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Use ipcs to see all IPC resources on your system: ipcs -m This shows System V shared memory segments with details like: SHMID: The segment identifier OWNER: User who created it PERMS: Permissions (octal format) BYTES: Size in bytes NATTCH: Number of processes attached For a more compact view focused on just what you need:…
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 test operator, which checks if a file…
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 (A): ssh-keygen -t ed25519 -C “user@hostname” -f…
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 time and synchronization status: timedatectl status…
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 boot, the system will check…
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…
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…
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…
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…
To load a kernel module automatically at system startup, create a configuration file in /etc/modules-load.d/ with a .conf extension. The systemd-modules-load.service daemon reads these files during early boot and loads the specified modules. Basic method Create a new configuration file. For the ixgbe driver example: echo “ixgbe” | sudo tee /etc/modules-load.d/ixgbe.conf Or use your editor…
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…
When you need to break up a large gzip file into smaller chunks, you have several practical options depending on your constraints. Using zcat with split The most straightforward approach is to decompress the gzip file and split it simultaneously: zcat large_file.gz | split -b 100M – chunk_ gzip chunk_* This decompresses large_file.gz, pipes it…
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…
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”…
Every process running on a Unix-like system has a parent process. The parent process ID (PPID) identifies which process spawned the current one — critical information when debugging process hierarchies, managing child processes, or writing robust shell scripts. Built-in variable The simplest approach uses Bash’s $PPID variable: echo $PPID This prints the PPID of the…
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…
On Linux systems, the root filesystem (/) can be on various device types — a raw disk partition, an LVM logical volume, or other storage configurations. Finding the underlying physical disk requires checking the device hierarchy, which differs depending on the storage setup. Quick method with df and lsblk The simplest approach uses lsblk with…
Sometimes you need to find the ASCII character that comes after a given character. This is useful for generating sequences, creating substitution ciphers, or manipulating character ranges in shell scripts. Using printf with ASCII Values The most portable and straightforward approach uses printf to convert between characters and their ASCII numeric values: #!/bin/bash get_next_char() {…