Command to check the udp connection status from a remote machine

 nc -vz -u xxx.xxx.xxx.xxx <portnumber>

Check TLS version running on the Linux server using NMAP.

https://casesup.com/category/knowledgebase/howtos/how-to-check-supported-tls-and-ssl-version

Found the below steps in an caseup.com portal. 

nmap --script ssl-enum-ciphers -p 443 www.google.com

Starting Nmap 6.40 ( http://nmap.org ) at 2017-08-10 11:15 +03
Nmap scan report for www.google.com (216.58.208.100)
Host is up (0.012s latency).
rDNS record for 216.58.208.100: sof01s11-in-f100.1e100.net
PORT STATE SERVICE
443/tcp open https
| ssl-enum-ciphers:
| TLSv1.0:
| ciphers:
| TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_RSA_WITH_AES_256_CBC_SHA - strong
| compressors:
| NULL
| TLSv1.1:
| ciphers:
| TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_RSA_WITH_AES_256_CBC_SHA - strong
| compressors:
| NULL
| TLSv1.2:
| ciphers:
| TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_GCM_SHA256 - strong
| TLS_RSA_WITH_AES_256_CBC_SHA - strong
| TLS_RSA_WITH_AES_256_GCM_SHA384 - strong
| compressors:
| NULL
|_ least strength: strong

Nmap done: 1 IP address (1 host up) scanned in 7.03 seconds

Solaris Server SNMP

Monitoring Solaris Server services using custom OID's

Assumption: SNMP server side configuration is completed

# vi /etc/sma/snmp/snmpd.conf
exec pscheduler_snmpd /bin/bash /usr/bin/Scheduler_snmpd.sh
 
Place the scripts under /usb/bin/
# cat /usr/bin/Scheduler_snmpd.sh
count=`ps -ef | grep BBL |egrep -i 'CHECK1|CHECK2'|wc -l` > /dev/null
if [ $count -eq 2 ]
then
   echo "1"
else
   echo "0"
fi

Set the permission of the script to  (would prefer only execute permission)
#chmod 777 /usr/bin/Scheduler_snmpd.sh

Restart the SNMP service on the Solaris server by running command
 #svcsadm restart sma




 












 

 

Power shell to access Internet behind a proxy server with authentication

• $Creds=Get-Credential
•  $proxy = New-Object System.Net.WebProxy
• $proxy.Address = [uri]"http://xxx.xxx.xxx.xxx:xx"
• $proxy.Credentials = $Creds
• [System.Net.WebRequest]::DefaultWebProxy = $proxy
• Invoke-WebRequest -Uri "https://google.com" -UseBasicParsing

Useful links to refer.

1. http://woshub.com/using-powershell-behind-a-proxy/
2. https://stackoverflow.com/questions/38005341/the-response-content-cannot-be-parsed-because-the-internet-explorer-engine-is-no 

Custom Monitoring using SNMP Script for a specific service. - The script is written to avoid false alerts generated due to custom monitoring. 

This will trigger multiple SNMP monitoring attempts (3 times) before calling the failure.

a=0

while [ $a -lt 3 ]

do

   snmpwalk -v2c -c 'XXXXXsecretkeyXXXXXXX' | grep "customvalue" >> /dev/null

   if [ $? = 0 ]; then

        echo "80"

        exit

   else

        sleep 3

        a=`expr $a + 1`

   fi

        echo "0"

done

-

Check for network ports

• netstat -nat 
• netstat -tunlp 
• netstat -nlpu|grep snmp

Excellent examples of sed for shell scripting

Sed Command

Wake on Lan for Ubuntu

Wakeonlan - Ubuntu

Changing a specific value in a file using sed

/bin/sed -i.bak -e 's/^SELINUX=.*/SELINUX=disabled/g' /etc/selinux/config

Disable IPv6 on Linux

Sometime you may want to disable IPV6 on your Linux server. 

To check if IPV6 is running on your system
Run the following command.
#ifconfig  - This is show the ipv4 and ipv6 address

To disable ipv6
vi /etc/sysctl.conf

 Add the following lines at the bottom of the config file
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1
 
After saving the file, run the following command to apply the new changes.

