We’ve noticed problems with mouse cursor tracking, on Thunderbolt Macs attached to displays.
In the middle of moving the cursor with mouse or trackpad, the cursor jumps or skips making it difficult to control.
We tracked down the problem to background runs of system_profiler. Specifically, when system_profiler queries the display for information.
Running system_profiler without flags or with the SPDisplaysDataType data type triggers the problem.
To reproduce the problem at its worst, run the following in Terminal on a Thunderbolt Mac attached to a display and attempt to use the tracking device:
while [ 1 ]; do system_profiler SPDisplaysDataType; done
Apple is aware of the issue, but has stated that this is expected behavior.
Many tools that rely on system_profiler trigger the issue including JAMF Casper Suite, Puppet, and Apple Remote Desktop. These and other tools routinely inventory the Mac using system_profiler.
There is currently no workaround for getting display information such as Display serial number. And the only way to avoid the trigger is to run system profiler with each data type excluding SPDisplaysDataType.
If you think Apple should address the issue, please let them know.
Apple has some restrictions in place to prevent access to LaunchAgents running in a user session context.
But you may want to load or refresh a LaunchAgent as part of your install without requiring the user to log out and back in.
I prefer not to require logouts and reboots in my installation packages. Where possible, I use munki’s unattended option so software installs silently and the user is not prompted.
After some experimentation, I came up with this hacky method of getting a LaunchAgent to load from a package being installed as root. If you have a cleaner way to accomplish this, please let me know.
Sometimes you need to trigger a script when data changes in mysql. Sometimes there just aren’t other hooks into the system and the database is your last resort.
It seems like this would be a common use case with a simple solution, but no.
MySQL does support triggers.
However what you can do inside a trigger is limited to what you can do in mysql. This is good for security.
Using the following DOES NOT work!
\! /bin/ls >> /log/yourlog.txt
The !\ (bang or exclamation point + backslash) is a mysql console feature for running commands in the console. These are ignored on the actual server. Do not be fooled. Since you are testing in the console, it will appear to work once, but the trigger will not cause your code to fire.
So you have two options:
2.) MySQL UDF (plugin)
Yes, polling sucks. But what you can do is still create a trigger that uses a separate (maybe in memory) table for capturing the changes. Then your polling script only needs to look at that table to do its work.
So you could use something like this:
Create the temp_changes table (this example creates an in memory table):
CREATE TABLE temp_changes (changed_id INT, from_value VARCHAR(40), to_value VARCHAR(40)) ENGINE=MEMORY MAX_ROWS=500;
Create the mysql trigger:
CREATE TRIGGER tg1 AFTER UPDATE ON `table_i_want_to_watch`
FOR EACH ROW
INSERT INTO temp_changes SET from_value = OLD.column_i_want_to_track, to_value = NEW.column_i_want_to_track, changed_id = NEW.id;
The above will create a row in the temp_changes table with the old and new values and id of the column I want to track in the table I want to watch. Substitute column_i_want_to_track and table_i_want_to_watch with your own table and column names.
Read the MySQL trigger documentation if you need to do something different. This is just an example.
Now your external polling script can query only the temp_changes table without polling your whole database for changes.
MySQL UDF (plugin)
MySQL UDFs offer a powerful way to extend the functionality of your MySQL database. But with great power comes great responsibility right? (A. Yes.)
These plugins are written in C. They need to be compiled and installed in your mysql plugins folder on the mysql server.
Plugins add custom functions you your mysql server.
Security is a major concern with this option because these functions run with the same privileges as the mysqlserver user.
There are a number of plugins published here including
lib_mysqludf_sys, that will allow you to run shell commands.
Here is the justifiably scarey warning from that site:
Be very careful in deciding whether you need this function. UDFs are available to all database users – you cannot grant EXECUTE privileges for them. As the commandstring passed to
sys_execcan do pretty much everything, exposing the function poses a very real security hazard.
Even for a benign user, it is possible to accidentally do a lot of damage with it. The call will be executed with the privileges of the os user that runs MySQL, so it is entirely feasible to delete MySQL’s data directory, or worse.
SQL injection takes on new meaning when the attacker can also run any command on your server.
So my recommendation is to download the source and modify it to hard code a specific path to the executable you want to run if you go this route. I was going to do this, but I’ve had to move on to other endeavors now.
Using the UDF plugin still involves using the mysql trigger functionality. See Mike E’s solution on this stackoverflow post.
Pretty simple, but handy.
curl -X PUT –trace-ascii – -T /path/to/file/to/upload http://thewebdavhost.com/webdirectory/remotefilename
Note that a PUT will overwrite an existing file.
It can be tempting to store unstructured data as key value pairs to avoid lots of schema changes and capture dynamic data. But it can lead to problems.
- Overly complex queries/reporting
- No type support
My conclusion is that it is fine if you will only be accessing the data rather than querying it, or as a temporary capture means until you’ve identified where the data really belongs.
If you have another way to query, like a Lucene index it may also be perfectly fine.
A key value store NoSQL solution may be appropriate, but that brings with it other baggage. Depending on the NoSQL solution you choose, you may have to do some extra work to get the type of search you need or use a Lucene style indexing solution anyway.
If you are using PostgreSQL, you can get much of the best of both worlds using hstore.
And you can easily use it with rails!
This will have the drawback of not being portable to other SQL backends, but that may be a tradeoff worth making.
With the PostgreSQL solution, you can retain one datastore and still allow some ability to store unstructured key values. Then as needed, you can integrate these back into the schema to permanent normalized columns.
Once in a while you run into a package or program that will only work properly with a user logged in. This can ruin your day if you need to automated the deployment.
I found this method of automatically logging in a user (which is quite awesome).
Using that perl script along with a wrapper script can enable you to automate these can other cases where your only option is to have a user logged in.
I started writing a script to handle this, but it turned out I didn’t need it. The script is unfinished, but it may give you a head start if you are considering something similar.
It depends on a modified version of the perl script that accepts a username and password. Just swap out the user and password lines with these that accept arguments.
my $user = $ARGV;
my $pass = $ARGV;
and I comment out the line to automatically restarts the loginwindow.
No feature changes, just a few bug fixes:
- fix issue with replacing a url dock item
- add legacy support –hupdock option for backward compatibility
- fix paths with spaces when passing full path to plist