Linux Volume Management
The Linux Logical Volume Manager (LVM) is a mechanism for virtualizing disks. It allows you to abstract the physical layout of component storage devices for easier and flexible administration. It can create "virtual" disk partitions out of one or more physical hard drives, allowing you to grow, shrink, or move partitions from drive to drive as your requirements change. It also allows you to create larger partitions than you could achieve with a single drive.
Topics
LVM Basics
The main advantages of LVM are increased abstraction, flexibility, and control. Logical volumes can have meaningful names. Volumes can be resized dynamically as space requirements change and migrated between physical devices within the pool on a running system or exported easily. LVM also offers advanced features like snapshotting, striping, and mirroring.
To use LVM, you must understand several elements. First are the regular physical hard drives attached to the computer. The disk space on these devices is chopped up into partitions. Finally, a filesystem is written directly to a partition. By comparison, in LVM, Volume Groups (VGs) are split up into logical volumes (LVs), where the filesystems ultimately reside
Each Volume Group (VG) is made up of a pool of Physical Volumes (PVs). You can extend (or reduce) the size of a Volume Group by adding or removing as many PVs as you wish, provided there are enough PVs remaining to store the contents of all the allocated LVs. As long as there is available space in the VG, you can also grow and shrink the size of your LVs at will (although most filesystems don't like to shrink).
Physical Volumes:
Physical block devices or other disk-like devices (for example, other devices created by device mapper, like RAID arrays) are used by LVM as the raw building material for higher levels of abstraction. Physical volumes are regular storage devices. LVM writes a header to the device to allocate it for management.
Volume Groups
LVM combines physical volumes into storage pools known as volume groups. Volume groups abstract the characteristics of the underlying devices and function as a unified logical device with combined storage capacity of the component physical volumes.
Logical Volumes
A volume group can be sliced up into any number of logical volumes. Logical volumes are functionally equivalent to partitions on a physical disk, but with much more flexibility. Logical volumes are the primary component that users and applications will interact with.
Recipes
A. Creating new disk partion, physical volume, logical group and logical volume
Use fdisk command with list (-l) switch to list existing disks. fdisk is a menu-driven program for creation and manipulation of partition tables on a hard disk. Hard disks are divided into partitions and this division is described in the partition table. Using fdisk you can create a new partition, delete an existing partition, or change existing partition. Using fidsk you are allowed to create a maximum of four primary partition, and any number of logical partitions, based on the size of the disk.
> fdisk -l
Disk /dev/sda: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000dab3d
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 2099199 1048576 83 Linux
/dev/sda2 2099200 20971519 9436160 8e Linux LVM
Disk /dev/mapper/cl-root: 8585 MB, 8585740288 bytes, 16769024 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/cl-swap: 1073 MB, 1073741824 bytes, 2097152 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Use fdisk command with list (-l) switch to list existing disks. fdisk is a menu-driven program for creation and manipulation of partition tables on a hard disk. Hard disks are divided into partitions and this division is described in the partition table. Using fdisk you can create a new partition, delete an existing partition, or change existing partition. Using fidsk you are allowed to create a maximum of four primary partition, and any number of logical partitions, based on the size of the disk.
> fdisk -l Disk /dev/sda: 10.7 GB, 10737418240 bytes, 20971520 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x000dab3d Device Boot Start End Blocks Id System /dev/sda1 * 2048 2099199 1048576 83 Linux /dev/sda2 2099200 20971519 9436160 8e Linux LVM Disk /dev/mapper/cl-root: 8585 MB, 8585740288 bytes, 16769024 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/mapper/cl-swap: 1073 MB, 1073741824 bytes, 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes
This can be done by physically adding a new disk. If you are using a virtual machine, add a new virtual disk. You should be able to do this without shutting down system.
3) Reboot and use fidisk command again
fdisk -l
Reboot to get Linux to recognize new disk and use fdisk to make sure it works.
> reboot
Note that we have a new 5G disk called /dev/sdb with no partitions table listed at the botton section of the outpt.
