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10372 discussions

Wanted - algorithm for bufferless search for a pattern in a stream
by Chris Green 08 Aug '12

08 Aug '12

I can see how to do this in principle but I can't iron out the details and I'm sure there must be some ready made code for doing it 'out there' on the internet. It's just rather difficult to come up with search terms when I don't know what to call it. To explain in detail I want to search for a (constant) string in a byte stream that I can't rewind and I don't want to use any significant buffer space (the constant string I'm looking for is quite long). So, obviously one reads a byte at a time from the stream to see if it matches the first character of the constant string, if that matches one moves on to the second, etc. When the whole string has been matched then it's found - so far so good. However, when a character *doesn't* match one can't go back up the input stream, *but* we know the previous characters as they're the ones in the constant string that we have matched so far. Thus we can 'wind back' by using the constant string for the number of characters that did match and then continue down the stream. If anyone can follow that rubbish explanation then could they possibly tell me what the algorithm is called and/or point me at some sample code? -- Chris Green

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[ALUG Announce] ALUG Norwich Pub Meet Thursday 9th August
by Viperfang 06 Aug '12

06 Aug '12

ALUG Announce Please send announcements to Announce(a)lists.alug.org.uk Unsub, change settings via http://lists.alug.org.uk/mailman/listinfo/announce ----- Hello Norwich Aluggers, Our monthly ALUG Norwich social meeting will be held this Thursday, 9th August at The Coach and Horses (82 Thorpe Road, Norwich, NR1 1BA). The meeting officially starts at 8pm, although some people may arrive earlier. More information on those people can be found on the list and the IRC channel. If you are unsure if you will recognise us then make yourself and your intent to attend known by either posting on list or visiting us on IRC so we can look out for you rather than hiding in the corner. Optionally you could ask at the bar if they know where the geeky computer weirdos are and they'll point you in the right direction (seriously!). Another possibility is look for heaps of electronics on a table that may possibly look like movie props that would used for detonating explosives. Feel free to bring electronics/laptops/gadgets to the meet, you will by no means be alone. Ben Bewick aka Viperfang NB: This mail is automated, please refer to the usual sources for more information. ALUG Contact Details: Website : http://www.alug.org.uk/ IRC : #alug on irc.alug.org.uk List : http://lists.alug.org.uk/mailman/listinfo Twitter : http://twitter.com/anglianlug Identica: TBA Facebook: http://www.facebook.com/group.php?gid=2381613902 ----- Send discussion replies to main(a)lists.alug.org.uk (Reply-To set) Unsub, change settings via http://lists.alug.org.uk/mailman/listinfo/announce

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Forcing "Sender:" in exim4
by Ted.Harding＠wlandres.net 05 Aug '12

05 Aug '12

Greetings All! I have just (!!! -- after about 4 years ... !!!) that in my Debian Etch setup 'sendmail' is aliased to 'exim4': ls -l `which sendmail` /usr/sbin/sendmail -> exim4 My mailer (MUA) setup presumes sendmail. I have configured the MUA so that, in the headers for outgoing mail, I have set: Sender: ted.harding@wlandres (same as my "From:" and "Reply-To:" addresses). That is how the header appears while the message is still in the "outbox" folder. However, when I send the mail out, it seems that exim4 changes the "Sender:" address to "ted@deb", "deb" being the name of my machine on my home LAN (as set in /etc/hosts), and "ted" being the user. As a result, when the mail is received outside my LAN, the receiving host sees the header: Sender: ted@deb instead of what I want it to be! This sometimes results in rejection when the receiving host does not recognise the sender domain. Now, while I know my way round sendmail itself, I find I am disorientated by trying to make out how to customise exim4 configuration. (I've tried reading the man pages). What I want to do is ensure that exim4 (aliased as 'sendmail') either does not change the "Sender:" header as it is while still in the outbox, or else sets it anyway to Sender: ted.harding(a)wlandres.net And it could also be useful, though not essential, if, should I happen to mail as a different user on the same machine, e.g. "efh", it could preserve the domain and insert the user, e.g. Sender: efh(a)wlandres.net My mind is blank about how to set about configuting exim4, so I need very basic instructions (preferably with outline explanation). Maybe a configuration file (where and how?) change, or a command line option to exim4 (the latter is probably simpler for me, since I can enter such options in my MUA setup). With thanks! Ted. ------------------------------------------------- E-Mail: (Ted Harding) <Ted.Harding(a)wlandres.net> Date: 04-Aug-2012 Time: 17:07:50 This message was sent by XFMail -------------------------------------------------

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For Pi users
by nev young 03 Aug '12

03 Aug '12

Something that may be of interest to both ALUG and 2600 members is this magazine (it's free) for the Raspberry Pi. The url is http://www.themagpi.com Nev

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LAN traffic sniffing/monitoring - good tools and methods - help wanted
by Chris Green 31 Jul '12

