Ubuntu 18.04 Bionic Beaver Linux enables Internet Protocol Version 6 (IPv6) by default. However, in certain situations, some users may find it desirable to disable IPv6 support or to re-enable it after it has been disabled. Disabling IPv6 support (Permanently) Disable ipv6 built-in kernel module. 1. Edit /etc/default/grub and append ipv6.disable=1 to GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT like the following … [Read more...] about How to Disable IPv6 on Ubuntu 18.04 Bionic Beaver Linux
How to Capture More Logs in /var/log/dmesg for CentOS/RHEL
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
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 rename a KVM VM with virsh
The syntax is to rename a KVM VM with virsh is as follows: # virsh domrename {domain} {new-name} Let's see an example of renaming a VM using virsh. 1. To rename VM from serverA to serverB, first shutdown the VM: # virsh shutdown serverA 2. Now to rename a VM, run: # virsh domrename serverA serverB Domain successfully renamed 3. To start the VM/domain: # virsh start serverB Rename KVM domain with virsh and XML 1. First get domain information in XML and save it to a new … [Read more...] about How to rename a KVM VM with virsh
How To Create “A CRS Managed” ACFS FileSystem On Oracle RAC Cluster (ASM/ACFS 11.2)
1. Create the mount points on all the nodes (as root user): # mkdir /goldengate 2. Connect to the ASM instance & create the ACFS diskgroup (from the +ASM1 instance): SQL> CREATE DISKGROUP ACFSTEST EXTERNAL REDUNDANCY DISK 'ORCL:ASMDISK18' SIZE 4157 M DISK 'ORCL:ASMDISK19' SIZE 4157 M ATTRIBUTE 'compatible.asm' = '11.2', 'compatible.advm' = '11.2'; Diskgroup created. 3. Create the ACFS volume (from the +ASM1 instance): SQL> ALTER DISKGROUP ACFSTEST ADD VOLUME ACFSTESTVOL SIZE … [Read more...] about How To Create “A CRS Managed” ACFS FileSystem On Oracle RAC Cluster (ASM/ACFS 11.2)
How to Check Storage Type in Engine Database (OLVM)
This is a small how-to post to check the storage type in Engine Database. Table storage_server_connections has all connections information. Run below command on OLVM to get the connection information: $ /usr/share/ovirt-engine/dbscripts/engine-psql.sh -c "select connection,iqn,port,storage_type from storage_server_connections;" connection | iqn | port | storage_type ------------------------------+-----+------+-------------- The field storage_type will give: value 1 for NFS value 3 … [Read more...] about How to Check Storage Type in Engine Database (OLVM)
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
How to set “max_report_luns” and “max_luns” on CentOS/RHEL 6 to scan more than 512 LUNs
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