- Roundtable - muug.ca

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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interesting unix pipe problem (stop whole pipe chain on first match)
by Trevor Cordes 01 Jun '20

01 Jun '20

For the punters out there... think you can find a better (shorter command line? no signals?) way to solve this interesting problem? I want to run an nmap on a network range, but have it quit (with output) the instant it finds the first "up" host. Nmap doesn't seem to have any way to achieve this. So I thought why not use unix pipes to do this? Oh ya, let's throw on a maximum run time too. So the goal is to run as quickly as we can to find one host on the network (the normal case), with the total time capped at something lower than nmap seems to want to take. And I need a way to still tell if the whole enchilada found something or not, and I want to wait for that result to come in. I need to take different action on whether we found a host or not. Note, nmap timeout and rtt options seem to apply per-host so even with sane-ish numbers, nmap will still often take 40-60s to run this command. Here's what I've come up with (view in monospace): echo 192.168.101 | \ timeout 30 bash -c \ " \ sint=\$(cat); \ (nmap -ddd -vvv --send-ip \ --host-timeout 5s --max-rtt-timeout 1s --initial-rtt-timeout 500ms \ --max-retries 1 -S \$sint.1 -sn -PE \$sint.2 \$sint.254-254 2>&1 & \ echo \$! >&3) \ 3>pidnmap \ | grep --line-buffered -P 'RCVD.{0,30}?ICMP.{0,60}?Echo reply' \ | (head -1 && kill \$(<pidnmap) 2>&1) \ " \ |grep RCVD || echo "no hosts found" I initially thought head would sigpipe the nmap once it got it's one line... and maybe it is, but nmap doesn't quit. So I have to explicitly kill the nmap later to make sure it truly dies rather than continue its 60s run. Hence the convoluted pid/kill stuff. I tried pkill -g0 at first, but it ate all the output and made it impossible to tell if we got output or not. And using return values (ideal) seems completely hopeless as soon as signals are involved. And no, setting /bin/timeout to the very minimum time I'm willing to tolerate (say 10s?) is not a good solution either, as I really want this command to return in the < 100ms it takes in the normal case. So, other than hacking nmap to immediately respond to sigpipe or adding a "quit after finding X up hosts" option, does anyone see a better UNIXy way to do this? The general problem isn't nmap specific... it's really a problem of shortcircuiting out of any long-running program when we see a certain line of its output. Heck, maybe there's already a coreutil or moreutil that does this generally somehow, but I couldn't find it faster than I could write the above! My gut says it's just got to be easier than this!! I couldn't believe how convoluted the solution quickly became.

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