CentOS/RHEL 8

Question: How tp add a rule using firewall-cmd to drop/reject specific IP connecting to the server? This can be used as an added security on the server. firewall-cmd is the most common method of managing firewalld configurations (both running as well as permanent). This tool is a part of the firewalld package. 1. Create new […]

This post explains how to rotate Tang Server Keys and update the Clevis Client. Note, below is an example hence all certificates, keys and device names/uuid’s are fictional. Change the keys on the tang server 1. Check existing key: # ls -la /var/db/tang total 8 dr-xrws—. 2 tang tang 84 Jun 26 11:24 . drwxr-xr-x. […]

Question: How to create an encrypted XFS filesystem that’s automatically unlocked at boot using clevis (client) and tang (server)? Red Hat has included disk encryption for years with Linux Unified Key Setup-on-disk-format (LUKS). This solution is easy to implement and configure for your encryption needs, but the management and practicality of its key management is […]

Network interface teaming was introduced from CentOS/RHEL 7 as a more extensible and scalable alternative to network bonding. This post describes how to configure network teaming on CentOS/RHEL 7/8. The examples provided are based on Oracle Linux 8.2 system (Oracle VirtualBox 6.1 guest virtual machine) with two network interfaces using NetworkManager. Specifically, the Network Manager […]

This post explains how to find the OS version which was first installed on a CentOS/RHEL system. CentOS/RHEL 6 Run grep -m1 “label =” /var/log/anaconda.storage.log to find the original installation OS version. Current version: # cat /etc/redhat-release CentOS Linux release 6.10 Original installation version: # grep -m1 “label =” /var/log/anaconda.storage.log label = EL6.8_x86_64_Disc_1_20160518 size = […]

Question: How to Calculate the percentage of memory reserved by Huge Pages? 1. Inspect the memory parameters: # cat /proc/meminfo MemTotal: 98721456 kB MemFree: 1277612 kB MemAvailable: 12186676 kB Buffers: 20496 kB Cached: 11013124 kB SwapCached: 4820 kB Active: 2303780 kB Inactive: 9716992 kB Active(anon): 716672 kB Inactive(anon): 582092 kB Active(file): 1587108 kB Inactive(file): 9134900 […]

The Problem Unable to start polkitd service, which in turn affects other services as well. # systemctl restart polkit ** (pkttyagent:32189): WARNING **: 13:59:48.884: Unable to register authentication agent: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.PolicyKit1 was not provided by any .service files Error registering authentication agent: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.PolicyKit1 was not provided by any .service files […]

This note exemplifies how to configure VLAN on bonding network interface on CentOS/RHEL 7 and 8. The configuration of the switch to support VLAN tagging is not covered in this note. You do not need to do anything for configuring native VLAN on CentOS/RHEL, since it only depends on the switch configuration. 1. Check that […]

This note explains how to install GUI on CentOS/RHEL 8. During installation, this GUI package was not selected at the software selection phase. And so after installation, the screen boots into CLI prompt and not GUI. When checked with the Available Environment Groups in grouplist it still shows “Server with GUI” as shown in an […]

Problem /tmp is not automatically mounted after reboot even though an entry is present in /etc/fstab. Below outputs show an example of the issue: # uptime 16:44:11 up 2 min, 1 user, load average: 0.21, 0.55, 0.44 # df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 252G 0 252G 0% /dev tmpfs 252G […]