> fdisk -l
Disk /dev/sda: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000dab3d
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 2099199 1048576 83 Linux
/dev/sda2 2099200 20971519 9436160 8e Linux LVM
Disk /dev/sdb: 5368 MB, 5368709120 bytes, 10485760 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/cl-root: 8585 MB, 8585740288 bytes, 16769024 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/cl-swap: 1073 MB, 1073741824 bytes, 2097152 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
As an alternative to rebooting, you can use this command
ls /sys/class/scsi_host/ | while read host ; do echo "- - -" > /sys/class/scsi_host/$host/scan ; done
fdisk is a menu-driven program for creation and manipulation of partition tables on a hard disk. Hard disks are divided into partitions and this division is described in the partition table. Using fdisk you can create a new partition, delete an existing partition, or change existing partition. Using fidsk you are allowed to create a maximum of four primary partition, and any number of logical partitions, based on the size of the disk.
Run fdisk for disk /dev/sdb
> fdisk /dev/sdb Welcome to fdisk (util-linux 2.23.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Command (m for help): ^C
Use m to show menu
Command (m for help): m Command action a toggle a bootable flag b edit bsd disklabel c toggle the dos compatibility flag d delete a partition g create a new empty GPT partition table G create an IRIX (SGI) partition table l list known partition types m print this menu n add a new partition o create a new empty DOS partition table p print the partition table q quit without saving changes s create a new empty Sun disklabel t change a partition's system id u change display/entry units v verify the partition table w write table to disk and exit x extra functionality (experts only) Command (m for help):
Create a new 40M partition and write (w) changes to disk.
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p):
Using default response p
Partition number (1-4, default 1):
First sector (2048-10485759, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-10485759, default 10485759): +40M
Partition 1 of type Linux and of size 40 MiB is set
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Now if you do an fdisk again, you will see new partition called /dev/sdb1
fdisk -l Disk /dev/sda: 10.7 GB, 10737418240 bytes, 20971520 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x000dab3d Device Boot Start End Blocks Id System /dev/sda1 * 2048 2099199 1048576 83 Linux /dev/sda2 2099200 20971519 9436160 8e Linux LVM Disk /dev/sdb: 5368 MB, 5368709120 bytes, 10485760 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0xfd11b535 Device Boot Start End Blocks Id System /dev/sdb1 2048 83967 40960 83 Linux Disk /dev/mapper/cl-root: 8585 MB, 8585740288 bytes, 16769024 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/mapper/cl-swap: 1073 MB, 1073741824 bytes, 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes
Next we want to change partition type to type Linux LVM.
> fdisk /dev/sdb Command (m for help): t Selected partition 1 Hex code (type L to list all codes): 8e Changed type of partition 'Linux' to 'Linux LVM' Command (m for help): p Disk /dev/sdb: 5368 MB, 5368709120 bytes, 10485760 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x5d93b896 Device Boot Start End Blocks Id System /dev/sdb1 2048 4196351 2097152 8e Linux LVM
5) Create a Physical Volume with command pvcreate
pvcreate /dev/sdb1
Physical Volume
Physical volume is the actual storage device that will be used in the LVM configuration. It can be an entire disk, a partition on disk or a LUN on the SAN. You can use pvcreate to create the physical volume. To use the device for an LVM logical volume the device must be initialized as a physical volume (PV). The LVM label identifies the device as an LVM physical volume. It contains a random unique identifier (the UUID) for the physical volume. The pvcreate command initializes Physical Volume for later use by the Logical Volume Manager (LVM). Each Physical Volume can use a disk partition, or the whole disk.
Syntax
pvcreate [physical volume name]
where physicalvolumename is name of your disk or partition. The fdisk -l command will provide you with this name.
Create Physical Volume where name is a partition created with fdisk or disk name
> pvcreate /dev/sdb1 Physical volume "/dev/sdb1" successfully created.
