDs, and passwords local clients use to talk to servers
as well as IP addresses, round trip times, and other information are con‐
tained in the map file. While cdcc is set-UID, it uses the real UID only
when accessing the map file. It refuses to display sensitive information
such as passwords unless the real UID is the same as the effective UID.
Note that cdcc needs to be set to a UID that can read and write the map
file, but that UID need not be 0.
Cdcc is also used to send commands to DCC servers to tell them to stop,
reload their lists of DCC IDs, turn on tracing, and so forth.
Many commands sent to DCC servers require a numeric DCC ID and a password
recognized by the server. A DCC password is a 1-32 character string that
does not contain blank, tab, newline or carriage return characters. The
ID is specified with the id operation. If cdcc is run with a real UID
that can read the ids file and a password is not specified (see the
password operation), then the current password for the specified ID in
the ids file will be used. If no ids file is available and a password
and DCC ID are not specified, cdcc uses the anonymous DCC client-ID. DCC
servers do not expect a password from clients using the anonymous client-
ID, but they also won't honor control requests.
Operations that modify the map file can only be performed when the real
UID is sufficient to modify the file directly. Trying to perform an
operation that requires a password without specifying a server-ID or
without using a UID that can access the ids file produces an error mes‐
sage complaining about a "privileged operation."
Commands and operations are read from the command line or from stdin. A
series of op1 op2 ... operations followed a - (a dash) causes operations
to be read from stdin after the command line operations are processed.
Semi-colons or newlines separate commands in UNIX command-line "words,"
as well as when commands are read from stdin. Since each command line
operation must be a shell "word," quotes are often required as in
% cdcc "load map.txt"
or
% cdcc "host localhost;info" stats
OPTIONS
The following options are available:
-V displays the version of the DCC controller. Two or more -V options
show the options with which it was built.
-B sends error messages from the DCC server to both stderr and stdout
instead of only stderr.
-d enables debugging output from the DCC client software. Additional
-d options increase the number of messages. See the debug command.
-q quiets initial complaints about the map file and some messages about
successful commands. See the quiet command.
-h homedir
overrides the default DCC home directory, /var/dcc. See the homedir
operation.
-c ids
specifies the file containing DCC IDs and passwords known by local
DCC servers. An ids file that can be read by others cannot be used.
The format of the ids file is described in dccd(8).
op1 op2 ...
are operations or commands such as "id 100; stop". Commands or
operations specified on the command line are performed before the
first interactive request. The last command can be - to specify
that additional commands should be read from stdin.
OPERATIONS
Local operations include the following:
help [command]
lists information about one or all available commands and opera‐
tions.
exit stops cdcc
grey [on | off]
switches between DCC and greylist servers.
homedir [path]
displays or specifies the DCC home directory, /var/dcc.
file [map]
displays or specifies the name or path of the map file. The string
"-" specifies the default file /var/dcc/map.
new map [map]
creates a new, empty file for DCC server host names, port numbers,
passwords, and so forth. There must not already be a file of the
same name. The default is map in the DCC home directory.
delete host[,port]
deletes the entry in the map file for host and UDP port. If
greylist mode has been set with the grey on command, the entry for
the grelist server at host is deleted.
add host[,port] [RTT+adj|RTT-adj] [Greylist] [client-ID [password]]
adds an entry to the map file. The port can be "-" to specify the
default DCC server port number.
An adjustment to the round trip time is between -2000 and +2000 and
follows the string RTT. The adjustment is added to the average
measured round trip time when the DCC client software picks the
"nearest" DCC server, or the server with the smallest RTT. If an
IP address is mentioned more than once in the list of servers, for
example because it is among the addresses for more than one server
name, conflicts among RTT adjustments are resolved by picking the
adjustment with the largest absolute value.
Greylist marks an entry for a greylist servers. Greylist is
assumed if greylist mode has been set with the grey on command, See
dccd(8).
If both the client-ID and the password are absent, the anonymous
client-ID, 1, is used. The string anon is equivalent to the anony‐
mous client-ID. A null password string is assumed if the password
is missing and the client-ID is 1 or also missing.
load info-file
loads the current parameter file with the host names, port numbers,
IDs, and passwords in info-file. Standard input is understood if
info-file is "-".
A suitable file can be created with the info operation. It con‐
sists of ignored blank or comment lines starting with '#' and other
lines in the same format as the arguments to the add operation.
