- <div class="title"><a href="http://people.skolelinux.org/pere/blog/I_want_the_courts_to_be_involved_before_the_police_can_hijack_a_news_site_DNS_domain___domstolkontroll_.html">I want the courts to be involved before the police can hijack a news site DNS domain (#domstolkontroll)</a></div>
- <div class="date">19th May 2016</div>
- <div class="body"><p>I just donated to the
-<a href="http://www.nuug.no/dns-beslag-donasjon.shtml">NUUG defence
-"fond"</a> to fund the effort in Norway to get the seizure of the news
-site popcorn-time.no tested in court. I hope everyone that agree with
-me will do the same.</p>
-
-<p>Would you be worried if you knew the police in your country could
-hijack DNS domains of news sites covering free software system without
-talking to a judge first? I am. What if the free software system
-combined search engine lookups, bittorrent downloads and video playout
-and was called Popcorn Time? Would that affect your view? It still
-make me worried.</p>
-
-<p>In March 2016, the Norwegian police seized (as in forced NORID to
-change the IP address pointed to by it to one controlled by the
-police) the DNS domain popcorn-time.no, without any supervision from
-the courts. I did not know about the web site back then, and assumed
-the courts had been involved, and was very surprised when I discovered
-that the police had hijacked the DNS domain without asking a judge for
-permission first. I was even more surprised when I had a look at
-<a href="https://web.archive.org/web/*/http://popcorn-time.no">the web
-site content on the Internet Archive</A>, and only found news coverage
-about Popcorn Time, not any material published without the right
-holders permissions.</p>
-
-<p>The seizure was widely covered in the Norwegian press (see for
-example <a href="http://www.hegnar.no/Nyheter/Naeringsliv/2016/03/Popcorn-time.no-beslaglagt-av-OEkokrim">Hegnar Online</a> and
-<a href="http://itavisen.no/2016/03/08/okokrim-har-beslaglagt-popcorn-time-no/">ITavisen<a/>
-and
-<a href="http://www.nrk.no/kultur/okokrim-gar-til-aksjon-mot-popcorn-time-1.12842452">NRK</a>),
-at first due to the press release sent out by Økokrim, but then based
-on
-<a href="http://blogg.torvund.net/2016/03/09/okokrims-beslag-i-domenet-popcorn-time-no/">protests
-from the law professor Olav Torvund</a> and
-<a href="http://www.klassekampen.no/article/20160311/ARTICLE/160319995">lawyer
-Jon Wessel-Aas</a>. It even got some
-<a href="https://torrentfreak.com/norwegian-authorities-sued-over-popcorn-time-domain-seizure-160418/">coverage
-on TorrentFreak</a>.</p>
-
-<p>I
-<a href="http://people.skolelinux.org/pere/blog/NUUG_contests_Norwegian_police_DNS_seizure_of_popcorn_time_no.html">
-wrote about the case a month ago</a>, when the
-<a href="http://www.nuug.no/">Norwegian Unix User Group</a> (NUUG),
-where I am an active member, decided to ask the courts to test this seizure.
-The request was denied, but NUUG and its co-requestor EFN have not
-given up, and now they are rallying for support to get the seizure
-legally challenged. They accept both bank and Bitcoin transfer for
-those that want to support the request.</p>
-
-<p>If you as me believe news sites about free software should not be
-censored, even if the free software have both legal and illegal
-applications, and that DNS hijacking should be tested by the courts, I
-suggest you <a href="http://www.nuug.no/dns-beslag-donasjon.shtml">show
-your support by donating to NUUG</a>.</a>
+ <div class="title"><a href="http://people.skolelinux.org/pere/blog/Detecting_NFS_hangs_on_Linux_without_hanging_yourself___.html">Detecting NFS hangs on Linux without hanging yourself...</a></div>
+ <div class="date"> 9th March 2017</div>
+ <div class="body"><p>Over the years, administrating thousand of NFS mounting linux
+computers at the time, I often needed a way to detect if the machine
+was experiencing NFS hang. If you try to use <tt>df</tt> or look at a
+file or directory affected by the hang, the process (and possibly the
+shell) will hang too. So you want to be able to detect this without
+risking the detection process getting stuck too. It has not been
+obvious how to do this. When the hang has lasted a while, it is
+possible to find messages like these in dmesg:</p>
+
+<p><blockquote>
+nfs: server nfsserver not responding, still trying
+<br>nfs: server nfsserver OK
+</blockquote></p>
+
+<p>It is hard to know if the hang is still going on, and it is hard to
+be sure looking in dmesg is going to work. If there are lots of other
+messages in dmesg the lines might have rotated out of site before they
+are noticed.</p>
+
+<p>While reading through the nfs client implementation in linux kernel
+code, I came across some statistics that seem to give a way to detect
+it. The om_timeouts sunrpc value in the kernel will increase every
+time the above log entry is inserted into dmesg. And after digging a
+bit further, I discovered that this value show up in
+/proc/self/mountstats on Linux.</p>
+
+<p>The mountstats content seem to be shared between files using the
+same file system context, so it is enough to check one of the
+mountstats files to get the state of the mount point for the machine.
