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Manual Reference Pages  -  DNS-TERROR (1)


dns-terror - fast log file IP address resolver




dns-terror [-v...] [-orsz] [-d db-file] [-c adns-conf-str] [-m mark-size] [-p parallel-queries] [-f skip-fields]


dns-terror reads log files, resolves the IP addresses that are resolvable, and optionally writes the results back out. Optionally it reads and saves the results in a DB file, to cache results between runs.

It reads IP addresses to resolve from the standard input, one per line. Other data on a line before or after the IP address is ignored (although it may be passed through with the -o option).

Before running dns-terror, it is best to run unlimit, because this program can use a lot of memory and create large files (depending on the size of the input files).

dns-terror uses the adns library (a parallel, asynchronous resolver) and caches the results in a tree structure in memory for speed.


-p parallel-queries Set the size of the query pipeline. Defaults to 1000 outstanding DNS queries. When this number of queries are outstanding, the program waits for one of them to complete before it reads another input line. Experiment with different values to find the optimal one for your environment. The optimal value depends at least on the response times of the DNS servers you are using and the speed of your CPU. A good approach is to run repeated tests with -d ’’ (no DB file cache) on the same log file, increasing the value of -p each time until you find a point where higher values no longer result in significant time savings or increased CPU utilization.
-o Copy the input lines to the standard output with IP addresses resolved. In this mode, the -p option is multiplied by 20 to determine the maximum number of log lines that may be buffered in memory before forcing the program to wait for the first buffered line’s outstanding DNS query to complete. The default is 1000 times 20, or 20,000 lines.
-z Write the output in gzipped form. This only has an effect when the -o option is given. If you would have gzipped the output file immediately after resolving it, using this option instead is faster. Automatic gunzipping of the input to dns-terror is not currently supported.
-f skip-fields Skip skip-fields blank-separated fields at the start of each line before expecting an IP address. Default 0. Useful for processing W3C format log files, such as IIS 4 produces.
-v Increases output verbosity each time it is given, up to 3 (currently). The more, the messier.
-d db-file Save results to DB file db-file. Defaults to ip2host.db. If given as the empty string (-d ’’), no DB file is used, and the results are lost when the program exits.
-m mark-size Print a notice every mark-size input lines. During the drain time at the end, after all the input lines have been read, print a notice after every 1/10 of the remaining DNS queries that are outstanding have been answered or timed out.
-s Sync the cached results to the DB file on disk at each mark.
-r Read in only positive cached results from the DB file, to make another pass at resolving the negative ones.
-c adns-conf-str adns configuration string to use instead of /etc/resolv.conf and the various optional environment variables. One or more lines in a format like resolv.conf, with directives:

nameserver domain search

plus some additional directives:

sortlist options clearnameservers include

One approach is to make an alternate conf file and use -c "include adns.conf". Also, adns as of v0.6 reads /etc/resolv-adns.conf (if it exists) after /etc/resolv.conf.

If an unofficial patch (supplied with this package) is applied to adns, the following adns options are available (separate them with blank space if giving more than one):

udpmaxretries:N Maximum number of times to retry a (UDP) DNS query before giving up. Default 15.
udpretryms:N Number of milliseconds between retries. Default 2000 (2 seconds). Thus, the default timeout for a query is 15 times 2000 milliseconds = 30000 milliseconds, or 30 seconds. That is a fairly long time to wait for a DNS query to complete or timeout. Faster performance will result from reducing udpmaxretries to produce a timeout more in the 10-15 second range; however, some responses will be missed that way, so the percentage of IP addresses successfully resolved will be somewhat lower.
On a single processor machine, it is generally faster to use remote nameservers rather than a local caching nameserver ( A local caching nameserver will have cached a few addresses that are needed, but not most of them. For most addresses, it will have to go out to the remote ones anyway, and so it’s just an unnecessary intermediary (using the same CPU) processing the queries. Since dns-terror does its own caching, it’s best to ignore a nameserver on the loopback interface and specify a list of nameservers using -c. On a multiprocessor machine, there may be an advantage to using a local nameserver.

dns-terror does negative caching in the DB file; unresolvable IP addresses have an empty value in the file. Each DB file entry contains a timestamp of when it was written, preceding the value (hostname). It is stored in host byte order, since processing large files over a network file system is dumb. Old entries should be removed periodically using expire-ip-db.

dns-terror ignores the time-to-live on nameserver records. The TTL could be stored in the DB file, but it is questionable whether that would provide a significant gain in accuracy, and it could negate much of the speed benefit of the DB file.


ip2host.db Default DB file for caching results.
/etc/resolv.conf Default resolver configuration.


SIGHUP closes and reopens the DB file (useful if it was rolled).
SIGTERM closes the DB file without saving, and exits.


convert-ip-db(1), dig(1), expire-ip-db(1), make-report(1), resolver(5)


There is a tradeoff between completeness and running time. It would be prudent to compare the output of this program with the output of a simpler resolver until you are confident that your configuration of it is working well. You might use dig to spot-check some addresses that are not resolved, and/or use the -v option to dns-terror to check on why (name server failure, no response, etc.).

All cached results from the DB file are held in memory for speed, so the program’s memory footprint can become large.


David MacKenzie <>. Thanks to Josh Osborne <> for ideas and an earlier implementation. Please send comments and bug reports to <>.
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Fastresolve DNS-TERROR (1) February 2000

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