use pvs to display all physical volumes. Note that Physical Volume (PV) /dev/sdb1 has no associated Volume Group (VG)
> pvs PV VG Fmt Attr PSize PFree /dev/sda2 cl lvm2 a-- <9.00g 0 /dev/sdb1 lvm2 --- 40.00m 40.00m
Use pvdisplay to display information about a specific physical volume or all physical volumes
> pvdisplay --- Physical volume --- PV Name /dev/sda2 VG Name cl PV Size <9.00 GiB / not usable 3.00 MiB Allocatable yes (but full) PE Size 4.00 MiB Total PE 2303 Free PE 0 Allocated PE 2303 PV UUID m6sySf-hYek-Pcpn-6ST4-AvRc-OXl1-brv53d "/dev/sdb1" is a new physical volume of "40.00 MiB" --- NEW Physical volume --- PV Name /dev/sdb1 VG Name PV Size 40.00 MiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID hVMo7W-zuOj-oUql-lCJi-Me1b-7HZW-CzN5kG
6) Create a Volume Group using a Physical Volumes
vgcreate myVolumeGroup /dev/sdb1
Volume Groups (VG)
Logical volume management is a technique for deploying logical rather than physical storage. With LVM, "logical" partitions can span across physical hard drives and can be resized (unlike traditional ext3 "raw" partitions). A physical disk is divided into one or more physical volumes (PVs), and logical volume groups (VGs) are created by combining PVs.
Physical volumes are combined into volume groups (VGs). This creates a pool of disk space out of which logical volumes can be allocated. Within a volume group, the disk space available for allocation is divided into units of a fixed-size called extents. An extent is the smallest unit of space that can be allocated, Within a physical volume, extents are referred to as physical extents. A logical volume is allocated into logical extents of the same size as the physical extents. The extent size is thus the same for all logical volumes in the volume group. The volume group maps the logical extents to physical extents.
syntax:
vgcreate [name] [list of physical volumes]
example:
> vgcreate myVolumeGroup /dev/sdb1 Volume group "myVolumeGroup" successfully created
If you want volume group to contain multiple partitions:
> vgcreate myVolumeGroup /dev/sdb1 /dev/sdb2 /dev/sdb3
To display all volume groups:
> vgs VG #PV #LV #SN Attr VSize VFree cl 1 2 0 wz--n- <9.00g 0 myVolumeGroup 1 0 0 wz--n- 36.00m 36.00m
display contents of volume group or all volume groups.
> vgdisplay --- Volume group --- VG Name myVolumeGroup System ID Format lvm2 Metadata Areas 1 Metadata Sequence No 1 VG Access read/write VG Status resizable MAX LV 0 Cur LV 0 Open LV 0 Max PV 0 Cur PV 1 Act PV 1 VG Size 36.00 MiB PE Size 4.00 MiB Total PE 9 Alloc PE / Size 0 / 0 Free PE / Size 9 / 36.00 MiB VG UUID VNmBiJ-39lb-c941-YIKU-1b0n-Gtz3-fuLq2A --- Volume group --- VG Name cl System ID Format lvm2 Metadata Areas 1 Metadata Sequence No 3 VG Access read/write VG Status resizable MAX LV 0 Cur LV 2 Open LV 2 Max PV 0 Cur PV 1 Act PV 1 VG Size <9.00 GiB PE Size 4.00 MiB Total PE 2303 Alloc PE / Size 2303 / <9.00 GiB Free PE / Size 0 / 0 VG UUID oHLLvo-RdiR-PtyA-oHa8-kyjw-0KdN-kKdyZ5
7) Create a Logical Volume using part of Volume Group
lvcreate -L 10M -n myLogicalVolume myVolumeGroup
Logical Volumes
A logical volume provides storage virtualization. With a logical volume, you are not restricted to physical disk sizes. In addition, the hardware storage configuration is hidden from the software so it can be resized and moved without stopping applications or unmounting file systems.
syntax
lvcreate -n [logical volume name] - L [size] [volume group name]
where
n = name
L = size
Create a logical volume called myLogicalVolume using 12M of volme group myVolumeGroup
lvcreate -L 10M -n myLogicalVolume myVolumeGroup Logical volume "myLogicalVolume" created.
