Linux

You have accidentally removed a logical volume lv01 from the Volume group vg01. Now you want to recover the LV without losing the data. Follow the steps given below to recover LV (lv01) under VG (vg01). # lvremove vg01/lv01 Do you really want to remove active logical volume vg01/lv01? [y/n]: y Logical volume "lv01" successfully removed Recovering remove LV 1. Verify the archive file under the directory /etc/lvm/archive when the logical volume was removed. In my case the file with … [Read more...] about How to recover deleted Logical volume (LV) in LVM using vgcfgrestore

What is process priority (niceness) All process when spawned, they are assigned a priority based on a numeric value called as "nice value". The priority of a process denotes how much processor time allocated to that process. There are 40 niceness values, with –20 being the highest and +19 the lowest. Most system-started processes use the default niceness of 0. If the niceness value is high number like 19 the task will be set to the lowest priority and the CPU will process it whenever it gets a … [Read more...] about UNIX / Linux : How to change the niceness (priority) of a process

'set alias' for any command and the alias command will work fine on the interactive shell, whereas aliasing doesn't work inside the script. 1. Interactive shell # alias ls1='ls -lrt' # ls1 total 0 -rw-r--r-- 1 root root 0 Oct 12 12:14 file1 -rw-r--r-- 1 root root 0 Oct 12 12:14 file2 2. Inside the script # cat script.sh #!/bin/bash # Script to check the alias output alias ls1='ls -lrt' ls1 # chmod +x script.sh # ./script.sh ./script.sh: line 3: ls1: command not … [Read more...] about How to make alias command work in bash script or bashrc file

After a server crash or due to a human error, volume group device files are not seen under /dev directory. The device files were removed from the filesystem after the system crash, probably due to a filesystem corruption. # cd /dev # ls vg01 ls: cannot access vg01: No such file or directory If you check the output of lvdisplay command you would see the vg intact and without any error. # lvdisplay --- Logical volume --- LV Path /dev/vg01/lv01 LV Name … [Read more...] about How to recreate LVM device files under /dev directory using vgmknodes

So, here is the situation - pvcreate and vgcreate command throws errors shown below. # pvcreate /dev/sdd1 Can't open /dev/sdd1 exclusively. Mounted filesystem? # vgcreate vg1 /dev/sdd1 Can't open /dev/sdd1 exclusively. Mounted filesystem? Unable to add physical volume '/dev/sdd1' to volume group 'vg1'. Probable Cause of the error LVM will only create a pv label on a device if it is not currently in use. There are some of the other various causes for this issue, which include's: The … [Read more...] about LVM error : Can’t open /dev/sdx exclusively. Mounted filesystem?

Whats is a disk partition Partitioning divides a disk drive into one or more logical disks. Each partition is treated as a separate disk with its own file system. Partition information is stored in a partition table. There are 2 types of partitions that can be created using the fdisk utility : Primary Partitions Extended Partitions Primary Vs extended partitions - The original partitioning scheme for PC hard disks allowed only four partitions, called primary partitions. - To create … [Read more...] about Linux / UNIX : How to create extended partition using fdisk

The device node name of a disk (/dev/sda, /dev/hda, /dev/vda, etc.) may change in some situations. For example, after switching cables around or upgrading certain packages, sda & sdc could swap places. This causes problems when /etc/fstab references filesystems by the disk names. It is not safe to use block device node names like /dev/sda1 and /dev/vdb2 to refer to filesystems in /etc/fstab. Instead, use filesystem UUIDs (universally unique identifiers) or labels. Either of these allows for … [Read more...] about CentOS / RHEL : How to change the UUID of the filesystem

You can set the mounting options of a filesystem in the file /etc/fstab. For example : # cat /etc/fstab | grep data /dev/mapper/vg01-lv01 /data ext4 defaults 0 2 Viewing mount options of filesystem 1. To see what options a mounted filesystem is utilizing run the mount command can be ran without any arguments. You can also grep for a particular mount point as sometimes (specially if you are using RHEL/CentOS 7) you might get a huge list of system mount points. For example, data in the … [Read more...] about How to find the mounting options of currently mounted filesystem

To mount USB flash drive on any Linux system you will first need to know the disk partition name for the USB drive. Finding the partition name is an easy task. Follow the steps below to find the partition name and mounting it on a directory of your choice. 1. Check for the /var/log/messages file for the messages related to the USB flash drive. As soon as you connect a flash drive you would see messages about it. Oct 6 19:03:32 localhost kernel: usb 1-1: new high-speed USB device number 2 … [Read more...] about How to mount USB flash drive in Linux

The ask here is to merge 2 volume groups with existing LVs and there should be no data loss. For the purpose of this post, we have 2 VGs - vg01 and vg02. Both have one LV each created inside them as shown below : # vgs VG #PV #LV #SN Attr VSize VFree cl 1 2 0 wz--n- 19.00g 0 vg01 1 1 0 wz--n- 20.00g 10.00g vg02 1 1 0 wz--n- 20.00g 10.00g # lvs LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert root cl -wi-ao---- … [Read more...] about How to merge 2 volume groups (VGs) into one using vgmerge in LVM