CentOS/RHEL 8

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

The "rescan-scsi-bus.sh" can be used to scan new LUNs in a CentOS/RHEL machine. When 'rescan-scsi-bus.sh -i' is run, script execute as well a LIP_RESET (ISSUE_LIP) which may cause a disruption in I/O on the server and even cause an outage in case of a system running on heavy load. What is LIP (Loop Initialization Protocol)? LIP scans the interconnect and causes the SCSI layer to be updated to reflect the devices currently on the bus. A LIP is, essentially, a bus reset, and will cause device … [Read more...] about When to use rescan-scsi-bus.sh -i (LIP flag) in CentOS/RHEL

This post explains how to disable rpc.quotad service on CentOS/RHEL 6 or 7 machines. The protocol used by rpc.rquotad is an unsecured and obsolete protocol and should be disabled. Note: This procedure can disrupt NFS clients relying on disk quotas. To avoid issues, schedule a maintenance outage and stop these NFS clients. For CentOS/RHEL 6 or earlier 1. Edit the configuration file /etc/sysconfig/nfs to have an entry which reads RQUOTAD="no". For example: # grep RQUOTAD … [Read more...] about How to Disable rpc.quotad Service in CentOS/RHEL 6 and 7

What is Chronyd Service In CentOS/RHEL 7 and 8, the operating system's time is set on every boot based on the hardware clock, which is a small-battery driven clock located on the motherboard of your computer. Often, this clock is too inaccurate or has not been set right, therefore it's better to get your system time from a reliable source over the Internet (that uses real atomic time). The chrony daemon, chronyd, sets and maintains system time through a process of synchronization with a remote … [Read more...] about How to Enable Debug Mode for Chronyd Service in CentOS/RHEL 8

NX stands for No eXecute and XD stand for eXecute Disable is a technology used in processors to prevent the execution of certain types of code. NX/XD is a hardware cpu feature which is provided in almost all the hardware. Some BIOS has an advanced option of enabling or disabling it. This post will help to check NX/XD the feature is enabled or disabled. Use the following command to check the status of NX/XD from the OS level. For example: 1. From dmesg command: # dmesg | grep "Execute … [Read more...] about How to verify if NX/XD is Enabled or Disabled in CentOS/RHEL 7 and 8

Question: How to do set environment variables for use with a systemd service of MySQL Server? There are a number of different methods that can be used to set environment variables for a systemd service. The method used can vary depending on the Linux distribution and the version of the distribution. The MySQL manual states the service setup is done simply as (example only): [Service] LimitNOFILE=max_open_files PIDFile=/path/to/pid/file Nice=nice_level LimitCore=core_file_limit Method … [Read more...] about How to Set Environment Variables for a systemd Service in CentOS/RHEL 7

Some specific applications or processes may need higher resource values than the default systemd assigned values. It's possible to override the default resource limits assigned by systemd. Basically systemd sets the default limits for any process when it starts. For example: # cat /proc/1696/limits | grep "Max locked memory" Max locked memory 65536 65536 bytes From the above example, the Max Locked memory is 64K for the PID 1696, and for some process … [Read more...] about How to Set Resource Limits for a Process with Systemd in CentOS/RHEL 7 and 8

Question: How to disable the user list being shown when logging into a CentOS/RHEL 8 system? There are 2 ways to disable the user list being shown on the login screen in CentOS/RHEL 8. Per user Settings Globally Settings for all users Method 1 - Per User Setting In this method, an individual user is removed from the user list which appears on the login screen. So if we disable the user "sandy", it will not appear in the user list while other users will still be there on the … [Read more...] about How to Disable user list on GNOME login screen in CentOS/RHEL 8