Ozgur's notes...

Here you can fing a list of Basic linux system administration commands. Enjoy it :  A command is : A binary file kept under specific directory. Types of Commands 1. File and file system management: cat | cd | chmod | chown | chgrp | cp | du | df | file | fsck | ln | ls | lsof | mkdir | mount | mv | pwd | rm | rmdir | split | touch 2. Process management: at | chroot | crontab | kill | killall | nice | pgrep | pidof | pkill | ps | sleep | time | top | wait | watch User Management/Environment: env | finger | id | mesg | passwd | su | sudo | uname | uptime | w | wall | who | whoami | write Text processing: awk | cut | diff | ex | head | iconv | join | less | more | paste | sed | sort | tail | tr | uniq | wc | xargs 3. Network: inetd | netstat | ping | rlogin | traceroute 4. Searching find | grep | strings 5. Other: banner | bc | cal | man | size | yesFilesystem Utilities cd – Change to another directory location ls – List directory contents cp – Copy a file or directory to another location

  Your new daily given task is creating a new app in a new namespace. You investigated and found your image. Then you started to create your app. After app created you checked and realized that the your new apps pod is not starting! Here look at this example. I Used gitlab here as an instance. [ozgurk@myworkstation ~]$ oc new-app --name gitlab \ > --docker-image quay.io/redhattraining/gitlab-ce:8.4.3-ce.0 --> Creating resources ... imagestream.image.openshift.io "gitlab" created deployment.apps "gitlab" created service "gitlab" created --> Success  Until here, everything looking normal. Check your pod status :  [ozgurk@myworkstation ~]$ oc get pods NAME READY STATUS RESTARTS AGE gitlab-6d61db3479-yyjl 0/1 Error 1 43s As seen above, our pod is in a trouble. It's better to start investigation from pod logs. [ozgurk@myworkstation ~]$ oc logs pod/ gitlab-6d61db3479-yyjl ===========

 Openshift provides different kind of authentication mechanisms for authentication. Openshift comes with a default kubeadmin user as a factory default. In addition to default admin, in real world you want different users with different permission levels to separate roles.  You can use Ldap, Github or Github Enterprise, Keystone Server, OpenID Connect or HTPasswd authentication. All these methods are named as Identity providers.All methods are external solutions or requires additional servers/services to deploy to authenticate except HTPasswd authentication. HTPasswd authentication  consist of simple and locally managed password files. Simply, you define usernames and equivalent password for them. htpasswd file contains a list of users and their secrets. HTPasswd files keeps users password encrypted by several encryption algorithms like, MD5(default), SHA1, SHA256 and Bcrypt (Most secure for htpasswd.) Screenshot 1- A simple and sample htpasswd file A simple htpasswd file is similar to

Openshift and Kubernetes uses images to deploy containers for your projects. If you have a customized image and simply you want to use the same image in your another namespace  or project. In this case you have two options, Either you pull image from image registry that customized image come from or pull it from another project. You may not  use first option if your Kubernetes or Openshift environment is  closed to external or company policies denies it. Second option is a bit of complicated but also  useful too. Also you can scriptize it  for further use. Therefore, it comes! [ozgurkkisa@workstation ~]$ oc policy add-role-to-group \ -n project-common system:image-puller \ system:serviceaccounts:project-new clusterrole.rbac.authorization.k8s.io/system:image-puller added: "system:serviceaccounts:youruser-expose-image"  At the example above, you give image-puller access permission from project named project-common to serviceaccounts in project named project-new. By this way, D

 Unlike virtualization, in modern containerization technologies Kubernetes or Openshift doesn't include embedded storage with containers. Altough a standard vm contains embedded storage due to requirement of operation systems, already comes with virtual disks and it's storage space.  In Kubernetes,  Openshift and other variants, as an Administrator, you need to preconfigure the storage for for your containers/pods. You or your administrator needs to provide your node to persistent storage space(s). This spaces can be traditional block storage (iscsi, fc), file storage (cifs,nfs) or cloud storage (s3,azure files,ebs). Whatever technology you use, you need a Persistent Volume Claim (PVC) to provide persistent storage space to containers.  As a first task, I recommend you to create a resource quota for your PVC to limit exhausting storage space. I'm going to tell openshift to limit "the project" or "namespace" to use total 500GB storage space and maximum al

 As an engineer, administrator, operator, or developer, sometimes you need to learn certificate information from an application, host system, or whatever else. Almost all modern browsers allow you to get certificate information by simply clicking a red/green or crossed lock icon or following page information agents. But sometimes you can't use browsers, and you can't leave your CLI session due to a lack of connection problem or other factors. You can use the OpenSSL CLI tool to get basic certificate information on Linux. Openssl is a handy tool that allows you to save a bunch of certificate-based requirements, including getting certificates, renewing, generating a new one and of course getting information from them. In this article, you simply get the certificate information from a saved certificate. [ozgurkkisa@workstation]$ openssl x509 -in \ wildcard-api.pem -noout -subject -issuer -ext 'subjectAltName' -dates subject=C = US, ST = NC, L = Raleigh, O = "Red Ha

Hello from openshift! I have a question for you. When will expires your Openshift Router TLS (console) certificate? Here is a short solution to learn this info. Let's start! At first, login to your Openshift cluster. Then, create a variable for router tls certificate hostname : console=$(oc get route -n openshift-console console \ > -o jsonpath='{.spec.host}') After defining router hostname variable, check it : echo $console console-openshift-console.apps.ocp4.ozgurkkisa.com   And finally we are gonna learn what is the expiration of  our beloved Router TLS certificate by running curl https://$console -k -v 2>&1 | grep 'expire date' * expire date: Jun 22 16:43:53 2022 GMT Therefore, we have learned our OpenShift Router TLS certificate expiration date. By this you can write a to-do and  prepare yourself to replacing this certificate. Thats it!

  Undoubtedly, route have a key role to accessing your pods and their applications inside.  You may want to learn your whole Kubernetes or Openshift routes and their hostnames. Also you want to learn reachability of them. Here comes a shortcut! First step is creating a variable : hosts=$(oc get route -A \ -o jsonpath='{.items[*].spec.host}') You can ensure that just getting the hostnames,  rather than any other info by running : echo $hosts After this point we need a series of shell command to get names and HTTP status of our routes. For this task, write out the codes shown below :  for host in $hosts ; do \ curl https://$host -k -w "%{url_effective} %{http_code}\n" -o /dev/null -s ; \ done https://oauth-openshift.apps.ocp4.ozgurkkisa.com/ 403 https://console-openshift-console.apps.ocp4.ozgurkkisa.com/ 200 https://downloads-openshift-console.apps.ocp4.ozgurkkisa.com/ 200 https://alertmanager-main-openshift-monitoring.apps.ocp4.ozgurkkisa.com/ 403 https://grafan