newssys - USENET network news sys (neighbours) file

The file c/sys describes which news groups this site is willing to receive and which groups it is willing to transmit to each netnews neighbour. It is public information and is sent automatically to any site that sends a sendsys control message. A sys line has four fields, separated by colons:

system-name/exclusion1,c exclusion2...:subscriptions/c distributions:c flags:transmission command

A # as the first character in a line denotes a comment. Empty lines are ignored. A (non-comment) sys entry may be continued to the next line by putting a \ at the end of the current line. Spaces are permitted in sys only in comments, transmission command when it really is a command and not a filename, and, for B news compatibility, at the start of a continuation line (after a \ and a newline).

Of the sys fields, only the system-name need be present. If a field and all the fields after it are omitted, the colon immediately before that field and all the colons after it may be omitted too. The optional subfields (c exclusions and distributions) and their leading slashes may be omitted.

The system name is the name of the system being sent to, and is checked against site names in Path: headers to avoid sending an article back to a site that has seen it. The exclusions are also checked against the Path: header and articles are not sent to system name if they have visited any of the exclusions.

(The special system name ME stands for the name of the machine news is running on, as determined from c/whoami. The ME line, or a line whose system name is explicitly that of the machine news is running on, has a rather different meaning from that of the other sys file lines: its subscriptions subfield identifies the newsgroups that this site subscribes to (i.e. is willing to receive), and its other fields and subfields are ignored. There should be one such line in the file.)

subscriptions is a comma-separated list of newsgroup patterns specifying the newsgroups to be transmitted to the system; each newsgroup from the Newsgroups: header of each article is matched against the pattern list, and if any newsgroup matches the pattern list, the article is transmitted. The rules for matching a newsgroup against a single pattern are:

•

words in a newsgroup or a pattern are delimited by periods;

•

words of a pattern and a newsgroup match only if they are identical, except that the word all in a pattern matches any newsgroup word;

•

a newsgroup is matched against a pattern word by word, and all words must match for the newsgroup to match that pattern;

•

if the pattern has fewer words than the newsgroup, the pattern is implicitly extended to the same number of words by appending .all as many times as necessary;

•

if the newsgroup has fewer words than the pattern, the newsgroup does not match the pattern;

•

if pattern matches a newsgroup, !pattern mismatches that newsgroup.

A newsgroup matches a pattern list if, and only if, it matches at least one of the patterns and:

•

the newsgroup does not mismatch any of the patterns, or

•

the longest matched pattern is longer than the longest mismatched pattern (length is measured in number of words, with each explicit occurrence of all counted as slightly less than one word, and does not include the implicit extension of patterns with .all).

Note that order in the lists is not significant, and that ties are broken in favor of not matching. An example: comp,comp.sys.sun,!comp.sys matches all the comp groups, except the comp.sys groups but including comp.sys.sun.

The distributions in the Distribution: header are similarly matched against the distributions subfield, if any. If no distributions are supplied, Distribution: will be matched against the subscriptions instead. (The Distribution: header is ignored when receiving news; it is only significant when sending.)

Note that some older news software reportedly attached magical significance to the distributions ``world'' and ``local''; C News treats them as ordinary distribution names with no special properties (except that ``world'' is the default distribution of an article if none appears explicitly). For example, a distributions list like all,!local will not prevent local articles from being sent unless they contain explicit Distribution: local lines. Note too that the distribution ``world'' must be permitted (perhaps by the distribution ``all'') in order to feed Distribution:-less articles (the common case) to a site.

The flags are a set of letters describing how the article should be transmitted. Valid flags include f (interpret transmission command as a file name and write the article's file name relative to a and size in bytes on the end of it), F (like f but omit the size), I (like F but write Message-ID:s instead of filenames), n (like F but write a Message-ID: after each filename), Ln (only send articles generated within n hops of here; 0 is the default value for n), m (transmit only moderated groups), u (transmit only unmoderated groups). There are other obsolete ones.

The transmission command is executed by the shell with the article to be transmitted as the standard input. The substring `c %s' will be replaced at most once per command with the name of a file containing the article, relative to a (`c %%' is replaced by `c %'). The default is `c uux - -z -r sysname!rnewsc ' for a command; the PATH searched includes b/relay, so that the commands described in newsmail(8) are available as alternatives to uux. If one of the flags has caused this field to be taken as a filename, the default is a/out.going/sysname/togoc ; if a filename is given but it does not start with `/', it is assumed to be relative to the a/out.going directory.

A complex sys file. # line indicating what we are willing to receive; note local groups near end ME:comp,news,sci,rec,misc,soc,talk,can,ont,tor,ut,to # sample insignificant feed not using batching (for special situations only) huey:news.config,to.huey/all::uux - -r -gd huey!rnews # sample of mailing newsgroups to someone (note distribution) daisy:soc.women,soc.couples/all::mail daisy@duck # sample small feed using batching gladstone:comp.protocols.tcp-ip,rec.aviation/all:f: # sample major batched feed, including assorted regional newsgroups, with # (unnecessary) explicit file name dewey:comp,news,sci,rec,misc,soc,talk,can,ont,tor,ut,to.dewey/all:f:dewey/togo # sample long-haul feed; note no regional groups, exclusion of a local # distribution, and exclusion of anything that passed through him under # another name (needed because he puts that form, not just "donald", in # his Path lines) donald/donald.angry.duck:comp,news,sci,rec,misc,soc,talk,to.donald/all,!ut:f: # sample local-postings-only feed direct to major site (gets them out fast) scrooge:comp,news,sci,rec,misc,soc,talk,to.scrooge/all:Lf: # sample ihave/sendme link # NOTE, this is uucp ihave/sendme, not related to NNTP in any way. # Send ihave telling louie what we have -- batcher turns the batch into a # giant control message and posts it to "to.louie". louie.wehave/louie:comp,news,sci,rec,misc,soc,talk,!to/all:I: # Send the actual control messages louie:to.louie/all:f: # Also, since ihave/sendme is slow, send local postings to louie without # waiting for ihave/sendme louie:comp,news,sci,rec,misc,soc,talk,!to/all:Lf: # for a site we feed with snntp zaphod.mps.ohio-state.edu:all:n:a/out.nntp/zaphod.mps.ohio-state.edu (The ``to.sysname'' groups are normal newsgroups used for testing individual news feeds and conveying ihave/sendme messages.)

c/sys

newsbatch(8), relaynews(8)

Written by Geoff Collyer and Henry Spencer for the C News project.

The flags field is a bit of mess: there are too many formatting flags and they aren't orthogonal.