> lvdisplay --- Logical volume --- LV Path /dev/myVolumeGroup/myLogicalVolume LV Name myLogicalVolume VG Name myVolumeGroup LV UUID fcuP8G-hpw7-yEiE-eUzD-zBt2-XigK-umy2MJ LV Write Access read/write LV Creation host, time localhost.localdomain, 2017-12-08 22:57:43 -0500 LV Status available # open 0 LV Size 12.00 MiB Current LE 3 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:2 --- Logical volume --- LV Path /dev/cl/swap LV Name swap VG Name cl LV UUID VvlQgm-o9Qg-vTNA-mWyl-zdOP-umwH-Adr4xm LV Write Access read/write LV Creation host, time localhost.localdomain, 2017-12-08 15:56:57 -0500 LV Status available # open 2 LV Size 1.00 GiB Current LE 256 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:1 --- Logical volume --- LV Path /dev/cl/root LV Name root VG Name cl LV UUID zfVhd6-J1aw-9kgB-5ifE-AwH9-y8z4-gZashh LV Write Access read/write LV Creation host, time localhost.localdomain, 2017-12-08 15:56:58 -0500 LV Status available # open 1 LV Size <8.00 GiB Current LE 2047 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:0
Extending a volume group: extend volume group to 12Gig
lvextend -L12G /dev/myvg/lvol0
once logical volume is created, we can do fdisk (fdisk /dev/myVolumeGroup/lvol0) and make a file system
To look for existing logical drives:
lvmdiskscan scans all SCSI, (E)IDE disks, multiple, loop and network block devices in the system and lists them
# lvmdiskscan /dev/sda1 [ 29.30 GiB] /dev/sda2 [ 3.91 GiB] /dev/sda3 [ 46.80 GiB] 0 disks 3 partitions 0 LVM physical volume whole disks 0 LVM physical volumeslvchange lvextend lvmconfig lvmpolld lvremove lvscan lvconvert lvm lvmdiskscan lvmsadc lvrename lvcreate lvmchange lvmdump lvmsar lvresize lvdisplay lvmconf lvmetad lvreduce lvs
making directory to mount logical drive
mkdir /mnt/myMountPoint
formatting Logical Volumes using mkfs ("Make file system")
mkfs is a front-end program for the various file system builders (mkfs.fstype) available under Linux. It is used to build a Linux file system on a device, usually a hard disk partition. filesys is either the device name (e.g. /dev/hda1, /dev/sdb2), or a regular file that shall contain the file system. blocks is the number of blocks to be used for the file system. mkfs can be used to create several types of file systems including:
- mkfs - Some Linux Filesystems
mkfs.ext3 - Linux filesystem. Enancemenmt of mkfs.ext and mkfs.ext2
mkfs.ext4 - Linux filesystem. Enancemenmt of mkf3.ext with built-in journaling
mkfs.xfs - XFS filesystem
mkfs.msdos - DOS filesystem
mkfs.reiserfs - includes build in jopurnaling system
XFS is a highly scalable, high-performance file system. The mkfs.xfs command constructs an XFS filesystem by writing on a special file using the values found in the arguments of the command line.syntax:
mkfs.[file system type] [logical volume]
example:
mkfs.ext4 /dev/sda5
mkfs.ext4 /dev/myVolumeGroup/myLogicalVolume
formatting Logical Volumes using mkfs ("Make file system")
mkfs is simply a front-end for the various file system builders (mkfs.fstype) available under Linux. It is used to build a Linux file system on a device, usually a hard disk partition. filesys is either the device name (e.g. /dev/hda1, /dev/sdb2), or a regular file that shall contain the file system. blocks is the number of blocks to be used for the file system. mkfs can be used to create several types of file systems including:
- mkfs - Linux filesystem
- mkfs.ext3 - Linux filesystem. Enancemenmt of mkfs.ext and mkfs.ext2
- mkfs.ext4 - Linux filesystem. Enancemenmt of mkf3.ext with built-in journaling
- mkfs.xfs - XFS filesystem
- mkfs.msdos - DOS filesystem
- mkfs.reiserfs - includes build in jopurnaling system
syntax:
mkfs.xfs [logical volume]
example:
> mkfs.ext4 /dev/myVolumeGroup/myLogicalVolume
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
3072 inodes, 12288 blocks
614 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=12582912
2 block groups
