Archive for January, 2021

Debug and fix Virtuozzo / KVM broken Hypervisor error: ‘PrlSDKError(‘SDK error: 0x80000249: Unable to connect to Virtuozzo. You may experience a connection problem or the server may be down.’ on CentOS Linux howto

Thursday, January 28th, 2021

Reading Time: 6minutes


I've recently yum upgraded a CentOS Linux server runinng Virtuozzo kernel and Virtuozzo virtualization Virtual Machines to the latest available CentOS Linux release 7.9.2009 (Core) just to find out after the upgrade there was issues with both virtuozzo (VZ) way to list installed VZ enabled VMs reporting Unable to connect to Virtuozzo error like below:

[root@CENTOS etc]# prlctl list -a
Unable to connect to Virtuozzo. You may experience a connection problem or the server may be down. Contact your Virtuozzo administrator for assistance.

Even the native QEMU KVM VMs installed on the Hypervisor system failed to work to list and bring up the VMs producing another unexplainable error with virsh unable to connect to the hypervisor socket

[root@CENTOS etc]# virsh list –all
error: failed to connect to the hypervisor
error: Failed to connect socket to '/var/run/libvirt/libvirt-sock': No such file or directory

In dmesg cmd kernel log messages the error found looked as so:

[root@CENTOS etc]# dmesg|grep -i sdk

[    5.314601] PrlSDKError('SDK error: 0x80000249: Unable to connect to Virtuozzo. You may experience a connection problem or the server may be down. Contact your Virtuozzo administrator for assistance.',)

To fix it I had to experiment a bit based on some suggestions from Google results as usual and what turned to be the cause is a now obsolete setting for disk probing that is breaking libvirtd

Disable allow_disk_format_probing in /etc/libvirt/qemu.conf

The fix to PrlSDKError('SDK error: 0x80000249: Unable to connect to Virtuozzo comes to commenting a parameter inside 


which for historical reasons seems to be turned on by default it is like this

allow_disk_format_probing = 1

Resolution is to either change the value to 0 or completely comment the line:

[root@CENTOS etc]# grep allow_disk_format_probing /etc/libvirt/qemu.conf
# If allow_disk_format_probing is enabled, libvirt will probe disk
#allow_disk_format_probing = 1
#allow_disk_format_probing = 1

Debug problems with Virtuozzo services and validate virtualization setup

What really helped to debug the issue was to check the extended status info of libvirtd.service vzevent vz.service libvirtguestd.service prl-disp systemd services

[root@CENTOS etc]# systemctl -l status libvirtd.service vzevent vz.service libvirtguestd.service prl-disp

Here I had to analyze the errors and googled a little bit about it

Once this is changed I had to of course restart libvirtd.service and rest of virtuozzo / kvm services

[root@CENTOS etc]# systemctl restart libvirtd.service ibvirtd.service vzevent vz.service libvirtguest.service prl-disp

Another useful tool part of a standard VZ install that I've used to make sure each of the Host OS Hypervisor components is running smoothly is virt-host-validate(tool is part of libvirt-client rpm package)

[root@CENTOS etc]# virt-host-validate
  QEMU: Checking for hardware virtualization                                 : PASS
  QEMU: Checking if device /dev/kvm exists                                   : PASS
  QEMU: Checking if device /dev/kvm is accessible                            : PASS
  QEMU: Checking if device /dev/vhost-net exists                             : PASS
  QEMU: Checking if device /dev/net/tun exists                               : PASS
  QEMU: Checking for cgroup 'memory' controller support                      : PASS
  QEMU: Checking for cgroup 'memory' controller mount-point                  : PASS
  QEMU: Checking for cgroup 'cpu' controller support                         : PASS
  QEMU: Checking for cgroup 'cpu' controller mount-point                     : PASS
  QEMU: Checking for cgroup 'cpuacct' controller support                     : PASS
  QEMU: Checking for cgroup 'cpuacct' controller mount-point                 : PASS
  QEMU: Checking for cgroup 'cpuset' controller support                      : PASS
  QEMU: Checking for cgroup 'cpuset' controller mount-point                  : PASS
  QEMU: Checking for cgroup 'devices' controller support                     : PASS
  QEMU: Checking for cgroup 'devices' controller mount-point                 : PASS
  QEMU: Checking for cgroup 'blkio' controller support                       : PASS
  QEMU: Checking for cgroup 'blkio' controller mount-point                   : PASS
  QEMU: Checking for device assignment IOMMU support                         : PASS
  QEMU: Checking if IOMMU is enabled by kernel                               : WARN (IOMMU appears to be disabled in kernel. Add intel_iommu=on to kernel cmdline arguments)
   LXC: Checking for Linux >= 2.6.26                                         : PASS
   LXC: Checking for namespace ipc                                           : PASS
   LXC: Checking for namespace mnt                                           : PASS
   LXC: Checking for namespace pid                                           : PASS
   LXC: Checking for namespace uts                                           : PASS
   LXC: Checking for namespace net                                           : PASS
   LXC: Checking for namespace user                                          : PASS
   LXC: Checking for cgroup 'memory' controller support                      : PASS
   LXC: Checking for cgroup 'memory' controller mount-point                  : PASS
   LXC: Checking for cgroup 'cpu' controller support                         : PASS
   LXC: Checking for cgroup 'cpu' controller mount-point                     : PASS
   LXC: Checking for cgroup 'cpuacct' controller support                     : PASS
   LXC: Checking for cgroup 'cpuacct' controller mount-point                 : PASS
   LXC: Checking for cgroup 'cpuset' controller support                      : PASS
   LXC: Checking for cgroup 'cpuset' controller mount-point                  : PASS
   LXC: Checking for cgroup 'devices' controller support                     : PASS
   LXC: Checking for cgroup 'devices' controller mount-point                 : PASS
   LXC: Checking for cgroup 'blkio' controller support                       : PASS
   LXC: Checking for cgroup 'blkio' controller mount-point                   : PASS
   LXC: Checking if device /sys/fs/fuse/connections exists                   : PASS

One thing to note here that virt-host-validate helped me to realize the  fuse (File system in userspace) module kernel support enabled on the HV was missing so I've enabled temporary for this boot with modprobe and permanently via a configuration like so:

