Warning: CentOS/RedHat 7.4 installs FreeRADIUS 3 with breaking changes

When you run yum upgrade on a CentOS/RedHat 7 instance, you will be upgraded to 7.4. If you have a FreeRADIUS server, you will be upgraded from version 2 to 3, and your server will likely stop authenticating! Good times! Fortunately, the solution was not complicated for us, because we had good documentation. Symptoms Your … Continue reading Warning: CentOS/RedHat 7.4 installs FreeRADIUS 3 with breaking changes

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Managing persistent disks on Google Compute Engine

It can confusing when you have multiple persistent disks on an instance running on Google Compute Engine. For example, a server may have separate disks for the filesystem root, MySQL data, logs, and /tmp. Once you've created the Compute Engine disks and attached each one to the instance, how do you know which Compute Engine … Continue reading Managing persistent disks on Google Compute Engine

Synology DiskStation DS1515+ Review

Summary: The Synology DS 1515+ is a capable little NAS with a large feature set, but it has some software reliability issues and limited technical support. Hardware The DS1515+ is a compact unit that feels sturdy. It holds five 2.5" or 3.5" drives, and 3.5" drives can be installed without any tools. You will need … Continue reading Synology DiskStation DS1515+ Review

anacron run-parts generates invalid or malformed syslog messages

On RedHat and CentOS 6 and 7, anacron generates syslog messages that are mangled when they are forwarded by rsyslog. I found the cause and a solution in a comment by Tomas Heinrich on this old Fedora bug. Sadly, that bug was closed instead of getting fixed, probably because Fedora is oriented toward desktop users … Continue reading anacron run-parts generates invalid or malformed syslog messages

Making Windows work for Linux and OS X admins

If you are a Linux or OS X power user, then you're used to having all the necessary tools built into your OS. When you log into a Windows system (What! No command line?) you may feel lost. These tools and shortcuts will help you be productive on Windows systems. Windows Shortcuts Alt-x is a … Continue reading Making Windows work for Linux and OS X admins

Troubleshooting SSSD, realm, kerberos, and SSH

SSSD (System Security Services Daemon) allows Linux systems (specifically, Red Hat, CentOS, and Fedora) to verify identity and authenticate against remote resources. If you have a CentOS or Red Hat enterprise system, and you need to authenticate against a domain controller such as FreeIPA or Active Directory, SSSD is the way to go. I use … Continue reading Troubleshooting SSSD, realm, kerberos, and SSH

LVM device-mapper: reload ioctl failed: Invalid argument

LVM2 (Logical Volume Management) is pretty amazing, but when something goes wrong, it's not easy to troubleshoot. This is not the fault of the tools, but a reflection┬áthat LVM is relatively┬ánew in Linux, and not widely understood. What I Tried to Do I tried to increase the size of a logical volume with the lvextend … Continue reading LVM device-mapper: reload ioctl failed: Invalid argument

Monitoring with SNMP, Part 3: Automate active monitoring with Nagios

My last post showed how to monitor networked devices with SNMP. You could try to remember to manually check the status of things periodically, but that would be missing the point of computers. Instead, automate your monitoring with Nagios, a web-based monitoring tool for Linux that automates the process of actively querying devices and doing … Continue reading Monitoring with SNMP, Part 3: Automate active monitoring with Nagios

Monitoring with SNMP, Part 2: Command-line tools for active SNMP

In Part 1, I summarized the basic concepts of SNMP and defined the terms and acronyms used in this post. Now, I will show how to use SNMP to monitor actual devices. As an example, I will monitor an enterprise-grade uninterruptible power supply (UPS) and power distribution unit (PDUs) from Tripp-Lite. These devices have an … Continue reading Monitoring with SNMP, Part 2: Command-line tools for active SNMP