The default limit of maximum luns that can be presented in a CentOS/RHEL 6 is 512. But in many cases, you may want to increase this limit. There is a parameter of the SCSI core module to control the number of multiple LUNs. View Current Settings To view the current setting of "max_luns" parameter, use the below command: # systool -v -m scsi_mod Module = "scsi_mod" Attributes: uevent = Parameters: default_dev_flags = "0" eh_deadline = "-1" … [Read more...] about How to set “max_report_luns” and “max_luns” on CentOS/RHEL 6 to scan more than 512 LUNs
How to Check the Size og yum Channels in CentOS/RHEL
Question: How to find out how large a yum channel repository is, to know how much data the channel will sync to a local yum repository? To see the actual size of the repository use either the 'yum repolist -v' or 'yum repoinfo' command. Example for checking the size of "CentOS-8 - AppStream" yum channel Run the command as shown below to get the size of the Repo "CentOS-8 - AppStream". The command works even without the double quotes around the repo name. # yum repoinfo "CentOS-8 - … [Read more...] about How to Check the Size og yum Channels in CentOS/RHEL
How to Check vendor of installed RPM packages in Linux
This is a quick how-to post on checking the vendor of the installed rpms on a system. In some scenarios, a custom rpm package may not be compatible or supported on the specific system or environment. This post will help you identify the vendor of rpm which are either thrid party or not native to the OS provider. List vendor information of RPMs To List all the rpm with the vendor infromation, use the --queryformat(--qf) option. # rpm -qa --queryformat '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} … [Read more...] about How to Check vendor of installed RPM packages in Linux
TimeFinder SnapVX Concepts and SnapVX Operations
TimeFinder SnapVX Overview TimeFinder SnapVX provides a highly efficient mechanism for taking periodic point-in-time copies of source data without the need for target devices. Target devices are required only for presenting the point-in-time data to another host. Sharing allocations between multiple snapshots makes it highly space-efficient. A write to the source volume will only require one snapshot delta to preserve the original data for multiple snapshots. If a source track is shared with a … [Read more...] about TimeFinder SnapVX Concepts and SnapVX Operations
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
How to Use Udev Rules to Create oracleasm Disks in CentOS/RHEL 8
This post will help to configure Oracleasm disks using Udev rules in 2 node cluster. On first node 1. List the disks: [root@node01 ~]# lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 2G 0 disk sdb 8:16 0 2G 0 disk Note: Create partitions for the disks. 2. Find the disk ID: [root@node01 ~]# udevadm info --query=all --name=/dev/sda | egrep "WWN|SERIAL" E: ID_SCSI_SERIAL=[id] E: ID_SERIAL=0QEMU_QEMU_HARDDISK_AAAAAAAAA E: … [Read more...] about How to Use Udev Rules to Create oracleasm Disks in CentOS/RHEL 8
How to Configure an NFSv4-only Client using nfsconf in CentOS/RHEL 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
How to Schedule Tasks Using at in Linux
The atd Daemon The atd daemon allows users to submit jobs to be performed at a later time, such as "at 2:00am". In order to use the atd daemon, it must be running. Users can confirm that atd is running simply by examining a list of running processes: $ ps aux | grep atd daemon 4730 0.0 0.2 1420 532 ? S 15:42 0:00 /usr/sbin/atd madonna 5570 0.0 0.2 3572 640 pts/2 S 16:43 0:00 grep atd Notice that the seventh column specifies what terminal a process is associated … [Read more...] about How to Schedule Tasks Using at in Linux
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
How to use ansible-config to discover and investigate configuration options
Viewing Configuration Options If you want to find out what options are available in the configuration file, use the ansible-config list command. It will display an exhaustive list of the available configuration options and their default settings. This list may vary depending on the version of Ansible that you have installed and whether you have any additional Ansible plugins on your control node. Each option displayed by ansible-config list will have a number of key-value pairs associated … [Read more...] about How to use ansible-config to discover and investigate configuration options