- Roundtable - muug.ca

MUUG Online Meeting, Tuesday, Sept 8, 7:30pm -- AWS Quickstart, RTFM: fd(1)
by Gilbert E. Detillieux 01 Sep '20

01 Sep '20

The Manitoba UNIX User Group (MUUG) will be holding its next monthly meeting online, on Tuesday, September 8th, at 7:30pm: AWS Quickstart For the new user, the multitude of AWS services and configurations can be daunting. Wyatt Zacharias will show how to start an AWS account from scratch, including how to properly set up your user credentials, and how to get a VM up and running for the first time. RTFM: fd(1) - a simple, fast, user-friendly alternative to find(1) Most Linux users are all too familiar with the find command and its frustrating syntax. This month, Brad Vokey will show us an alternative to the find command, called fd. Some of the features of fd: convenient syntax: fd PATTERN instead of find -iname '*PATTERN*', colourized terminal output, it's fast!, uses smart case by default, ignores hidden directories and files by default, ignores patterns from your .gitignore by default, uses proper PCRE, and the command name is 50% shorter than find. :-) Door Prizes On top of the usual assortment of e-books on offer this month, we'll have a hard copy of the O'Reilly book "Unicode Explained" as a door prize. The book will be available for pick-up, drop-off, or snail-mailing. Join the meeting: https://jitsi.merlin.mb.ca/muug.2020.09 The group holds its 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. For more information about MUUG, and its monthly meetings, check out their web server: https://muug.ca/ Help us promote this month's meeting, by putting this poster up on your workplace bulletin board or other suitable public message board, or linking to it on social media: https://muug.ca/meetings/MUUGmeeting.pdf -- Manitoba UNIX User Group E-mail: <gedetil(a)muug.ca> c/o Gilbert E. Detillieux Web: http://muug.ca/ University of Manitoba Phone: (204)474-8161 Winnipeg MB CANADA R3T 2N2 Fax: (204)474-7609

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Battery replacement service
by Kevin McGregor 31 Aug '20

31 Aug '20

Sorry for off topic posting. Does anyone know of a place where I can get a battery replaced for an early 2015 MacBook Pro? It gets a very low repairability score, and I don’t want to try it myself.

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sshd: Corrupted MAC on input.
by Gilbert E. Detillieux 11 Aug '20

11 Aug '20

I've been getting errors such as the following on one of my systems recently... Jul 29 11:15:33 localhost sshd[26456]: Corrupted MAC on input. Jul 29 11:15:33 localhost sshd[26456]: ssh_dispatch_run_fatal: Connection from 123.123.12.34 port 61436: message authentication code incorrect These tend to happen during large rsync runs, which causes rsync to abort. Following some advice I found on The Google, I tried setting various different values for the "MACs" keyword in sshd_config, but it doesn't seem to change the behaviour. (And, yes, I did remember to restart the sshd service after each config change. Running "ssh -vvv" to the host shows that it's negotiating the new MAC protocol.) What's the likely cause of this? A bad NIC? Bad RAM? (I'm guessing something is corrupting the packets once in a while, but I'm not sure what. If so, it seems to get past TCP's error correcting.) Has anyone else come across this before, and have a suggestion? Thanks, Gilbert -- Gilbert E. Detillieux E-mail: <gedetil(a)cs.umanitoba.ca> Dept. of Computer Science Web: http://www.cs.umanitoba.ca/~gedetil/ University of Manitoba Phone: (204)474-8161 Winnipeg MB CANADA R3T 2N2 Fax: (204)474-7609

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hung mysql transaction locks after a php runtime error?
by Trevor Cordes 01 Aug '20

01 Aug '20

I'm doing a lot with mysql innodb transactions in php these days. I'm wondering, if I start a transaction and use "FOR UPDATE" to lock a bunch of rows (or maybe more critically, the "next auto-insert row"), and then PHP hits a runtime error (say a call to non-existant function), will something in php or mysql (or probably more precisely php's mysqli library) rollback my transaction? Or will my transaction locks stay in place until the next user of that php-fpm thread calls "rollback" or "start transaction"? ... possibly hanging a subsequent web hit if they need the locked rows! (Yes, innodb_lock_wait_timeout in mysql will eventually clear things up, but I'm using the default of 50 to be safe, and I don't want an end user UX to wait 50s for a page load!) I'm using php's default mysqli persistence options, so the connection, while not "pooled", does persist across web page hits (for performance reasons). I'm guessing if I turned off all mysql persistence in php that mysql itself would rollback when it senses the lost connection. However, I'm not sure how much performance I'll lose if php can't use connection persistence? I assume this problem would also exist for other db engines and other hit-based web languages (with persistence). Maybe it's late, but I'm having a hard time coming up with test case that proves what is going on one way or another. However, I could swear that I've already hit the problem and had web hits hang until restarting mysql. In the meantime I'm putting a "rollback" call in my mysql connect function so after (re)connecting to a persistence connection it'll rollback any previous-errored-out-hit leftover garbage. However, with many fpm threads/ps's who knows if the errored-out thread will get a new hit right away!

