Linux Missive: March 2022

Sunday 27 March 2022

Install Java with Apt on Ubuntu 20.04

sudo apt update

java -version

Command 'java' not found, but can be installed with:

sudo apt install default-jre # version 2:1.11-72, or

sudo apt install openjdk-11-jre-headless # version 11.0.14+9-0ubuntu2~20.04

sudo apt install openjdk-16-jre-headless # version 16.0.1+9-1~20.04

sudo apt install openjdk-17-jre-headless # version 17.0.2+8-1~20.04

sudo apt install openjdk-8-jre-headless # version 8u312-b07-0ubuntu1~20.04

sudo apt install openjdk-13-jre-headless # version 13.0.7+5-0ubuntu1~20.04

sudo apt install default-jre

<...>

java -version

openjdk version "11.0.14" 2022-01-18

OpenJDK Runtime Environment (build 11.0.14+9-Ubuntu-0ubuntu2.20.04)

OpenJDK 64-Bit Server VM (build 11.0.14+9-Ubuntu-0ubuntu2.20.04, mixed mode, sharing)

sudo apt install default-jdk

<...>

javac -version

javac 11.0.14

Tuesday 22 March 2022

Install Docker on Ubuntu 20.04

sudo apt update

sudo apt-get install ca-certificates curl gnupg lsb-release

sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

sudo echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

sudo apt-get update

sudo apt-get install docker-ce docker-ce-cli containerd.io docker-compose-plugin

sudo docker --version

Docker version 20.10.13, build a224086

sudo systemctl status docker

● docker.service - Docker Application Container Engine

Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)

Active: active (running) since Tue 2022-03-22 16:21:57 PDT; 2min 37s ago

...

#check Docker is working correctly

sudo docker run hello-world

#list complete list of available subcommands

docker

#for more information on a command

docker COMMAND --help

#view system-wide information

sudo docker info

#crawl Docker Hub and return a listing of all images

sudo docker search ubuntu

#see the images that have been downloaded

sudo docker images

#view the active containers

sudo docker ps

#view all containers — active and inactive

sudo docker ps -a

#view the latest container

sudo docker ps -l

#start container with the ID/NAME

sudo docker start container_ID/container_NAME

#stop container with the ID/NAME

sudo docker stop container_ID/container_NAME

#delete container

sudo docker rm container_ID/container_NAME

Ref: docs.docker.com

Thursday 17 March 2022

Ansible Vault Simple Examples

#encrypt a file

ansible-vault encrypt file_name

New Vault password:

Confirm New Vault password:

Encryption successful

#view encrypted files

ansible-vault view file_name

Vault password:

#edit encrypted files

ansible-vault edit file_name

Vault password:

#change password of encrypted files

ansible-vault rekey --ask-vault-pass file_name

Vault password:

New Vault password:

Confirm New Vault password:

Rekey successful

#decrypt files

ansible-vault decrypt --ask-vault-pass file_name

Vault password:

Decryption successful

#use vault password file

echo "password" > password_file

ansible-vault encrypt file_name --vault-password-file=password_file

Encryption successful

TASK [Deploy tomcat config] fatal: [localhost]: FAILED! => {"msg": "an error occurred while trying to read the file '/path/to/file_name': [Errno 13] Permission denied: b'/path/to/file_name'.

Issue

TASK [Deploy tomcat config] *****************************************************************************************************************************************************************

fatal: [localhost]: FAILED! => {"msg": "an error occurred while trying to read the file '/path/to/file_name': [Errno 13] Permission denied: b'/path/to/file_name'. [Errno 13] Permission denied: b'/path/to/file_name'"}

Troubleshoot

809755 -rw-r----- 1 root root 7598 Mar 16 18:33 file_name

sudo chown -R user:user file_name

809755 -rw-r----- 1 user user 7598 Mar 16 18:33 file_name

Wednesday 16 March 2022

Ansible ping: Check connectivity status of target remote hosts

mkdir ansible

cd ansible

vim inventory.ini

[webservers]

[all:vars]

ansible_connection=ssh

ansible_user=user_name

ansible_ssh_pass=password

ansible_port=42006

ansible_ssh_common_args='-o StrictHostKeyChecking=no'

#ansible -m ping -i inventory.ini all

ansible -m ping -i inventory.ini webservers

localhost | SUCCESS => {

"ansible_facts": {

"discovered_interpreter_python": "/usr/bin/python3"

"changed": false,

"ping": "pong"

}

Check connectivity between ansible and the target.

ping module checks connectivity using inventory file.

