The Linux Page


REST hook trigger needs a polling url (ZSE007)

As I'm working on a Zap application (see Zapier). I got this error about my triggers:

REST hook trigger needs a polling url (ZSE007)

So... I understand that they want to have a URL to do a poll and they even have documentation that explains why they want to poll in case of a REST hook Zap: Whenever the user wants to test the Zap, the application will get some data using the polling method. That way they can get that data specifically for one test and not force you to generate an trigger. One problem with testing with an actual trigger is that any other Zap listening to the same trigger ...

tar: .../public_html/wp-content: file changed as we read it

I created a little script to generate a daily tarball as a backup of a customer website.

Everyday, though, I would get the following error:

tar: .../public_html/wp-content: file changed as we read it

As you can see, the website is using Wordpress.

The error, though, I could not replicate when I would run the tar command by hand. What gives?

Looking closer into it, I noticed that my crontab setup would actually run the cron.php at the same time as the backup would run:

# m h  dom mon dow   command
  0 3  *   *   *     /.../backups/

*/10 * *   *   *     cd /.../public_html ...

How to find fail2ban errors when logs/errors don't make it anywhere?

Today I noticed that my fail2ban wasn't running.

Looking into it, I could see that an error was happening on startup. This pretty much always mean that something's wrong in the configuration files.

sudo systemctl start fail2ban
Job for fail2ban.service failed because the control process exited with error code.
See "systemctl status fail2ban.service" and "journalctl -xe" for details.

However, somehow, systemd would not show me the error with the status or checking the journal and it would not write anything to the /var/log/fail2ban.log file which stayed ...

SSL_ERROR_RX_UNEXPECTED_NEW_SESSION_TICKET and ssl3_get_message:unexpected message

Today we had a problem with a combo of website that we never tried to run together.

Looking into it, it was definitely a problem with SSL. However, Apache2 would tell us absolutely nothing about it. No error or access logs. I think this is because it would happen at the time Apache and the client negotiate the SSL connection and Apache does not report such problems (at least by default, it might in case you turn on some debug mode?)

We had two different settings for two websites using the snakeoil certificate (As we test on VM machines, we use the snakeoil certificate as an easy way to check ...

Error trying to upgrade software on an Ubuntu system

Today I got a really strange error. Part of the message was:

E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/<some name>
E: The package lists or status file could not be parsed or opened.

That seemed really bizarre. I had never seen such an error before...

So I searched for it and one thing to know is that the files under that directory are temporary, so you can actually delete them. apt-get knows how to regenerate them.

So in other words you can do something like this:

sudo rm /var/lib/apt/lists/<some file>
# or ...

Writing a Shell Script from cmake

In cmake, you have a cool feature which allows you to create a file.

First you use a WRITE, then you use the APPEND to add more lines to the file.

That file may be a shell script, though. In that case, you run in a problem whenever you want to write a variable which uses the curly brackets (as in ${TEST}), because cmake sees those as its own variables.

There is an example of script that we use in our Snap! development.

file( WRITE  ${lint_script} "#!${BASH}\n"                                                            )
file( APPEND ${lint_script} "if test \${3##*.} = ...

Apache2 error: client denied by server configuration

I installed a website on a brand install installation of Ubuntu 14.04 (opposed to an upgrade from earlier versions) and the same website would not start...

Apache2 would give me the following error:

client denied by server configuration

which did not seem to tell me anything... I search for the error and the first page that popped up was a page by Apache2 and they said to add the deny/allow trick. I tried that and it did not help.

    <Directory /my/special/directory>
        Order allow,deny
        Allow from all

Search further, I found an answer on ...

Recover name of message registered with RegisterWindowMessage()

Today I was confronted with an error in a process that would run in the background and slowly fill up the Windows message queue when it should have been dormant.

I looked at the messages that were being processed once the process woke up and the message number was 0xC10C or so. Nothing in the software has such a number. So I looked around and found out that the message was one of those created using the RegisterWindowMessage() function. (This is wrong in that application since the messages are never used from external applications, but oh well... that does not change the basic problem.)

So, ...

Convert XML tags and text to a String

Today I started testing a lot of my JavaScript / jQuery code from a website I am building for a customer. I got an error, at some point, saying:

SCRIPT5007: Unable to get property 'replace' of undefined or null reference

The error was in link with the 'replace' function being referenced on an innerHTML of an element. More specifically, one of those XML element (probably the top most one.)

The fact is that Internet Explorer does not support innerHTML in an XML document. Not to be too surprised about that, XML is not HTML so there is really no reason why innerHTML should be ...

xhtml2pdf generating an error under 14.04+

Note: This bug is fixed in Ubuntu 16.04

Working on a website I have to convert invoices to PDF so end users have the ability to print and share the invoices from the website.

In order to do that, I generate an HTML page with the invoice which also gets displayed in the website, and then convert that HTML to PDF with xhtml2pdf. I use that tool instead of whtmltopdf because it does not require X11 to work. The other tool is said to require Qt and X11 and we do not want those things on our backend servers.

So... I upgraded to 14.04 and the tool stopped working with an ugly error:

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    When one of the early computers stopped working, it felt like the program was wrong. The fact was that a bug was crowling inside and generating electrical problems. Once the bug was removed and the computer fixed, the program worked again. Since then, a problem in a computer program is called a bug. The word de-bug means removing the bugs from the software program.