Problem: I have a host that has 2 active network interfaces. One is used as a management port (
eth0), one is used as an FTP dropbox (
Both can route to the Internet, but all connections other than FTP on eth1 are blocked via iptables. The default route uses the interface for the FTP dropbox, but I have a static route configured for the subnet that includes my management and monitoring hosts so that I can SSH to the host and check on host availability, disk space, mail queue, etc.
However, the static route means that I cannot monitor the FTP dropbox, since FTP connection attempts coming in on one interface and IP address are then routed out via the management interface and IP address.
Solution: Use policy-based routing to direct the system to consult a different routing table for connections coming in on the FTP interface.
It sounds easy enough.
Continue reading Linux policy based routing
I had always been under the impressions that when moving a file from one Linux filesystem to another (i.e. a new inode is created), that
mv is essentially a
cp command followed by an
That’s not quite correct. It is essentially a
cp --archive command followed by an
Continue reading cp, mv, ownership and attributes
In my previous post I mentioned that I am learning about Podman, a tool for running containers that does not require a daemon process (like the Docker daemon) or root privileges.
In this post I would like to demonstrate why running containers with root privileges could be dangerous.
Continue reading Using Docker to get root access
I have recently been learning about podman, a tool for running containers that has a command syntax that matches Docker, but that does not require a Docker daemon and which does not require root privileges.
I ran into some unexpected problems publishing ports with Podman, which had to do with my default DROP policy on the iptables FORWARD chain. Below I will demonstrate some of the differences between Docker and Podman in terms of iptables changes, and provide a workaround for Podman.
Continue reading Docker versus Podman and iptables
I’ve played with Docker containers but haven’t really done anything, useful or otherwise, with them. I decided to create a Docker image that includes a web-based chatbot. You can find the Git repository for this (including the finished
Dockerfile) at https://github.com/cherdt/docker-nltk-chatbot
Continue reading Running a Python Flask application in a Docker container
I’d previously been using the Docker driver with Kitchen CI and kitchen-ansible to test my Ansible playbooks. I really like using Kitchen CI. Test-driven infrastructure development! Regression testing! It’s great.
There were several reasons I decided to switch from the Docker driver to Vagrant. My target hosts are all either VMs or bare metal servers, so Vagrant VMs more closely resemble that environment. In particular, there are a couple areas where Docker containers don’t perform well for this purpose:
- Configuring and testing SELinux settings
- Configuring and testing systemd services
Continue reading Kitchen CI – using the Vagrant driver
I had the idea of applying Scrabble scores to DGA domains over the summer of 2018, but the idea was rekindled when I saw Marcus Ranum‘s keynote at BroCon 2018. He talked about the advantages of scoring systems: they are fast, they are simple, and they can be surprisingly effective.
Domain Generating Algorithms (DGAs)
Malware uses DGAs to generate hundreds or thousands of new domain names daily. The malware then attempts to contact some or all of the domains. If a successful attempt is made to a control server, the malware will receive new instructions for malicious activity. The people and systems managing the malware need only register one new domain a day, but a defender would have to anticipate and/or discover thousands a day. To read more about DGAs, I recommend these articles from Akamai:
Scrabble Scores and DGAs
I’ve noticed that some, not all Domain Generating Algorithms produce unreadable domains like:
Continue reading Identifying DGA domains using Scrabble scores: a naive approach
E-mail is not a good way to get my attention in a timely fashion. E-mail is inherently asynchronous, and healthy minds may ignore it for hours or even days at a time. So how do I handle monitoring alerts? One way is by using PagerDuty, a service that can call, text, or send push notifications to you (among other features).
I followed the steps at PagerDuty’s Icinga2 Integration Guide, but no alerts were coming through. What went wrong?
Continue reading Icinga2 and PagerDuty integration
The GitHub Enterprise – Using LDAP documentation lists FreeIPA as a supported LDAP service.
Although I was able to successfully test a basic LDAP connection, the test failed after I specified the Email (using value “mail”) and SSH key (using value “ipaSshPubKey”) fields. I received the following error: Continue reading Integrating FreeIPA authentication with GitHub Enterprise
Earlier today I got an alert that the LDAP service on my FreeIPA server was down. This was not long after I had received another alert that the drive space on the
/var partition was critical. I logged on, freed up some drive space, and tried to start the service:
$ sudo ipactl start
Starting Directory Service
Failed to start Directory Service: Command '/bin/systemctl start dirsrv@FREEIPA-OSRIC-NET.service' returned non-zero exit status 1
I tried running systemctl directly to see the error message:
$ sudo systemctl start dirsrv@FREEIPA-OSRIC-NET.service
Continue reading ipactl error: Failed to start Directory Service: Command ‘/bin/systemctl start dirsrv@FREEIPA-OSRIC-NET.service’ returned non-zero exit status 1