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Sat, 9 Dec 2017

Laser Menorah

— SjG @ 6:49 pm

You know, this title is misleading. The reality is a whole lot more boring. Maybe next year, I should take inspiration from the title.

This is more of a lazy Saturday afternoon project. I wanted to use some designs that I’ve been kicking around. So I took a sea of hexagons and a tree in Affinity Designer and mucked about for a bit until I had something where I more or less liked the look.

Next, I grabbed a slice of poplar (available in 8″ x 24″ x 0.25″ slabs at Home Deport, as “Hobby Poplar”) and drove over to CRASH Space. While it’s mega-take-apart-day, I scurried over to the laser cutter. I converted the design to PDF, loaded it up in Corel Draw, used the Epilog printer-driver, and sent it to the laser cutter. The poplar cuts very nicely.

Here’s a link to the PDF of the laser-cut portion, if you want to cut a copy yourself.2017-12-09-hexonorah-cut.pdf

I brought the pieces home, sanded lightly, drilled a few holes, and mounted the vertical piece onto the base, carefully mis-aligning it with the major axis of the elliptical base. Ah well.

I drilled holes where I would mount the candle holders themselves (after all, poplar is pretty, but not ideal as a holder for things on fire). For the actual sockets, I used some nice quarter-inch brass compression caps (also from Home Depot). I drilled a center hole, pushed through a brad, and then soldered it with a torch.

Next, let things cool, dried off the sockets, and put it all together.

The final result is not as attractive as I had imagined it. It’s a little … I dunno, squat? Perhaps the next iteration will have more dramatic tree-like branches emerging to hold the candles.

OK. Next year, forget the design. We’ll just go with lasers.

Sat, 7 Oct 2017

Simple file monitor

— SjG @ 11:59 am

Say you host a few web sites for various folks, and you give them write access to a directory on your server. Well, then, my friend, you’re as big a fool as I am.

Maybe you want to mitigate this foolhardiness by keeping an eye on what these folks upload. For example, when I see a user uploading SuperBulletinBoardThatIsTotallyNotASpamTool.php or SuperWordPressPasswordSharingPlugin.php, I can call them and explain why I’m deleting it. I can be a slightly-less-bastard operator from heck.

So here’s a quick bash script that I use. It’ll also help to alert you if somehow one of the WordPress sites gets compromised, and rogue php files get installed. It ignores commonly changing files or things we’re not interested in like images. It shouldn’t be considered an intrusion detection system, or a robust security auditing tool — this wouldn’t really help in the case of an actual hacker with any l33t skillz at all. It’s just a quick information source.


rm -f /tmp/fcl.txt

rm -f /tmp/fcld.txt

/usr/bin/find /var/www/ -type f -ctime -1 | /bin/egrep -v "\\.git|\\.svn|(*.jpg$)|(*.gif$)|(*.pdf$)|wp-content\\/cache|files\\/cache\\/zend_cache" > /tmp/fcl.txt

xargs -0 -n 1 ls -l < <(tr \\n \\0 /tmp/fcld.txt

[ -s /tmp/fcld.txt ] && /usr/bin/mail -s "MYDOMAIN.COM FILES UPDATED" < /tmp/fcld.txt

Throw it into a crontab, and there you have it. You'll get an email with a list of files changed in the past day.

Wed, 27 Sep 2017

Seasonal Palettes

— SjG @ 7:43 pm

Over the years, I’ve written various JavaScript mandala-generators. I like giving variety to the color sets used, and in the past, I’ve hand-crafted collections of colors which I’ve given descriptive names like “Earthy,” “Angst,” and “Scorchio.”

For a new project, I wanted seasonal palettes. Being a northern-hemisphere dweller, I think of January as cool colors, May as yellows and greens, August as ambers and oranges, etc. Rather than hand assemble them, I thought this would be a good use for the Interwebs.

So I wrote a bash/php/ImageMagick script that would hit with a seasonal search term to bring back the first twenty-five matching pictures. It then made a composite of the pictures, did a pixelation process, reduced the colors to a minimum set, and built a palette from them.

With excuses of fair use, here’s a visual of that process, using the example where the search terms were “Landscape July”:

1. Images are brought down, each scaled to fit in a 64 x 64 pixel square, and then they’re all combined into a single image.

2. The combined image is pixelated by scaling to 5% of the original size, then scaling back up to a larger size.

3. To get a little more punch and a little less muddy, the pixelated image has its histogram equalized

4. For good measure, the script then reduces the image to 32 colors.

Now, some of this may be redundant. For example, we could easily skip step 2, since we’re reducing colors in step 4. However, this way we sort of reduce the color space before we equalize the histogram. Maybe I should experiment with other paths here.

In any case, the results for my first search term “($month) Landscape” was not very good:

I tried some other search terms for good measure.

