Wednesday, May 22, 2024

Multiple ways to extrract zip files in linux terminal

I downloaded a big zip file (5.9GB) for an application, and as usual, to unzip it, just use unzip command.

$ unzip

I received this error, which is unusual.

Error when extracting using unzip command

Then I search around to find any other zip application that can extract the file. I am pretty confident that file is fine, since the provider has provided a md5sum file, and it matches. I ended up trying "jar" command. To install jar in ubuntu, simply run below command:
$ sudo apt update && sudo apt install fastjar -y

Once installed, extract the zip file using below command
$ jar xvf

Unfortunately, jar is also unable to extract the file, with below error:
Error when extracting using jar command

The I encounter another robust archiver called 7z, which can be installed in ubuntu using below command:
$ sudo apt update && sudo apt install 7zip -y

To extract a zip file, simply run this command:
$ 7z x

Even though 7z reported some error as well, but it managed to extract the file. 
Error when extracting using 7z command

There you go, 3 commands to extract a zip file. So do not worry if you are unable to extract any zip file, you can always try a few commands to get the job done.

Thursday, November 30, 2023

Draws ASCII Shapes Around Text in Linux Terminal

Boxes is an application to draw boxes and shapes around text in linux terminal. For those who cannot imagine, below is one example of how boxes is used:

To install boxes, simply run below command in any debian like linux distro:
$ sudo apt update && sudo apt install boxes -y

To use it, simply echo any text and pipe it to boxes
$ echo "this is linuxwave" | boxes

Boxes comes with 59 designs by default. We can list all the styles by typing:
$ boxes -l

To use the designs, simply append -d flag, and provide the name of the design. For example, to use unicornsay style:
$ echo "this is linuxwave" | boxes -d unicornsay

And you will get something like this

As usual, to know more about a command, simply use man command
$ man boxes

Monday, November 20, 2023

Install clustercontrol v2 on ubuntu 22.04 using podman

Clustercontrol is a database cluster management system, developed by, that ease up the work of database cluster deployment and management, using a nice web interface. Please follow below steps to install clustercontrol v2 using podman.

First, install podman
$ sudo apt update && sudo apt install podman -y

Configure podman registries. Add below lines into the end of /etc/containers/registries.conf
registries = ['']

Pull the latest clustercontrol image
$ podman pull severalnines/clustercontrol

Create necessary directories
$ mkdir -p clustercontrol/{backups,cmon.d,cmonlib,datadir,prom-conf,prom-data,sshkey}

Create ssh key, and save them into clustercontrol/sshkey
$ ssh-keygen -t ed25519
Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/myuser/.ssh/id_ed25519): /home/myuser/clustercontrol/sshkey/id_ed25519    
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 

Start clustercontrol
$ podman run -d --name clustercontrol \
-h clustercontrol \
-p 5000:80 \
-p 5001:443 \
-p 9443:9443 \
-p 19501:19501 \
-v $PWD/clustercontrol/cmon.d:/etc/cmon.d \
-v $PWD/clustercontrol/datadir:/var/lib/mysql \
-v $PWD/clustercontrol/sshkey:/root/.ssh \
-v $PWD/clustercontrol/cmonlib:/var/lib/cmon \
-v $PWD/clustercontrol/backups:/root/backups \
-v $PWD/clustercontrol/prom-data:/var/lib/prometheus \
-v $PWD/clustercontrol/prom-conf:/etc/prometheus \

Create username, and set password for the user
$ podman exec -it clustercontrol bash
# s9s user --create --generate-key --controller="https://localhost:9501" --group=admins myuser
# s9s user --change-password --new-password=anypassword myuser

Open a web browser, and browse to the ip address of the server with port 5001 for https

Login using the user and password created above

Friday, November 10, 2023

Using psql without entering password

Sometimes, we need to run psql command without entering the password, even though the account is protected with password. The usual situations are, when we are running the psql command in a script, or we have to constantly monitor the output of psql commands using watch. Here is the method on how to achieve that.

Create a .pgpass file inside the user's home directory who's going to access psql without password

$ touch ~/.pgpass

Follow below format to add the user's details into pgpass


$ echo "" > ~/.pgpass

We can also use wildcard, such as *. If you password contains ":" or "\", use "\" to escape them

$ echo "*:*:mydatabase:myuser:mysuperlongpassword" > ~/.pgpass

Give a proper permission to the file, nobody accept the owner of the home directory is allowed to use the file
$ chmod 0600 ~/.pgpass
Now we should be able to use psql to mydatabase as myuser, without entering any password
$ psql -h localhost -U myuser mydatabase

Saturday, November 4, 2023

Postgresql 16 streaming replication on ubuntu 22.04

Streaming Replication is a feature in PostgreSQL that allows continuous shipping and application of WAL XLOG records to standby servers to keep them current.

Below is the steps to configure streaming replication using postgresql 16 on ubuntu 22.04, with one master and one slave.

First, install postgresql in all nodes by referring here.

In master node, do below steps:

- add this configuration (uncomment wherever necessary) in /etc/postgresql/16/main/postgresql.conf. For one slave node, set max_wal_senders to 3, and add 2 for every additional slave nodes, according to percona.
listen_addresses = '*'
wal_level = replica
max_wal_senders = 3
 - create a user for replication
$ sudo su - postgres
postgres@master:~$ createuser --replication -P replicauser 
- allow replication from slave's ip address. Add below line in /etc/postgresql/16/main/pg_hba.conf, assuming our slave node's ip address is
host    replication     replicauser                    scram-sha-256
- Restart postgres
$ sudo systemctl restart postgresql

In slave node, do below steps:

- remove postgresql data directory which is /etc/postgresql/16/main (we can also rename it to save as a backup)

$ sudo su - postgres

postgres@slave:~$ rm -rf /etc/postgresql/16/main

- set a proper permission to the data directory

postgres@slave:~$ chmod 700 /etc/postgresql/16/main

- copy data from master (assuming master's ip address is

postgres@slave:~$ pg_basebackup -h -U replicauser -D /var/lib/postgresql/16/main/

- add standby.signal file inside postgresql data directory, to tell postgresql that this is a standby node

postgres@slave:~$ touch /var/lib/postgresql/16/main/standby.signal

- add below configuration (uncomment wherever necessary) /etc/postgresql/16/main/postgresql.conf

listen_addresses = '*'

hot_standby = on

primary_conninfo = 'host= port=5432 user=replicauser password=1' 

- restart postgresql

$ sudo systemctl restart postgresql

Verify the replication is working 

- in master, check pg_stat_replication table

$ sudo su - postgres

postgres=# select client_addr, state from pg_stat_replication where usename like 'replicauser';

- Check if walsender process is running in master

$ ps -ef | grep wal


- Check if walreceiver is running in slave

$ ps -ef | grep wal

We can also create a database in master, and verify that the same database appear in slave almost instantly .