Linux


System

Description Command
Boot into CLI mode. sudo systemctl set-default multi-user.target
Boot into desktop mode. sudo systemctl set-default graphical.target

SSH

Description Command
Create private/public SSH key file using 2048 bit encryption and with a comment. The command creates files under ~/.ssh folder. ssh-keygen -b 2048 -C user@host.domain
Push public SSH key to a server ssh-copy-id -p 41111 -i ~/.ssh/id_rsa.pub mhan@remote.server.com
Reset (SELinux) permissions related to SSH. This may be needed if all else fails to correct the issue of system not accepting public keys. restorecon -R -v ~/.ssh

Disk

Search

LVM

Physical volume

Description Command
Initialize for use as LVM physical volume. pvcreate /dev/sdb1
Scanning for block devices. lvmdiskscan
Display the physical volumes. pvdisplay
Show all physical devices. pvscan
Prevent allocation of physical extents on the free space of one or more physical volumes. pvchange -x n /dev/sdb1
Resize. pvresize
Remove LVM label. pvremove

Volume group

Description Command
Create a volume group. vgcreate vg1 /dev/sdb1 /dev/sdc1
Add a physical volume to a volume group. vgextend vg1 /dev/sdd1
Display volume group. vgdisplay new_vg
Scan disks for volume groups. vgscan
Remove a physical volume from a volume group. vgreduce group_name /dev/sdc1
Change the maximum number of logical volumes of volume group vg00 to 128. vgchange -l 128 /dev/vg00
Activate or deactivate a volume group. vgchange -a n my_volume_group
Remove a volume group. vgremove officevg
Split the physical volumes of a volume group and create a new volume group. $ vgsplit bigvg smallvg /dev/ram15
Volume group "smallvg" successfully split from "bigvg"
Merge the inactive volume group my_vg into the active or inactive volume group databases giving verbose runtime information. vgmerge -v databases my_vg
Change the name of a volume group. vgrename vg02 my_volume_group

Users

UID or GID

Description Command
Check UID. id -u username
Check GID. id -g username
Check all of the groups a user belongs to. id -G username
Check UID and all of the groups a user belongs to. id username

File

Permissions

Letter Number
r 4
w 2
x 1
rw- 6
r-x 5
rwx 7