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 flush parameter The simplest…
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 manager still works: sudo yum…
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 command-line tool: virsh vcpuinfo <domain-name> This…
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 reliable approach. Most distributions use…
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 core functionality (EL8+). Unlike older…
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. It’s lightweight and doesn’t require additional guest agents….
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 ignored) SIGCONT: Resumes a paused process…
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 using hdfs fsck with output parsing: hdfs fsck…
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 ^ matches the start of each line and PREFIX…
Several approaches exist to detect active file access in Linux, ranging from simple procfs inspection to sophisticated kernel-level tracking. Using lsof The most straightforward method is lsof (list open files), which shows all files currently open by running processes: lsof /path/to/file This returns process ID, user, file descriptor, and access mode. To check only write…
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 lm-sensors sudo apt install lm-sensors # Debian/Ubuntu…
EncFS is a FUSE-based encrypted overlay filesystem that was once popular for transparent file encryption. However, its use on Android has become impractical due to Android’s security architecture. Here’s what you need to know in 2026. Why EncFS Doesn’t Work Well on Android Anymore Android’s evolution has made direct EncFS usage difficult: Scoped Storage (enforced…
The modification time (mtime) indicates when a file’s content was last changed. This is critical for scripting, backups, logging, and dependency tracking in builds. Using stat The stat command is the most reliable tool for retrieving mtime programmatically: stat -c %Y filename This outputs the Unix timestamp (seconds since epoch). For nanosecond precision: stat -c…
When you need to reverse-lookup an IP address against your local /etc/hosts file, several tools can help. This is different from a full DNS reverse lookup — you’re checking only against the static mappings on your local system. Why this matters By default, most hostname resolution tools check /etc/hosts first before querying DNS servers. If…
When you modify /etc/fstab, systemd doesn’t automatically pick up the changes. You need to explicitly tell systemd to reload its configuration and apply the new mount points. The Basic Reload To force systemd to recognize changes in /etc/fstab, run: sudo systemctl daemon-reload This tells systemd to re-read all unit files and configuration, including the mounts…
The command journalctl -b -1 should show the previous boot’s journal, but on many systems it returns: Failed to look up boot -1: No such boot ID in journal This happens because persistent journal storage isn’t enabled by default. Without it, journald only keeps logs in volatile memory (/run/log/journal), which gets cleared on shutdown. Enable…
Understanding file descriptors is fundamental to shell scripting. By default, your shell has three standard streams: STDOUT (FD 1): Standard output, where commands print results STDERR (FD 2): Standard error, where commands print errors and diagnostics STDIN (FD 0): Standard input, where commands read data Basic Output Print to STDOUT: echo “This goes to stdout”…
To get the parent process ID (PPID) of the running process, use the os.getppid() function: import os ppid = os.getppid() print(f”Parent Process ID: {ppid}”) This returns the process ID of the parent process as an integer. On Unix-like systems, this is straightforward. On Windows, the behavior is consistent as well. Accessing Full Process Information For…
Bash has several native flags that help you trace and validate script execution before and during runtime. Trace mode (-x): Executes the script while printing each command before it runs. bash -x script.sh This prints expanded commands to stderr, showing variable substitution and command execution order. You can enable tracing for specific sections using set…
Every shell script runs as a process with a unique ID (PID). You need this ID for process management, logging, temporary file naming, and cleanup operations. The $$ variable The special variable $$ expands to the PID of the current shell process: echo $$ This returns a single integer — the PID of your current…