Here’s “($month) colors”:

Here’s “($month) thoughts”:

And finally, here’s “($month) skies”:

I have a few conclusions. First, it’s obvious that a hand-created set of palettes would be better. The pictures Flickr returned for each search term didn’t match my expectations very well. Perhaps I’d have done better with season names instead of month names. Lastly finding the best palette from an image is a problem that Google tells me many have worked on. I’m assuming others have probably done better than I.

But it’s a curious question — what are the “characteristic” colors from an image? My approach largely comes down to the number of pixels of a given general color. Are there lots of blues? My approach will have at least some blue. But if an accent color is “important,” whatever that means, my approach will probably lose it.

In any case, it’s probably back to mandalas and hand-crafted palettes for the next project.

Thu, 21 Sep 2017

Time Machine Backups

— SjG @ 3:37 pm

I use Time Machine for my local desktop backups. It’s a nice solution. It sits there quietly backing stuff up, keeping multiple revisions of files, and even keeping it all encrypted so if the external drive gets swiped it’s not going to be easy to get at the data.

Of course, it’s no substitute for a revision control system for code, nor is it good for situations where the office gets annihilated due to stray meteorite or drone strike. It’s not a complete solution, but it’s part of a broader collection of solutions.

Today I was reminded of some of the limitations. I used Time Machine to migrate to a new machine. That’s a pretty sweet process. You wait for a few hours of disk read time, and suddenly a new machine is populated with all your old settings, applications, data, and so on from your old machine.

But I found some things that weren’t quite right. Most of them had to do with processes that keep open files or databases, and don’t get backed up in a clean fashion.

  • Interestingly, Safari didn’t propagate Ublock Origin, which was a manually-added extension. This was the only surprising one of the bunch.
  • MySQL databases. I hadn’t shut down the MySQL server when the backup ran, so the table files from the Time Machine restore were corrupted. I was able to copy the files off the old machine (after shutting down mysqld gracefully), and use those.
  • TimeKeeper‘s datastore files were all corrupted. I had to delete them, and re-export/import the data from the old machine.
  • VMWare Virtual Machines. I knew they’d get corrupted if backed up by TimeMachine for the same reason as the above, but then I forgot that they weren’t backed up. I had to manually copy them off the old machine. This reminded me — if I want backups of my VMs, I need to do it myself!

That’s all thus far. Nothing too surprising, but a good reminder. Just because you’re backing up, doesn’t necessarily mean you’re backing up stuff in a restorable state!

Thu, 31 Aug 2017

Getting nagios back up and running… again.

— SjG @ 12:42 pm

Nagios monitoring on one Centos 6.9 server seemed to have stopped working after an upgrade. All the tests showed status OK, but they hadn’t actually run in days.

Looking at the service details was weird, because the next scheduled check was about a minute in the past.

The Nagios help page wasn’t. And we’re running Core 4.3.x anyway, without a MySQL database.

The first clue was a bunch of lines in the event log:
Error: Could not open check result queue directory '/var/log/nagios/spool/checkresults' for reading.

Turns out we didn’t even have a /var/log/nagios/spool directory. Creating those directories helped. But Nagios still wouldn’t start from the usual startup scripts. Nothing in the main log. But then, another clue.

Who doesn’t love to see shit like this:

$ cat /var/log/nagios/nagios.configtest
ERROR: Errors in config files – see log for details: /var/log/nagios/nagios.configtest

So the startup script /etc/init.d/nagios searches for warnings, and aborts if they exist. It’s supposed to log them. For some reason it didn’t.

You can manually get those warnings and errors yourself by running

/usr/sbin/nagios -v /etc/nagios/nagios.cfg (adjust paths as appropriate).

I ended up with a bunch of warnings for deprecated parameters. So I went in and edited my config files to remove them or update them to the new equivalents. Oh yes. Software authors, please keep in mind: nothing pleases your users more than changing the names of variables in config files. We users live for this shit. When, oh when, will the author of our software next change “retry_check_interval” to “retry_interval”?

Fixing all of the warnings was not enough, though. The startup script gave the message “Starting nagios:” and then silently died. Well, sort of. It actually was starting now, but brokenly:

# ps aux | grep -i nagios
nagios 12610 0.0 0.0 12296 1220 ? Ss 16:36 0:00 /usr/sbin/nagios -d /etc/nagios/nagios.cfg
nagios 12611 0.0 0.0 0 0 ? Z 16:36 0:00 [nagios] <defunct>
nagios 12612 0.0 0.0 0 0 ? Z 16:36 0:00 [nagios] <defunct>
nagios 12613 0.0 0.0 0 0 ? Z 16:36 0:00 [nagios] <defunct>
nagios 12614 0.0 0.0 0 0 ? Z 16:36 0:00 [nagios] <defunct>
nagios 12616 0.0 0.0 11780 520 ? S 16:36 0:00 /usr/sbin/nagios -d /etc/nagios/nagios.cfg
root 12744 0.0 0.0 103328 876 pts/0 S+ 16:44 0:00 grep -i nagios

