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• iptables drops some packets on port 80 and i don't know the cause.

  - by Janning

  Hi, We are running a firewall with iptables on our Debian Lenny system. I show you only the relevant entries of our firewall. Chain INPUT (policy DROP 0 packets, 0 bytes) target prot opt in out source destination ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 state NEW Chain OUTPUT (policy DROP 0 packets, 0 bytes) target prot opt in out source destination ACCEPT all -- * lo 0.0.0.0/0 0.0.0.0/0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED LOGDROP all -- * * 0.0.0.0/0 0.0.0.0/0 Some packets get dropped each day with log messages like this: Feb 5 15:11:02 host1 kernel: [104332.409003] dropped IN= OUT=eth0 SRC= DST= LEN=1420 TOS=0x00 PREC=0x00 TTL=64 ID=18576 DF PROTO=TCP SPT=80 DPT=59327 WINDOW=54 RES=0x00 ACK URGP=0 for privacy reasons I replaced IP Addresses with and This is no reason for any concern, but I just want to understand what's happening. The web server tries to send a packet to the client, but the firewall somehow came to the conclusion that this packet is "UNRELATED" to any prior traffic. I have set a kernel parameter ip_conntrack_ma to a high enough value to be sure to get all connections tracked by iptables state module: sysctl -w net.ipv4.netfilter.ip_conntrack_max=524288 What's funny about that is I get one connection drop every 20 minutes: 06:34:54 droppedIN= 06:52:10 droppedIN= 07:10:48 droppedIN= 07:30:55 droppedIN= 07:51:29 droppedIN= 08:10:47 droppedIN= 08:31:00 droppedIN= 08:50:52 droppedIN= 09:10:50 droppedIN= 09:30:52 droppedIN= 09:50:49 droppedIN= 10:11:00 droppedIN= 10:30:50 droppedIN= 10:50:56 droppedIN= 11:10:53 droppedIN= 11:31:00 droppedIN= 11:50:49 droppedIN= 12:10:49 droppedIN= 12:30:50 droppedIN= 12:50:51 droppedIN= 13:10:49 droppedIN= 13:30:57 droppedIN= 13:51:01 droppedIN= 14:11:12 droppedIN= 14:31:32 droppedIN= 14:50:59 droppedIN= 15:11:02 droppedIN= That's from today, but on other days it looks like this, too (sometimes the rate varies). What might be the reason? Any help is greatly appreciated. kind regards Janning

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• Locale variables have no effect in remote shell (perl: warning: Setting locale failed.)

  - by Janning

  I have a fresh ubuntu 12.04 installation. When i connect to my remote server i got errors like this: ~$ ssh example.com sudo aptitude upgrade ... Traceback (most recent call last): File "/usr/bin/apt-listchanges", line 33, in <module> from ALChacks import * File "/usr/share/apt-listchanges/ALChacks.py", line 32, in <module> sys.stderr.write(_("Can't set locale; make sure $LC_* and $LANG are correct!\n")) NameError: name '_' is not defined perl: warning: Setting locale failed. perl: warning: Please check that your locale settings: LANGUAGE = (unset), LC_ALL = (unset), LC_TIME = "de_DE.UTF-8", LC_MONETARY = "de_DE.UTF-8", LC_ADDRESS = "de_DE.UTF-8", LC_TELEPHONE = "de_DE.UTF-8", LC_NAME = "de_DE.UTF-8", LC_MEASUREMENT = "de_DE.UTF-8", LC_IDENTIFICATION = "de_DE.UTF-8", LC_NUMERIC = "de_DE.UTF-8", LC_PAPER = "de_DE.UTF-8", LANG = "en_US.UTF-8" are supported and installed on your system. perl: warning: Falling back to the standard locale ("C"). locale: Cannot set LC_ALL to default locale: No such file or directory No packages will be installed, upgraded, or removed. 0 packages upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 0 B of archives. After unpacking 0 B will be used. ... I don't have this problem when i connect from an older ubuntu installation. This is output from my ubuntu 12.04 installation, LANG and LANGUAGE are set $ locale LANG=de_DE.UTF-8 LANGUAGE=de_DE:en_GB:en LC_CTYPE="de_DE.UTF-8" LC_NUMERIC=de_DE.UTF-8 LC_TIME=de_DE.UTF-8 LC_COLLATE="de_DE.UTF-8" LC_MONETARY=de_DE.UTF-8 LC_MESSAGES="de_DE.UTF-8" LC_PAPER=de_DE.UTF-8 LC_NAME=de_DE.UTF-8 LC_ADDRESS=de_DE.UTF-8 LC_TELEPHONE=de_DE.UTF-8 LC_MEASUREMENT=de_DE.UTF-8 LC_IDENTIFICATION=de_DE.UTF-8 LC_ALL= Does anybody know what has changed in ubuntu to get this error message on remote servers?

