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
CentOS/RHEL 7
Unable to Start RDMA Services on CentOS/RHEL 7
The Problem The RDMA service fails to start on CentOS/RHEL 7 machine. 'journalctl -r' command shows the below errors: Oct 11 11:01:15 geeklab systemd-modules-load: Failed to insert 'rds_rdma': Address family not supported by protocol Oct 11 11:01:15 geeklab systemd-modules-load: Failed to insert 'rds_rdma': Address family not supported by protocol Oct 11 11:01:15 geeklab systemd-modules-load: Failed to insert 'resilient_rdmaip': Address family not supported by protocol Oct 11 11:01:15 … [Read more...] about Unable to Start RDMA Services on CentOS/RHEL 7
How to set “max_report_luns” and “max_luns” on CentOS/RHEL 7 to scan more than 16,383 LUNs
From CentOS/RHEL 7, the default value of parameter max_report_luns has been increased from 512 to 16383. Consequently, CentOS/RHEL 7.x can now discover more than 511 LUNs when the system scans the SCSI interconnect using the Report LUNs mechanism. Increasing this value beyond 16383 is generally not required. But if you want to increase it, then change the values for either max_report_luns or max_luns in the kernel options line in /etc/default/grub. Note: The specific kernel option line within … [Read more...] about How to set “max_report_luns” and “max_luns” on CentOS/RHEL 7 to scan more than 16,383 LUNs
Repairing filesystem issues at Boot in CentOS/RHEL 7 and 8
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
Beginners Guide to Tuning Profiles in CentOS/RHEL
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
Beginners Guide to Managing Package Module Streams in CentOS/RHEL 8
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
How to Create a MySQL Docker Container for Testing
Docker is a container runtime environment that allows programs to operate in a jailed environment without any required external dependencies. Containers are similar in some concepts to virtual machines, however, they do not use a hypervisor and run in a single kernel instance, often sharing the instance with other containers. One of the prime features of containerization is the lack of external dependencies; the container has all of the runtime libraries and components needed to run the … [Read more...] about How to Create a MySQL Docker Container for Testing
How to extract RAR files in CentOS/RHEL 7 and 8
There is no default utility in CentOS/RHEL 7 systems to extract a .rar file. This post outlines the steps to install the unar package and use of unar command to extract files with .rar extension. 1. Log in as a root user (or use sudo) and configure the latest EPEL repositories to be able to install the unar package: # yum install epel-release Note: I recommend to disable all the existing repositories and just enable the EPEL repository if you do not want to face any conflict. 2, Now … [Read more...] about How to extract RAR files in CentOS/RHEL 7 and 8
How to Disable os-prober in CentOS/RHEL 7
What is os-prober The os-prober package detects all operating systems available on the machine and returns the results in a generic machine-readable format. Sometimes os-prober may cause problems when probing some special disks (Ex: Oracle ASM disks). This post describes how to disable os-prober. Disabling os-prober os-prober is invoked by the command grub2-mkconfig when generating a new GRUB configuration file. Running grub update on a busy Oracle ASM LUNS with OS probe results in timeouts … [Read more...] about How to Disable os-prober in CentOS/RHEL 7
How to enable additional scsi logging in CentOS/RHEL
Question: How to turn on scsi extended debug messages? What are the field/flag definitions of scsi_logging_level? Additional scsi logging messages can be enabled by writing to /proc/sys/dev/scsi/logging_level either via use of the echo or preferably the sysctl command. The kernel parameter consists of ten packed fields, each 3 bits in length. Each field can have a value of 0 to 7. The higher the field's value, the more verbose the logging of messages associated with that field type. NOTE: … [Read more...] about How to enable additional scsi logging in CentOS/RHEL