8192 blocks per group, 8192 fragments per group
1536 inodes per group
Superblock backups stored on blocks:
8193
Allocating group tables: done
Writing inode tables: done
Creating journal (1024 blocks): done
Writing superblocks and filesystem accounting information: done
> lvdisplay --- Logical volume --- LV Path /dev/myVolumeGroup/myLogicalVolume LV Name myLogicalVolume VG Name myVolumeGroup LV UUID Kz7sOf-e3L6-YrjD-KVGq-Unin-4ohQ-R69Pcu LV Write Access read/write LV Creation host, time localhost.localdomain, 2017-03-10 12:43:34 -0800 LV Status available # open 0 LV Size 1.00 GiB Current LE 256 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:0
Mounting Volumes
used to "mount" a file directory of a device or partition to a directory
examples:
Mount myLogicalVolume to directory /mnt/myMountPoint
/dev/mapper/myVolumeGroup-myLogicalVolume /mnt/myMountPoint ext4 defaults 0 0
to see if it works
df -h /dev/mapper/cl-root 17G 1.3G 16G 8% / devtmpfs 478M 0 478M 0% /dev tmpfs 489M 0 489M 0% /dev/shm tmpfs 489M 6.8M 482M 2% /run tmpfs 489M 0 489M 0% /sys/fs/cgroup tmpfs 489M 8.0K 489M 1% /tmp /dev/sda1 1014M 168M 847M 17% /boot /dev/mapper/myVolumeGroup-myLogicalVolume 11M 204K 9.6M 3% /mnt/myMountPoint tmpfs 98M 0 98M 0% /run/user/0
9) Make directory to mount file system and mount file system using mount command
mkdir /mnt/myMountPoint
mount /dev/myVolumeGroup/myLogicalVolume /mnt/myMountPoint
9.1 Create a directory on which to mount logical drive
mkdir /mnt/myMountPoint
9.2 Mount Volume
used to "mount" a file directory of a device or partition to a directory
examples:
Mount /dev/sda1 to directory /mnt/myMountPoint
mount /dev/mapper/myVolumeGroup-myLogicalVolume /mnt/myMountPoint
to see if it worked
> df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/cl-root 8.0G 1.2G 6.9G 15% / devtmpfs 478M 0 478M 0% /dev tmpfs 489M 0 489M 0% /dev/shm tmpfs 489M 6.8M 482M 2% /run tmpfs 489M 0 489M 0% /sys/fs/cgroup /dev/sda1 1014M 168M 847M 17% /boot tmpfs 98M 0 98M 0% /run/user/0 /dev/mapper/myVolumeGroup-myLogicalVolume 11M 204K 9.6M 3% /mnt/myMountPoint
10) Add an entry to /etc/fstab file to make it permanent.
/dev/mapper/myVolumeGroup-myLogicalVolume /mnt/myMountPoint defaults ext4 0 0
Add an entry to /etc/fstab file to make it permanent.
/dev/mapper/myVolumeGroup-myLogicalVolume /mnt/myMountPoint defaults ext4 0 0
Make sure to get syntax correctly or system may fail on reboot!
To test syntax before rebooting
mount -a
example of fstab entry
/etc/fstab # <device> <dir> <type> <options> <dump> <fsck> /dev/sda1 / ext4 defaults,noatime 0 1 /dev/sda2 none swap defaults 0 0 /dev/sda3 /home ext4 defaults,noatime 0 2
Where:
- device - describes the block special device or remote filesystem to be mounted.
- dir describes the mount directory,
- type the file system type,
- options the associated mount options,
- dump is checked by the dump utility. This field is usually set to 0, which disables the check,
- fsck - sets the order for filesystem checks at boot time. For the root device it should be 1, For other partitions it should be 2, or 0 to disable checking,
Introduction to fstab
The configuration file /etc/fstab contains the necessary information to automate the process of mounting partitions. Partitions listed in fstab can be configured to automatically mount during the boot process. The options for mount and fstab are similar. The syntax of a fstab entry is :
fields description <device> The device/partition (by /dev location or UUID) that contain a file system. <mount point> The directory on your root file system (aka mount point) from which it will be possible to access the content of the device/partition (note: swap has no mount point). A mount point is a location on your directory tree to mount the partition. In Centos/Red Hat, the default location is the /mnt directory. You may use any name you wish for the mount point, but you must create the mount point before you mount the partition.
