Programming language tutorials, syntax guides, and language-specific features.
Perl gives you straightforward ways to send output to both standard output and standard error. Understanding the difference matters — STDOUT handles normal program output, while STDERR carries diagnostics, warnings, and error messages. Separating them lets users redirect, log, or suppress errors independently. Basic Output Methods The simplest approach uses print with filehandles: print STDOUT…
The fundamental distinction between standard output and standard error matters for proper program behavior, logging, and stream redirection. Here’s how to handle both correctly. Basic Approach with fprintf() The simplest method uses fprintf() to write to specific streams: #include <stdio.h> int main() { fprintf(stdout, “This goes to standard output\n”); fprintf(stderr, “This goes to standard error\n”);…
The most direct way to check your Zimbra installation version is through the zmcontrol utility: zmcontrol -v This returns the version string of your Zimbra deployment. Run this command on any Zimbra server in your environment — the output will be identical across all nodes in a cluster. Alternative Methods If zmcontrol isn’t available or…
The epoch timestamp (seconds since January 1, 1970 UTC) is fundamental for Unix timekeeping. Every process needs reliable time access — whether for logging, scheduling, or benchmarking. Basic Second-Level Precision For simple timestamp needs, use time(): #include <time.h> time_t now = time(NULL); printf(“Current epoch: %ld\n”, (long)now); This returns seconds since epoch as a time_t. It’s…
The Unix epoch (seconds since January 1, 1970 UTC) is the standard for representing time across systems. Perl gives you straightforward access to this value. Basic epoch timestamp The simplest way to get the current epoch time: my $epoch = time(); print $epoch; # prints something like 1735689600 The time() function returns an integer representing…
When working with Hadoop Distributed File System (HDFS), files containing spaces in their names require special handling during the hdfs dfs -put command. Without proper escaping or quoting, the shell interprets spaces as delimiters, splitting the filename into multiple arguments. Direct Upload with Quoting The simplest approach is to wrap the filename in quotes: hdfs…
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…
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…
EncFS is a FUSE-based encrypted filesystem that lets you create an encrypted directory without a separate partition. Installation approaches vary depending on your distribution version and repository availability. Using Distribution Repositories On modern RHEL-based systems (CentOS Stream, Rocky Linux 9+, AlmaLinux 9+), EncFS is typically available in the EPEL repository: sudo dnf install epel-release sudo…
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…
The default TeX Live packages available through standard repositories are often outdated and incomplete. The official TeX Live installer provides access to current versions and the full package collection, though it requires around 4-5GB of disk space. Prerequisites Before starting, ensure you have the required dependencies installed: sudo yum groupinstall -y “Development Tools” sudo yum…
When trying to mount an encrypted EncFS directory as a normal user, you may encounter this error: $ encfs -s ~/t/.enc ~/t/enc EncFS Password: fuse: failed to exec fusermount: Permission denied fuse failed. Common problems: – fuse kernel module not installed (modprobe fuse) – invalid options — see usage message Even though the same command…
Dia is a diagram editor useful for creating flowcharts, UML diagrams, and other technical drawings. While it’s not in Rocky Linux 9’s default repositories, you can install it through EPEL (Extra Packages for Enterprise Linux). Prerequisites You’ll need root access or sudo privileges. Verify your system: cat /etc/os-release Enable EPEL Repository Install the EPEL repository…
The most common approach is using Apache’s mod_rewrite module. Add this to your .htaccess file in your document root: <IfModule mod_rewrite.c> RewriteEngine On RewriteCond %{HTTP_HOST} !^www\. [NC] RewriteCond %{HTTP_HOST} !^$ RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [L,R=301] </IfModule> This uses a 301 permanent redirect, which tells browsers and search engines that the www version is canonical. The conditions…
HP printers and scanners on Rocky Linux, CentOS, or RHEL require the HPLIP (HP Linux Imaging and Printing) package. This guide covers the complete setup process. Install HPLIP packages Start by installing the core HPLIP packages: sudo dnf install hplip hplip-gui hpijs On older CentOS 7 systems, use yum instead of dnf. HPLIP may prompt…
Spaces in file and directory paths are a common source of rsync failures. When paths contain spaces, the shell interprets them as argument separators unless you properly escape or quote them. Here’s how to handle this correctly. The core issue When rsync receives an unquoted path with spaces, the shell splits it at each space….
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…
aria2 is a lightweight, multi-protocol download manager that supports HTTP(S), FTP, BitTorrent, and Metalink protocols. It’s particularly useful for resumable downloads, parallel connections, and command-line automation. Prerequisites You’ll need root or sudo access. This guide covers CentOS 7, CentOS Stream, and Rocky Linux 8+. For older systems still on CentOS 7, package availability may be…
curlftpfs is a FUSE-based filesystem that lets you mount FTP/SFTP servers as local directories. This is useful for treating remote FTP locations like local storage without downloading files individually. Prerequisites FUSE kernel module loaded (usually default on modern systems) Root or sudo access Network connectivity to your FTP server Installation on RHEL/CentOS/Rocky Linux The curlftpfs…
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:…