Roundtable

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2555 discussions

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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Fix resolv.conf on WSL instantiation...
by Sean Cody 03 Jun '20

03 Jun '20

I must be having a rough week or just getting older but I can’t seem to come up with an elegant solution to this problem… Ok… I have WSL on my workstation, when I establish VPN to $work, WSL buggers resolv.conf. From: nameserver <mine> search <$homedomain> To: nameserver <mine> nameserver <$work1> nameserver <$work2> search <$workdomain> I have to manually take line 1 and move it to line 3 for internal resolution to work… EVERY DAMNED TIME WSL instantiates (while VPN is established). This is because $workdomain is blackholed publicly. My first thought was a stupid ed script to move line 1 to 3… that didn’t work so well (my ed skills are apparently lacking). Ideally the solution would note if there 3 or more nameserver lines, move the lines before ‘nameserver <$work1>’ to one line before the last file. I’d pop that into my .bashrc/.profile or similar. I couldn’t find how WSL manipulates the file itself otherwise I would have tried to change it… Anyone have any ideas there? -- Sean

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MUUG Online Meeting, Tuesday, June 9, 7:30pm -- Net-SNMP Setup
by Gilbert E. Detillieux 02 Jun '20

02 Jun '20

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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Apache comments
by Gilbert E. Detillieux 02 Jun '20

02 Jun '20

After using Apache httpd for over 20 years, I just discovered today, by accident, that comments are not allowed on the same line as directives in the configuration files... https://stackoverflow.com/questions/50084211/how-to-add-comment-in-apache-h… https://httpd.apache.org/docs/2.4/configuring.html#syntax Not sure how I've managed to edit those config files all these years without coming across this before! 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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