Mount points should not have spaces in the names. <file system type> Type of file system. Common types include: ext2, ext3, ext4, reiserFS, XFS <options> Use defaults in most cases. See documenation for special cases. example: defaults <dump> Enable or disable backing up of the device/partition (the command dump). This field is usually set to 0, which disables it. <pass num> Controls the order in which fsck checks the device/partition for errors at boot time. The root device should be 1. Other partitions should be 2, or 0 to disable checking. Fsck order is to tell fsck what order to check the file systems, if set to "0" file system is ignored. Often a source of confusion, there are only 3 options : Please refer to the examples section for sample entries. We have provided you some detailed explanations of each field: By default, Ubuntu now uses UUID to identify partitions. UUID=xxx.yyy.zzz To list your devices by UUID use blkid
Alternative ways to refer to partitions: A mount point is a location on your directory tree to mount the partition. The default location is /media although you may use alternate locations such as /mnt or your home directory. You may use any name you wish for the mount point, but you must create the mount point before you mount the partition. For example : /media/windows
You may either use auto or specify a file system. Auto will attempt to automatically detect the file system of the target file system and in general works well. In general auto is used for removable devices and a specific file system or network protocol for network shares. Examples: Options are dependent on the file system. You may use "defaults" here and some typical options may include : Ubuntu 8.04 and later uses relatime as default for linux native file systems. You can find a discussion of relatime here : http://lwn.net/Articles/244829. This relates to when and how often the last access time of the current version of a file is updated, i.e. when it was last read. I advise dmask=027,fmask=137 (using umask=000 will cause all your files to be executable). More permissive options would be dmask=000,fmask=111. For mounting samba shares you can specify a username and password, or better a credentials file. The credentials file contains should be owned by root.root with permissions = 0400 . Common options : For specific options with specific file systems see: This field sets whether the backup utility dump will backup file system. If set to "0" file system ignored, "1" file system is backed up. Dump is seldom used and if in doubt use 0. Fsck order is to tell fsck what order to check the file systems, if set to "0" file system is ignored. Often a source of confusion, there are only 3 options : In practice, use "1" for your root partition, / and 2 for the rest. All partitions marked with a "2" are checked in sequence and you do not need to specify an order. Use "0" to disable checking the file system at boot or for network shares. You may also "tune" or set the frequency of file checks (default is every 30 mounts) but in general these checks are designed to maintain the integrity of your file system and thus you should strongly consider keeping the default settings. The blkid program prints the type of content (e.g. filesystem or swap) that a block device holds.
When device is specified, tokens from only this device are displayed.
The fstab file uses can use UUID to identify partitions to mount.
example: To un-mount use command umount. Make sure that you are not in the directory you want to umount. then increase size of file system This feature is useful to attach windows volumes to Linux<>
to mount /temp to 10.1.1.14/temp
This will only remain until reboot. To maintain permanently add to /etc/fstab file
LUKS is the standard for Linux hard disk encryption. By providing a standard on-disk-format, it does not only facilitate compatibility among distributions, but also provides secure management of multiple user passwords. Install cryptsetup utility Initialize the volume, and set an initial key or passphrase see mapping for /dev/mapper/backup2 use status for the mapping: Dump LUKS headers Format LUKS partition Clean drive: write zeros to /dev/mapper/backup2 encrypted device. This will allocate block data with zeros.[Device] [Mount Point] [File System Type] [Options] [Dump] [Pass]
example: /dev/myVolumeGroup/myLogicalVolume
example: /dev/myVolumeGroup/myLogicalVolume
Device
sudo blkid
Mount point
sudo mkdir /media/windows
File System Type
Options
Dump
Pass (fsck order)
Other commands:
blkid
> blkid
/dev/sda1: UUID="d3c2f6a4-9eeb-41d8-8a56-35899de9b422" TYPE="xfs"
/dev/sda2: UUID="2f4bda65-9282-454e-b485-c02ac1b1d10a" TYPE="swap"
/dev/sda3: UUID="7170e712-f9df-43a4-b9bb-777ddb66eaa4" TYPE="xfs"
/dev/sdb1: UUID="vmhfqT-35TA-YLsr-4n8c-HUSl-VUtg-zYvccG" TYPE="LVM2_member"
/dev/mapper/myVolumeGroup-myLogicalVolume: UUID="f28f02f5-8ff7-4657-8af6-c4e2331a75e1" TYPE="ext4"
umount /mnt/myLogicalVolume
or
umount /dev/sda5
To Resize a Logical Volume and file system
lvrersize -L 14G /dev/dir/myDir
xfs_growfs /dev/dir/myDir
Mount remote file systems or remote volumes
mount -t cifs -o username=myuser password=Password //10.1.1.14/temp /temp
//10.1.1.14/temp /temp cifs users,rw username=myuser,password=Password //10.1.1.14/temp /temp 0 0
Using LUKS for encryption
# yum install cryptsetup-luks
To encrpt /dev/xvdc.