# to load it one time
[root@CENTOS etc]#  modprobe fuse
# to load fuse permnanently on next boot

[root@CENTOS etc]#  echo fuse >> /etc/modules-load.d/fuse.conf

Disable selinux on CentOS HV

Another thing was selinux was enabled on the HV. Selinux is really annoying thing and to be honest I never used it on any server and though its idea is quite good the consequences it creates for daily sysadmin work are terrible so I usually disable it. It could be that a Hypervisor Host OS might work just normal with the selinux enabled but just in case I decided to remove it. This is how

[root@CENTOS etc]#  sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             targeted
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     allowed
Max kernel policy version:      31

To temporarily change the SELinux mode from targeted to permissive with the following command:

[root@CENTOS etc]#  setenforce 0

Edit /etc/selinux/config file and set the SELINUX mod to disabled

[root@CENTOS etc]# vim /etc/selinux/config
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#       enforcing – SELinux security policy is enforced.
#       permissive – SELinux prints warnings instead of enforcing.
#       disabled – No SELinux policy is loaded.
# SELINUXTYPE= can take one of these two values:
#       targeted – Targeted processes are protected,
#       mls – Multi Level Security protection.

Finally rebooted graceously the machine just in case with the good recommended way to reboot servers with shutdown command instead of /sbin/reboot

[root@CENTOS etc]# shutdown -r now

The advantage of shutdown is that it tries to shutdown each service by sending stop requests but usually this takes some time and even a shutdown request could take longer to proccess as each service such as a WebServer application is being waited to close all its network connections etc. |
However if you want to have a quick reboot and you don't care about any established network connections to third party IPs you can go for the brutal old fashioned /sbin/reboot 🙂

Create simple proxy http server with netcat ( nc ) based tiny shell script

Tuesday, January 26th, 2021

Reading Time: 4minutes


The need of proxy server is inevitable nowadays especially if you have servers located in a paranoid security environments. Where virtually all is being passed through some kind of a proxy server. In my work we have recently started a  CentOS Linux release 7.9.2009 on HP Proliant DL360e Gen8 (host named rhel-testing).

HP DL360e are quite old nowadays but since we have spare servers and we can refurnish them to use as a local testing internal server Hypervisor it is okay for us. The machine is attached to a Rack that is connected to a Secured Deimilitarized Zone LAN (DMZ Network) which is so much filtered that even simple access to the local company homebrew RPM repository is not accessible from the machine.
Thus to set and remove software from the machine we needed a way to make yum repositories be available, and it seems the only way was to use a proxy server (situated on another accessible server which we use as a jump host to access the testing machine).

Since opening additional firewall request was a time consuming non-sense and the machine is just for testing purposes, we had to come with a solution where we can somehow access a Local repository RPM storage server for which we have a separate /etc/yum.repos.d/custom-rpms.repo definition file created.

This is why we needed a simplistic way to run a proxy but as we did not have the easy way to install privoxy / squid / haproxy or apache webserver configured as a proxy (to install one of those of relatively giant piece of software need to copy many rpm packages and manually satisfy dependencies), we looked for a simplistic way to run a proxy server on jump-host machine host A.

A note to make here is jump-host that was about to serve as a proxy  had already HTTP access towards the RPM repositories and could normally fetch packages with curl or wget via it …

For to create a simple proxy server out of nothing, I've googled a bit thinking that it should be possible either with BASH's TCP/IP capabilities or some other small C written tool compiled as a static binary, just to find out that netcat swiss army knife as a proxy server bash script is capable of doing the trick.

Jump host machine which was about to be used as a proxy server for http traffic did not have enabled access to tcp/port 8888 (port's firewall policies were prohibiting access to it).Since 8888 was the port targetted to run the proxy to allow TCP/IP port 8888 accessibility from the testing RHEL machine towards jump host, we had to issue first on jump host:

[root@jump-host: ~ ]# firewall-cmd –permanent –zone=public –add-port=8888/tcp

To run the script once placed under /root/ on jump-host we had to run a never ending loop in a GNU screen session to make sure it runs forever:

Original script used taken from above article is:

#!/bin/sh -e


if [ $# != 3 ]
    echo "usage: $0 <src-port> <dst-host> <dst-port>"
    exit 0

TMP=`mktemp -d`
trap 'rm -rf "$TMP"' EXIT
mkfifo -m 0600 "$BACK" "$SENT" "$RCVD"
sed 's/^/ => /' <"$SENT" &
sed 's/^/<=  /' <"$RCVD" &
nc -l -p "$1" <"$BACK" | tee "$SENT" | nc "$2" "$3" | tee "$RCVD" >"$BACK"


Above script you can download here.

I've tested the script one time and it worked, the script syntax is:

 [root@jump-host: ~ ]#  sh
usage: <src-port> <dst-host> <dst-port>

To make it work for one time connection I've run it as so:


 [root@jump-host: ~ ]# sh 8888 80



To make the script work all the time I had to use one small one liner infinite bash loop which goes like this:

[root@jump-host: ~ ]#  while [ 1 ]; do sh 8888 80; done​

On rhel-testing we had to configure for yum and all applications to use a proxy temporary via

[root@rhel-tresting: ~ ]# export http_proxy=jump-host_machine_accessibleIP:8888

And then use the normal yum check-update && yum update to apply to rhel-testing machine latest RPM package security updates.

The nice stuff about the with netcat in a inifite loop is you will see the binary copy of traffic flowing on the script which will make you feel like in those notorious Hackers movies ! 🙂

The stupid stuff is that sometimes some connections and RPM database updates or RPMs could be cancelled due to some kind of network issues.

To make the connection issues that are occuring to the improvised proxy server go away we finally used a slightly modified version from the original netcat script, which read like this.

#!/bin/sh -e


if [ $# != 3 ]
    echo "usage: $0 <src-port> <dst-host> <dst-port>"
        exit 0

        TMP=`mktemp -d`
        trap 'rm -rf "$TMP"' EXIT
        mkfifo -m 0600 "$BACK" "$SENT" "$RCVD"
        sed 's/^/ => /' <"$SENT" &
        sed 's/^/<=  /' <"$RCVD" &
        nc –proxy-type http -l -p "$1" <"$BACK" | tee "$SENT" | nc "$2" "$3" | tee "$RCVD" >"$BACK"

Modified version with –proxy-type http argument passed to netcat script u can download here.