#sysctl -p

To confirm the changes are applied, run the command
#ifconfig - This should not show ipv6 address any more
 

Securing Linux

Stop all unwanted services

#chkconfig --list |grep '3:on'

#chkconfig cups off

#chkconfig postfix off

#chkconfig atd off

#chkconfig ip6tables off

#chkconfig lvm2-monitor off

#chkconfig mdmonitor off

#chkconfig rpcidmapd off

#chkconfig nfslock off

#chkconfig mcelogd off

#chkconfig xinetd off

#chkconfig inetd off

Remove all unwanted packages

#rpm -e

Disable Root login

#vi /etc/ssh/sshd_config

PermitRootLogin no

#service sshd restart

Create a service account with Sudo Access

• Create a service account

#useradd

#passwd

(provide a strong password)

• Provide Sudo Access to service account _ In this case i have given all root access

#visudo

lbadmin ALL=(ALL)       ALL

Disable alt+ctrl+del key switch for reboot

#vi "/etc/init/control-alt-delete.conf"

Hash both the lines

#start on control-alt-delete

#exec /sbin/shutdown -r now "Control-Alt-Delete pressed"

Allow ssh access only from specific subnets or IP address

#vi /etc/hosts.allow

sshd:

#vi /etc/hosts.deny

sshd: ALL

 Restrict access to server for specific subnet.

# Generated by iptables-save v1.4.7 on Fri Jun 12 15:39:00 2015

*filter

:INPUT ACCEPT [75:5272]

:FORWARD ACCEPT [0:0]

:OUTPUT ACCEPT [68:5268]

-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

-A INPUT -p icmp -j ACCEPT

-A INPUT -i lo -j ACCEPT

-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT

-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT

-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT

-A OUTPUT -p udp --dport 123 -j ACCEPT

-A INPUT -p udp --sport 123 -j ACCEPT

-A OUTPUT -p tcp --dport 123 -j ACCEPT

-A INPUT -p tcp --sport 123 -j ACCEPT

-A INPUT -j REJECT --reject-with icmp-host-prohibited

-A FORWARD -j REJECT --reject-with icmp-host-prohibited

COMMIT

Set IP tables to start at reboot

#chkconfig iptables on

Apply the new IP table rules by running command

#service iptables start

Check all accounts have password set to them. No account should be without password less loging

grep -v ':x:' /etc/passwd

Cannot initiate the connection to 80:80 (0.0.0.80)

When running apt-get update command, if you receive the below mentioned error

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-backports/restricted/i18n/Translation-en_US  Cannot initiate the connection to 80:80 (0.0.0.80). - connect (22: Invalid argument)

Edit the following file
vi /etc/apt/apt.conf

Hash out the following entry
#Acquire::http::Proxy "ProxyIP:ProxyPort";


Now try #apt-get update, this should update the repository informaiton

View database output in tabular format

mysql -u root -p 

mysql>\P less -S

Create USB Boot disk for different flavours of operating system.

Create USB Boot Disk for different flavours of OS

Windows 8 and Windows 2012 rebooting issue on Proxmox VM

When you boot any VM and try to install Windows 8 or Windows 2012, the VMs will go into a continuous reboot. This is due to the missing CPU flag settings.

To fix this issue modify the VM configuration file of the VM

cd /etc/pve/qemu-server
vi 106.conf  ( Assuming 106.conf is the VM on which you are installing Win8 or Win2012)

balloon: 1024
bootdisk: ide0
cores: 2
args: -cpu qemu64,+sep,+cx16,+lahf_lm
ide0: PROXMOX6_VMVOL:106/vm-106-disk-1.qcow2,format=qcow2,size=32G
ide2: ISO:iso/Windows_8.1_x64.iso,media=cdrom,size=5227698K
memory: 2048
name: OPSI-Windows8
net0: virtio=DA:3B:63:57:3C:6F,bridge=vmbr0,tag=103
ostype: other
sockets: 1

Single liner to ping a subnet from command line

for ip in 192.168.10.{1,2,3..254};do ping -c 1 $ip;done

Shell - List number of lines once the search pattern matches

awk '/PATTERN/ {for(i=1; i<=5; i++) {getline; print}}' filename

The above command will search the key word "PATTERN" once it is matched, it will print the below 5 lines after the search string from the text file.

Server Provisioning / De-provisioning on Proxmox using Shell Script.

 Here is my attempt to simplify server provisioning / De-provisioning on Proxmox using shell script. Hope you find it useful.