Note that output of the info command will lack passwords unless it
is run by a privileged user.
host [hostname]
specifies the host name of the DCC server to which commands should
be sent. If hostname is "-", the current default DCC server is
chosen.
port [port]
specifies the UDP port number of the DCC server to which commands
should be sent. The default is 6277 or 6276 depending on the set‐
ting of the greylist mode controlled with the grey command.
password secret
specifies the password with which to sign commands sent to the DCC
server specified with the server and port operations.
id [ID]
specifies or displays the numeric DCC ID for commands sent to the
DCC server specified with the server and port operations. If no
password is specified with the password command, the password is
sought in the local ids.
info [-N]
displays information about the connections to DCC servers. It
starts with the current date and name of the current map file or
says that cdcc is using the implicit file created with the server
and port operations. It then says when host names will next be
resolved into IP addresses, the smallest round trip time to the IP
addresses of known DCC servers. The host name, UDP port number (or
dash if it is the default), DCC client-ID, and password (if cdcc is
used by a privileged user) are shown in one line per configured DCC
server.
The currently preferred IP address is indicated by an asterisk.
The "brand" of the server, its DCC ID, and its IP address are dis‐
played in one line per IP address. The performance of the server
at each IP address in the most recent 32 operations is displayed in
a second line. The second line ends with the measured delay
imposed by the server on requests with this client's ID.
-N displays the reverse DNS name of each server.
RTT [-N]
measures the round trip time to the DCC servers. It does this by
discarding accumulated information and forcing a probe of all
listed server IP addresses.
Beware that when run with sufficient privilege, the RTT operation
is like the info and load operations and displays cleartext pass‐
words.
-N displays the reverse DNS name of each server.
debug Op Ar on | off | TTL=x
increases or decreases debugging information from the DCC client
software or sets the IP TTL on queries to the server. See -d.
Some operating systems do not include the functions required to
change the IP TTL. Others include the required functions but have
no apparent effect.
quiet [on | off]
makes commands more quiet or more verbose.
IPv6 [on | off | only]
clients to try to use IPv6 and IPv4, IPv4 only, or IPv6 only.
SOCKS [on | off]
tell DCC to use the SOCKS5 protocol if they have been built with a
SOCKS library. The socks library linked with the DCC client must
be configured appropriately, often including knowing which DCC
servers must be connected via the SOCKS proxy and which can be
reached directly. DCC clients use SOCKS functions such as
Rsendto() with all or no servers depending on the setting of this
switch.
src [- |] IPaddress[,IPv6address]
displays or configures the source address of DCC client requests.
- removes the explicit configuration of the source, while IPaddress
or IPaddress,IPv6address sets it. This makes sense only on multi-
homed hosts. It can be useful for passing firewalls.
DCC SERVER COMMANDS
Commands that can be sent to a DCC server include the following. Most of
the commands must be used with the server's ID specified with the id com‐
mand. The specified ID is included in the commands sent to the server
The command itself is digitally signed with the first password associated
with the ID in the ids file. The server requires that the signature
match one of the passwords associated with the ID in its ids file.
delck type hex1 hex2 hex3 hex4
asks the server to delete the type checksum with value hex1 hex2
hex3 hex4. The type and checksum values can be found in dccproc(8)
and dccm(8) log files or computed with dccproc -QC.
There are very few situations where it makes sense to bother to
delete checksums. For example, mail that was accidentally reported
with a target count of "MANY" is either private and so will not be
seen by other people and so will not be affected, or it is bulk and
its source so must have already been whitelisted by recipients.
stats [all | clear]
displays current status and statistics from the current DCC server
or for all known DCC servers. The server's counters will be cleared
after they are displayed when the server's ID has been specified
with the id ID operation.
clients [-nsiaVAK] [-I id] [max [thold]] [addr[/prefix]]
display some of the clients recently seen by the server.
-n display only the IP addresses and not the names of clients.
-s sort the clients by the number of requests they have made.
-i count clients with the same client-ID as single entities.
-I id display information only about clients using client-ID id.
-a produce 24 hour average numbers of requests.
-A display only anonymous clients.
-K display only clients using client-IDs other than the anony‐
mous ID of 1.
