Articles

175 entries

• 0107 Proxmox VE command line cheat sheet: qm, pct, pvecm, pvesm and more The Proxmox VE commands you use most: qm for VMs, pct for containers, pvesm for storage, pvecm for the cluster, vzdump for… Intermediate · Reference · Linux Article Clusters & high availability · VMs & containers 15 Oct 2026
• 0110 Fix: TASK ERROR: VM is locked (backup) A VM or container still carries a backup lock, usually after a backup was interrupted. Check that no backup is running, then… Beginner · Fix · Linux Article Backup & restore · VMs & containers 15 Oct 2026
• 0111 Fix: can’t lock file ‘/var/lock/qemu-server/lock-VMID.conf’ – got timeout Another task is holding the VM's local lock file, so a new action timed out waiting for it. Find the running or… Intermediate · Fix · Linux Article VMs & containers 15 Oct 2026
• 0112 Fix: TASK ERROR: cluster not ready – no quorum? The node is not part of a quorate cluster, so /etc/pve is read-only and guests cannot be started or changed. Restore the… Advanced · Fix · Linux Article Clusters & high availability 15 Oct 2026
• 0115 What is Oracle Private Cloud Appliance (PCA)? Hardware, enclaves and release lines Oracle Private Cloud Appliance is a factory-built rack of compute, storage and network hardware with its own cloud software. Release 3.x offers… Beginner · Concept · Linux Article Architecture & concepts 15 Oct 2026
• 0116 PCA 3.x Compute Enclave concepts: tenancies, compartments, VCNs, instances, images and shapes The PCA 3.x Compute Enclave uses OCI building blocks: a tenancy holds compartments, which hold networks, instances and storage. Instances are built… Beginner · Concept · Linux Article Architecture & concepts · Compute, networking & storage 15 Oct 2026
• 0117 Configure the OCI CLI for Oracle Private Cloud Appliance 3.x Point the standard OCI CLI at a PCA 3.x Compute Enclave: create an API key, write ~/.oci/config with the appliance as the… Intermediate · How-to · Any system Article Compute, networking & storage 15 Oct 2026
• 0118 Create a compute instance on PCA 3.x with the Compute Web UI or OCI CLI Launch a VM in the Private Cloud Appliance 3.x Compute Enclave: gather an image, shape, subnet and SSH key, then create the… Intermediate · How-to · Any system Article Compute, networking & storage 15 Oct 2026
• 0119 PCA 3.x networking basics: create a VCN, subnets and security lists On Private Cloud Appliance 3.x, instances need a VCN and a subnet. Create them in the Compute Web UI or OCI CLI… Intermediate · How-to · Any system Article Compute, networking & storage 15 Oct 2026
• 0120 Block volumes on PCA 3.x: create, attach and mount a data disk Add storage to a Private Cloud Appliance 3.x instance: create a block volume, attach it as paravirtualized, then format and mount it… Intermediate · How-to · Any system Article Compute, networking & storage 15 Oct 2026
• 0121 PCA 3.x Service CLI basics: connecting and finding your way around The Service CLI administers the Private Cloud Appliance 3.x Service Enclave. Connect with SSH on port 30006 and use list, show, help,… Intermediate · Reference · Any system Article Administration & monitoring 15 Oct 2026
• 0122 PCA 3.x health monitoring and upgrade workflow overview How Private Cloud Appliance 3.x reports health (Grafana, Prometheus, Loki, platform health checks) and how appliance upgrades work: ISO images, an upgrade… Advanced · Concept · Linux Article Administration & monitoring 15 Oct 2026
• 0123 KVM vs QEMU vs libvirt: how Linux virtualization fits together KVM is the Linux kernel part that uses CPU virtualization extensions, QEMU is the program that emulates a full machine around it,… Beginner · Concept · Linux Article Basics 15 Oct 2026
• 0124 virsh cheat sheet: everyday libvirt commands A quick reference for virsh: list, start, stop and inspect VMs, change CPUs and memory, manage networks, storage pools and snapshots, with… Intermediate · Reference · Linux Article Basics 15 Oct 2026
• 0125 Create a KVM virtual machine with virt-install Use virt-install to create libvirt/KVM guests: install from an ISO, run a text-only install over the serial console, or import a cloud… Intermediate · How-to · Linux Article Basics 15 Oct 2026
