CentOS/RHEL 8

The Problem Rebooting the CentOS/RHEL 8 server causes it to freeze. From the console output, the system is stuck at: ... [ 68.906159] dracut: Disassembling device-mapper devices Rebooting. [ 68.934073] kvm: exiting hardware virtualization [ 68.936622] sd 0:0:0:0: [sda] Synchronizing SCSI cache [ 68.938942] e100e: EEE TX LPI TIMER: 00000011 [ 69.018502] reboot: Restarting system [ 69.020000] reboot: machine restart After removing "rhgb quiet" and adding "debug rd.debug" in grub … [Read more...] about CentOS/RHEL 8: “ACPI MEMORY OR I/O RESET_REG” Server Hung after reboot

In CentOS/RHEL 8, ntp is no longer supported. chrony is enabled by default. For this reason, you might need to migrate from ntp to chrony. Note: In CentOS/RHEL 7 users had a choice to between ntp and chrony. But Starting from CentOS/RHEL 8, they have to use chrony instead of ntp. In standard CentOS/RHEL 8 servers, chrony should be installed and active already. It can be verified by executing: # systemctl status chronyd ● chronyd.service - NTP client/server Loaded: loaded … [Read more...] about How to Install NTP Service and Client in CentOS/RHEL 8

It is always advisable to keep the installed packages up to date, especially when it comes to security. In this post, we will see how to setup Automatic Update using the dnf-automatic tool. DNF tool provides automatic notifications of updates, download updates, and then install them automatically by using systemd timers. Below are three systemd timer units provided by dnf-automatic. dnf-automatic-notifyonly.timer: Notifies for available updates. dnf-automatic-download.timer: Downloads … [Read more...] about How to Configure Automatic Package Updates on the Server in CentOS/RHEL 8

The Problem Cannot reliably get networking to start on a server when using DHCP: # sudo /etc/init.d/network restart Restarting network (via systemctl): Job for network.service failed because the control process exited with error code. See "systemctl status network.service" and "journalctl -xe" for details. [FAILED] # journalctl -xe Nov 29 18:57:42 hostaname.domain.com dhclient[37653]: exiting. Nov 29 18:57:42 hostaname.domain.com network[37498]: [FAILED] Nov 29 18:57:42 … [Read more...] about Failed to start LSB: Bring up/down networking – On restarting network service CentOS/RHEL (DHCP client)

Sometimes not all log messages in /var/log/dmesg can be captured after Linux OS/kernel boots up because of too many block devices attached to the server. This post illustrates another way to record all bootup log messages besides configuring the serial console. Basically kernel parameter "log_buf_len" can be configured to increase kernel log buffer size, Name: log_buf_len, Set the size of the kernel log buffer. Synopsis: log_buf_len= n [ KMG ] Description: Set the size of the … [Read more...] about How to Capture More Logs in /var/log/dmesg for CentOS/RHEL

This post focuses on manually repairing the file-system configuration or corruption issues that stop the boot process. Diagnosing and fixing file system issues Errors in /etc/fstab and corrupt file systems can stop a system from booting. In most cases, systemd drops to an emergency repair shell that requires the root password. The following table lists some common errors and their results. Common File System Issues PROBLEM RESULT Corrupt file system systemd attempts to repair the … [Read more...] about Repairing filesystem issues at Boot in CentOS/RHEL 7 and 8

The nfsconf tool CentOS/RHEL 8 introduces the nfsconf tool to manage the NFS client and server configuration files under NFSv4 and NFSv3. Configure the nfsconf tool using /etc/nfs.conf (the /etc/sysconfig/nfs file from earlier versions of the operating system is deprecated now). Use the nfsconf tool to get, set, or unset NFS configuration parameters. The /etc/nfs.conf configuration file is composed of multiple sections starting with a key word in square brackets ([keyword]) with value … [Read more...] about How to Configure an NFSv4-only Client using nfsconf in CentOS/RHEL 8

Tuning Systems System administrators can optimize the performance of a system by adjusting various device settings based on a variety of use case workloads. The tuned daemon applies tuning adjustments both statically and dynamically, using tuning profiles that reflect particular workload requirements. Configuring Static Tuning The tuned daemon applies system settings when the service starts or upon the selection of a new tuning profile. Static tuning configures predefined kernel parameters … [Read more...] about Beginners Guide to Tuning Profiles in CentOS/RHEL

Introduction to Application Streams CentOS/RHEL 8.0 introduces the concept of Application Streams. Multiple versions of user-space components shipped with the distribution are now delivered at the same time. They may be updated more frequently than the core operating system packages. This provides you with greater flexibility to customize Red Hat Enterprise Linux without impacting the underlying stability of the platform or specific deployments. Traditionally, managing alternate versions of an … [Read more...] about Beginners Guide to Managing Package Module Streams in CentOS/RHEL 8