Friday 23 April 2021

How to link Google Colab with GitHub

Create a GitHub repository in which you want to keep Colaboratory notebooks.
Go to and add your GitHub account.

GitHub website window will open asking you to accept Colab's access to your GitHub account.
Once accepted that window will close and back in a popup window above will contain a list of all repositories in connected GitHub account. Select the one you created. As it's currently empty, there are no notebooks in there, it will show "No results".

If you create a notebook in Colab ( and want to add it to that GitHub repo, go to Colab's tab in the browser, File >> Save a copy in GitHub. 

After this, this notebook will appear in the list of notebooks available to be loaded into Colab:

Monday 19 April 2021

PostgreSQL on Ubuntu

Here are some my notes on PostgreSQL on Ubuntu.

To check the PostgreSQL version running:

$ postgres -V

Command 'postgres' not found, did you mean:

  command 'postgrey' from deb postgrey (1.36-5.1)

Try: sudo apt install <deb name>

Let's try to locate binaries:

$ locate bin/postgres

From the ouput above we can see that I have two versions of PostgreSQL installed on my system: 10 and 12. Let's find their full version numbers:

$ /usr/lib/postgresql/10/bin/postgres -V
postgres (PostgreSQL) 10.14 (Ubuntu 10.14-0ubuntu0.18.04.1)

$ /usr/lib/postgresql/12/bin/postgres -V
postgres (PostgreSQL) 12.6 (Ubuntu 12.6-0ubuntu0.20.04.1)

PostgreSQL Service

To check if postgres is listening on ports:

$ sudo netstat -ltnp | grep postgres
tcp        0      0*      LISTEN      1448/postgres     
tcp        0      0*      LISTEN      1456/postgres       

Let's see paths to these processes:

$ sudo pwdx 1448
1448: /var/lib/postgresql/12/main

$ sudo pwdx 1456
1456: /var/lib/postgresql/10/main

So it turned out that both versions of Postgres are currently running in parallel on my system. 

To check the current state of the service:

$ systemctl status postgresql
  postgresql.service - PostgreSQL RDBMS
     Loaded: loaded (/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
     Active: active (exited) since Sun 2021-04-18 21:13:14 BST; 18h ago
   Main PID: 1843 (code=exited, status=0/SUCCESS)
      Tasks: 0 (limit: 38289)
     Memory: 0B
     CGroup: /system.slice/postgresql.service

Apr 18 21:13:14 my_computer systemd[1]: Starting PostgreSQL RDBMS...
Apr 18 21:13:14 my_computer systemd[1]: Finished PostgreSQL RDBMS.

To start/stop the service:

$ systemctl start postgresql
$ systemctl stop postgresql

By default (upon installation) postgresql service is configured to start automatically upon computer launch:

$ cat /etc/postgresql/10/main/start.conf
# Automatic startup configuration
#   auto: automatically start the cluster
#   manual: manual startup with pg_ctlcluster/postgresql@.service only
#   disabled: refuse to start cluster
# See pg_createcluster(1) for details. When running from systemd,
# invoke 'systemctl daemon-reload' after editing this file.


The same output is for postgres v12.

To prevent service from starting upon computer reboot:

$ sudo vi /etc/postgresql/10/main/start.conf

...and replace auto with manual.


To get psql prompt if DB is running locally:

$ psql -h -U root -d test-db
Password for user root: 
psql (10.6 (Ubuntu 10.6-0ubuntu0.18.04.1), server 11.2 (Debian 11.2-1.pgdg90+1))
WARNING: psql major version 10, server major version 11.
         Some psql features might not work.
Type "help" for help.

Now we can list all tables:

test-db=# \dt
Did not find any relations.

To quit:

test-db-# \q