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KenjiGoh
KenjiGoh

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Windows Subsystem for Linux (WSL)

Writing here for sharing and also for my personal reference as I have very poor memory and tend to forget some commands.

For windows users, you can download WSL (Windows Subsystem for Linux) on powershell. WSL lets developers run a Linux environment directly on windows Read more here

After installing, in Command Prompt or PowerShell, type wsl and it will open the WSL terminal window:

wsl
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To open a VS Code, type code . from the ubuntu terminal.

code .
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Go back to root directory

cd /
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Mounting

/mnt is a standard subdirectory of the root directory on Linux. The /mnt/c/ directory basically means mounting on Windows C drive. Therefore if u see this path, it means u are accessing a folder that resides in Windows. Read more here

/mnt/c/<file_path>
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Windows-WSL

sudo means "super user do" - a Linux command that allows you to executedddd programs as a super user (aka root user)

sudo
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Before we go into installing new packages, lets cover some of the essential commands to help with troubleshooting.
Key terminologies to know:

  1. postgres is one of the default PostgreSQL database
  2. postgres is also the default admin user in PostgreSQL
  3. psql - interactive commandline tool

Basic Commands to Know

To check status of database:

sudo service postgresql status
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To start running your database

sudo service postgresql start
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To stop running your database

sudo service postgresql stop
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Installation of Packages

To update & upgrade our Ubuntu to latest packages:

sudo apt-get update && sudo apt-get upgrade
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To install package such as node, python or postgresql

sudo apt-get install <package>
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To check version, e.g. postgreSQL, you type either one of this.

psql -V psql --version
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To see all the command documentations, you can either type one of the following commands:

-? --help man postgres
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Show information about all PostgreSQL clusters

 pg_lsclusters
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Default Databases of Postgres

Most Postgres servers have three databases defined by default: template0, template1 and postgres. (yes it is a little confusing for first-timer, default user is postgres and one of the default database name is also postgres)

The default admin user, postgres, needs a password assigned in order to connect to a database. By default, the postgres user has no password and can hence only connect if ran by the postgres system user. Therefore, we have to set a password for the postgres user:

sudo passwd postgres
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You will see the command line change to postgres=#

To exit the postgres=#, enter \q or Ctrl+D:

\q
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To switch from root user to the default admin user, postgres.

su - postgres
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You will see something like this. You can now run commands as the PostgreSQL superuser.

postgres@DESKTOP-ORMQU9O:~$
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To create a new user:

createuser --interactive --pwprompt
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You will be prompt the following:

postgres@DESKTOP-ORMQU9O:~$ createuser --interactive --pwprompt Enter name of role to add: kenji Enter password for new role: Enter it again: Shall the new role be a superuser? (y/n)
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I (postgres user in this case) have created a new user called kenji.

To create a new database called simple_blog:

createdb simple_blog
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To destroy a database:

dropdb simple_blog
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Using psql Interactive Shell as default postgres user

To run Postgres with psql interactive shell (you can also just type psql), it will prompt you for a password:

sudo -u postgres psql
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You will be greeted with the following:

psql (12.9 (Ubuntu 12.9-0ubuntu0.20.04.1)) Type "help" for help. postgres=#
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Press Ctrl+D to exit and we will return to this:

postgres@DESKTOP-ORMQU9O:~$
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Here we can switch to the new user we have just created:

postgres@DESKTOP-ORMQU9O:~$ su - kenji
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And you will then see this instead (after password prompt):

kenji@DESKTOP-ORMQU9O:~$
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We can enter the psql command line by typing:

kenji@DESKTOP-ORMQU9O:~$ psql
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And you will see this:

psql (12.9 (Ubuntu 12.9-0ubuntu0.20.04.1)) Type "help" for help. kenji=#
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psql is an interactive terminal program that allows you to interactively enter, edit and execute SQL commands. Remember to put ';' to end the SQL statement.

With psql shell open, to see what user accounts have been created:

kenji=# \du
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To see all other available backslash commands:

kenji=# \?
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To exit the help log, type '\q' and press Enter:

kenji=# \q
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We can also check connection info to see port which database, which user and which port you are connected to:

kenji=# \conninfo
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You will see this:

You are connected to database "kenji" as user "kenji" via socket in "/var/run/postgresql" at port "5432".
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Start psql to specific database you have created

When not in psql shell, You can also startup psql to a specific database with the below commaned:

psql simple_blog
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You will be greeted with the following:

psql (12.9 (Ubuntu 12.9-0ubuntu0.20.04.1)) Type "help" for help. simple_blog=#
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To see all database:

\l
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You can write SQL statement directly, remember to end with semi-colon:

simple_blog=# CREATE TABLE my_table ( simple_blog(# first integer not null default 0, simple_blog(# second text) simple_blog-# ; CREATE TABLE
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Now if you type '\d my_table', you will see the created table

simple_blog=# \d my_table Table "public.my_table" Column | Type | Collation | Nullable | Default --------+---------+-----------+----------+--------- first | integer | | not null | 0 second | text | | |
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As always, to learn more, it is best to read the documentation, as some solutions shared by others might be outdated.

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