-V include the DCC protocol versions used by clients.
max display only the max most recent clients.
max thold display the most recent max clients that have made at
least thold requests.
addr[/prefix] restricts the results to the DCC client with that IP
address or clients with addresses in that block of addresses.
Individual clients in a blacklisted block of addresses in the
server's /var/dcc/blacklist file are not displayed unless
explicitly requested by address or address block.
Clients with IDs marked with an asterisk (*) used the wrong password
for that client-ID.
The mechanism that implements this command involves asking the DCC
server for the first approximately 100 clients, then the second
about 100, and so on, If entries change position in the complete
list maintained by the server between requests, the displayed list
will have duplicate or missing entries. Only clients since the last
use of stats clear are displayed.
stop
tells the DCC server to exit.
system stop
tells the DCC server to exit so that the operating system can be
shut down. This tells the DCC server on some systems to delete the
dcc_db.hash file to speed system shut down. The file will be
rebuilt automatically by dbclean when the DCC server is restarted.
clean stop
tells the DCC server to exit after applying fsync() to the database.
reload IDs
tells the local DCC server to reload its DCC ids file immediately.
This command is not strictly needed. Every several minutes, the DCC
server notices if the file has been changed and automatically reads
it.
flood check
tells the DCC server to check for changes in the flod file and try
to restart any of the streams to peers that are broken.
flood shutdown
tells the DCC server to cleanly stop flooding checksums to and from
peers. The server will wait for sending and receiving peers to
agree to stop. Each flood shutdown or flood halt request increases
a count of reasons why the server should not flood checksums.
flood halt
tells the DCC server to abruptly stop flooding checksums to and from
peers.
flood rewind server-ID
tells the DCC server to ask its peer with server-ID to rewind and
resend its stream of checksums.
flood ffwd in server-ID
tells the DCC server to ask its peer to "fast forward" or skip to
the end of the incoming flood.
flood ffwd out server-ID
tells the DCC server to "fast forward" or skip to the current end of
the flood to its peer.
flood resume
tells the DCC server to reduce the number of reasons to not flood
checksums increased by flood shutdown and flood halt. When the num‐
ber of reasons reaches zero, the server tries to resume flooding.
flood list
displays the list of current incoming and outgoing floods. Each
line contains the server-ID of the peer, the IP address and port
used for the outgoing flood, the address for the incoming flood if
different, and the host name. Only the server-IDs of flooding peers
are disclosed with the server's ID.
flood stats [clear] { server-ID | all }
displays counts of checksum reports sent and received by the current
flooding connections to and from server-ID or all flooding connec‐
tions and then optionally clears the counts.
DB clean
is used by dbclean to tell the server that the database expiration
has begun.
DB new
is used by dbclean to tell the server that the database cleaning is
complete.
flush cache
tells the server to flush its cache and to keep it clean.
cache ok
tells the server to resume normal operations after flush cache.
clock check
asks the DCC server to say how much its clock differs from the local
clock.
clock kludge +/-seconds
adjusts the timestamps in server commands to make it possible to
control servers with inaccurate clocks.
trace default
turns on ANON and CLNT tracing and turns off all others.
trace mode {on|off}
turns the server's tracing mode on or off. Mode must be one of:
ADMN administrative requests from cdcc
ANON errors by anonymous clients
CLNT errors by authenticated clients
RLIM rate-limited messages
QUERY all queries and reports
RIDC messages concerning the report-ID cache that is used to
detect duplicate reports from clients
FLOOD1 messages about inter-server flooding connections
FLOOD2 messages about flooded reports
IDS unknown server-IDs in flooded reports
BL blacklisted clients
DB odd database events
WLIST reports of whitelisted checksums from authenticated, not
anonymous DCC clients
cdcc exits with 0 on success, and >0 if an error occurs in operations
specified on the command line.
FILES
/var/dcc default DCC home directory unless changed by the homedir opera‐
tion.
map memory mapped file in the home DCC home directory of server
host names, port numbers, passwords, measured round trip times
(RTT), and so forth.
ids list of IDs and passwords, as described in dccd(8). It is only
required by systems running the DCC server, but is used by cdcc
if available.
SEE ALSOdbclean(8), dcc(8), dccd(8), dblist(8), dccifd(8), dccm(8), dccproc(8),
dccsight(8).
HISTORY
Implementation of cdcc was started at Rhyolite Software in 2000. This
document describes version 1.3.154.
December 03, 2013
