Disk usage of mysql DB

To calculate the disk usage of your DBs in mysql

 

you can use “DU” which is less reliable and if you hosting on cloud database services, you cannot use this.

du -sh /var/lib/mysql/database

OR

use the below query.

 

select table_schema, sum((data_length+index_length)/1024/1024) AS MB from information_schema.tables group by 1;

Port forwarding using ssh

 

How to use port forwarding when you are behind a firewall.

to access a service running locally on the remote server.

To setup a proxy

ssh -L 3128:localhost:80 <username>@YOURREMOTESERVER

REMOTE Port forwarding

Below example could be used to access RDP behind a firewall, but accessible from YOURREMOTESERVER

ssh -L 3389:YOURREMOTE_SERVER_WHERESERIVERUN_IP:3389 <username>@YOURREMOTESERVER -N

3389 – RDP port

N – will not start a terminal session.

 

 

Use localhost as the hostname/IP to establish connection from your desktop

compressing a pdf to a lower size

Use Ghost Script from commandline

gs -sDEVICE=pdfwrite -dNOPAUSE -dQUIET -dBATCH -dPDFSETTINGS=/screen -dCompatibilityLevel=1.6 -sOutputFile=pdfoutsmallfile.pdf pdfinputlargefile.pdf

-dNOPAUSE – disable the interactive prompting
pdfwrite – create pdf files
-dCompatibilityLevel=1.6 – compatibility with each versions of adobe. Use 1.3,1.4,1.6,1.7
-sOutputFile – name of the output file.

Port check script

#!/bin/bash
RED=’\033[0;31m’
GREEN=”\033[0;32m”
NC=’\033[0m’ # No Color

function checkport {
if nc -zv -w30 $1 $2 <<< ” &> /dev/null
then
echo “${GREEN}[O]${NC} $1:$2”
else
echo “${RED}[C]${NC} $1:$2”
fi
}

printf “server list:”;
read server
printf “ports list[enter for default]:”
read ports_to_check

if [[ $ports_to_check = “” ]]; then
echo “using default port list”;
ports_to_check=”22 389 3306 8080″; #enter your default list of ports here
echo “$ports_to_check”;
fi

for i in $server;do
{
echo “==========================================”
for j in $ports_to_check ; do
checkport $i $j
done
}; done

Find your tomcat version

Sometimes you might need to figure out your tomcat version from within the folder where you run tomcat from. The below command will help you get the details.

java -cp lib/catalina.jar org.apache.catalina.util.ServerInfo

/usr/share/tomcat7$ java -cp lib/catalina.jar org.apache.catalina.util.ServerInfo
Server version: Apache Tomcat/7.0.81
Server built: Aug 11 2017 10:21:27 UTC
Server number: 7.0.81.0
OS Name: Linux
OS Version: 3.13.0-95-generic
Architecture: amd64
JVM Version: 1.7.0_75-b13
JVM Vendor: Oracle Corporation

how to wget from a site with authentication

when you got to download from a site that ask for authentication details use the below flags to specify the user and password details

 

wget  –user=’yourusernamehere’ –password=’yourpasswordhere’ –auth-no-challenge  https://yoururlhere.com

ERROR 1217 (23000) at line 287: Cannot delete or update a parent row: a foreign key constraint fails

ERROR 1217 (23000) at line 287: Cannot delete or update a parent row: a foreign key constraint fails

If you got this error, it means that you are trying to restore a database sql file which got dependancy on other tables.

To override and restore anyway, add this to the top of the .sql dump file

SET FOREIGN_KEY_CHECKS = 0;

This will make sure that the foreign key checks are disabled for the session while restoring.

How to monitor database restore progress

Use the mysql admin tool to see the rows inserted

mysqladmin -u root -p extended -r -i 10 |grep ‘Innodb_rows_inserted ‘

Also you can use the processlist command inside mysql to view the activity. This will be best if there are no other activities going on the mysql db

mysql> show processlist;