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
Archives for August 2019
How to Migrate CentOS/RHEL 6 iptables Rules to CentOS/RHEL 7 firewalld
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
How to Trace Python Scripts using trace.py
More and more scripts for administrative tasks on Linux OS are written by Python. This post aims to introduce a tool to trace Python statement execution. Python is a dynamic object-oriented programming language which can be used to develop various types of software. It offers strong support for integration with other languages and tools and comes with extensive standard libraries. In Linux distributions, Python is widely used to write administrative tools, such as printer configuration package … [Read more...] about How to Trace Python Scripts using trace.py
Time goes out of sync on a node running CentOS/RHEL 7
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
Unable to set a GRUB password on a Raspberry Pi 3 system
The Problem grub-rpi3.efi is built on RPI3 image build stage, and it is missing a crucial module for password prompt: # efibootmgr -v -v Could not read variable 'BootNext': No such file or directory error trace: vars.c:332 vars_get_variable(): open(/sys/firmware/efi/vars/BootNext-8be4df61-93ca-11d2-aa0d-00e098032b8c/raw_var, O_RDONLY) failed: No such file or directory lib.c:139 efi_get_variable(): ops->get_variable failed: No such file or directory Could not read variable … [Read more...] about Unable to set a GRUB password on a Raspberry Pi 3 system
How to disable NUMA on EFI Boot Loaders using GRUB2 (CentOS/RHEL 6)
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)