Setting up your own authoritative DNS server jots

What’s this? These are somewhat random jots I made while setting up an authoritative BIND server, so that a simple VPS machine can function standalone. Well, almost standalone, as it takes some help from a slave DNS to supply the second DNS entry. But even if that slave goes away suddenly, the show will go [...]

The art of setting up a sendmail server on Debian 8

But why? Fact number one: Running your own mail server is the most likely cause for messing up, and that can mean an intrusion to the server or just turning it into a public toilet for spam. Nevertheless, if mail delivery is important to you, there’s probably no way around. And I’m not talking about [...]

Digging to the root with DNS queries

Introduction This is an explicit walkthrough on how a domain name is resolved. Doing the recursion manually, that is. And then some remarks on the mess with DNS glue records. Getting the root servers $ dig NS . ; <<>> DiG 9.11.3-1ubuntu1.2-Ubuntu <<>> NS . ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: [...]

The SPF, DKIM and DMARC trio: Making your email appear decent

Intro Whether you just want your non-Gmail personal email to get through, or you have a website that produces transactional emails (those sent by your site or web app), there’s a long fight with spam filters ahead. The war against unsolicited emails will probably go on as long as email is used, and it’s an [...]

SMTP tidbits for the to-be postmaster

This is a quick overview of the parts of an SMTP session that are relevant to SPF and mail server setup. Just a sample SMTP session For a starter, this is what an ESMTP session between two mail servers talking on port 25 can look like (shamelessly copied from this post, which also shows how [...]

Perl, DBI and MySQL wrongly reads zeros from database

TL;DR: SELECT queries in Perl for numerical columns suddenly turned to zeros after a software upgrade. This is a really peculiar problem I had after my web hosting provider upgraded some database related software on the server: Numbers that were read with SELECT queries from the database were suddenly all zeros. Spoiler: It’s about running [...]

Traces of a (failed, I hope) web server attack

I suddenly got the following line in public_html/error_log: [06-Feb-2019 17:51:53] PHP Deprecated: Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set ‘always_populate_raw_post_data’ to ‘-1′ in php.ini and use the php://input stream instead. in Unknown on line 0 So I took a closer look on the logs: [...]

Solved: Missing ktorrent icon on Linux Mint / Cinnamon

Running ktorrent on Linux Mint 19 (Tara), the famous downwards-arrow icon was invisible on the system tray. Which made it appear like the program had quit when it was actually minimized. Clicking the empty box made ktorrent re-appear. Solution: Invoke the Qt5 configuration tool $ qt5ct and under the Appearance tab set “Style” to gtk2 [...]

Better than netstat: lsof tells us who is listening to what

Be sure to read the first comment below, where I’m told netstat can actually do the job. Even though I have to admit that I still find lsof’s output more readable. OK, so we have netstat to tell us which ports are opened for listening: $ netstat -n -a | grep “LISTEN ” Thanks, that [...]

Outgoing SMTP mail servers considerations

Mail with gmail.com as From address vanishing It started really bad: Someone asked me why he hasn’t received an answer from me in two weeks, and I had answered his mail the same day I got his. It turned out that Gmail had thrown mail into the black hole without any warning. Probably the updated [...]