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PSA - Systems not booting up after installing BootHole patches
by Alberto Abrao 01 Aug '20

01 Aug '20

Originally reported for RedHat/CentOS, seems to affect Ubuntu, Debian and Fedora as well. Can confirm that my Fedora Server did not come back after the update+reboot cycle of today. Debian and Ubuntu servers have the update installed, but are not configured to restart automatically, so they are still working: https://arstechnica.com/gadgets/2020/07/red-hat-and-centos-systems-arent-bo… Kind regards, Alberto Abrao

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Rackmount Systems to give away
by Gerald Brandt 10 Jul '20

10 Jul '20

Hi, I have three rackmount systems I don't want any more. Free for the taking. One is a dual Xeon with 32GB of RAM. The other two are AMDs, also with 32 GB RAM. I don't remember CPU specs. AMD

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Cron entries for sunrise and sunset
by Troy Denton 05 Jul '20

05 Jul '20

A fun side project of mine - I've patched the Debian 'cron' source to provide @sunrise and @sunset, similar to @reboot https://github.com/trdenton/tron The motivation for this was to change zoneminder <https://zoneminder.com/> motion detection parameters based on the amount of sunlight. I don't have any other use for it yet, but it might serve to inspire similar ideas -Troy

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Shell exec(2) help?
by Adam Thompson 05 Jul '20

05 Jul '20

I've written a shell script that redownloads itself and re-executes itself, but I'm not quite seeing the behaviour I'd expect out of "exec sh". Instead of one process, I get an infinite progression of shells that finally blows up when I hit ulimits. The script: ===BOF=== curl -s $URL/targets \ | while read TGTNAME TGTIP ; do ( echo -n "." mtr \ --interval 0.1 \ --gracetime 1 \ --timeout 1 \ --report-wide \ --report-cycles 600 \ --show-ips \ --aslookup \ --no-dns \ ${TGTIP} \ | awk -f parse.awk -v TGT=${TGTNAME} \ | psql -q -b -h $PGHOST -U $PGUSER $PGDB ) & wait & done # start all over again sleep 60 & wait curl -s $URL/go.sh | exec sh ===EOF=== The key items are the backgrounding of mtr/awk/psql, which appears to work properly - there's 12 lines in "targets" and I only see 12 mtr/awk/psql process groups at a time - the sleeping + waiting (which theoretically reaps all children and grandchildren, I think) and the final "exec". Except instead of exec'ing, I run an infinite sequence of shells, each one a child of the previous. E.g. from pstree(1): # pstree -lp 1628 screen(1628)─┬─bash(1629)───sh(12707)───sh(12854)───sh(12986)───sh(13154)───sh(13309)───sh(13444)───sh(13579)───sh(13709)───sh(13842)───sh(13979)───sh(14101)───sh(14242)───sh(14396)───sh(14530)───sh(14655)───sh(14795)───sh(14935)───sh(15076)───sh(15203)───sh(15353)───sh(15490)───sh(15624)───sh(15753)───sh(15891)───sh(16023)───sh(16154)───sh(16282)───sh(16418)───sh(16551)───sh(16696)───sh(16842)───sh(16975)───sh(17112)───sh(17241)───sh(17388)───sh(17522)───sh(17664)───sh(17824)───sh(17956)───sh(18096)───sh(18233)───sleep(18279) I think the problem has something to do with the fact the final exec is on the RHS of a pipe, and thus is executing inside a subshell, but how do I fix this? Thanks, -Adam

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Re: [RndTbl] Shell exec(2) help?
by Stephen Moffat 02 Jul '20

02 Jul '20

Hi if you are open to another option, I've used the "at" command to reschedule a script from itself. This would allow you to download a new version of the script and have it execute as you expect, without the recursive PID issue. like: echo ${0} | at now + 1 minute Cheers.

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Reminder: MUUG Online Meeting, Tonight, June 9, 7:30pm -- Net-SNMP Setup
by Gilbert E. Detillieux 09 Jun '20

09 Jun '20

A reminder that the online MUUG meeting is happening this evening... -------------------------------------------------------------------- The Manitoba UNIX User Group (MUUG) will be holding its next monthly meeting online, on Tuesday, June 9th, at 7:30pm: Daemon Dash: Net-SNMP Setup Simple Network Management Protocol (SNMP) is a widely used protocol for monitoring the health and welfare of network equipment (e.g. routers), computer equipment and even devices like UPS's. Net-SNMP is a suite of applications used to implement SNMP v1, SNMP v2c and SNMP v3 using both IPv4 and IPv6. Adam Thompson will demonstrate how to quickly set up the Net-SNMP daemon using the built-in configuration tools. We will also attempt to do an online "door prize" draw this month! Join the meeting: https://jitsi.merlin.mb.ca/muug.2020.06 The group holds its 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. For more information about MUUG, and its monthly meetings, check out their web server: https://muug.ca/ Help us promote this month's meeting, by putting this poster up on your workplace bulletin board or other suitable public message board, or linking to it on social media: https://muug.ca/meetings/MUUGmeeting.pdf -- Manitoba UNIX User Group E-mail: <gedetil(a)muug.ca> c/o Gilbert E. Detillieux Web: http://muug.ca/ University of Manitoba Phone: (204)474-8161 Winnipeg MB CANADA R3T 2N2 Fax: (204)474-7609

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