Roundtable April 2016

roundtable@muug.ca

13 participants
14 discussions

programatically determine if DNS is down or blocked?
by Trevor Cordes 06 Apr '16

06 Apr '16

I have a program that needs to do DNS lookups, etc. Things will go Really Wonky if there's a problem with DNS (from a client perspective). Thus, I'd like the program to be able to check if DNS isn't working. In this particular setup, the box runs its own named with a view setup for resolution/caching. In particular, I want to test that: 1. named is running and answering calls to its port 2. named is getting real answers from the net (i.e. doing its recursive resolution properly; and port 53 to outside NS's isn't being blocked) 3. (rare) root NS's aren't getting DDoS'd / whole world's DNS is down I want to do this inside a perl or php program, but any language pseudo-code will be fine as a template. I don't want to run a full-blown monitoring program separately. Ideally, I'll have some php like: function IsDnsOk() { check named check resolution ok } To be used possibly like: while (!IsDnsOk()) { sleep 10; } $important_dns_result=gethostbyname($host); But I want any check to be fairly lightweight. I don't want to fire off useless DNS lookups to root name servers at a potential rate of thousands a minute. Plus, I guess I have to worry about cached results making things look ok when they are really not. Any solution I implement will probably be designed to only run these tests once a minute or something, which won't catch the instant DNS goes down, but will mitigate the damage caused. I can think of a number of fairly simple tests I can try, but they feel kind of kludgy. Is there a better way? Ideally, the PHP calls, like gethostbyname would be able to return a "down" status, but they decided to lump in to the same return value failure due to no dns record and failure due to any other reason. Thanks!

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MUUG Meeting, Apr 12, 7:30pm -- GNUPlot & NFS
by Gilbert Detillieux 05 Apr '16

05 Apr '16

The Manitoba UNIX User Group (MUUG) will be holding its next monthly meeting on Tuesday, April 12. The meeting topic for this month is as follows: GNUPlot Brian Lowe will be presenting gnuplot, a powerful mathematical graphing and charting program. In constant development for the past thirty years, gnuplot is a mature command-driven program capable of producing presentation-ready charts and graphs. Brian will be showing some of the more impressive 2D and 3D graphs gnuplot can produce, and a couple of practical charts he's used the program for. Daemon-Dash: NFS In this month's Dæmon Dash segment, Adam Thompson will demonstrate simple, common use cases for NFS (Network File System) sharing. The group holds its general meetings at 7:30pm on the second Tuesday of every month from September to June. (There are no meetings in July and August.) Meetings are open to the general public; you don't have to be a MUUG member to attend. ****************************************************************** Please note our *NEW* meeting location for this month: *Room 3M60* (3rd floor) Manitoba Hall, University of Winnipeg, entrance on Ellice Ave. between Spence St. and Balmoral St. Parking is available on the surrounding streets and in the lots on nearby streets. Look for signage once you're at the building, or ask a security guard. ****************************************************************** For more information about MUUG, and its monthly meetings, check out their web server: http://www.muug.mb.ca/ Help us promote this month's meeting, by putting this poster up on your workplace bulletin board or other suitable public message board: http://www.muug.mb.ca/meetings/MUUGmeeting.pdf -- Manitoba UNIX User Group E-mail: <gedetil(a)muug.mb.ca> c/o Gilbert E. Detillieux Web: http://www.muug.mb.ca/ University of Manitoba Phone: (204)474-8161 Winnipeg MB CANADA R3T 2N2 Fax: (204)474-7609

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Muug.ca Mirror Admin?
by Theodore Baschak 03 Apr '16

03 Apr '16

Just curious who's the administrator of the muug.ca mirror? I'm getting errors on the Debian Jessie (Stable) distribution: ERROR: W: Failed to fetch http://muug.ca/mirror/debian/dists/jessie/main/i18n/Translation-en Hash Sum mismatch Theodore Baschak https://ciscodude.net/ https://theodorebaschak.com/ http://mbix.ca/

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shrink to smaller disk, offsite
by Trevor Cordes 02 Apr '16

02 Apr '16

I have an interesting problem. Linux box. /, /boot, swap on 3 RAID1 partitions 2 disks currently RAID is degraded, just using 1 750G disk. / (ext3) is 700G, only 200G used. No LVM. I added a 500G SSD. I want that to be the new 2nd RAID1 disk. I need to shrink / to be ~450G before I can do this. resize2fs can only do shrink on unmounted. That's a problem. RAID1 can shrink the RAID block dev once I get the fs shrunk, so that's not a problem. I'm offsite and want to find a way to do this without going onsite and using single-user mode or a boot cd. Options? I guess I could make a new, smaller RAID1 / on the SSD, quiet down all services, and do a cp -a or cpio or something? Then get the system to boot off the new / and ignore the old one, and reboot. Besides in theory, has anyone actually do a whole cpio or cp -a of an entire *running* / and been successful? Sample command lines? I guess nowadays there would be zero dev files that need to be copied because udev recreates them all? So it's literally just files, dirs, links and fifos that need copying? Any options using just ext3 and mdadm tools? Surely there must be some way... unless the no-shrink-mounted makes that impossible. Maybe I'm missing something. Thanks!

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Roundtable April 2016