31 Jul '12

I want somehow (if it's possible) to monitor the packets going into and out of one ethernet address/MAC address on my LAN. I think it's currently plugged into a port on my 8-port Gigabit switch but I'm not absolutely sure of that. The LAN comprises a Draytek Vigor ADSL router talking to the outside world and a Linksys 8-port Gigabit router with most of my LAN systems plugged into that. I think a couple of the four ports on the ADSL router may be in use in addition to the one that connects to the 8-Port Gigabit switch. Is there any 'easy' way to monitor all traffic to/from one specific IP address on the LAN from my desktop computer or will the switches on the LAN prevent it seeing most of the traffic? Actually even being able to see all traffic between my desktop and the device I'm interested in would probably be sufficient as 'lack of traffic' might well be enough to tell me what I want to know. So what are the best/easiest packet sniffers to run on a desktop machine that would allow me to 'see' all traffic to/from a specific IP address? -- Chris Green

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2600 meeting at 18:00 on Friday the 3rd August.
by Viperfang 31 Jul '12

31 Jul '12

Quick heads up about this months Norwich 2600 meeting, more info at http://www.norwich2600.co.uk

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Xen and OOM killer
by Richard Lewis 30 Jul '12

30 Jul '12

Hi ALUG, I've been managing a Xen hypervisor for about nine months now and occasionally I get problems with DomUs running out of memory. The clients are all students and most of them are running WordPress blogs. The instances of OOM errors I've seen seem to be related to Apache and students serving up large image files. I'm thinking that this shouldn't really be happening; serving up a few ~1MB files shouldn't really be causing Apache to make the OS exhaust *all* available memory, should it? Even if it were servicing several requests simultaneously. Some details: * The host is a Dell PowerEdge x86_64 system with 32 GB RAM * The host OS is Debian 6.0 * We're running Xen 4.0.1 from Debian * The guests all run Debian 6.0 * Each guest has 15 GB of storage, 512 MB RAM, and 1 GB of swap * We currently have ~40 guests running Below is some console output from a DomU that suffered this problem earlier today. You can see that the OOM killer killed Apache. And I'm guessing it killed sshd too as I couldn't connect to the guest. I couldn't find any errors in Xen's logs. Any thoughts on what might be going on here? And come September we'll have a short window in which we could alter out setup. Any suggestions for better ways of providing virtual machines? Perhaps alternatives hypervisors? Or some mechanism other than hypervisors? Cheers, Richard (Working from home: <http://pic.twitter.com/NetsgOS2>) -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Richard Lewis ISMS, Computing Goldsmiths, University of London t: +44 (0)20 7078 5134 j: ironchicken(a)jabber.earth.li @: lewisrichard s: richardjlewis http://www.richardlewis.me.uk/ -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- [ 1656.306197] rs:main Q:Reg invoked oom-killer: gfp_mask=0x201da, order=0, oom_adj=0 [ 1656.306215] rs:main Q:Reg cpuset=/ mems_allowed=0 [ 1656.306222] Pid: 1135, comm: rs:main Q:Reg Not tainted 2.6.32-5-xen-amd64 #1 [ 1656.306230] Call Trace: [ 1656.306242] [<ffffffff810b7318>] ? oom_kill_process+0x7f/0x23f [ 1656.306251] [<ffffffff810b783c>] ? __out_of_memory+0x12a/0x141 [ 1656.306259] [<ffffffff810b7993>] ? out_of_memory+0x140/0x172 [ 1656.306268] [<ffffffff810bb742>] ? __alloc_pages_nodemask+0x4ec/0x5fe [ 1656.306278] [<ffffffff810bcca9>] ? __do_page_cache_readahead+0x9b/0x1b4 [ 1656.306286] [<ffffffff810bcdde>] ? ra_submit+0x1c/0x20 [ 1656.306294] [<ffffffff810b5a66>] ? filemap_fault+0x17d/0x2f6 [ 1656.306302] [<ffffffff810cba22>] ? __do_fault+0x54/0x3c3 [ 1656.306313] [<ffffffff8130c7d1>] ? __wait_on_bit_lock+0x76/0x84 [ 1656.306323] [<ffffffff8100c3a5>] ? __raw_callee_save_xen_pud_val+0x11/0x1e [ 1656.306333] [<ffffffff810cdda8>] ? handle_mm_fault+0x3b8/0x80f [ 1656.306342] [<ffffffff8100ecf2>] ? check_events+0x12/0x20 [ 1656.306351] [<ffffffff8130fb26>] ? do_page_fault+0x2e0/0x2fc [ 1656.306360] [<ffffffff8130d9c5>] ? page_fault+0x25/0x30 [ 1656.306366] Mem-Info: [ 1656.306370] Node 0 DMA per-cpu: [ 1656.306376] CPU 0: hi: 0, btch: 1 usd: 0 [ 1656.306381] Node 0 DMA32 per-cpu: [ 1656.306388] CPU 0: hi: 186, btch: 31 usd: 75 [ 1656.306397] active_anon:55210 inactive_anon:55287 isolated_anon:1350 [ 1656.306398] active_file:10 inactive_file:11 isolated_file:26 [ 1656.306400] unevictable:0 dirty:0 writeback:171 unstable:0 [ 1656.306401] free:1180 slab_reclaimable:922 slab_unreclaimable:2187 [ 1656.306402] mapped:16 shmem:7 pagetables:7768 bounce:0 [ 1656.306422] Node 0 DMA free:2032kB min:80kB low:100kB high:120kB active_anon:6168kB inactive_anon:6312kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:14868kB mlocked:0kB dirty:0kB writeback:8kB mapped:20kB shmem:0kB slab_reclaimable:0kB slab_unreclaimable:76kB kernel_stack:16kB pagetables:292kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:3 all_unreclaimable? yes [ 1656.306456] lowmem_reserve[]: 0 489 489 489 [ 1656.306467] Node 0 DMA32 free:2688kB min:2788kB low:3484kB high:4180kB active_anon:214672kB inactive_anon:214836kB active_file:40kB inactive_file:44kB unevictable:0kB isolated(anon):5400kB isolated(file):104kB present:500960kB mlocked:0kB dirty:0kB writeback:676kB mapped:44kB shmem:28kB slab_reclaimable:3688kB slab_unreclaimable:8672kB kernel_stack:1232kB pagetables:30780kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:328 all_unreclaimable? yes [ 1656.306501] lowmem_reserve[]: 0 0 0 0 [ 1656.306512] Node 0 DMA: 4*4kB 1*8kB 0*16kB 1*32kB 1*64kB 1*128kB 1*256kB 1*512kB 1*1024kB 0*2048kB 0*4096kB = 2040kB [ 1656.306537] Node 0 DMA32: 232*4kB 2*8kB 1*16kB 0*32kB 1*64kB 3*128kB 1*256kB 0*512kB 1*1024kB 0*2048kB 0*4096kB = 2688kB [ 1656.306561] 8628 total pagecache pages [ 1656.306566] 8586 pages in swap cache [ 1656.306571] Swap cache stats: add 1078026, delete 1069440, find 120149/196407 [ 1656.306579] Free swap = 4kB [ 1656.306583] Total swap = 1048568kB [ 1656.308293] 131072 pages RAM [ 1656.308302] 4044 pages reserved [ 1656.308307] 22558 pages shared [ 1656.308311] 123779 pages non-shared [ 1656.308317] Out of memory: kill process 489 (apache2) score 125474 or a child [ 1656.308324] Killed process 964 (apache2)

