Category: Stupid Linux Tricks

Gourmet Recipe Manager problems under recent Fedora releases

Posted by Tim – November 8, 2012

The Gourmet Recipe Manager program is a very useful way to store and find recipes, but it has been essentially useless since about Fedora 11 (give or take).

The problem is that this app uses an SQLite database to keep its recipes and accesses the database using SQLAlchemy. Version 0.7 is seriously broken relative to Gourmet.

The cure, once you know it, is relatively easy – at least as long as you don’t have any other apps depending on SQLAlchemy (and I didn’t). First, check to see if you do:

rpm -q --whatrequires python-sqlalchemy

If gourmet is your only dependent (or you don’t care/feel brave), remove the 0.7 sqlalchemy package by brute force:

rpm --erase --nodep python-sqlalchemy

Download one of the 0.6 versions of sqlalchemy. If you have a 64-bit system, be sure to get the 64-bit RPM, which includes the 32-bit version.

Install the downloaded sqlalchemy RPM

rpm -ivh python-sqlalchemy-0.6.xxxxxx.rpm

Fire up gourmet. One of the easiest ways to see if it works is just to type a search. If it returns search results, you’re OK!

Making Apache mod_rewrite and the ajp Tomcat connector work together

Posted by Tim – November 20, 2010

Apache’s URL rewriting facility can be used to shape URLs piped to Tomcat, but it’s not as simple as it seems.

The basic action is straightforward. First incoming URLs are processed by mod_rewrite, then they are matched up against JkMount definitions to find the appropriate Tomcat connector to use.

The problem is, what Tomcat sees isn’t what you’d expect to have come out from the rewrite process.

What actually happens is that before being submitted to mod_rewrite, the incoming URL is converted to server-relative form. After rewriting, the resulting URL is then reassembled, including the parts that Tomcat doesn’t want or need. Including the Apache DocumentBase path.

To prevent this problem, just qualify the last rewrite rule in the process with the “PT” directive to let Apache know to “Pass Through” the URL without reassembly. So, for example:

RewriteRule ^/$ /mywebapp/index.jsp [L,PT]
JkMount /mywebapp/* ajp13

Howto: Installing TracDiscussion

Posted by Tim – May 19, 2010

TracDiscussion allows adding discussion forums to the Trac (http://edgewall.org) system. Unfortunately, there’s not a lot of info on how to to it.

In a perfect world, you’d just issue the command “easy_install TracDiscussion” and bam-you’re-done. In this world, not yet, anyway.

Installing TracDiscussion requires installing some prerequisite packages. If you’re running Trac 11 or later, you don’t need to install the web administraction package, since it’s now part of Trac. Yes, they say that, but rather ambiguously, so this is an unqualified statement. Secondly, you need a spam filter. You’re dealing with email, spam is now about 90% of all email, so you need a filter.

Installing the actual TracDiscussion plugin isn’t all that hard even lacking a functional direct easy_install. Just go to the SVN archives, pick the project directory whose name matches your trac version and use the Subversion export command to download it. Then run easy_install against the downloaded directory.

That’s only half the battle. At that point, restart your HTTP server to reload the Trac configuration. You should see the TracDiscussion plugin listed on the admin plugins page. Select all options. In particular, select the installation option. If you don’t select that one, the extra tables won’t get added to your database.

You’ll probably get an error page backin instructing you to run the trac-admin update command. Do that from a command shell. If using PostgreSQL it will probably tell you to disable database backup on the upgrade. Hopefully you’re doing regular PostgreSQL backups anyway, but you might want to kick off a manual PostgreSQL backup before doing the Trac upgrade just for good luck’s sake.

You may want to edit the [notifications ]section of your trac.ini file in order to configure email.Then restart HTTP. And backup the newly-updated database.

With luck, “discussion” will now appear as one of the items on your Trac menubar and there will be a Discussions management section on the sidebar menu of the admin page.

Trac: Permission denied connecting to PostgreSQL Server

Posted by Tim – July 5, 2009

Another one of those obscure things that a web search didn’t turn up. Using the “psql” command-line utility, it was possible to connect to and access the PostgreSQL Trac database. However, the webapp failed, with “cannot connect to server: Permission denied”. No amount of tweaking the firewalls or the pg_hba.conf file would help.

It turns out that the permission wasn’t PostgreSQL, it was selinux. It was forbidding psycopg from opening a database connection while running inside Apache. It wants a “allow httpd_t postgresql_port_t:tcp_socket name_connect;”.

A message shows up in /var/log/audit/audit.log – if you think to look there.

Embedding graphviz-generated scalable graphics in an OpenOffice Document

Posted by Tim – July 23, 2008

You can insert graphics into an OpenOffice Writer document – or any of a number of other document editing programs. It’s generally a simple “Insert picture/from file…” menu option.

Getting it not to look like garbage is the hard part. Most images are bitmaps and scaling bitmaps usually results in images that are either “chopped” or have lines that “stairstep”. And, of course, the text can be really ugly.

There is a class of image file that scales, and this is the structured image class of files. It includes SVG, Windows Metafile, and PostScript drawing commands as well as the (Windows-only) Visio embedded object.

Unfortunately, the geniuses determined the supported set of image files that the graphviz utility would generate and the geniuses who defined the images that OpenOffice Writer would import did not have lunch in the same building. About the only commonality is EPS, and in the Fedora standard RPM, EPS is not one of the options presently (mid-2008) included for graphviz.

Failing that, there’s a fairly easy workaround. Have graphviz output a PDF. PDF’s contain PostScript. There’s a utility named “pdftops” that can extract that PostScript and wrap it up in an EPS wrapper. Note that this isn’t the same program as “pdf2ps”!

Example:

dot -oBackingBeans.pdf -v -Tpdf BackingBeans.dot
pdf2ps -eps BackingBeans.pdf BackingBeans.eps

It’s probably pipeable, but this will do.

One other thing remains. The default font selection on my system wasn’t all that beautiful, so I overrode it:

graph[fontpath="/usr/share/fonts/liberation", fontsize=12, fontname="LiberationSans-Regular"];

Here, too, I’ve done the “brute force” thing and supplied the fontpath internally and manually. I should actually set up the environment, but I had other priorities that day and custom fonts are reputedly a pain in graphviz anyway. The “-v” option on graphviz lets you see what font is actually getting pulled, by the way.

Stupid Linux tricks

Posted by Tim – July 23, 2008

A compendium of things I’ve found valuable when using Linux and other related open-source software