These kernel messages from the libata driver indicate SATA link-layer errors between your drive and controller. They look alarming, but they’re usually fixable — and the fix is typically hardware-related, not a software or drive firmware issue. What These Error Messages Mean When you see messages like this in dmesg: ata4.00: exception Emask 0x10 SAct…
When you connect an external hard drive with LVM volumes to a RHEL, CentOS, or Rocky Linux system, the logical volumes don’t automatically appear in /dev. Unlike some distributions that handle this automatically, you need to manually activate them using vgchange. Activating LVM Volumes First, plug in your external drive. Then activate all logical volumes…
When you try to create a filesystem on a disk with mkfs, you may see this error: # mkfs -t ext4 /dev/sdd1 mke2fs 1.42.8 (20-Jun-2013) /dev/sdd1 is apparently in use by the system; will not make a filesystem here! Even though the device isn’t mounted, mkfs refuses to proceed. This safety mechanism prevents accidental data…
When you compile or run screen on a remote host where you lack root privileges, you’ll often hit this error: Cannot make directory ‘/var/run/screen’: Permission denied This happens because screen needs a socket directory to manage sessions, and /var/run/screen is owned by root. If screen isn’t already installed system-wide, you can’t create this directory without…
When you run a curl GET request with spaces in the query string, the shell interprets the space as a separator and truncates the URL: curl “http://example.com/send?msg=hello world” The space causes the shell to treat world as a separate argument, so only hello gets sent. You need to properly URL-encode the space (and other special…
When sending POST requests through a Squid proxy with curl, you may encounter a proxy error that blocks the request, even though the same request works fine with GET. The issue typically appears as: ERROR The requested URL could not be retrieved The root cause is the Expect: 100-continue header that curl automatically adds to…
When you see output like this from hdfs dfsadmin -report, you need to understand what each metric means and how to respond: Under replicated blocks: 139016 Blocks with corrupt replicas: 9 Missing blocks: 0 Understanding block states in HDFS is essential for cluster health. The distinction between these categories determines how urgent your response needs…
If you’re running AdSense responsive ads on a content area narrower than full viewport width, you’ve probably noticed the ads default to horizontal (leaderboard) formats instead of the vertical rectangle ads that typically perform better. You can control which ad sizes appear by modifying the ad format parameter. The Problem with Auto Format When you…
When troubleshooting wireless performance, you need to know both the negotiated link speed and actual throughput. ethtool won’t help here — it’s for wired interfaces. For wireless adapters, you’ll need different tools depending on what information you’re after. Using iwconfig for link speed The iwconfig command shows the currently negotiated link rate between your adapter…
When you need to verify the current link speed of a network interface — whether it’s running at 10Mbps, 100Mbps, 1Gbps, or higher — ethtool is the standard tool for the job. Using ethtool to check interface speed The basic command is straightforward: ethtool eth0 Replace eth0 with your actual interface name. Here’s sample output:…
SSH performs reverse DNS lookups on connecting clients by default. If your DNS infrastructure is slow or misconfigured, this can add several seconds to every login attempt. Disabling this lookup is a straightforward performance optimization, especially in cloud environments where internal IPs often lack valid PTR records. Disable the UseDNS Setting Edit /etc/ssh/sshd_config: sudo nano…
The glibc implementation of strstr() is a practical case study in algorithm selection. Rather than a naive O(n*m) search, it uses the Two-Way string matching algorithm for better performance on both short and long needles. The Basic Approach The strstr() function in glibc (found in string/strstr.c) starts with a quick check: it scans forward comparing…
Gmail’s SMTP service is widely used for automated mail sending, but it enforces strict rate limits to prevent abuse. Understanding these limits is critical when building mail applications or batch sending systems. Official Rate Limits Google’s official documentation on sending limits is at https://support.google.com/mail/answer/22839. The key constraints are: 500 recipients per day maximum: Sending to…
When processing delimited data in Bash, you often need to drop the last N fields from each line without knowing the total field count. The naive cut -d’.’ -f1 approach fails immediately when field counts vary. Given input like: systemd.3.gz systemd.mount.3.gz systemd.mount.f.3.gz You want to remove the last 2 fields (.3.gz) to get: systemd systemd.mount…
Vim is fast by default, but plugins can introduce noticeable lag during startup or while editing. Finding the culprit requires systematic profiling of both startup time and runtime behavior. Profile Vim startup time The quickest way to identify slow plugins is to measure how long Vim takes to initialize: vim –startuptime profile.log This creates a…
YouCompleteMe’s installation script fails on Fedora with a CMake error about missing PYTHON_LIBRARIES and PYTHON_INCLUDE_DIRS, even when Python is already installed. The error looks like this: CMake Error at /usr/share/cmake/Modules/FindPythonLibs.cmake:201 Could NOT find PythonLibs (missing: PYTHON_LIBRARIES PYTHON_INCLUDE_DIRS) The issue is that you have the Python runtime libraries installed but not the development headers needed for…
Xen hypervisor command line options are kernel parameters passed during boot that control how the Xen hypervisor initializes and operates. These affect CPU scheduling, memory management, virtualization features, debugging, and more. Finding Xen Command Line Options The official documentation is the authoritative source for Xen hypervisor parameters. For your installed Xen version, consult: Official Xen…
EPS (Encapsulated PostScript) files are vector graphics commonly used in academic papers, technical documentation, and professional publishing. If you need to modify an EPS file, you have several options depending on your workflow and the complexity of edits required. Using Inkscape Inkscape is the most straightforward tool for editing EPS files on Linux. It’s a…
Google Custom Search Engine (now part of Programmable Search Engine) lets you offload search functionality to Google’s infrastructure. Redirecting WordPress search queries to CSE can improve search quality, especially for large sites with poor built-in search performance. How it works WordPress uses the s query parameter by default when processing searches from the search form….
When your C: drive fills up with user profile data, moving the entire user directory to another drive is a legitimate solution—but it requires careful execution and understanding of the tradeoffs involved. Why This Matters User profiles contain everything: Documents, Desktop, Downloads, AppData, and all application settings. On a full C: drive, this can easily…