the group can be specified in the inventory file.

ansible all -m ping -v

#Using /etc/ansible/ansible.cfg as config file

localhost | SUCCESS => {

"ansible_facts": {

"discovered_interpreter_python": "/usr/bin/python3"

"changed": false,

"ping": "pong"

}

ansible webservers -m ping

#to check connectivity manually

ssh -p 42006 username@IP

#check ssh port

sudo netstat -tnlup | grep ssh

tcp 0 0 0.0.0.0:42006 0.0.0.0:* LISTEN 1006/sshd: /usr/sbi

tcp6 0 0 :::42006 :::* LISTEN 1006/sshd: /usr/sbi

| UNREACHABLE! => { "changed": false, "msg": "Failed to connect to the host via ssh: ssh: connect to host localhost port 22: Connection refused",

Issue

ansible -m ping -i inventory.ini webservers

localhost | UNREACHABLE! => {

"changed": false,

"msg": "Failed to connect to the host via ssh: ssh: connect to host localhost port 22: Connection refused",

"unreachable": true

}

Troubleshoot

#specify port number

ansible_port=42006

| UNREACHABLE! => { "changed": false, "msg": "Failed to connect to the host via ssh: Invalid multiplex command.", "unreachable": true

Issue

ansible -m ping -i inventory.ini webservers

localhost | UNREACHABLE! => {

"changed": false,

"msg": "Failed to connect to the host via ssh: Invalid multiplex command.",

"unreachable": true

}

Troubleshoot

vim devops.ini

ansible_ssh_common_args='-O StrictHostKeyChecking=no'

#change to

ansible_ssh_common_args='-o StrictHostKeyChecking=no'

Result

ansible -m ping -i devops.ini webservers

localhost | SUCCESS => {

"ansible_facts": {

"discovered_interpreter_python": "/usr/bin/python3"

"changed": false,

"ping": "pong"

}

Monday 14 March 2022

ansible-playbook fatal: [localhost]: FAILED! => {"changed": false, "msg": "Unable to start service nginx: Job for nginx.service failed because the control process exited with error code.

Issue

ansible-playbook demo_playbook.yml -i demo_ansible.ini --user=user-name --extra-vars "ansible_sudo_pass=password"

PLAY [This demo playbook] *******************************************************************************************************************************************************************

TASK [Gathering Facts] **********************************************************************************************************************************************************************

ok: [localhost]

TASK [This is to install nginx software] ****************************************************************************************************************************************************

changed: [localhost]

TASK [This is restart the nginx service] ****************************************************************************************************************************************************

fatal: [localhost]: FAILED! => {"changed": false, "msg": "Unable to start service nginx: Job for nginx.service failed because the control process exited with error code.\nSee \"systemctl status nginx.service\" and \"journalctl -xe\" for details.\n"}

PLAY RECAP **********************************************************************************************************************************************************************************

localhost : ok=2 changed=1 unreachable=0 failed=1 skipped=0 rescued=0 ignored=0

systemctl status nginx.service

● nginx.service - A high performance web server and a reverse proxy server

Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)

Active: failed (Result: exit-code) since Sun 2022-03-13 05:03:15 PDT; 2min 13s ago

Docs: man:nginx(8)

Process: 9296 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, status=0/SUCCESS)

Process: 9297 ExecStart=/usr/sbin/nginx -g daemon on; master_process on; (code=exited, status=1/FAILURE)

Mar 13 05:03:13 ubuntu nginx[9297]: nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)

Mar 13 05:03:13 ubuntu nginx[9297]: nginx: [emerg] bind() to [::]:80 failed (98: Address already in use)

Mar 13 05:03:14 ubuntu nginx[9297]: nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)

Mar 13 05:03:14 ubuntu nginx[9297]: nginx: [emerg] bind() to [::]:80 failed (98: Address already in use)

Mar 13 05:03:14 ubuntu nginx[9297]: nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)

Mar 13 05:03:14 ubuntu nginx[9297]: nginx: [emerg] bind() to [::]:80 failed (98: Address already in use)

Mar 13 05:03:15 ubuntu nginx[9297]: nginx: [emerg] still could not bind()

Mar 13 05:03:15 ubuntu systemd[1]: nginx.service: Control process exited, code=exited, status=1/FAILURE

Mar 13 05:03:15 ubuntu systemd[1]: nginx.service: Failed with result 'exit-code'.

Mar 13 05:03:15 ubuntu systemd[1]: Failed to start A high performance web server and a reverse proxy server.

cat /var/log/nginx/error.log