An important thing to remember about rulesets in /etc/sysconfig/iptables is that they are chains. The first rule is applied, followed by the second, and so on. It’s the opposite of CSS that way. More specific rules should go first, while all-encompassing rules should go last.

I was trying to open the usual DB2 ports on RHEL. For some reason, nothing was working.

It turned out that this line was at fault:

-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited

This rejects all incoming traffic not otherwise allowed. The line has to go last in the file, after all the open port definitions.

Here’s how you solve either of the following errors on Ubuntu (and possibly Debian):

device br0 already exists; can't create bridge with the same name
device eth0 is already a member of a bridge; can't enslave it to bridge br1.

Removing the device specs from /etc/network/interfaces and restarting the network doesn’t actually remove the device if already active. You need to do it manually.

List the active devices:

And then do this to any that you don’t want there, such as br0, eth0, eth1, etc:

This deactivates the device. At this point you’ll need to restart the network layer twice:

And you should be sitting pretty. On some systems, networking is known as network, as in:

TeXnicCenter is an excellent IDE for developing TeX documents on Windows. It follows the usual interface conventions and is quite helpful in getting started and debugging. TeX is the standard page layout language for writing mathematical and scientific papers.

Here are some excellent tutorials for getting started with TeX.

The IDE requires MikTeX for actually compiling TeX files into PDF, PS, and so on.

After I installed Suse Linux Enterprise Desktop 10, I tried to update it. It prompted me for a root password even though the install hadn’t asked for one — it had only created a regular user. Sudo didn’t help.

I tried booting in single-user mode, but that also prompted me for the root password.

Finally, I appended init=/bin/bash to the Linux boot command in GRUB. That booted me in a passwordless command line, letting me run passwd and fix things.

Trac is an excellent web-based wrapper for SVN that adds bug tracking, a wiki, and several handy project management features. I keep setting up new repositories up for all the little projects we cook up in DB2 Technical Marketing, so I thought I’d write up a guide.

Installing Trac, SVN, and dav_svn for Apache2 is left as an exercise for the reader.

Create a new SVN repository:

Create a new Trac environment:

Change the owner to Apache so that it can read and write:

Navigate to Apache site settings:

If you want Trac to support multiple repositories, edit the trac file to look like this:

The above assumes that all the repositories are in /var/trac

Navigate to Apache settings:

Append to dav_svn.conf:

The above lets you check out from http://yoursite/svn/Project

If you like, you can add a new user to dav_svn.psswd:

Users can then be granted permissions by editing the dav_svn.authz file. Sample file:

Restart Apache:

killall apache2
apache2

You now have have an Trac/SVN install with SVN at http://yoursite/svn/Project and Trac at http://yoursite/trac.cgi