authconfig The Linux user password hashing algorithm is also configurable. Use the authconfig command to determine the current algorithm being used, or to set it to something different. To determine the current algorithm: # authconfig –test | grep hashing password hashing algorithm is sha512 Change the hashing algorithm To change the algorithm, use the –passalgo […]
Archives for September 2016
CentOS / RHEL : How to assemble a software RAID in Rescue mode
mdadm (multiple devices admin) is an extremely useful tool for running RAID systems. It’s is a tool for creating, managing, and monitoring RAID devices using the md driver. It can be used as a replacement for the raidtools, or as a supplement. The pos describes a way to assemble a software RAID in rescue mode. […]
CentOS / RHEL : How To Shrink LVM Root File System
During system installation, one may allocate an over-generous amount of disk space to the root partition and may later wish to reclaim any unused space. The post describes how to reduce the space allocated to an root file system on a Linux Volume Manager (LVM) logical volume. Note : this procedure applies only if the […]
CentOS / RHEL : How to migrate storage (LVM) with pvmove Command
Solution: Existing Configuration : Existing Physical Volume: 1.5 TB, /dev/mapper/mpathX Existing Volume Group: data_vg Existing Logical Volume: lv_data01 (/dev/mapper/data_vg-lv_data01) We need to move to the following configuration : Physical Volume: 1.5TB, /dev/mapper/mpathY Volume Group: data_vg Logical Volume: data (/dev/mapper/data_vg-lv_data01) Note: Please take complete backup before performing the storage migration Steps 1. Begin by pvcreate’ing the […]
RHEL 7 – RHCSA Notes : Schedule tasks using at and cron
RHEL 7 – RHCSA Notes (Cheat Sheets) – Linux can run tasks automatically, and comes with automated tasks utilities: cron, anacron, at, batch. – cron jobs can run as often as every minute. – A scheduled cron job is skipped if the system is down. – anacron can run a job only once a day. […]
RHEL 7 – RHCSA Notes : Start, stop, and check the status of network services.
RHEL 7 – RHCSA Notes (Cheat Sheets) systemd service units – Previous versions of Oracle Linux use scripts in the /etc/rc.d/init.d directory to control services. – In Oracle Linux 7, these scripts have been replaced by systemd service units. – Use the systemctl command to list information about service units. To list all loaded service […]
RHEL / CentOS : How to shrink LVM volume
Unlike increasing the LVM volume size, to shrink the volume we need to umount the filesystem. Shrinking LVM volume can not be done online. Before shrinking the volume make sure you have taken the backup of the mount point. Shrinking volume has a chance of data corruption. Example given in this post applies to both […]
CentOS / RHEL 6 : How to password protect grub (Password-Protected Booting)
The GRUB bootloader stores the password in a plaintext file, so any encrypted form of the password is required. To generate an encrypted password we may use grub-crypt command. Until now we have used the command grub-md5-crypt. But now MD5 is widely-considered broken. grub-crypt uses SHA-256 or SHA-512 hashes, which are considered more secure. The […]
CentOS / RHEL 6 : How to extract initramfs image and edit/view it
In some cases you may want to extract the initramfs image file to check built-in contents. This post provides steps to extract initramfs image files for RHEL 6. Steps 1. Locate your initramfs image and check the file type. # ls -la /boot/initramfs-$(uname -r).img -rw-r–r–. 1 root root 16196566 Feb 4 2015 /boot/initramfs-2.6.32-358.el6.x86_64.img # file […]