With –proxy-type http yum check-update works normal just like with any normal fully functional http_proxy configured.

Next step wasto make the configuration permanent you can either add to /root/.bashrc or /etc/bashrc (if you need the setting to be system wide for every user that logged in to Linux system).

[root@rhel-tresting: ~ ]#  echo "http_proxy=http://jump-host_machine_accessibleIP:8888/" > /etc/environment

If you need to set the new built netcat TCP proxy only for yum package update tool include proxy only in /etc/yum.conf:

[root@rhel-tresting: ~ ]# vi /etc/yum.conf

That's all now you have a proxy out of nothing with just a simple netcat enjoy.

KVM Virtual Machine RHEL 8.3 Linux install on Redhat 8.3 Linux Hypervisor with custom tailored kickstart.cfg

Friday, January 22nd, 2021

Reading Time: 6minutes


If you don't have tried it yet Redhat and CentOS and other RPM based Linux operationg systems that use anaconda installer is generating a kickstart file after being installed under /root/{anaconda-ks.cfg,initial-setup- ks.cfg,original-ks.cfg} immediately after the OS installation completes. Using this Kickstart file template you can automate installation of Redhat installation with exactly the same configuration as many times as you like by directly loading your /root/original-ks.cfg file in RHEL installer.

Here is the official description of Kickstart files from Redhat:

"The Red Hat Enterprise Linux installation process automatically writes a Kickstart file that contains the settings for the installed system. This file is always saved as /root/anaconda-ks.cfg. You may use this file to repeat the installation with identical settings, or modify copies to specify settings for other systems."

Kickstart files contain answers to all questions normally asked by the text / graphical installation program, such as what time zone you want the system to use, how the drives should be partitioned, or which packages should be installed. Providing a prepared Kickstart file when the installation begins therefore allows you to perform the installation automatically, without need for any intervention from the user. This is especially useful when deploying Redhat based distro (RHEL / CentOS / Fedora …) on a large number of systems at once and in general pretty useful if you're into the field of so called "DevOps" system administration and you need to provision a certain set of OS to a multitude of physical servers or create or recreate easily virtual machines with a certain set of configuration.

1. Create /vmprivate storage directory where Virtual machines will reside

First step on the Hypervisor host which will hold the future created virtual machines is to create location where it will be created:

[root@redhat ~]#  lvcreate –size 140G –name vmprivate vg00
[root@redhat ~]#  mkfs.ext4 -j -b 4096 /dev/mapper/vg00-vmprivate
[root@redhat ~]# mount /dev/mapper/vg00-vmprivate /vmprivate

To view what is the situation with Logical Volumes and  VG group names:

[root@redhat ~]# vgdisplay -v|grep -i vmprivate -A7 -B7
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  – currently set to     8192
  Block device           253:0


  — Logical volume —
  LV Path                /dev/vg00/vmprivate
  LV Name                vmprivate
  VG Name                vg00
  LV UUID                VVUgsf-FXq2-TsMJ-QPLw-7lGb-Dq5m-3J9XJJ
  LV Write Access        read/write
  LV Creation host, time, 2021-01-20 17:26:11 +0100
  LV Status              available
  # open                 1
  LV Size                150.00 GiB

Note that you'll need to have the size physically available on a SAS / SSD Hard Drive physically connected to Hypervisor Host.

To make the changes Virtual Machines storage location directory permanently mounted add to /etc/fstab

/dev/mapper/vg00-vmprivate  /vmprivate              ext4    defaults,nodev,nosuid 1 2

[root@redhat ~]# echo '/dev/mapper/vg00-vmprivate  /vmprivate              ext4    defaults,nodev,nosuid 1 2' >> /etc/fstab


2. Second we need to install the following set of RPM packages on the Hypervisor Hardware host

[root@redhat ~]# yum install qemu-kvm qemu-img libvirt virt-install libvirt-client virt-manager libguestfs-tools virt-install virt-top -y

3. Enable libvirtd on the host

[root@redhat ~]#  lsmod | grep -i kvm
[root@redhat ~]#  systemctl enable libvirtd

4. Configure network bridging br0 interface on Hypervisor

In /etc/sysconfig/network-scripts/ifcfg-eth0 you need to include:


Next use nmcli redhat configurator to create the bridge (you can use ip command instead) but since the tool is the redhat way to do it lets do it their way ..

[root@redhat ~]# nmcli connection delete eno3
[root@redhat ~]# nmcli connection add type bridge autoconnect yes con-name br0 ifname br0
[root@redhat ~]# nmcli connection modify br0 ipv4.addresses ipv4.method manual
[root@redhat ~]# nmcli connection modify br0 ipv4.gateway
[root@redhat ~]# nmcli connection modify br0 ipv4.dns
[root@redhat ~]# nmcli connection add type bridge-slave autoconnect yes con-name eno3 ifname eno3 master br0
[root@redhat ~]# nmcli connection up br0

5. Prepare a working kickstart.cfg file for VM

Below is a sample kickstart file I've used to build a working fully functional Virtual Machine with Red Hat Enterprise Linux 8.3 (Ootpa) .

# Run the Setup Agent on first boot
firstboot --enable
ignoredisk --only-use=vda

# Use network installation
#url --url=
##url --url=

# Use text mode install

# System language
#lang en_US.UTF-8
keyboard --vckeymap=us --xlayouts='us'
# Keyboard layouts
##keyboard us
lang en_US.UTF-8

# Root password
rootpw $6$gTiUCif4$YdKxeewgwYCLS4uRc/XOeKSitvDJNHFycxWVHi.RYGkgKctTMCAiY2TErua5Yh7flw2lUijooOClQQhlbstZ81 --iscrypted

# network-stuff
# place ip=your_VM_IP, netmask, gateway, nameserver hostname 
network --bootproto=static --ip= --netmask= --gateway= --nameserver= --device=eth0 --noipv6 --onboot=yes
# if you need just localhost initially configured uncomment and comment above
##network В --device=lo --hostname=localhost.localdomain

