Command line utilities for managing users and groups
useradd, userm od, userdel > Standard utilities for adding, modifying, and deleting user accounts.
groupadd, groupmod,groupdel > Standard utilities for adding, modifying, and deleting groups.
gpasswd > Standard utility for administering the /etc/group configuration file.
pwck, grpck > Utilities that can be used for verification of the password, group,and associated shadow files.
pwconv, pwunconv > Utilities that can be used for the conversion of passwords to shadow passwords, or back from shadow passwords to standard passwords
Activating and Deactivating Volume Groups
When you create a volume group it is, by default, activated. This means that the logical volumes in that group are accessible and subject to change.
There are various circumstances for which you need to make a volume group inactive and thus unknown to the kernel. To deactivate or activate a volume group, use the -a (–available) argument of the vgchange command.
The following example deactivates the volume group my_volume_group.
# vgchange -a n my_volume_group
If clustered locking is enabled, add ’e’ to activate or deactivate a volume group exclusively on one node or ’l’ to activate or/deactivate a volume group only on the local node. Logical volumes with single-host snapshots are always activated exclusively because they can only be used on one node at once.
Creating Volume Groups
To create a volume group from one or more physical volumes, use the vgcreate command. The vgcreate command creates a new volume group by name and adds at least one physical volume to it.
The following command creates a volume group named vg1 that contains physical volumes /dev/sdd1 and /dev/sde1.
# vgcreate vg1 /dev/sdd1 /dev/sde1
When physical volumes are used to create a volume group, its disk space is divided into 4MB extents, by default. This extent is the minimum amount by which the logical volume may be increased or decreased in size. Large numbers of extents will have no impact on I/O performance of the logical volume.
You can specify the extent size with the -s option to the vgcreate command if the default extent size is not suitable.
Scanning Disks for Volume Groups to Build the Cache File
The vgscan command scans all supported disk devices in the system looking for LVM physical volumes and volume groups. This builds the LVM cache in the /etc/lvm/.cache file, which maintains a listing of current LVM devices.
LVM runs the vgscan command automatically at system startup and at other times during LVM operation, such as when you execute a vgcreate command or when LVM detects an inconsistency. You may need to run the vgscan command manually when you change your hardware configuration, causing new devices to be visible to the system that were not present at system bootup. This may be necessary, for example, when you add new disks to the system on a SAN or hotplug a new disk that has been labeled as a physical volume.
You can define a filter in the lvm.conf file to restrict the scan to avoid specific devices.
SYNOPSIS
DESCRIPTION
lvm.conf is loaded during the initialisation phase of lvm (8). This file can in turn lead to other files being loaded - settings read in later override earlier settings. File timestamps are checked between commands and if any have changed, all the files are reloaded.
Use lvm dumpconfig to check what settings are in use.
# lvm dumpconfig
devices {
dir=”/dev”
scan=”/dev”
preferred_names=[]
filter=”a/.*/”
cache_dir=”/etc/lvm/cache”
cache_file_prefix=”"
write_cache_state=1
sysfs_scan=1
md_component_detection=1
ignore_suspended_devices=0
}
Displaying Volume Groups
There are two commands you can use to display properties of LVM volume groups: vgs and vgdisplay.
The vgscan command, which scans all the disks for volume groups and rebuilds the LVM cache file, also displays the volume groups.
The vgs command provides volume group information in a configurable form, displaying one line per volume group. The vgs command provides a great deal of format control, and is useful for scripting.
The vgdisplay command displays volume group properties (such as size, extents, number of physical volumes, etc.) in a fixed form. The following example shows the output of a vgdisplay command for the volume group new_vg. If you do not specify a volume group, all existing volume groups are displayed.
# vgdisplay new_vg
— Volume group —
VG Name new_vg
System ID
Format lvm2
Metadata Areas 3
Metadata Sequence No 11
VG Access read/write
VG Status resizable
DESCRIPTION
vgdisplay allows you to see the attributes of VolumeGroupName (or all volume groups if none is given) with it’s physical and logical volumes and their sizes etc.
vgs (8) is an alternative that provides the same information in the style of ps (1).