• 0126 KVM snapshots and cloning with virsh and virt-clone Take, list, revert and delete libvirt snapshots with virsh, understand internal vs external and disk-only snapshots, and clone a stopped VM with… Advanced · How-to · Linux Article Basics 15 Oct 2026
• 0127 Fix: “Requested operation is not valid: network ‘default’ is not active” A libvirt VM will not start because the virtual network it uses, usually the NAT network 'default', is stopped. Start the network… Intermediate · Fix · Linux Article Basics 15 Oct 2026
• 0131 Kubernetes architecture: control plane, nodes, kubelet and etcd A Kubernetes cluster is a control plane that stores and decides the desired state, plus worker nodes that run your containers. This… Beginner · Concept · Linux Article Concepts 15 Oct 2026
• 0132 Pods, ReplicaSets and Deployments explained A Pod runs one or more containers together, a ReplicaSet keeps a fixed number of identical Pods alive, and a Deployment manages… Beginner · Concept · Linux Article Concepts · Workloads & services 15 Oct 2026
• 0133 Services and Ingress: exposing an app in Kubernetes A Service gives a changing set of Pods one stable address. ClusterIP is internal, NodePort and LoadBalancer reach outside, and an Ingress… Intermediate · Concept · Linux Article Ingress & networking 15 Oct 2026
• 0134 ConfigMaps and Secrets: configuration outside the image ConfigMaps hold plain settings and Secrets hold sensitive values, injected into Pods as environment variables or files. Secrets are only base64-encoded, not… Intermediate · Concept · Linux Article Config, secrets & storage 15 Oct 2026
• 0135 Deploy your first app on Kubernetes A step-by-step tutorial: write a Deployment and a Service in YAML, apply them, reach the app, add health probes, roll out a… Beginner · How-to · Linux Article Ingress & networking · Workloads & services 15 Oct 2026
• 0136 Persistent storage in Kubernetes: PersistentVolumes, claims and StorageClasses How to give a Pod storage that survives restarts: request it with a PersistentVolumeClaim, let a StorageClass provision it, and mount it.… Intermediate · How-to · Linux Article Config, secrets & storage · Workloads & services 15 Oct 2026
• 0137 Helm basics: install a chart, override values, upgrade and roll back Helm installs packaged Kubernetes apps called charts. Learn to add a repository, install a release, customize it with values files, upgrade it… Intermediate · How-to · Any system Article Helm 15 Oct 2026
• 0138 Kubernetes RBAC basics: least-privilege access for a service account RBAC controls who may do what in a cluster with Roles, ClusterRoles and bindings. This guide grants a CI service account deploy… Advanced · How-to · Linux Article Concepts · Config, secrets & storage 15 Oct 2026
• 0140 kubectl cheat sheet: the commands you use every day A compact reference of everyday kubectl commands: contexts and namespaces, listing and inspecting objects, logs and exec, applying changes, rollouts, scaling and… Beginner · Reference · Any system Article Concepts · Troubleshooting 15 Oct 2026
• 0142 Fix: ImagePullBackOff and ErrImagePull in Kubernetes The pod cannot start because the node failed to pull the container image. Read the "Failed to pull image" event to see… Intermediate · Fix · Linux Article Troubleshooting 15 Oct 2026
• 0143 Fix: CrashLoopBackOff in Kubernetes The container starts, exits, and Kubernetes waits longer before each restart. Read the previous container's logs and its exit code to find… Intermediate · Fix · Linux Article Troubleshooting 15 Oct 2026
• 0144 Fix: Pod stuck in Pending with “0/3 nodes are available: Insufficient cpu” The scheduler cannot find a node with enough unreserved CPU for the pod's request. Compare the request with node allocatable resources, then… Advanced · Fix · Linux Article Troubleshooting · Workloads & services 15 Oct 2026
• 0145 Fix: OOMKilled (exit code 137) in Kubernetes A container used more memory than its limit and the kernel killed it. Confirm the reason, measure real usage, then raise the… Advanced · Fix · Linux Article Troubleshooting · Workloads & services 15 Oct 2026