# System authorization information
authconfig --enableshadow --passalgo=sha512 --enablefingerprint

# skipx

# Firewall configuration
firewall --disabled

# System timezone
timezone Europe/Berlin

# Clear the Master Boot Record

# Repositories
## Add RPM repositories from KS file if necessery
#repo --name=appstream --baseurl=
#repo --name=baseos --baseurl=
#repo --name=inst.stage2 --baseurl= ff=/dev/vg0/vmprivate
##repo --name=rhsm-baseos В  В --baseurl=
##repo --name=rhsm-appstream --baseurl=
##repo --name=os-baseos В  В  В --baseurl=
##repo --name=os-appstream В  --baseurl=
#repo --name=inst.stage2 --baseurl=

# Disk partitioning information set proper disk sizing
##bootloader --location=mbr --boot-drive=vda
bootloader --append=" crashkernel=auto tsc=reliable divider=10 plymouth.enable=0 console=ttyS0 " --location=mbr --boot-drive=vda
# partition plan
clearpart --all --drives=vda --initlabel
part /boot --size=1024 --fstype=ext4 --asprimary
part swap --size=1024
part pv.01 --size=30000 --grow --ondisk=vda
##part pv.0 --size=80000 --fstype=lvmpv
#part pv.0 --size=61440 --fstype=lvmpv
volgroup s pv.01
logvol / --vgname=s --size=15360 --name=root --fstype=ext4
logvol /var/cache/ --vgname=s --size=5120 --name=cache --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var/log --vgname=s --size=7680 --name=log --fstype=ext4 --fsoptions="defaults,nodev,noexec,nosuid"
logvol /tmp --vgname=s --size=5120 --name=tmp --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /home --vgname=s --size=5120 --name=home --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /opt --vgname=s --size=2048 --name=opt --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var/log/audit --vgname=s --size=3072 --name=audit --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var/spool --vgname=s --size=2048 --name=spool --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var --vgname=s --size=7680 --name=var --fstype=ext4 --fsoptions="defaults,nodev,nosuid"

# SELinux configuration
selinux --disabled
# Installation logging level
logging --level=debug

# reboot automatically


# Tune Linux vm.dirty_background_bytes (IMAGE-439)
# The following tuning causes dirty data to begin to be background flushed at
# 100 Mbytes, so that it writes earlier and more often to avoid a large build
# up and improving overall throughput.
echo "vm.dirty_background_bytes=100000000" >> /etc/sysctl.conf

# Disable kdump
systemctl disable kdump.service

Important note to make here is the MD5 set root password string in (rootpw) line this string can be generated with openssl or mkpasswd commands :

Method 1: use openssl cmd to generate (md5, sha256, sha512) encrypted pass string

[root@redhat ~]# openssl passwd -6 -salt xyz test

Note: passing -1will generate an MD5 password, -5 a SHA256 encryption and -6SHA512 encrypted string (logically recommended for better security)

Method 2: (md5, sha256, sha512)

[root@redhat ~]# mkpasswd –method=SHA-512 –stdin

The option –method accepts md5, sha-256 and sha-512
Theoretically there is also a kickstart file generator web interface on Redhat's site here however I never used it myself but instead use above kickstart.cfg

6. Install the new VM with virt-install cmd

Roll the new preconfigured VM based on above ks template file use some kind of one liner command line  like below:

[root@redhat ~]# virt-install -n RHEL8_3-VirtualMachine –description "CentOS 8.3 Virtual Machine" –os-type=Linux –os-variant=rhel8.3 –ram=8192 –vcpus=8 –location=/vmprivate/rhel-server-8.3-x86_64-dvd.iso –disk path=/vmprivate/RHEL8_3-VirtualMachine.img,bus=virtio,size=70 –graphics none –initrd-inject=/root/kickstart.cfg –extra-args "console=ttyS0 ks=file:/kickstart.cfg"

7. Use a tiny shell script to automate VM creation

For some clarity and better automation in case you plan to repeat VM creation you can prepare a tiny bash shell script:

VM_DESCR='CentOS 8.3 Virtual Machine';
# size is in Gigabytes

virt-install -n "$VMNAME" –description "$VM_DESCR" –os-type=Linux –os-variant=rhel8.3 –ram=8192 –vcpus=8 –location="$ISO_LOCATION" –disk path=$VM_IMG_FILE,bus=virtio,size=$IMG_VM_SIZE –graphics none –initrd-inject=/root/$KS_FILE –extra-args "console=ttyS0 ks=file:/$KS_FILE"

A copy of script can be downloaded here

Wait for the installation to finish it should be visualized and if all installation is smooth you should get a login prompt use the password generated with openssl tool and test to login, then disconnect from the machine by pressing CTRL + ] and try to login via TTY with

[root@redhat ~]# virst list –all
 Id   Name        State
RHEL8_3-VirtualMachine   running

[root@redhat ~]#  virsh console RHEL8_3-VirtualMachine


One last thing I recommend you check the official documentation on Kickstart2 from CentOS official website

In case if you later need to destroy the VM and the respective created Image file you can do it with:

[root@redhat ~]#  virsh destroy RHEL8_3-VirtualMachine
[root@redhat ~]#  virsh undefine RHEL8_3-VirtualMachine

Don't forget to celebreate the success and give this nice article a credit by sharing this nice tutorial with a friend or by placing a link to it from your blog 🙂



Enjoy !

How to add local user to admin access via /etc/sudoers with sudo su – root / Create a sudo admin group to enable users belonging to group become superuser

Friday, January 15th, 2021

Reading Time: 3minutes


Did you had to have a local users on a server and you needed to be able to add Admins group for all system administrators, so any local user on the system that belongs to the group to be able to become root with command lets say sudo su – root / su -l root / su – root?
If so below is an example /etc/sudoers file that will allow your users belonging to a group local group sysadmins with some assigned group number

Here is how to create the sysadmins group as a starter

linux:~# groupadd -g 800 sysadmins

Lets create a new local user georgi and append the user to be a member of sysadmins group which will be our local system Administrator (superuser) access user group.