Starting directly from the command line worked:

# /usr/sbin/nagios -d /etc/nagios/nagios.cfg
# ps aux | grep nagios
nrpe 7282 0.0 0.0 41380 1340 ? Ss 16:51 0:00 /usr/sbin/nrpe -c /etc/nagios/nrpe.cfg -d
nagios 8010 0.0 0.0 16404 1280 ? Ss 17:31 0:00 /usr/sbin/nagios -d /etc/nagios/nagios.cfg
nagios 8011 0.0 0.0 10052 920 ? S 17:31 0:00 /usr/sbin/nagios –worker /var/spool/nagios/cmd/nagios.qh
nagios 8012 0.0 0.0 10052 920 ? S 17:31 0:00 /usr/sbin/nagios –worker /var/spool/nagios/cmd/nagios.qh
nagios 8013 0.0 0.0 10052 920 ? S 17:31 0:00 /usr/sbin/nagios –worker /var/spool/nagios/cmd/nagios.qh
nagios 8014 0.0 0.0 10052 920 ? S 17:31 0:00 /usr/sbin/nagios –worker /var/spool/nagios/cmd/nagios.qh
nagios 8015 0.0 0.0 15888 552 ? S 17:31 0:00 /usr/sbin/nagios -d /etc/nagios/nagios.cfg
root 8018 0.0 0.0 100956 616 pts/0 S+ 17:31 0:00 tail -f /var/log/nagios/nagios.log
root 8037 0.0 0.0 103328 856 pts/1 S+ 17:32 0:00 grep nagios

When things get this weird, there are only two options. Well, three, if you include the “rm -rf /” option. But the other two are: 1) reboot and see if stuff magically starts working, or 2) see what SELinux is breaking.

# tail -f /etc/audit/audit.log
type=AVC msg=audit(1504137329.209:41): avc: denied { execute_no_trans } for pid=7731 comm=”nagios” path=”/usr/sbin/nagios” dev=dm-0 ino=1201464 scontext=unconfined_u:system_r:nagios_t:s0 tcontext=system_u:object_r:nagios_exec_t:s0 tclass=file

Yup. As expected, SELinux breaking stuff.

So, my preferred way to solve this kind of problem now is to snip out all relevant the AVC “denied” sections from the log into a single file (which I called audit.log), and then using audit2allow to create a new module. Since there’s already a nagios module (containing insufficient privileges), I created a nagios2 module:

# audit2allow -M nagios2 < audit.log # semodule -i nagios2.pp

Hooray! After a few iterations of this process (discovering other blocked operation, granting them permission, restarting nagios), everything was working but check_disk_smb, which was returning “results from smbclient not suitable” even as it worked fine when tested from the command-line as follows:

# su – nagios -s /bin/bash -c “/usr/lib64/nagios/plugins/check_disk_smb -H SMBHOST -s share -a 10.X.X.X -u nagios -p \”password\” -w 90 -c 95″
Disk ok – 16.71G (11%) free on \\SMBHOST\share | ‘share’=134108676096B;136850492620.8;144453297766.4;0;152056102912

Diving in and editing check_disk_smb to throw the actual error message, I found nagios getting a “ERROR: Could not determine network interfaces, you must use a interfaces config line” from smbclient. So I edited /etc/samba/smb.conf, and explicitly told samba which interfaces it had available:

interfaces = lo eth0 10.X.X.X/24

Le sigh. Now this error went away, and I got to go for another fun and challenging round of “find all the SMB operations that SELinux is breaking.” This time, I got tripped up the “dontaudits” — there were operations being blocked, but not logged. I was saved by TrevorH and sfix, helpful people in Freenode’s #centos IRC channel:

TrevorH: semodule -DB to disable dontaudit rules, stay permissive, recreate, use the audit log to generate a policy as per the wiki
13:14 TrevorH: @selinux
13:14 centbot: Useful resources for SELinux: | | | |
13:15 _SjG_: Thanks
13:16 TrevorH: semodule -B when done (as well as setenforce 1)
13:25 _SjG_: TrevorH: thanks, that resolved it.
13:25 _SjG_: so what I was missing is that there can be donaudit rules that were preventing specific operations from showing up in the audit log?
13:28 TrevorH: yes
13:28 sfix: _SjG_: yep, there’s permissions in the policy that we know are requested but don’t want to allow for whatever reason. dontaudits are our way of preventing them from cluttering the audit log.
13:29 sfix: dontaudits tend to be a bit over-eager though

So there you have it.

I was finally back to where I had been mere days before.

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