+I assume this will not show lazy umounted NFS points, nor NFS mount
+points in a different process context (ie with a different filesystem
+view), but that does not worry me.</p>
+
+<p>The content for a NFS mount point look similar to this:</p>
+
+<p><blockquote><pre>
+[...]
+device /dev/mapper/Debian-var mounted on /var with fstype ext3
+device nfsserver:/mnt/nfsserver/home0 mounted on /mnt/nfsserver/home0 with fstype nfs statvers=1.1
+ opts: rw,vers=3,rsize=65536,wsize=65536,namlen=255,acregmin=3,acregmax=60,acdirmin=30,acdirmax=60,soft,nolock,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=129.240.3.145,mountvers=3,mountport=4048,mountproto=udp,local_lock=all
+ age: 7863311
+ caps: caps=0x3fe7,wtmult=4096,dtsize=8192,bsize=0,namlen=255
+ sec: flavor=1,pseudoflavor=1
+ events: 61063112 732346265 1028140 35486205 16220064 8162542 761447191 71714012 37189 3891185 45561809 110486139 4850138 420353 15449177 296502 52736725 13523379 0 52182 9016896 1231 0 0 0 0 0
+ bytes: 166253035039 219519120027 0 0 40783504807 185466229638 11677877 45561809
+ RPC iostats version: 1.0 p/v: 100003/3 (nfs)
+ xprt: tcp 925 1 6810 0 0 111505412 111480497 109 2672418560317 0 248 53869103 22481820
+ per-op statistics
+ NULL: 0 0 0 0 0 0 0 0
+ GETATTR: 61063106 61063108 0 9621383060 6839064400 453650 77291321 78926132
+ SETATTR: 463469 463470 0 92005440 66739536 63787 603235 687943
+ LOOKUP: 17021657 17021657 0 3354097764 4013442928 57216 35125459 35566511
+ ACCESS: 14281703 14290009 5 2318400592 1713803640 1709282 4865144 7130140
+ READLINK: 125 125 0 20472 18620 0 1112 1118
+ READ: 4214236 4214237 0 715608524 41328653212 89884 22622768 22806693
+ WRITE: 8479010 8494376 22 187695798568 1356087148 178264904 51506907 231671771
+ CREATE: 171708 171708 0 38084748 46702272 873 1041833 1050398
+ MKDIR: 3680 3680 0 773980 993920 26 23990 24245
+ SYMLINK: 903 903 0 233428 245488 6 5865 5917
+ MKNOD: 80 80 0 20148 21760 0 299 304
+ REMOVE: 429921 429921 0 79796004 61908192 3313 2710416 2741636
+ RMDIR: 3367 3367 0 645112 484848 22 5782 6002
+ RENAME: 466201 466201 0 130026184 121212260 7075 5935207 5961288
+ LINK: 289155 289155 0 72775556 67083960 2199 2565060 2585579
+ READDIR: 2933237 2933237 0 516506204 13973833412 10385 3190199 3297917
+ READDIRPLUS: 1652839 1652839 0 298640972 6895997744 84735 14307895 14448937
+ FSSTAT: 6144 6144 0 1010516 1032192 51 9654 10022
+ FSINFO: 2 2 0 232 328 0 1 1
+ PATHCONF: 1 1 0 116 140 0 0 0
+ COMMIT: 0 0 0 0 0 0 0 0
+
+device binfmt_misc mounted on /proc/sys/fs/binfmt_misc with fstype binfmt_misc
+[...]
+</pre></blockquote></p>
+
+<p>The key number to look at is the third number in the per-op list.
+It is the number of NFS timeouts experiences per file system
+operation. Here 22 write timeouts and 5 access timeouts. If these
+numbers are increasing, I believe the machine is experiencing NFS
+hang. Unfortunately the timeout value do not start to increase right
+away. The NFS operations need to time out first, and this can take a
+while. The exact timeout value depend on the setup. For example the
+defaults for TCP and UDP mount points are quite different, and the
+timeout value is affected by the soft, hard, timeo and retrans NFS
+mount options.</p>
+
+<p>The only way I have been able to get working on Debian and RedHat
+Enterprise Linux for getting the timeout count is to peek in /proc/.
+But according to
+<ahref="http://docs.oracle.com/cd/E19253-01/816-4555/netmonitor-12/index.html">Solaris
+10 System Administration Guide: Network Services</a>, the 'nfsstat -c'
+command can be used to get these timeout values. But this do not work
+on Linux, as far as I can tell. I
+<ahref="http://bugs.debian.org/857043">asked Debian about this</a>,
+but have not seen any replies yet.</p>
+
+<p>Is there a better way to figure out if a Linux NFS client is
+experiencing NFS hangs? Is there a way to detect which processes are
+affected? Is there a way to get the NFS mount going quickly once the
+network problem causing the NFS hang has been cleared? I would very
+much welcome some clues, as we regularly run into NFS hangs.</p>
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