To create a user with a specific desired userid lets check in /etc/passwd and create it:

linux:~# grep :811: /etc/passwd || useradd -u 811 -g 800 -c 'Georgi hip0' -d /home/georgi -m georgi

Next lets create /etc/sudoers (if you need to copy paste content of file check here)and paste below configuration:

linux:~# mcedit /etc/sudoers

## Updating the locate database
# Cmnd_Alias LOCATE = /usr/bin/updatedb


## Storage
# Cmnd_Alias STORAGE = /sbin/fdisk, /sbin/sfdisk, /sbin/parted, /sbin/partprobe, /bin/mount, /bin/umount

## Delegating permissions
# Cmnd_Alias DELEGATING = /usr/sbin/visudo, /bin/chown, /bin/chmod, /bin/chgrp

## Processes
# Cmnd_Alias PROCESSES = /bin/nice, /bin/kill, /usr/bin/kill, /usr/bin/killall

## Drivers
# Cmnd_Alias DRIVERS = /sbin/modprobe

Cmnd_Alias PASSWD = /usr/bin/passwd [a-zA-Z][a-zA-Z0-9_-]*, \
                    !/usr/bin/passwd root

Cmnd_Alias SU_ROOT = /bin/su root, \
                     /bin/su – root, \
                     /bin/su -l root, \
                     /bin/su -p root

# Defaults specification

# Refuse to run if unable to disable echo on the tty.
Defaults   !visiblepw

# Preserving HOME has security implications since many programs
# use it when searching for configuration files. Note that HOME
# is already set when the the env_reset option is enabled, so
# this option is only effective for configurations where either
# env_reset is disabled or HOME is present in the env_keep list.
Defaults    always_set_home
Defaults    match_group_by_gid

Defaults    env_reset

# Adding HOME to env_keep may enable a user to run unrestricted
# commands via sudo.
# Defaults   env_keep += "HOME"
Defaults    secure_path = /sbin:/bin:/usr/sbin:/usr/bin

## Next comes the main part: which users can run what software on
## which machines (the sudoers file can be shared between multiple
## systems).
## Syntax:
##      user    MACHINE=COMMANDS
## The COMMANDS section may have other options added to it.
## Allow root to run any commands anywhere
root    ALL=(ALL)       ALL

## Allows members of the 'sys' group to run networking, software,
## service management apps and more.

## Allows people in group wheel to run all commands
%wheel  ALL=(ALL)       ALL

## Same thing without a password
# %wheel        ALL=(ALL)       NOPASSWD: ALL

## Allows members of the users group to mount and unmount the
## cdrom as root
# %users  ALL=/sbin/mount /mnt/cdrom, /sbin/umount /mnt/cdrom
## Allows members of the users group to shutdown this system
# %users  localhost=/sbin/shutdown -h now

%sysadmins            ALL            = SU_ROOT, \
                                   NOPASSWD: PASSWD

## Read drop-in files from /etc/sudoers.d (the # here does not mean a comment)
#includedir /etc/sudoers.d

zabbix  ALL=(ALL) NOPASSWD:/usr/bin/grep

Save the config and give it a try now to become root with sudo su – root command

linux:~$ id
uid=811(georgi) gid=800(sysadmins) groups=800(sysadmins)
linux:~$ sudo su – root

w00t Voila your user is with super rights ! Enjoy 🙂


Configure rsyslog buffering on Linux to avoid message lost to Central Logging server

Wednesday, January 13th, 2021

Reading Time: 2minutes


1. Rsyslog Buffering

One of the best practice about logs management is to send syslog to a central server. However, a logging system should be capable of avoiding message loss in situations where the server is not reachable. To do so, unsent data needs to be buffered at the client when central server is not available. You might have recently noticed that many servers forwarding logs messages to a central server do not have buffering functionalities activated. Thus I strongly advise you to have look to this documentation to know how to check your configuration:

Rsyslog buffering with TCP/UDP configured

In rsyslog, every action runs on its own queue and each queue can be set to buffer data if the action is not ready. Of course, you must be able to detect that "the action is not ready", which means the remote server is offline. This can be detected with plain TCP syslog and RELP, but not with UDP. So you need to use either of the two. In this howto, we use plain TCP syslog.

– Version requirement

Please note that we are using rsyslog-specific features. The are required on the client, but not on the server. So the client system must run rsyslog (at least version 3.12.0), while on the server another syslogd may be running, as long as it supports plain tcp syslog.

How To Setup rsyslog buffering on Linux

First, you need to create a working directory for rsyslog. This is where it stores its queue files (should need arise). You may use any location on your local system. Next, you need to do is instruct rsyslog to use a disk queue and then configure your action. There is nothing else to do. With the following simple config file, you forward anything you receive to a remote server and have buffering applied automatically when it goes down. This must be done on the client machine.

# Example:
# $ModLoad imuxsock             # local message reception
# $WorkDirectory /rsyslog/work  # default location for work (spool) files
# $ActionQueueType LinkedList   # use asynchronous processing
# $ActionQueueFileName srvrfwd  # set file name, also enables disk mode
# $ActionResumeRetryCount -1    # infinite retries on insert failure
# $ActionQueueSaveOnShutdown on # save in-memory data if rsyslog shuts down
# *.*       @@server:port

Short SSL generate new and self-signed certificates PEM, view and convert to and from PKCS12 to java key store cookbook commands cheat sheet

Tuesday, January 12th, 2021

Reading Time: 2minutes


Below is a short compilation of common used openssl commands (a kind of cookbook) helpful for sysadmins who has to commonly deal with OpenSSL certificates.

Lets say you have to generate new certificate / key and a PEM files, prepare self-signed certificates, show CSR / PEM or KEY ssl file contents, get information about certificate such as expiry date a type of encryption algorithm or sign certificate with self-signed authority convert PEM to PKCS12, convert from PKCS12 file format to .PEM, convert java X509 to java key store SSL encryptionor convert java key store format certificate to PKCS12, then below will be of use to you.

