Archives for August 2019

The Task Create an LVM snapshot of the root filesystem. Revert Snapshot Changes To An Earlier State. The Solution 1. Before proceeding make sure LVM Volume Group (VG) has enough space for the snapshot. # vgs VG #PV #LV #SN Attr VSize VFree ol 2 2 0 wz--n- 12.00g 1.01g 2. In this example we are creating a root snapshot of 512M. Here "snap" is the snapshot name of a root volume. # lvcreate -L 512M -s -n snap /dev/ol/root Logical volume "snap" created. 3. … [Read more...] about How to Create An LVM Snapshot Of The Root Filesystem And Restore To An Earlier State

Below we demonstrate three common methods for transforming the iptables rules into the firewalld controls. Our example shows the transformation of one iptables rule output by the iptables-save command: LOG_TEST_NEW - [0:0] -A LOG_TEST_NEW -m limit --limit 2/min -j LOG --log-prefix "New Connection" The example rule logs up to two log entries per minute. The log entry is labeled with the string "New Connection." Using The firewalld GUI (Applications -> Sundry -> Firewall) 1. Create a Rule … [Read more...] about How to Migrate CentOS/RHEL 6 iptables Rules to CentOS/RHEL 7 firewalld

The Scenario The system is not configured to use the ntpd service to synchronize time and date. CentOS/RHEL 7 uses systemd to manage services. The timedatectl utility is distributed as part of the systemd, and allows you to review and change the configuration of the system clock: change the current date and time, set the time zone, or enable automatic synchronization of the system clock with a remote server. The NTP service is enabled, but as this system is running CentOS/RHEL 7, … [Read more...] about Time goes out of sync on a node running CentOS/RHEL 7

The purpose of this post is to explain the steps to disable NUMA on servers which use the EFI boot loader. GRUB 2 is the default EFI-mode boot loader, so the steps are based on GRUB2. 1. Take a backup of /etc/default/grub configuration file. # cp -p /etc/default/grub /etc/default/grub_backup 2. Edit /etc/default/grub file and replace numa=on to numa=off. # vi /etc/default/grub .. GRUB_CMDLINE_LINUX_DEFAULT="root=LABEL=DBSYS bootarea=dbsys bootfrom=BOOT ro loglevel=7 panic=60 debug … [Read more...] about How to disable NUMA on EFI Boot Loaders using GRUB2 (CentOS/RHEL 6)

CentOS/RHEL has a new package manager called DNF which can be used to install packages on CentOS/RHEL 8 systems. DNF or Dandified YUM is the next-generation version of the Yellowdog Updater Modified (yum), a package manager for rpm-based distributions in CentOS/RHEL 8. It also resolves dependencies automatically. The following is an example of how to use DNF to check which repositories are enabled and to then install a package from an enabled repository. 1. To check the list of … [Read more...] about How to install packages using dnf in CentOS/RHEL 8

CentOS/RHEL 8 distributes sets of related RPM packages that form a logical unit (such as different components of an application or a group of tools) as modules, with these modules being able to be enabled or disabled on the system. How can a user or administrator of an OL8 system determine what modules are installed or are enabled or disabled on their system? Modules a set of RPM packages that are grouped together and must be installed together. They can contain several streams (AppStreams) … [Read more...] about How to list all modules and check if they are enabled or disabled in CentOS/RHEL 8

In CentOS/RHEL 8, the default iptables network packet filtering framework been replaced with the nftables framework. As the designated successor to iptables, ip6tables, arptables, and ebtables, the nftables framework includes packet classification facilities and several improvements, which provide added convenience and improved performance over the previously used packet-filtering tools. In this post we will discuss on how to migrate existing iptables rules to nftables in CentOS/RHEL … [Read more...] about How To Migrate Existing Iptables rules to Nftables In CentOS/RHEL 8