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OT Maths Jam
by Steve Engledow 26 Jul '12

26 Jul '12

Hi folks, Would anyone be interested in a Norwich maths jam? See http://www.mathsjam.com/ for (fairly vague) details or check the twitter account (@MathsJam). tl;dr: We get together in a pub on the second-to-last tuesday of the month and be geeky. I know, it sounds like the pubmeet; but this time we be geeky about mathsy things! I reckon there ought to be enough maths geeks among the linux geeks for this to be relevant :) Steve

3 3

Pubmeet report
by Steve Engledow 25 Jul '12

25 Jul '12

Hi all, It's been a while since a pubmeet had a write-up but I thought it was worth a go :) On a suggestion from rlp10, last night ended up being somewhat of a PGP key-signing party. All of us around the table (there were 6 of us) - plus one passer-by that I happened to know - had PGP (or rather GPG) keys so, over the course of the night, we managed to each sign eachothers keys. There was even provision of ID and encrypted emails sent to verify identity and key ownership. A fairly textbook key-signing I'd say. Additionally, we collectively managed to get a sensible mutt config together for getting GPG integrated and working. For reference, the magical invocation to make mutt understand encrypted/signed mail from Macs and Thunderbird is: message-hook '!(~g|~G)~b"^-----BEGIN\ PGP\ (SIGNED\ )?MESSAGE"' "exec check-traditional-pgp" Stick that in your .muttrc and it all works nicely. (You need a `source /path/to/muttrc.gpg`) line in there somewhere too. The path varies by distro.) Aside from the PGP-related fun, katsmeat had brought an interesting old PC that had a built-in LCD display and ran Microsoft BASIC (I don't remember what the machine actually was) and I offloaded a load of old hardware onto rlp10 \o/ The food didn't seem as good as usual. The beer did. Until next month! Steve (Stilvoid)

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SyncNorwich
by Paul Grenyer 25 Jul '12

25 Jul '12

Hi All I just wanted to make sure you guys were all aware of www.syncnorwich.com, a new group for people in Norwich interested in Technology, Startups and Agile. Out next event is some lightning talks on the 16th August and there's a Norwich lunch on the 23rd August. -- Thanks Paul Paul Grenyer e: paul.grenyer(a)gmail.com b: paulgrenyer.blogspot.com t: pjgrenyer SyncNorwich: http://www.syncnorwich.com ACCU Member: License to code: http://www.accu.org

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