# cryptsetup -y -v luksFormat /dev/xvdc
# cryptsetup luksOpen /dev/xvdc backup2
ls -l /dev/mapper/backup2
# cryptsetup -v status backup2
# cryptsetup luksDump /dev/xvdc
# dd if=/dev/zero of=/dev/mapper/backup2
B. Remove disk/partion/physical volume/logical group/logical volume
Steps to completely undue previous process and delete/remove disk, partion, physical volume, logical group and logical volume
1. unmount partion
umount /dev/myVolumeGroup/myLogicalVolume2. remove mount point
rm -r /dev/myVolumeGroup/myLogicalVolume3. Remove Volume Group
> vgremove myVolumeGroup Do you really want to remove volume group "myVolumeGroup" containing 1 logical volumes? [y/n]: y Do you really want to remove active logical volume myVolumeGroup/myLogicalVolume? [y/n]: y Logical volume "myLogicalVolume" successfully removed Volume group "myVolumeGroup" successfully removed
4. Remove Physical Volume
> pvremove /dev/sdb1 Labels on physical volume "/dev/sdb1" successfully wiped.
5. in VM console
goto VM proprties and delete disk 2 and disk 36. remove entry in file /etc/fstab
7. reboot and check everthing is gone
C. Rename a Logical Volume
To rename a logical Volume use lvrename, but first have to umount the logical volume.
umount /dev/myVolumeGroup/myLogicalVolume lvrename /dev/myVolumeGroup/myLogicalVolume /dev/myVolumeGroup/myLogicalVolumeNEW mount /dev/myVolumeGroup/myLogicalVolumeNEW /mnt/myMountPoint
add entry to /etc/fstab file to make it permanent.
/dev/myVolumeGroup/myLogicalVolumeNEW /mnt/myMountPoint defaults ext4 0 0
To confirm change has been done:
> df -h Filesystem Size Used Avail Use% Mounted on /dev/sda3 28G 1.2G 27G 4% / devtmpfs 479M 0 479M 0% /dev tmpfs 489M 0 489M 0% /dev/shm tmpfs 489M 50M 439M 11% /run tmpfs 489M 0 489M 0% /sys/fs/cgroup /dev/sda1 297M 152M 145M 52% /boot tmpfs 98M 0 98M 0% /run/user/0 /dev/mapper/myVolumeGroup-myLogicalVolumeNEW 976M 2.6M 907M 1% /mnt/myMountPoint
D. To resize a Logical Volume
To resize a logical Volume, we first have to un mount the logical volume.
umount /dev/myVolumeGroup/myLogicalVolume
e2fsck is used to check a Linux extended file system. the -f switch forces checking even if filesystem is marked clean.
> e2fsck -f /dev/myVolumeGroup/myLogicalVolume e2fsck 1.42.9 (28-Dec-2013) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/myVolumeGroup/myLogicalVolume: 11/128016 files (0.0% non-contiguous), 26684/512000 blocks
Next perform lvresize command and re-mount partition. Note that this will likely destroy any filesystem located on that volume, so take appropriate backup first.
lvresize -L 400M /dev/myVolumeGroup/myLogicalVolume WARNING: Reducing active logical volume to 400.00 MiB. THIS MAY DESTROY YOUR DATA (filesystem etc.) Do you really want to reduce myVolumeGroup/myLogicalVolume? [y/n]: y Size of logical volume myVolumeGroup/myLogicalVolume changed from 500.00 MiB (125 extents) to 400.00 MiB (100 extents). Logical volume myVolumeGroup/myLogicalVolume successfully resized.