1. Generate Private RSA Keywith 2048 bits

# openssl genrsa -out $ (hostname -f) .key 2048

2. Create CSR file

# openssl req -new -key $ (hostname -f) .key -out $ (hostname -f) .csr

3. Create a Self Certified Certificate:

# openssl x509 -req -days 30 -in $ (hostname -f) .csr -signkey $ (hostname -f) .key -out $ (hostname -f) .crt
Enter password:

# openssl rsa -in key.pem -out newkey.pem

4. Show CSR file content

# openssl req -in newcsr.csr -noout -text

5. Get Certificate version / serial number / signature algorithm / RSA key lenght / modulus / exponent etc.

# openssl x509 -in newcert.pem -noout -text

6. Server certificate as CA self signeded

# openssl ca -in newcert.csr -notext -out newcert.pem

7. Generate a certificate signing request based on an existing certificate

# openssl x509 -x509toreq -in certificate.crt -out CSR.csr -signkey privateKey.key

8. Convert .pem / .key / .crt file format to pkcs12 format

# openssl pkcs12 -export -in newcert.pem -inkey newkey.key -certfile ca.crt -out newcert.p12

9. Convert pkcs12 pfx to common .pem

# openssl pkcs12 -in mycert.pfx -out mycert.pem

10. The Formats available

# openssl x509 -inform the -in certificate.cer -out certificate.crt

11. Convert a pkcs # 7 certificate into PEM format

# openssl pkcs7 -in cert.p7c -inform DER -outform PEM -out certificate.p7b
# openssl pkcs7 -print_certs -in certificate.p7b -out certificate.pem

12. Convert X509 to java keystore file

# java -cp not-yet-commons-ssl-0.3.11.jar org.apache.commons.ssl.KeyStoreBuilder pass_for_new_keystore key.key certificate.crt

13. Convert java keystore file to pkcs12

# keytool -importkeystore -srckeystore keystore.jks -destkeystore intermediate.p12 -deststoretype PKCS12

Listing installed RPMs by vendor installed on CentOS / RedHat Linux

Friday, January 8th, 2021

Reading Time: 3minutes

Listing installed RPMs by vendor installed on CentOS / RedHat Linux

Listing installed RPMs by vendor is useful sysadmin stuff if you have third party software installed that is not part of official CentOS / RedHat Linux and you want to only list this packages, here is how this is done


[root@redhat ~]# rpm -qa –qf '%{NAME} %{VENDOR} %{PACKAGER} \n' | grep -v 'CentOS' | sort

criu Virtuozzo Virtuozzo (
gskcrypt64 IBM IBM
gskssl64 IBM IBM
ipxe-roms-qemu Virtuozzo Virtuozzo (
libevent (none) (none)
libguestfs-appliance Virtuozzo Virtuozzo (
libguestfs-tools-c Virtuozzo Virtuozzo (
libguestfs Virtuozzo Virtuozzo (
libprlcommon Virtuozzo Virtuozzo (
libprlsdk-python Virtuozzo Virtuozzo (
libprlsdk Virtuozzo Virtuozzo (
libprlxmlmodel Virtuozzo Virtuozzo (
libtcmu Virtuozzo Virtuozzo (
libvcmmd Virtuozzo Virtuozzo (
libvirt-client Virtuozzo Virtuozzo (
libvirt-daemon-config-nwfilter Virtuozzo Virtuozzo (
libvirt-daemon-driver-interface Virtuozzo Virtuozzo (
libvirt-daemon-driver-network Virtuozzo Virtuozzo (
libvirt-daemon-driver-nodedev Virtuozzo Virtuozzo (
libvirt-daemon-driver-nwfilter Virtuozzo Virtuozzo (
libvirt-daemon-driver-qemu Virtuozzo Virtuozzo (
libvirt-daemon-driver-storage-core Virtuozzo Virtuozzo (
libvirt-daemon-driver-storage Virtuozzo Virtuozzo (
libvirt-daemon-kvm Virtuozzo Virtuozzo (
libvirt-daemon Virtuozzo Virtuozzo (
libvirt-libs Virtuozzo Virtuozzo (
libvirt-python Virtuozzo Virtuozzo (
libvirt Virtuozzo Virtuozzo (
libvzctl Virtuozzo Virtuozzo (
libvzevent Virtuozzo Virtuozzo (
openvz-logos Virtuozzo Virtuozzo (
p7zip-plugins Fedora Project Fedora Project
ploop-lib Virtuozzo Virtuozzo (
ploop Virtuozzo Virtuozzo (
prlctl Virtuozzo Virtuozzo (
prl-disk-tool Virtuozzo Virtuozzo (
prl-disp-service Virtuozzo Virtuozzo (
python2-lockfile Fedora Project Fedora Project
python2-psutil Fedora Project Fedora Project
python-daemon Fedora Project Fedora Project
python-subprocess32 Virtuozzo Virtuozzo (
qemu-img-vz Virtuozzo Virtuozzo (
qemu-kvm-common-vz Virtuozzo Virtuozzo (
qemu-kvm-vz Virtuozzo Virtuozzo (
qt Virtuozzo Virtuozzo (
rkhunter Fedora Project Fedora Project
seabios-bin Virtuozzo Virtuozzo (
seavgabios-bin Virtuozzo Virtuozzo (
spfs Virtuozzo Virtuozzo (
TIVsm-API64 IBM (none)
TIVsm-APIcit IBM (none)
TIVsm-BAcit IBM (none)
TIVsm-BA IBM (none)
vcmmd Virtuozzo Virtuozzo (
vmauth Virtuozzo Virtuozzo (
vzctl Virtuozzo Virtuozzo (
vzkernel Virtuozzo Virtuozzo (
vzkernel Virtuozzo Virtuozzo (
vztt_checker Virtuozzo Virtuozzo (
vztt_checker Virtuozzo Virtuozzo (
vztt-lib Virtuozzo Virtuozzo (
vztt Virtuozzo Virtuozzo (
zabbix-agent (none) (none)


That instructs rpm to output each package's name and vendor, then we exclude those from "Red Hat, Inc." (which is the exact string Red Hat conveniently uses in the "vendor" field of all RPMs they pacakge).