• 0149 OpenShift vs Kubernetes vs OKD: what OpenShift adds OpenShift is Red Hat's Kubernetes platform and OKD is its community distribution. Both add projects, routes, builds, image streams, Operators and stricter… Beginner · Concept · Linux Article Concepts · Concepts 15 Oct 2026
• 0150 Logging in with oc and working with OpenShift projects Install the oc client, log in with a password, browser or token, then create, switch and inspect projects. Covers where oc stores… Beginner · How-to · Any system Article Concepts · Deploying applications 15 Oct 2026
• 0151 Tutorial: deploy a small web app on OpenShift and expose it with a Route A step-by-step first deployment: create a project, build a static website from Git with Source-to-Image, publish it on an HTTPS Route, then… Beginner · How-to · Any system Article Deploying applications 15 Oct 2026
• 0152 Build and deploy from source with oc new-app and Source-to-Image How oc new-app turns a Git repository or an image into a running app, how Source-to-Image and Docker builds are chosen, and… Intermediate · How-to · Any system Article Deploying applications 15 Oct 2026
• 0153 Expose apps with OpenShift Routes: edge, passthrough and re-encrypt TLS A Route publishes a service on a host name through the OpenShift router. Learn when to use plain HTTP, edge, passthrough or… Intermediate · How-to · Any system Article Deploying applications · Ingress & networking 15 Oct 2026
• 0154 OpenShift app configuration: environment, ConfigMaps, Secrets and persistent storage Set environment variables, load ConfigMaps and Secrets into a Deployment as variables or files, and give it persistent storage with a PersistentVolumeClaim,… Intermediate · How-to · Any system Article Config, secrets & storage · Deploying applications 15 Oct 2026
• 0155 Security Context Constraints (SCC) and why root containers fail on OpenShift SCCs decide which user ID, capabilities and volumes a pod may use. Learn how restricted-v2 assigns random UIDs, how to see which… Advanced · Concept · Linux Article Cluster administration · Concepts 15 Oct 2026
• 0156 Operators, the software catalog (OperatorHub) and OLM on OpenShift Operators automate installing and running software on OpenShift. Learn the difference between cluster Operators and add-on Operators, and how OLM uses catalogs,… Intermediate · Concept · Linux Article Cluster administration · Concepts 15 Oct 2026
• 0157 oc cheat sheet: everyday OpenShift CLI commands The oc commands you use every day, grouped by task: login and projects, apps and builds, routes, config, debugging, permissions and admin… Intermediate · Reference · Any system Article Deploying applications · Troubleshooting 15 Oct 2026
• 0160 Fix: Permission denied in a container on OpenShift because of the random UID A container that works under Docker or Kubernetes crashes on OpenShift with permission denied, because restricted-v2 runs it with a random non-root… Advanced · Fix · Linux Article Troubleshooting 15 Oct 2026
• 0161 Fix: Error from server (Forbidden): … is forbidden: User … cannot … in OpenShift oc refuses a command with Error from server (Forbidden). The message names the user, verb, resource and project. Learn how to read… Intermediate · Fix · Any system Article Cluster administration · Troubleshooting 15 Oct 2026
• 0164 systemd services: systemctl and journalctl basics systemd starts and supervises services on most Linux servers. systemctl starts, stops and enables them; journalctl shows their logs. Beginner · Concept · Linux Article Services & systemd 15 Oct 2026
• 0165 Write a systemd service unit for your own app Turn any long-running program into a proper service: create a unit file, run it as an unprivileged user, restart it on failure… Intermediate · How-to · Linux Article Services & systemd 15 Oct 2026
• 0166 Replace a cron job with a systemd timer A systemd timer runs a service on a schedule like cron, but logs every run to the journal, can catch up missed… Intermediate · How-to · Linux Article Services & systemd 15 Oct 2026
