Linux Tutorials and Command Line Guides - Page 11

Create a system-level systemd service that starts at boot and runs as a dedicated non-root user and group on Ubuntu, Debian, Fedora, RHEL, Rocky Linux, AlmaLinux, CentOS Stream and Oracle Linux.

Learn how to secure BIND primary-to-secondary DNS zone transfers with TSIG on RHEL, Rocky Linux, AlmaLinux, and CentOS Stream using HMAC-SHA256.

Restart or reload cron in Linux with systemctl restart cron on Ubuntu and Debian or crond on RHEL and Rocky Linux, and when a reload is actually needed.

Learn which command to use to restart, reload, or reconnect networking on RHEL, Rocky Linux, AlmaLinux, CentOS Stream, Oracle Linux, and Fedora—from nmcli reload to legacy network.service workflows.

Compare RPM and DEB Linux packages, including package structure, metadata, dependencies, scripts, signatures, installation commands, querying, repositories, conversion risks and supported distributions.

Compare the RHEL and Debian Linux families, including RPM vs DEB, DNF vs APT, repositories, release models, lifecycle, security, support, configuration, cloud images and server use cases.

Compare Rocky Linux, AlmaLinux and Red Hat Enterprise Linux by compatibility policy, governance, repositories, support, lifecycle, certifications, migration paths and production use cases.

Compare Fedora, CentOS Stream and Red Hat Enterprise Linux, including their development flow, release lifecycle, package freshness, stability, support, subscriptions, repositories and best use cases.

Learn how Unix, Linux, GNU/Linux and Linux distributions relate, why Ubuntu, Debian, Fedora, RHEL, Rocky Linux and Arch differ beyond desktop themes, and how to identify your distro from the shell.

Install Java on RHEL, Rocky Linux, AlmaLinux, CentOS Stream, Oracle Linux, or Fedora using OpenJDK, Eclipse Temurin, or Oracle JDK, then configure alternatives, JAVA_HOME, updates, verification, and uninstall.

Install JasperReports Server on RHEL, Rocky Linux, AlmaLinux, CentOS Stream, Oracle Linux, or Fedora using the evaluation binary installer with bundled components or a production WAR deployment on supported Tomcat and …

Install EPEL on RHEL 8–10, Rocky Linux, AlmaLinux, CentOS Stream and Oracle Linux. Enable CRB or PowerTools, verify EPEL and fix repository errors.

Use grubby on RHEL, Rocky Linux, AlmaLinux, CentOS Stream, Oracle Linux, and Fedora to check the running kernel, pick a persistent default, and verify the choice before reboot.

Compare DNF4 and DNF5 command differences, plugins, history syntax, and group handling, and learn what to change in scripts before your distribution moves to DNF5.

Download RPM packages with all dependencies using DNF on RHEL, Rocky Linux, AlmaLinux, Fedora, CentOS Stream, and Oracle Linux for offline installation.

Fix curl error 60 and similar HTTPS failures on Linux when corporate SSL inspection replaces public certificates with a private root CA trusted on Windows but missing from the Linux trust store.

List users in Linux with getent, /etc/passwd, who, and id. Filter normal and system accounts, see logged-in sessions, and check whether a user exists on Ubuntu and RHEL.

Use OpenSSL to view PEM, CRT, CER, chain, bundle, PFX, and P7B certificates. Check expiry, SAN, fingerprint, remote TLS certs, and verify chains.

List groups in Linux with getent, groups, id, and /etc/group. Check user group membership, list group members, and compare primary vs supplementary groups.

Learn how to configure http_proxy, https_proxy and no_proxy environment variables in Linux temporarily, permanently, system-wide, and for tools like curl, wget, apt, git and Docker.

Install Node.js on Ubuntu with apt nodejs, NodeSource setup scripts, NVM for multiple versions, or the official nodejs.org linux-x64 tar.xz under /opt, verify with node --version and npm --version, and uninstall per …

Back up a PKCS12 truststore, check the keytool alias and SHA-256 fingerprint, import a CA only when missing, and exit cleanly for Ansible, systemd, and CI pipelines.

Create a code-signing keypair with keytool, sign a sample JAR with jarsigner, verify the signature, and read the PKIX chain warnings jarsigner prints for a self-signed certificate.

Create Java mTLS keystore and truststore files with keytool and OpenSSL, then run a mutual TLS HttpsServer lab that fails without a client cert and succeeds.

Set javax.net.ssl.trustStore and keyStore JVM properties after building a PKCS12 file with keytool: property names, -D flags, JAVA_TOOL_OPTIONS, and a lab that fails without trustStore then succeeds.

Fix PKIX after importing into the wrong cacerts. Find the Java truststore your app actually uses, including bundled JRE cacerts, and import with keytool.

Renew an expired TLS certificate in an existing Java PKCS12 keystore by checking expiry with keytool -list -v, exporting a CSR from the same alias, and importing the CA-signed reply without deleting the private key.

Fix keytool Invalid keystore format by matching JKS or PKCS12 storetype to the file, avoiding PEM certificates as keystores, and repairing empty or corrupt keystore paths.

Build a custom PKCS12 Java truststore with keytool for Docker and Kubernetes: RUN importcert in the image, set JAVA_TOOL_OPTIONS with trustStoreType=PKCS12, or use an initContainer with a mounted CA Secret and emptyDir …

Find which Java cacerts file your application actually uses: compare JAVA_HOME, java.home, bundled JRE paths, and javax.net.ssl.trustStore overrides before importing a CA certificate.