By default, rpm -qa uses the format '%{NAME}-%{VERSION}-%{RELEASE}', and it's nice to see version and release, and on 64-bit systems, it's also nice to see the architecture since both 32- and 64-bit packages are often installed. Here's how I did that:

[root@redhat ~]# rpm -qa –qf '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} %{VENDOR} %{PACKAGER} \n' | grep -v 'CentOS' | sort

criu- Virtuozzo Virtuozzo (
gskcrypt64-8.0-55.17.x86_64 IBM IBM
gskssl64-8.0-55.17.x86_64 IBM IBM
ipxe-roms-qemu-20170123-1.git4e85b27.1.vz7.5.noarch Virtuozzo Virtuozzo (
libevent-2.0.22-1.rhel7.x86_64 (none) (none)
libguestfs-1.36.10-6.2.vz7.12.x86_64 Virtuozzo Virtuozzo (
libguestfs-appliance-1.36.10-6.2.vz7.12.x86_64 Virtuozzo Virtuozzo (
libguestfs-tools-c-1.36.10-6.2.vz7.12.x86_64 Virtuozzo Virtuozzo (
libprlcommon-7.0.162-1.vz7.x86_64 Virtuozzo Virtuozzo (
libprlsdk-7.0.226-2.vz7.x86_64 Virtuozzo Virtuozzo (
libprlsdk-python-7.0.226-2.vz7.x86_64 Virtuozzo Virtuozzo (
libprlxmlmodel-7.0.80-1.vz7.x86_64 Virtuozzo Virtuozzo (
libtcmu-1.2.0-16.2.vz7.x86_64 Virtuozzo Virtuozzo (
libvcmmd-7.0.22-3.vz7.x86_64 Virtuozzo Virtuozzo (
libvirt-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-client-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-config-nwfilter-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-driver-interface-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-driver-network-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-driver-nodedev-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-driver-nwfilter-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-driver-qemu-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-driver-storage-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-driver-storage-core-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-daemon-kvm-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-libs-3.9.0-14.vz7.38.x86_64 Virtuozzo Virtuozzo (
libvirt-python-3.9.0-1.vz7.1.x86_64 Virtuozzo Virtuozzo (
libvzctl-7.0.506-1.vz7.x86_64 Virtuozzo Virtuozzo (
libvzevent-7.0.7-5.vz7.x86_64 Virtuozzo Virtuozzo (
openvz-logos-70.0.13-1.vz7.noarch Virtuozzo Virtuozzo (
p7zip-plugins-16.02-10.el7.x86_64 Fedora Project Fedora Project
ploop-7.0.137-1.vz7.x86_64 Virtuozzo Virtuozzo (
ploop-lib-7.0.137-1.vz7.x86_64 Virtuozzo Virtuozzo (
prlctl-7.0.164-1.vz7.x86_64 Virtuozzo Virtuozzo (
prl-disk-tool-7.0.43-1.vz7.x86_64 Virtuozzo Virtuozzo (
prl-disp-service-7.0.925-1.vz7.x86_64 Virtuozzo Virtuozzo (
python2-lockfile-0.11.0-17.el7.noarch Fedora Project Fedora Project
python2-psutil-5.6.7-1.el7.x86_64 Fedora Project Fedora Project
python-daemon-1.6-4.el7.noarch Fedora Project Fedora Project
python-subprocess32-3.2.7-1.vz7.5.x86_64 Virtuozzo Virtuozzo (
qemu-img-vz-2.10.0-21.7.vz7.67.x86_64 Virtuozzo Virtuozzo (
qemu-kvm-common-vz-2.10.0-21.7.vz7.67.x86_64 Virtuozzo Virtuozzo (
qemu-kvm-vz-2.10.0-21.7.vz7.67.x86_64 Virtuozzo Virtuozzo (
qt-4.8.7-2.vz7.2.x86_64 Virtuozzo Virtuozzo (
rkhunter-1.4.6-2.el7.noarch Fedora Project Fedora Project
seabios-bin-1.10.2-3.1.vz7.3.noarch Virtuozzo Virtuozzo (
seavgabios-bin-1.10.2-3.1.vz7.3.noarch Virtuozzo Virtuozzo (
spfs-0.09.0010-1.vz7.x86_64 Virtuozzo Virtuozzo (
TIVsm-API64-8.1.11-0.x86_64 IBM (none)
TIVsm-APIcit-8.1.11-0.x86_64 IBM (none)
TIVsm-BA-8.1.11-0.x86_64 IBM (none)
TIVsm-BAcit-8.1.11-0.x86_64 IBM (none)
vcmmd-7.0.160-1.vz7.x86_64 Virtuozzo Virtuozzo (
vmauth-7.0.10-2.vz7.x86_64 Virtuozzo Virtuozzo (
vzctl-7.0.194-1.vz7.x86_64 Virtuozzo Virtuozzo (
vzkernel-3.10.0-862.11.6.vz7.64.7.x86_64 Virtuozzo Virtuozzo (
vzkernel-3.10.0-862.20.2.vz7.73.29.x86_64 Virtuozzo Virtuozzo (
vztt-7.0.63-1.vz7.x86_64 Virtuozzo Virtuozzo (
vztt_checker-7.0.2-1.vz7.i686 Virtuozzo Virtuozzo (
vztt_checker-7.0.2-1.vz7.x86_64 Virtuozzo Virtuozzo (
vztt-lib-7.0.63-1.vz7.x86_64 Virtuozzo Virtuozzo (
zabbix-agent-3.2.11-1.el7.x86_64 (none) (none)

Backup entire Live Linux Operating System bit by bit with dd, partimage, partclone clonezilla

Thursday, January 7th, 2021

Reading Time: 3minutes


This is an old stuff that we UNIX / Linux sysadmins use frequently when we need to migrate operating system from a certain older machine server to another newer one.
However I decided to blog it as it an interesting to know to a new grown junior sysadmins.

To Create a bit to bit data backup with dd command,
the following command is used to create a backup with dd, which takes the entire data content (including partition table etc.) with it:

dd if = / dev / [hard disk 1] of = / dev / [hard disk 2] bs = 512 conv = noerror, sync

For explanation:


"if" stands for the hard drive to be read from.
"of" stands for the hard drive to be written to.
Important! if and of must not be interchanged under any circumstances! In the worst case, the data on the disk to be read will otherwise be irrevocably overwritten!