• 0167 Fix: Job for nginx.service failed because the control process exited with error code systemctl prints this when a service's start command exits with an error. The real reason is in journalctl; for nginx it is… Intermediate · Fix · Linux Article Networking & firewalls · Services & systemd 15 Oct 2026
• 0169 Add a new disk: partition, format and mount it by UUID Find a new disk with lsblk, partition it with parted, create an ext4 or XFS filesystem and mount it permanently through /etc/fstab… Intermediate · How-to · Linux Article Disks, LVM & filesystems 15 Oct 2026
• 0170 LVM explained: physical volumes, volume groups and logical volumes LVM puts a flexible layer between disks and filesystems, so you can grow volumes, add disks and take snapshots without repartitioning. Intermediate · Concept · Linux Article Disks, LVM & filesystems 15 Oct 2026
• 0172 Fix: No space left on device Writes fail because a filesystem is full, out of inodes, or holding space for deleted files that are still open. Find which… Beginner · Fix · Linux Article Disks, LVM & filesystems 15 Oct 2026
• 0173 Set a static IP address: nmcli on RHEL vs netplan on Ubuntu RHEL, Rocky and AlmaLinux configure networking with NetworkManager (nmcli); Ubuntu Server uses netplan YAML. Here is the same static IP setup in… Intermediate · How-to · Linux Article Networking & firewalls 15 Oct 2026
• 0174 Network and DNS troubleshooting commands: ip, ss, dig, resolvectl A layer-by-layer cheat sheet for "the server cannot reach X": interfaces and routes with ip, listening ports with ss, and name resolution… Beginner · Reference · Linux Article Networking & firewalls 15 Oct 2026
• 0175 Open ports with firewalld and ufw firewalld (RHEL, Rocky, AlmaLinux) and ufw (Ubuntu) are friendly front ends to the kernel firewall. Allow SSH first, then open only the… Intermediate · How-to · Linux Article Networking & firewalls 15 Oct 2026
• 0176 apt vs dnf: package commands and automatic security updates The everyday package commands on Debian/Ubuntu (apt) and RHEL/Rocky/Alma (dnf) side by side, plus how to turn on automatic security updates on… Beginner · Reference · Linux Article Packages & updates 15 Oct 2026
• 0177 Users, groups and sudo on Debian, Ubuntu and RHEL How Linux accounts and groups work, how to create users, and how sudo gives admin rights through the sudo group on Debian/Ubuntu… Beginner · Concept · Linux Article Users, sudo & hardening 15 Oct 2026
• 0181 Ansible concepts: inventory, modules, playbooks, idempotency and roles Ansible configures many servers over SSH from one control machine. Learn the core pieces: inventory, modules, tasks, playbooks, roles, and why runs… Beginner · Concept · Linux, macOS Article Ansible 15 Oct 2026
• 0184 Ansible Vault: keep passwords and keys encrypted in your repo Ansible Vault encrypts variable files or single values so secrets can live in Git next to your playbooks. Create, edit and rekey… Advanced · How-to · Linux, macOS Article Ansible 15 Oct 2026
• 0185 Ansible ad-hoc commands cheat sheet One-line ansible commands for quick jobs across many servers: ping hosts, run a command, copy files, manage packages, users and services, gather… Intermediate · Reference · Linux, macOS Article Ansible 15 Oct 2026
• 0186 Fix: Ansible UNREACHABLE! Failed to connect to the host via ssh Ansible could not open an SSH session to the host, so no task ran. The text after the colon tells you why:… Intermediate · Fix · Linux, macOS Article Ansible · SSH & servers 15 Oct 2026
• 0187 Terraform concepts: providers, state, plan and apply, modules, and OpenTofu Terraform describes infrastructure in code, compares it with what exists, and changes only the difference. Learn providers, resources, state, the plan/apply loop,… Beginner · Concept · Any system Article Terraform 15 Oct 2026
• 0189 Terraform remote state: backends, locking and migrating local state Move Terraform state from a local file into a shared backend such as S3 with locking, so a team can work safely.… Advanced · How-to · Any system Article Terraform 15 Oct 2026
• 0190 Fix: Terraform Error acquiring the state lock Another run holds the lock on your Terraform state, or a crashed run left it behind. Find out who holds it, wait… Advanced · Fix · Any system Article Terraform 15 Oct 2026