****************************************************************************
#!/bin/bash

echo " Proxmox OpenVZ Server Provisioning Tool"
echo ""
echo " Please select from the below choices"
echo ""
echo " 1. KVM Server Instance Provisioning"
echo " 2. KVM Server Instance Decommissioning"
echo ""
read -p "Please enter you numerical choice: " choice

echo $choice

if [ "$choice" -lt 1 ] || [ "$choice" -gt 2 ]; then
                        echo "Wrong choice selection - Existing the program - Please try again"
                        exit
                if [ "$choice" -eq 1 ]; then
                        echo " Initiating Server Provisioning Procedure"
                elif [ "$choice" -eq 2 ]; then
                        echo " Initiating Server Decommissioning Procedure"

                fi

fi

case $choice in
1)
##### SECTION FOR TOTAL NUMBER OF SERVER AND OPERATING SYSTEM SELECTION #####
echo "Enter the number of servers needed (1-5)"
echo ""
read -p "Please enter the numerical value: " kvmsrvno
if [ "$kvmsrvno" -le 0 ] || [ "$kvmsrvno" -gt 5 ]
        then
                echo "Please try again by entering a valid number between (1-6)"
                exit
        else
                echo "Enter the number corresponding to the operating system 1.Windows2012 2.Windows2008R2 3.WindowsXP 4.Windows7 5.RedHat6 6.CentOS6"
                read -p "Please enter the numerical value: " kvmselection
    if [ "$kvmselection" -le 0 ] || [ "$kvmselection" -gt 6 ]
        then
                echo "Please try again by entering a valid number between 1,2,3,4,5 or 6"
        exit
    fi
fi
#echo "The operating system selected is $kvmselection"

############################################################fngetvmid() {
        pvesh get /cluster/resources --type vm |grep -i vmid |sort -n |awk '{print $3}' > /mnt/pve/ISO/automation_scripts/allocated_vmid
while read avail_vmid
do
                grep -x $avail_vmid /mnt/pve/ISO/automation_scripts/allocated_vmid > /dev/null
        if [ `echo $?` -ne 0 ]
        then
                VMID=$avail_vmid
                echo $VMID
                exit
        fi
done <  /mnt/pve/ISO/automation_scripts/vmidlist
}
#vm_id=$(fngetvmid)

##############################################################
fngetkvmhostname() {
case $kvmselection in
  1)
        hostname=Win2012-$vm_id;
        clntmpt=128;;
  2)
        hostname=Win2008R2-$vm_id;
        clntmpt=125;;
  3)
        hostname=WindowsXP-$vm_id;
        clntmpt=126;;
  4)
        hostname=Windows7-$vm_id;
        clntmpt=127;;
  5)
        hostname=Redhat6-$vm_id;
        clntmpt=123;;
  6)
        hostname=CentOS6-$vm_id;
        clntmpt=116;;
 esac
}

##################################################################
count=1
while [ "$count" -le "$kvmsrvno" ]
    do
        #ip_addr=$(fngetip)
        vm_id=$(fngetvmid)
        fngetkvmhostname
        pvesh create /nodes/`hostname`/qemu/$clntmpt/clone --newid $vm_id --full --name=$hostname #--pool="$poolname"
                #echo $ip_addr >> /mnt/pve/ISO/automation_scripts/allocated_list
        echo "#################################################################"
        count=`expr $count + 1`
        done;
break;;

2)
        echo "KVM Server Decommissioning Initiated"
        echo ""
        echo "Please specify the VMIDs of the instances to be decommissioned (Use comma separated values)"
        echo ""
        read -p "Please enter the numerical value: " delvid

        IFS=","
        for vmid in $delvid
        do
        #v_delip=`grep -i IP_ADDRESS /etc/vz/conf/$vmid.conf |sed -r 's/[^\"]*([\"][^\"]*[\"][,]?)[^\"]*/\1 /g' | sed "s/\"//g"`
        #delip=sed
        qm stop $vmid
        qm destroy $vmid
        #sed -i "s/$delip//g" "/opt/automation_scripts/allocated_list"
        #sed -i '/^$/d' "/opt/automation_scripts/allocated_list"
        echo "#################################################################"
        done;
break;;
esac
********************************************************************

Time and date setting in CentOS

View the current time and the timezone setting on the server by running the below command
#date

Steps to change the timezone settings.

 Make a backup of the current localtime file
#mv /etc/localtime /etc/localtime.bak

Create a new zone file setting using the below command. (Below example for India)
#ln -s /usr/share/zoneinfo/Asia/Calcutta /etc/localtime

Manually Set Data and Time using the following command
date -s "13 Feb 2015 10:30:00"

Configuring PXE Boot on Redhat 6

how-to-configure-pxe-server-in-rhel-6