LaTeX BibTeX Error: “I found no citation commands” If you’re getting this error when running bibtex on your auxiliary file, it typically means your document has no citations, even though BibTeX is being invoked: This is BibTeX, Version 0.99d (TeX Live 2015/Debian) The top-level auxiliary file: main.aux The style file: latex8.bst I found no citation…
Checking if STDERR is redirected in Bash You need to detect whether STDERR (file descriptor 2) is connected to a terminal or redirected to a file or pipe. This is useful for conditional logging, color output, or error handling that depends on the output destination. Using file descriptor tests The primary method is the -t…
SSH Key-Based Authentication and Remote Command Execution Password-less SSH login is faster, more secure, and essential for automation. Combining it with remote command execution lets you run tasks on servers from your local machine without interactive authentication. Setting Up SSH Key-Based Authentication Generate SSH Keys First, generate an ED25519 key pair on your local machine…
Finding Differences Between Files on Windows The diff command on Linux is standard, but Windows doesn’t ship with an equivalent by default. You have several solid options depending on whether you prefer command-line or GUI tools. Command-Line Alternatives If you want a command-line experience similar to Linux diff: Windows PowerShell (built-in, Windows 10+): Compare-Object (Get-Content…
Setting the System Time on Linux Accurate system time is critical for log timestamps, security operations, certificate validation, and coordinating across distributed systems. Modern Linux distributions handle time synchronization automatically, but you’ll occasionally need to set the time manually. Using timedatectl The standard tool for time management on systemd systems is timedatectl. Check your current…
Work-Conserving vs Non-Work-Conserving I/O Schedulers I/O schedulers in Linux sit between application requests and physical disk hardware, deciding the order in which I/O operations execute. The fundamental difference between work-conserving and non-work-conserving schedulers comes down to how they handle idle periods. Work-Conserving Schedulers A work-conserving scheduler must dispatch a pending I/O request whenever one exists,…
Installing alien on CentOS/Rocky Linux to convert .deb to .rpm alien is a straightforward package converter available in EPEL that handles conversion between .deb, .rpm, Slackware, and other package formats. This is useful when you need to install Debian packages on RPM-based systems. Prerequisites You need EPEL (Extra Packages for Enterprise Linux) enabled. On CentOS…
HDFS Checkpointing: Forcing Metadata Snapshots The NameNode in HDFS maintains the filesystem namespace in memory. The Secondary NameNode (or Checkpoint Node in HA setups) periodically merges the namespace image (fsimage) with the edit logs to create a new checkpoint. Understanding how to force this process is essential for cluster maintenance and recovery operations. How Checkpointing…
Force fsck on Next Reboot Filesystem corruption occasionally happens. When it does, you need fsck to run before the system fully mounts its filesystems. Here’s how to force a filesystem check during the next boot. Using touch to Mark Filesystems The traditional method is to create /forcefsck: sudo touch /forcefsck sudo reboot On the next…
Understanding Interrupt Handling Interrupts are fundamental to how your Linux system handles hardware and software events. Monitoring them in real-time helps identify performance bottlenecks, device driver issues, and CPU load imbalances. Here’s how to check interrupts effectively. Quick Live Monitoring with /proc/interrupts The simplest approach is reading /proc/interrupts directly: cat /proc/interrupts This shows a snapshot…
Flushing STDOUT in Python By default, Python buffers stdout when it’s not connected to a terminal — typically when you redirect output to a file, pipe to another command, or run inside a container. This buffering can hide output until the buffer fills or the program exits, making debugging and log monitoring difficult. Using the…
Installing GFortran on RHEL-Based Systems GFortran is the GNU Fortran compiler from the GCC toolchain. It’s essential for scientific computing, numerical simulations, and legacy Fortran code maintenance. Quick Install On modern RHEL-based systems (RHEL 9+, Rocky Linux, AlmaLinux, CentOS Stream): sudo dnf install gcc-gfortran On CentOS 7 (EOL since June 2024), the older yum package…
Finding vCPU Thread IDs in QEMU/KVM When you’re managing KVM virtual machines on a Linux host, you often need to identify which OS threads correspond to vCPU threads. This is essential for CPU pinning, performance analysis, and troubleshooting resource contention. Using virsh to List vCPU Thread IDs The most straightforward approach is through virsh, libvirt’s…
CPU Resource Limiting in Linux Limiting CPU resources for individual users is essential for preventing resource exhaustion, maintaining fair system performance, and isolating workloads. Whether you’re managing multi-user systems, shared hosting environments, or need to constrain specific applications, Linux provides several proven methods. Using cgroups (Control Groups) Modern cgroups v2 offer the most flexible and…
Disabling fastestmirror in CentOS/RHEL systems The fastestmirror plugin automatically selects the fastest package mirror for your system. While useful, you might want to disable it if you’re experiencing slow mirror detection, prefer a specific mirror, or troubleshoot package manager issues. The plugin is provided by yum-plugin-fastestmirror (on older EL7 systems) or as part of DNF’s…
Sharing Data Between Host and Guest in QEMU/KVM When running virtual machines with QEMU/KVM, you’ll frequently need to transfer files or share directories between the host and guest systems. Several methods work well depending on your use case and performance requirements. 9p (Virtio) Filesystem The 9p protocol is the most straightforward approach for sharing directories….
Pausing and resuming processes with signals You can pause and resume any process on Linux using signals without stopping it completely. This is useful for managing resource-heavy jobs, debugging, or controlling execution flow without losing process state. Using SIGSTOP and SIGCONT The standard approach uses two signals: SIGSTOP: Pauses a process (cannot be caught or…
Finding Files with Replication Factor 1 in HDFS Files with replication factor 1 are a liability in production HDFS clusters. They have no redundancy, meaning a single node failure results in data loss. Identifying and fixing these files should be part of your regular cluster maintenance. Using the HDFS CLI The most straightforward approach is…
Adding a Prefix to Each Line in Bash Several methods exist to prepend a prefix string to each line of text. The right approach depends on your input source and performance requirements. Using sed The sed stream editor is the most portable and efficient approach: sed ‘s/^/PREFIX/’ file.txt This uses a substitution command where ^…
Getting the Highest Temperature from All Sensors Monitoring server temperatures is essential for preventing hardware damage and maintaining system stability. Linux provides several tools to query thermal sensors and identify which components are running hot. Using lm-sensors The most reliable approach is lm-sensors, a userspace tool that reads temperature data from kernel drivers: # Install…