Linux

• Add User with No Login 

[root@testsvr01 ~]# useradd  -s /sbin/nologin -p password user

• Modify sshd_config File 

[root@testsvr01 ~]# vi  /etc/ssh/sshd_config

    #Subsystem      sftp    /usr/libexec/openssh/sftp-server   

   Subsystem sftp internal-sftp

   Match Group user
   ForceCommand internal-sftp
   ChrootDirectory /home/user
   X11Forwarding no
   AllowTcpForwarding no

• Check Available Disk

[root@testsvr01~]# lsblk
NAME                  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                     8:0    0  100G  0 disk
sdb                     8:16   0  500G  0 disk
sdc                     8:32   0  500G  0 disk
└─vg_pgdata-lv_pgdata 253:2    0  500G  0 lvm  /pgdata
sr0                    11:0    1 1024M  0 rom
vda                   252:0    0  100G  0 disk
├─vda1                252:1    0  500M  0 part /boot
└─vda2                252:2    0 99.5G  0 part

• Check Available Disk

[root@testsvr01~]# lsblk
NAME          MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda             8:0    0   60G  0 disk
├─sda1          8:1    0    1G  0 part /boot
└─sda2          8:2    0   59G  0 part
  ├─rhel-root 253:0    0 35.6G  0 lvm  /
  ├─rhel-swap 253:1    0    6G  0 lvm  [SWAP]
  └─rhel-home 253:2    0 17.4G  0 lvm  /home
sdb             8:16   0  250G  0 disk
sdc             8:32   0  250G  0 disk

See the below Query to find Unused index in PostgreSQL

[root@testsvr01~]# useradd sysadmin -G wheel

[root@testsvr01~]# passwd sysadmin
Changing password for user sysadmin.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root@testsvr01~]#

MBR Backup

[root@testsvr01~]#  dd if=/dev/sda1 of=/opt/mbr_backup bs=512 count=1

0+1 records in
0+1 records out
115 bytes (115 B) copied, 0.0001912 s, 601 kB/s

[root@testsvr01~]#

[root@testsvr01~]# rpm -q kernel
kernel-3.10.0-1160.15.2.el7.x86_64
kernel-3.10.0-1160.21.1.el7.x86_64
kernel-3.10.0-1160.24.1.el7.x86_64
kernel-3.10.0-1160.36.2.el7.x86_64
kernel-3.10.0-1160.71.1.el7.x86_64
[root@ehapp01 ~]# package-cleanup --oldkernels --count=1
Loaded plugins: fastestmirror, langpacks
--> Running transaction check
---> Package kernel.x86_64 0:3.10.0-1160.15.2.el7 will be erased
---> Package kernel.x86_64 0:3.10.0-1160.21.1.el7 will be erased

[root@testsvr01~]# df -Th | grep "^/dev"
/dev/mapper/rhel-root xfs        50G  8.8G   42G  18% /
/dev/vda1             xfs       497M  199M  299M  40% /boot
/dev/mapper/rhel-home xfs        46G  8.9G   37G  20% /home
[root@testsvr01~]#

[root@testsvr01~]# yum install yum-utils

[root@testdbsvr01~]# dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-8-x86_64/pgdg-redhat-repo-latest.noarch.rpm
[root@testdbsvr01~]# dnf -qy module disable postgresql

[root@testdbsvr01~]# dnf install -y postgresql12-server

[root@testdbsvr01~]# dnf install -y postgresql12-contrib

[root@testdbsvr01~]# /usr/pgsql-12/bin/postgresql-12-setup initdb
Initializing database ... OK