"bs = 512" defines the block size. The value can be increased (which in turn increases the speed of the backup), but you should be sure that the file system to be backed up does not contain any errors. If you were to use block size 64k, for example, the speed of the backup is increased considerably – but if read errors occur within this block, the entire data block that dd has written contains unusable data. Therefore, when choosing the block size, you should always weigh data integrity and time against each other.
"noerror" tells dd to continue the backup in case of errors. Without this option, dd would stop the backup by default.
"sync" commands dd to replace the unreadable blocks with zeros in the event of errors in order to keep the data offset synchronous.
When performing a backup (as with other things that a longer period can take advantage of, it is always recommended (if you SSH is logged in and no direct access to a real Shell), the process either for CTRL + followed from bg to the background (can later be brought back to the foreground with fg ) or to use virtual session managers such as screen or byobu before executing the command.This prevents the process from dying if the SSH session is unintentionally terminated and you have to start over.

Of course there are plenty of other ways to make a mirror backup  cloneof a hard disk to lets say migrate to a new data center  using easier to use tools with (ncurses) Text menu interfaces to avoid bothering a complex typing on the console.
One such tool is Partclon:


PartClone cloning in action

Another text menu interface data cloning Linux tool commonly used by sysadms is partimage


Most sysadmins however prefer to use Clonezilla when something more cozy is required to do a bit to bit data copy.
Tthere is even a Live Linux CD distribution for that.

Clonezilla can mirror most types of filesystems and partiontions and could be used not only for UNIX / Linux / BSD filesystems Live OS data (backups) (EXT3 / EXT4 / XFS / ZFS etc)  migrations, but also for old NT4 Windows server partitions. One useful application of Clonezilla i can think of is if you want to configure or restore a whole office of Windows computers running on the same clean version of Windows and same hardware configurations PCs, after a Virus or trojan has striked it. By using it you can clone from a central well configured Windows release with the surrounding applications to all machines for up to an hour with Clonezilla and you can even do it over a network.

How to check Linux server power supply state is Okay / How to find out a Linux Power Supply is broken

Wednesday, January 6th, 2021

Reading Time: 4minutes


If you're a sysadmin and managing remotely Linux servers, every now and then if a machine is hanging without a reason it useful to check the server Power Supply state. I say that because often if the machine is mysteriously hanging and a standard Root Cause Analysis (RCA) on /var/log/messages /var/log/dmesg /var/log/boot etc. did not bring you to any different conclusion. The next step after you send a technician to reboot the machine is to check on Linux OS level whether Power Supply Unit (PSU) hardware on the machine does not have some issues.
As blogged earlier on how to use ipmitool to manage remote ILO remote boards etc. the ipmitool can also be used to check status of Server PSUs.

Below is example output of 2 PSU server whose Power Supplies are functioning normally.

[root@linux-server ~]# ipmitool sdr type "Power Supply"

PS Heavy Load    | 2Bh | ok  | 19.1 | State Deasserted
Power Supply 1   | 70h | ok  | 10.1 | Presence detected
Power Supply 2   | 71h | ok  | 10.2 | Presence detected
PS Configuration | 72h | ok  | 19.1 |
PS 1 Therm Fault | 75h | ok  | 10.1 | Transition to OK
PS 2 Therm Fault | 76h | ok  | 10.2 | Transition to OK
PS1 12V OV Fault | 77h | ok  | 10.1 | Transition to OK
PS2 12V OV Fault | 78h | ok  | 10.2 | Transition to OK
PS1 12V UV Fault | 79h | ok  | 10.1 | Transition to OK
PS2 12V UV Fault | 7Ah | ok  | 10.2 | Transition to OK
PS1 12V OC Fault | 7Bh | ok  | 10.1 | Transition to OK
PS2 12V OC Fault | 7Ch | ok  | 10.2 | Transition to OK
PS1 12Vaux Fault | 7Dh | ok  | 10.1 | Transition to OK
PS2 12Vaux Fault | 7Eh | ok  | 10.2 | Transition to OK
Power Unit       | 7Fh | ok  | 19.1 | Fully Redundant

Now if you have a server lets say on an old ProLiant DL360e Gen8 whose Power Supply is damaged, you will get an from ipmitool similar to:

[root@linux-server  systemd]# ipmitool sdr type "Power Supply"
Power Supply 1   | 30h | ok  | 10.1 | 100 Watts, Presence detected
Power Supply 2   | 31h | ok  | 10.2 | 0 Watts, Presence detected, Failure detected, Power Supply AC lost
Power Supplies   | 33h | ok  | 10.3 | Redundancy Lost

If you don't have ipmitool installed due to security or whatever but you have the hardware detection software dmidecode you can use it too to get the Power Supply state

[root@linux-server  systemd]# dmidecode -t chassis
# dmidecode 3.2
Getting SMBIOS data from sysfs.
SMBIOS 2.8 present.


Handle 0x0300, DMI type 3, 21 bytes
Chassis Information
        Manufacturer: HP
        Type: Rack Mount Chassis
        Lock: Not Present
        Version: Not Specified
        Serial Number: CZJ38201ZH
        Asset Tag:
        Boot-up State: Critical
        Power Supply State: Critical

        Thermal State: Safe
        Security Status: Unknown
        OEM Information: 0x00000000
        Height: 1 U
        Number Of Power Cords: 2
        Contained Elements: 0

To find only Power Supply info status on a server with dmideode.

# dmidecode –type 39


Plug between the power supply and the mainboard voltage / coms ATX specification

This can also be used on a normal Linux desktop PCs which usually have only 1U (one power supply) on many of Ubuntus and Linux desktops where lshw (list hardaware information) is installed to get the machine PSUs status with lshw 

 root@ubuntu:~# lshw -c power
       product: 45N1111
       vendor: SONY
       physical id: 1
       slot: Front
       capacity: 23200mWh
       configuration: voltage=11.1V
        Thermal State: Safe
        Security Status: Unknown
        OEM Information: 0x00000000
        Height: 1 U
        Number Of Power Cords: 2
        Contained Elements: 0

Finally to get an extensive information on the voltages of the Power Supply you can use the good old lm_sensors.

# apt-get install lm-sensors
# sensors-detect 
# service kmod start

# sensors
# watch sensors

As manually monitoring Power Supplies and other various data is dubious, finally you might want to use some centralized monitoring. For one example on that you might want to check my prior Zabbix to Monitor Hardware Hard Drive / Temperature and Disk with lm_sensors / smartd on Linux with Zabbix.