Applying Ubuntu Server security updates with a restart plan Apply Ubuntu Server security updates with an explicit service-restart and reboot plan. Installing packages does not always replace code already running…

Changing Ubuntu server networking with Netplan safely Change Ubuntu networking through the configuration owner and test the result before committing to a remote-only session. Netplan can generate backend…

Changing an AlmaLinux or Rocky Linux address with NetworkManager Use NetworkManager connection profiles to change an AlmaLinux or Rocky Linux network address. A connection profile is not always named after its device,…

Configuring log rotation for a custom Linux application Create a logrotate policy for a custom application so logs remain useful without consuming unlimited storage. Rotation must match how the application…

Creating a controlled rsync backup over SSH Use rsync over SSH for a controlled file-copy backup when its metadata and consistency model fit the data. A synchronized destination can mirror…

Creating a least-privilege sudo administrator on Linux Create an individual administrative account with only the privileges required for its job. A unique account improves accountability and allows access to…

Diagnosing Linux TLS errors caused by trust or clock problems TLS failures on a Linux client can come from a wrong clock, hostname mismatch, incomplete server chain or an inappropriate trust store. Identify the…

Diagnosing a Linux package repository signature failure A repository signature failure means the package manager could not authenticate the metadata or packages as expected. Investigate the trust chain before…

Diagnosing a Linux server with no free inodes A filesystem can run out of inodes while many gigabytes remain free. Inodes track files and directories, so millions of tiny sessions, cache objects or…

Diagnosing memory pressure before adding Linux swap Investigate Linux memory pressure before adding swap. Swap can provide breathing room for less-active pages, but sustained swapping can make an…

Extending a Linux logical volume safely Expand a Linux logical volume only after mapping the target filesystem through its logical volume, volume group and physical volumes. LVM growth and…

Finding deleted files that still consume disk space On Linux, deleting a filename does not release its storage while a process still holds the file open. This commonly explains why df remains high after…

Finding which process listens on a Linux network port Identify the process listening on a Linux port before changing firewall rules or stopping services. A reachable service requires a listener on the…

Inspecting an unbootable Linux server from rescue mode Rescue mode starts an independent environment so you can inspect an unbootable Linux server. Begin with identification and read-only data preservation.…

Installing an SSH key without losing existing server access Add a new SSH public key while retaining a working recovery session. The server receives the public key; the private key stays on your trusted device.…

Investigating SELinux denials without disabling enforcement Investigate an SELinux denial by matching the blocked action to the application's intended behavior. Keep enforcement enabled while correcting supported…

Investigating a failed systemd service A failed systemd unit records that a service did not complete its expected lifecycle. Read the failure evidence before repeatedly restarting it. The…

Investigating an out-of-memory process kill on Linux An out-of-memory kill is a protective action taken when a relevant memory domain cannot satisfy demand. Identify whether the kernel, a cgroup limit or…

Managing firewalld zones and permitted services Firewalld zones apply different trust policies to interfaces or source networks. Open a service in the zone that actually handles its traffic and…

Planning a supported Debian release upgrade Plan a Debian major-release upgrade using the release notes for the exact source, destination and architecture. Follow the supported sequence between…

Planning bootloader recovery on a Linux server Plan GRUB recovery according to the installed distribution, architecture and firmware boot mode. BIOS and UEFI procedures differ, and a kernel or…

Reading logs from the previous Linux boot Read the previous Linux boot journal to investigate a crash, failed startup or unexpected restart. A reboot can clear transient state, so preserve the…

Recovering from an SSH lockout using the server console Use the provider or hypervisor console to diagnose an SSH lockout without reinstalling the server. Separate network reachability, the listening daemon…

Recovering service when a Linux filesystem is full A full filesystem can stop databases, mail delivery, logging and application writes. Recover a measured amount of space while identifying what grew.…

Responding to a Linux filesystem that became read-only A filesystem that unexpectedly becomes read-only may be protecting itself after an error. Preserve data and investigate storage health before forcing it…

Restricting Ubuntu firewall access without locking out SSH Use UFW to permit required services and restrict administrative access on a self-managed Ubuntu server. Build the allow rules for your current…

Running a maintenance job with a systemd timer A systemd timer activates a service according to a schedule and gives you service status and journal evidence for the result. Use a timer for a defined…

Separating DNS failure from network failure on Linux Separate name-resolution failure from a network or application failure before changing Linux DNS settings. A hostname can resolve correctly while its…

Testing SSH configuration before reloading the service Validate OpenSSH server configuration before reloading it so a syntax error does not become a remote lockout. Syntax validation is necessary but does…

Testing a Linux server restore before an emergency A restore test proves that backups, credentials and operating instructions can recover the intended Linux service. Perform it in an isolated environment…

Testing a persistent filesystem mount before reboot Test a new persistent filesystem mount before rebooting. An incorrect /etc/fstab entry can leave a server waiting for a missing disk or entering…

Understanding high load average on a Linux server Linux load average measures runnable and certain waiting tasks over time; it is not simply the percentage of CPU used. A high value can reflect CPU…

Updating AlmaLinux or Rocky Linux safely with DNF Use DNF to apply supported updates within the installed AlmaLinux or Rocky Linux major release. Review the transaction and restart requirements rather…

Verifying Linux time synchronization and timezone Verify both the system clock and timezone when logs, certificates, scheduled jobs or authentication behave unexpectedly. The timezone controls…