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• apache mod_cache in v2.2 - enable cache based on url

  - by Janning

  We are using apache2.2 as a front-end server with application servers as reverse proxies behind apache. We are using mod_cache for some images and enabled it like this: <IfModule mod_disk_cache.c> CacheEnable disk / CacheRoot /var/cache/apache2/mod_disk_cache CacheIgnoreCacheControl On CacheMaxFileSize 2500000 CacheIgnoreURLSessionIdentifiers jsessionid CacheIgnoreHeaders Set-Cookie </IfModule> The image urls vary completely and have no common start pattern, but they all end in ".png". Thats why we used the root in CacheEnable / If not served from the cache, the request is forwarded to an application server via reverse proxy. So far so good, cache is working fine. But I really only need to cache all image request ending in ".png". My above configuration still works as my application server send an appropriate Cache-Control: no-cache header on the way back to apache. So most pages send a no-cache header back and they get not cached at all. My ".png" responses doesn't send a Cache-Control header so apache is only going to cache all urls with ".png". Fine. But when a new request enters apache, apache does not know that only .png requests should be considered, so every request is checking a file on disk (recorded with strace -e trace=file -p pid): [pid 19063] open("/var/cache/apache2/mod_disk_cache/zK/q8/Kd/g6OIv@woJRC_ba_A.header", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory) I don't want to have apache going to disk every request, as the majority of requests are not cached at all. And we have up to 10.000 request/s at peak time. Sometimes our read IO wait spikes. It is not getting really slow, but we try to tweak it for better performance. In apache 2.4 you can say: <LocationMatch .png$> CacheEnable disk </LocationMatch> This is not possible in 2.2 and as I see no backports for debian I am not going to upgrade. So I tried to tweak apache2.2 to follow my rules: <IfModule mod_disk_cache.c> SetEnvIf Request_URI "\.png$" image RequestHeader unset Cache-Control RequestHeader append Cache-Control no-cache env=!image CacheEnable disk / CacheRoot /var/cache/apache2/mod_disk_cache #CacheIgnoreCacheControl on CacheMaxFileSize 2500000 CacheIgnoreURLSessionIdentifiers jsessionid CacheIgnoreHeaders Set-Cookie </IfModule> The idea is to let apache decide to serve request from cache based on Cache-control header (CacheIgnoreCacheControl default to off). And before simply set a RequestHeader based on the request. If it is not an image request, set a Cache-control header, so it should bypass the cache at all. This does not work, I guess because of late processing of RequestHeader directive, see https://httpd.apache.org/docs/2.2/mod/mod_headers.html#early I can't add early processing as "early" keyword can't be used together with a conditional "env=!image" I can't change the url requesting the images and I know there are of course other solutions. But I am only interested in configuring apache2.2 to reach my goal. Does anybody has an idea how to achieve my goal?

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• java concurrency: many writers, one reader

  - by Janning

  I need to gather some statistics in my software and i am trying to make it fast and correct, which is not easy (for me!) first my code so far with two classes, a StatsService and a StatsHarvester public class StatsService { private Map<String, Long> stats = new HashMap<String, Long>(1000); public void notify ( String key ) { Long value = 1l; synchronized (stats) { if (stats.containsKey(key)) { value = stats.get(key) + 1; } stats.put(key, value); } } public Map<String, Long> getStats ( ) { Map<String, Long> copy; synchronized (stats) { copy = new HashMap<String, Long>(stats); stats.clear(); } return copy; } } this is my second class, a harvester which collects the stats from time to time and writes them to a database. public class StatsHarvester implements Runnable { private StatsService statsService; private Thread t; public void init ( ) { t = new Thread(this); t.start(); } public synchronized void run ( ) { while (true) { try { wait(5 * 60 * 1000); // 5 minutes collectAndSave(); } catch (InterruptedException e) { e.printStackTrace(); } } } private void collectAndSave ( ) { Map<String, Long> stats = statsService.getStats(); // do something like: // saveRecords(stats); } } At runtime it will have about 30 concurrent running threads each calling notify(key) about 100 times. Only one StatsHarvester is calling statsService.getStats() So i have many writers and only one reader. it would be nice to have accurate stats but i don't care if some records are lost on high concurrency. The reader should run every 5 Minutes or whatever is reasonable. Writing should be as fast as possible. Reading should be fast but if it locks for about 300ms every 5 minutes, its fine. I've read many docs (Java concurrency in practice, effective java and so on), but i have the strong feeling that i need your advice to get it right. I hope i stated my problem clear and short enough to get valuable help.

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