Linux powers most of the cloud infrastructure, supercomputers, and embedded systems globally. The field itself spans kernel development, system administration, performance tuning, networking, and DevOps. Researching systems effectively requires understanding where to look, what tools matter, and how to validate your findings against real-world constraints. Start With the Right Foundation Before diving into specific research,…
Process priority management is essential for ensuring critical tasks get CPU resources when needed. Linux provides several mechanisms to control how the kernel scheduler allocates CPU time to processes. Understanding Priority Levels Linux uses two priority concepts: Nice value: ranges from -20 (highest priority) to 19 (lowest priority). Default is 0. Real-time priority: ranges from…
Linux doesn’t provide a glibc wrapper for ioprio_set(), so you need to call it directly via syscall(). Here’s the basic approach: #include <unistd.h> #include <sys/syscall.h> syscall(SYS_ioprio_set, IOPRIO_WHO_PROCESS, pid, ioprio_value); Required definitions You’ll need to define the I/O priority classes, target types, and helper macros. Add these to your source file or header: /* I/O priority…
When the kernel migrates a process from one CPU’s runqueue to another, the Completely Fair Scheduler (CFS) must adjust the process’s virtual runtime (vruntime) to account for the different scheduling histories of each CPU. This prevents fairness issues where a migrated process could gain an unfair advantage on the destination CPU. How vruntime Adjustment Works…
When upgrading libvirt from an older version (like 1.2.2) to 2.5.0 or later, you may encounter a socket connection error when trying to create VMs: ERROR Failed to connect socket to ‘/var/run/libvirt/virtlogd-sock’: No such file or directory Domain installation does not appear to have been successful. This happens because libvirt 2.5.0 introduced the virtlogd daemon…
After a libvirt upgrade, VMs fail to start with the error: error: Failed to start domain kvm1 error: Network not found: no network with matching name ‘default’ This happens when the default NAT network (virbr0) isn’t automatically created during the upgrade. Quick fix: Restore the default network The fastest solution is to recreate the default…
Getting kernel function call stacks is essential for debugging driver issues, understanding kernel behavior, and performance profiling. The approach depends on what you’re trying to trace: live kernel execution, crash analysis, or post-mortem inspection. Using ftrace The kernel’s built-in ftrace framework is the first tool to reach for. It’s zero-overhead when disabled and has minimal…
These are often confused terms in concurrent programming and multiprocessor systems, but they address different problems in shared memory architectures. Memory Coherence deals with writes to the same memory location. A cache-coherent system ensures that any read of a data location returns the most recently written value. If CPU A writes to address X, then…
When running Ubuntu on older servers like Dell PowerEdge systems with legacy graphics cards (Matrox G200eR2, etc.), you may encounter extremely slow desktop performance. The issue typically stems from the X server falling back to unoptimized drivers or incorrect video mode detection. Identifying the problem First, check your current graphics configuration: lspci | grep -i…
VM exits occur when a guest VM transitions to hypervisor mode to handle privileged operations, I/O requests, or other events. Tracking exit counts and types helps identify performance bottlenecks, inefficient guest behavior, and hypervisor overhead. Quick Exit Statistics The debugfs interface provides a simple view of exit counts: cat /sys/kernel/debug/kvm/exits This shows aggregate exit counts…
VNC (Virtual Network Computing) provides a graphical remote desktop connection to Linux servers. It’s straightforward to set up and useful when you need GUI access to a headless or distant system. Installation On the server side, install a VNC server package. TigerVNC is the most reliable choice across distributions: Debian/Ubuntu: sudo apt install tigervnc-server tigervnc-common…
When you create VMs in KVM, they’re typically assigned IP addresses via DHCP. Finding those addresses so you can SSH in requires a few steps. Here are the practical approaches. Using virsh domiflist and ARP The traditional method combines virsh domiflist to get the VM’s MAC address, then looks it up in the ARP table:…
PARSEC is a widely-used CPU-bound benchmark suite containing real applications and complex third-party library dependencies. The installation can be challenging due to these external requirements, but following this guide will get you up and running. Prerequisites Before starting, install the required build tools and libraries: sudo apt-get update sudo apt-get install build-essential pkg-config gettext autoconf…
The NAS Parallel Benchmarks (NPB) remain a standard tool for evaluating HPC system performance, though landscape has shifted toward additional metrics like HPCG and memory bandwidth tests. This guide covers installation and basic usage. Prerequisites Before installing NPB, you’ll need: Fortran compiler — gfortran is the standard choice on most systems MPI implementation — OpenMPI…
When you initialize a new repository locally and try to push to GitHub or Bitbucket for the first time, you’ll likely encounter errors like: No refs in common and none specified; doing nothing. Perhaps you should specify a branch such as ‘master’. fatal: The remote end hung up unexpectedly This happens because your local repository…
[md] The dd command doesn’t evaluate arithmetic expressions in its parameters. If you try this: $ dd if=/dev/zero of=./4Ktest100M bs=4KB count=25000*9 dd: invalid number ‘25000*9′ You’ll get an error because dd expects literal numeric values, not expressions. The shell doesn’t expand 25000*9 as arithmetic — it’s passed to dd as a literal string. ## Using…
Monitoring directory growth is essential for tracking logs, temporary files, and catching runaway disk usage before it becomes a problem. Linux offers several approaches depending on whether you need simple periodic checks, interactive exploration, or event-driven monitoring. Simple periodic monitoring The watch command repeatedly runs a command at set intervals: watch -n 1 du -sh…
Writing a master thesis means protecting years of work. You need to handle three core concerns: preventing data loss from hardware failure or malware, ensuring 24/7 access to your work, and keeping it private until publication. The solution is version control with remote backup. Git provides local history and recovery, while a private remote repository…
When pushing to GitHub over HTTPS, you’ll see: error: The requested URL returned error: 403 Forbidden while accessing https://github.com/username/repo.git fatal: HTTP request failed This means Git connected to GitHub successfully, but your credentials were rejected. Common causes: Expired or revoked Personal Access Token (PAT) Using a password instead of a PAT (GitHub disabled password auth…
Skype periodically fails to start with a “system is unavailable” error when it can’t read or write to the user’s temporary directory. This typically happens when the temp folder becomes corrupted, has permission issues, or contains orphaned Skype cache files that prevent proper initialization. Understand the Problem On Windows, each user account has a temporary…