In this post, I am sharing basic steps for changing the default Windows Data Directory of the PostgreSQL in Linux.

When we install PostgreSQL on Linux operating system, by default it stores in “/var/lib/postgresql/[version]/data/”

Always best practice is to store database data on the separate drive instead of the system drives.

PostgreSQL: Change or Move Default Data Directory in Windows

Create a new directory:

mkdir postgres_data_dir

Give directory ownership to your Linux user:

chown user_name postgres_data_dir

Log in with your postgres user and initialize the database at the new location:

initdb -D /postgres/test/postgres_data_dir

OR

STOP and then START Postgres with new data directory:

postgres -D /postgres/test/postgres_data_dir

In this post, I am sharing complete steps for moving main PostgreSQL data directory to any new location in Linux.

When we install PostgreSQL on Linux operating system, by default it stores in “/var/lib/postgresql/[version]/data/”

Always best practice is to store database data on the separate drive instead of the system drives.

Check the current data directory:

postgres=# SHOW data_directory;

        data_directory
------------------------------
 /var/lib/postgresql/9.6/main

Stop the PostgreSQL Service:

sudo systemctl stop postgresql

Create a new directory:

mkdir postgres_data_dir

Give directory ownership to your Linux user:

chown user_name postgres_data_dir

Move existing PostgreSQL data/floder to the new location:

sudo rsync -av /var/lib/postgresql /test/postgres_data_dir/

Move old folder to the backup folder:

sudo mv /var/lib/postgresql/9.6/main /tmp/pg_backup

Change data folder in postgresql.conf file:

data_directory = '/test/postgres_data_dir/postgresql/9.6/main'

Start the service of PostgreSQL:

sudo systemctl start postgresql

Now check the data directory:

postgres=# SHOW data_directory; 

 		  data_directory
--------------------------------------------
/test/postgres_data_dir/postgresql/9.6/main

PostgreSQL recently launched the new pgAdmin 4 tool to access the PostgreSQL Database Server.
In this post, I am sharing steps to install pgAdmin 4 desktop mode in Ubuntu 16.04.

First, create a virtual environment:

sudo apt-get install virtualenv python-pip libpq-dev

Create pgadmin4 virtual environment:

cd
virtualenv pgadmin4

Now, go to pgadmin4 and activate it:

cd pgadmin4
source bin/activate

Download the pgadmin4:

wget https://ftp.postgresql.org/pub/pgadmin/pgadmin4/v1.4/pip/pgadmin4-1.4-py2.py3-none-any.whl

Just check the pgadmin4:

ls -ltr
 
postgres@ip-172-31-27-19:~/pgadmin4$ ls -ltr
total 24
drwxrwxr-x 3 postgres postgres 4096 Jul 18 20:07 lib
drwxrwxr-x 2 postgres postgres 4096 Jul 18 20:07 include
drwxrwxr-x 3 postgres postgres 4096 Jul 18 20:07 share
drwxrwxr-x 2 postgres postgres 4096 Jul 18 20:07 local
-rw-rw-r-- 1 postgres postgres   60 Jul 18 20:07 pip-selfcheck.json
drwxrwxr-x 2 postgres postgres 4096 Jul 18 20:07 bin

Now install pgadmin4:

pip install pgadmin4-1.4-py2.py3-none-any.whl

Do activate:

cd ~/pgadmin4
source bin/activate

Execute require python script:

python lib/python2.7/site-packages/pgadmin4/pgAdmin4.py

Check the output:

pgAdmin 4 - Application Initialisation
======================================
The configuration database - '/var/lib/postgresql/.pgadmin/pgadmin4.db' does not exist.
Entering initial setup mode...
NOTE: Configuring authentication for SERVER mode.
 
Enter the email address and password to use for the initial pgAdmin user account:
 
Email address: anveshpatel88@gmail.com
Password:
Retype password:
Password must be at least 6 characters. Please try again.
Password:
Retype password:
 
The configuration database has been created at /var/lib/postgresql/.pgadmin/pgadmin4.db
Starting pgAdmin 4. Please navigate to http://localhost:5050 in your browser.

Access pgadmin4 in a browser:

http://localhost:5050

In this post, I am sharing few DBA commands to start, stop, enable, disable SQL Server Service on Linux.
Microsoft released SQL Server 2017 with Linux so SQL DBA should know the basic commands of SQL Linux.

SQL Server 2017: Microsoft released Community Technical Preview (CTP 2.0) on 19th April 2017

First, check the status of SQL Server Service:

systemctl status mssql-server

Stop the SQL Server Service:

sudo systemctl stop mssql-server

Start the SQL Server Service:

sudo systemctl Start mssql-server

Disable the SQL Server Service:

sudo systemctl stop mssql-server

sudo systemctl disable mssql-server

Enable the SQL Server Service:

sudo systemctl enable mssql-server

sudo systemctl start mssql-server

Recently, I started to configure few of my DBA shell scripts in Linux Crontab.

Yesterday, I shared an important article on skip the execution of your shell script if it is running already.

If you forget to put the first line of your shell script something like “#!/bin/sh” and bash shell script something like “#!/bin/bash”, you cannot get the name of your running shell script.

It’s called a shebang and tells the parent shell which interpreter should be used to execute the script.

When you are running shell script in Linux, the operating system will look at the first few bytes of the file to decide the format of the program and how to execute it.

If you don’t use “#!/bin/sh” or “#!/bin/bash” on the first line, then the system will treat all the commands in that script as different commands.

So I would suggest please start to add it.

Check below screenshots without #!/bin/bash:

I created sample running.bash file to explain the importance “#!/bin/sh” or “#!/bin/bash”.