CHeck volume again
> e2fsck -f /dev/myVolumeGroup/myLogicalVolume
Resize the filesystem to match the LVs size, check and mount it
> resize2fs -p /dev/myVolumeGroup/myLogicalVolume > mount /dev/myVolumeGroup/myLogicalVolume /mnt/myMountPoint
The resize2fs program will resize ext2, ext3, or ext4 file systems. It can be used to enlarge or shrink an unmounted file system located on device. If the filesystem is mounted, it can be used to expand the size of the mounted filesystem, assuming the kernel supports on-line resizing.
> resize2fs -f -p /dev/myVolumeGroup/myLogicalVolume
E. To extend and existing logical volume
extend to 2.5G to existing logical volume
lvextend -L2500M /dev/myVolumeGroup/myLogicalVolume
add 200M to existing logical volume
lvextend -L+200M /dev/myVolumeGroup/myLogicalVolume
F. Using parted to create a partition instead of fdisk
The GNU parted utility is an alternative to the fdisk utility. It is equally useful for creating space for new operating systems, reorganizing disk usage, copying data on hard disks and disk imaging. The package contains a library, libparted, as well as well as a command-line frontend, parted, which can also be used in scripts. Note that some parted commands are not included in Red Hat/Centos version (for example: resize, resizepart).
Parted has similar functionality as fdisk. One reason to use parted is that it supports disks bigger than 2TB.
Here we use parted to see existing disks and partitions:
> parted -l Model: VMware, VMware Virtual S (scsi) Disk /dev/sda: 32.2GB Sector size (logical/physical): 512B/512B Partition Table: msdos Disk Flags: Number Start End Size Type File system Flags 1 1049kB 316MB 315MB primary xfs boot, lvm 2 316MB 2463MB 2147MB primary linux-swap(v1) 3 2463MB 32.2GB 29.7GB primary xfs lvm Model: VMware, VMware Virtual S (scsi) Disk /dev/sdb: 5369MB Sector size (logical/physical): 512B/512B Partition Table: pc98 Disk Flags:
use parted on a specific disk
> parted /dev/sdb GNU Parted 3.1 Using /dev/sdb Welcome to GNU Parted! Type 'help' to view a list of commands.
type m for menu
(parted) m
align-check TYPE N check partition N for TYPE(min|opt) alignment
help [COMMAND] print general help, or help on COMMAND
mklabel,mktable LABEL-TYPE create a new disklabel (partition table)
mkpart PART-TYPE [FS-TYPE] START END make a partition
name NUMBER NAME name partition NUMBER as NAME
print [devices|free|list,all|NUMBER] display the partition table, available devices, free space,
all found partitions, or a particular partition
quit exit program
rescue START END rescue a lost partition near START and END
rm NUMBER delete partition NUMBER
select DEVICE choose the device to edit
disk_set FLAG STATE change the FLAG on selected device
disk_toggle [FLAG] toggle the state of FLAG on selected device
set NUMBER FLAG STATE change the FLAG on partition NUMBER
toggle [NUMBER [FLAG]] toggle the state of FLAG on partition NUMBER
unit UNIT set the default unit to UNIT
version display the version number and copyright information of GNU Parted
On a new disk, the first think you have to do is mklabel command. This command creates a new disk label, of type label-type. The new disk label will have no partitions. For some reason, we use the msdos type for Linux OS.
(parted) mklabel msdos
Make a new 3 Gig Partion using parted:
(parted) mkpart primary ext4 1Gig 3Gig Warning: You requested a partition from 1074MB to 3221MB (sectors 2097152..6291456). The closest location we can manage is 1078MB to 3224MB (sectors 2104515..6297479). Is this still acceptable to you? Yes/No? Yes Warning: The resulting partition is not properly aligned for best performance. Ignore/Cancel? i
See what was created
(parted) p Model: VMware, VMware Virtual S (scsi) Disk /dev/sdb: 5369MB Sector size (logical/physical): 512B/512B Partition Table: pc98 Disk Flags: Number Start End Size File system Name Flags 1 1078MB 3224MB 2147MB primary
If you make a mistake you can use rm to remove disk partition
(parted) rm Partition number? 1
Use quit to exit
(parted) quit Information: You may need to update /etc/fstab.
You can now format the partition or perform LMV commands on the new partition.
For whole disk devices only the partition table must be erased, which will effectively destroy all data on that disk. This can be done by zeroing the first sector with:
dd if=/dev/zero of=PhysicalVolume bs=512 count=1