Check below screenshots with #!/bin/bash:

We configured lots of cron job in our production Linux – PostgreSQL Server. Different schedules like monitor the database performance, monitor the backup process, take a database backup, replicate a database copy.

We set few monitor cron jobs at every 5 minutes. Now the situation is, few monitoring scripts are running even more than 5 minutes, and as per the scheduled, same script could start the execution after 5 minutes.

Now, the same script is running more than one time.

We should monitor this kind of situation, and we should prevent the next execution of the same script if it is already in running state. It also helps us to reduce an unnecessary load on the database server.

I prepared below two options; you can embed any one of it in your shell script.

Option script 1:

if pidof -x $(basename $0) > /dev/null; then
  for p in $(pidof -x $(basename $0)); do
    if [ $p -ne $$ ]; then
	echo "*****************************************************************"
	echo "  ***Warning*** Script $0 is already running...So existing...    "
	echo "*****************************************************************"
	exit 1
    fi
  done
fi

Option script 2:

isrunning=`ps -ef | grep $(basename $0) | grep -v $$ | grep -v grep | wc -l`
 
if [ "$isrunning" -ne 0 ]; then
   echo "**************************************************************"
   echo "  ***Warning*** Script $0 is already running... So exiting... "
   echo "**************************************************************"
   exit 1
fi

Recently, I shared one article on PostgreSQL schemas migration.

PostgreSQL: Script to copy Table Data from one Schema to another Schema

The migration activities are very common for all DBAs. I found lots of different questions on migration exercises.
In this post, I am sharing a Linux shell script to copy your table data from one PostgreSQL Server to another PostgreSQL Server using psql command line.

I am just migrating the data; please create a blank table at your destination/second database server.

This is a utility script. Further, you can modify the script for generic use something like by adding parameters for host_name, database_name, table_name and others

Linux Bash Shell Script for data migration between PostgreSQL Servers:

#!/bin/bash
psql \
    -X \
    -U user_name \
    -h host_name1 \
    -d database_name \
    -c "\\copy tbl_Students to stdout" \
| \
psql \
    -X \
    -U user_name \
    -h host_name2 \
    -d database_name \
    -c "\\copy tbl_Students from stdin"

You can also filter the column list something like below script:

#!/bin/bash
psql \
    -X \
    -U user_name \
    -h host_name1 \
    -d database_name \
    -c "\\copy (SELECT Rno, Studname FROM tbl_Students) to stdout" \
| \
psql \
    -X \
    -U user_name \
    -h host_name2 \
    -d database_name \
    -c "\\copy tbl_Students from stdin"

In the previous post, I shared shell script like store psql result into record array.
In this post, I am sharing one more shell script to store the result of psql SELECT query into a Variable of Bash Shell Script.

This handy script is useful for a beginner who just started to write a PostgreSQL DBA Bash Shell Script. You need this kind of demonstration to store the result of psql query into variable mostly like count of records.

The value of this variable we can use for further validation something like data exists or not in the Table.

In the below script, I used two variables to store the count of a table, but do not forget to notice option ‘-t’ in the second query which returns only tuple value and without option ‘-t’ it returns all formatted text as well like column name, returned a row count.

We need only tuple value so we must use ‘-t’ option. Please check the below demonstration.

#!/bin/bash

DB_NAME=$1
RecordCount1=$( psql -d ${DB_NAME} -c "select count(1) from tbl_students" )
RecordCount2=$( psql -d ${DB_NAME} -t -c "select count(1) from tbl_students" )

echo "RecordCount1:"$RecordCount1
echo "RecordCount2:"$RecordCount2

The result:

RecordCount1: count ------- 9 (1 row)
RecordCount2: 9

Now a day, I am developing different Linux shell scripts to monitor the PostgreSQL database server. Later, I will share those shell scripts.

But before that, I want to share few basic things which we can embed in any one of our Shell scripts.

In this post, I am sharing a small shell script to iterate the result of psql SELECT using RECORD ARRAY and WHILE LOOP.
Using that, we can do further processing and validation on each record.

Script to iterate the table result:

#!/bin/bash

DB_NAME=$1
psql -d ${DB_NAME} -At -c "select rno, studname, studclass from tbl_students" \
    | while read -a Record ; do
    rno=${Record[0]}
    studname=${Record[1]}
    studclass=${Record[2]}

    echo "${rno} ${studname} ${studclass}"
done

rno | studname
-----+----------+-----------
1 | Anvesh
2 | Neevan
3 | Toby
5 | Roy
4 | Jenny
6 | Kaviy
7 | Martin
8 | Laxmi
9 | Nion
(9 rows)

PostgreSQL is a powerful, open source object-relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness.

I am going to share few steps on how to install PostgreSQL 9.4 on Ubuntu 14.04.

First, check the version of Ubuntu:

lsb_release -sc

You need to add the latest PostgreSQL repository for the latest version, otherwise It will install PostgreSQL 9.3. This is for trusty version.

sudo add-apt-repository "deb https://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main"

Update and Install PostgreSQL 9.4:

sudo apt-get update
sudo apt-get install postgresql-9.4

Default postgres super user and postgres database is created. You need to set a password for the postgres super user.

ubuntu@:~$ sudo passwd postgres
Enter new UNIX password:****
Retype new UNIX password:****
passwd: password updated successfully

If service is not started, you can start the PostgreSQL service.

sudo service postgresql start

Connect PostgreSQL server using postgres user:

ubuntu@:~$ su postgres
Password:****

Create a sample database:

createdb database_name

Connect to that database:

psql -d database_name

Create a sample table:

create table Test (rno integer);

Exit to database session:

\q

Exit to PostgreSQL server:

exit