When you’re working in a Makefile, you often need to reference files relative to where the Makefile itself is located. This is especially useful for multi-directory projects or when your build system needs to know its own location. The Solution Make provides the MAKEFILE_LIST variable, which contains the names of all makefiles that have been…
Tethering your iPhone to your computer’s internet connection via USB is useful when you need a stable, low-power connection or want to avoid wireless overhead. This guide covers the practical setup on Windows and how to configure your iPhone to use your PC’s internet. Windows USB Tethering Setup On Windows 10/11: Install iTunes or Apple…
SSH key management becomes critical when you’re handling multiple identities across different hosts. By default, ssh tries keys in a specific order, but you can explicitly configure which key to use for particular hosts through the SSH config file. Using ~/.ssh/config The cleanest approach is to define host-specific key configurations in ~/.ssh/config. This file lets…
To check whether a function exists in Bash, use the type builtin with the -t option. This returns a string identifying what the name is: alias, keyword, function, builtin, or file. Basic Check The simplest approach: if [[ $(type -t f1) == “function” ]]; then echo “f1 is defined as a function” fi This works…
Bash maintains a set of built-in options that control script behavior. You disable them using set +o followed by the option name, or with short flags like set +x. The Basic Syntax set +o option-name Or using short flag notation: set +x The + sign disables an option; – enables it. This works for both…
You can retrieve detailed metadata about an S3 object using the aws s3api head-object command. This is useful when you need to check object properties, sizes, modification times, or custom metadata without downloading the entire file. Basic Usage The simplest form queries an object’s metadata: aws s3api head-object –bucket test-hkust –key dir2/fileupload/fb0c6353-a90c-4522-9355-7cd16cf756ff.file.txt This returns output…
Most modern systems have thermal sensors built into the CPU and motherboard. Reading these sensors is essential for monitoring system health, diagnosing performance issues, and preventing thermal throttling or hardware damage. Install lm-sensors The standard tool for reading hardware sensors on Linux is lm-sensors. Install it on your system: Debian/Ubuntu: sudo apt install lm-sensors RHEL/CentOS/Fedora:…
The YARN resource scheduler determines how cluster resources are allocated to jobs. By default, Hadoop uses the Capacity Scheduler, but you can switch to an alternative like the Fair Scheduler or configure different scheduling policies. Identifying Your Current Scheduler Check which scheduler is currently active by examining your configuration: grep -A 2 “yarn.resourcemanager.scheduler.class” $HADOOP_HOME/etc/hadoop/yarn-site.xml The…
The usermod command is the standard tool for modifying user accounts. To change a username, use the -l (or –login) option: sudo usermod -l user1 u1 This changes the login name from u1 to user1. However, there’s an important caveat: usermod only updates the /etc/passwd file. The user’s home directory, mail spool, and other resources…
You need to check whether a directory exists in your $PATH variable. This is useful when verifying that a tool installation succeeded, or when debugging shell initialization scripts. The regex approach Since $PATH uses colons as separators, a regex is the most straightforward method: if [[ “$PATH” =~ (^|:)”/usr/local/mytool/bin”(:|$) ]]; then echo “Directory found in…
The standard systemctl enable command should work for rpcbind.service, but if you’re seeing it fail to start after reboot, there are several approaches to troubleshoot and fix the issue. Check the Current State First, verify the actual status: systemctl status rpcbind.service systemctl is-enabled rpcbind.service If is-enabled returns disabled, the service wasn’t properly enabled. Check for…
If you’ve set up passwordless SSH login with key-based authentication but lftp keeps prompting for a password, you need to explicitly configure it to use your SSH keys. The basic approach The simplest method is to pass an empty password to lftp, which signals it to fall back on SSH key authentication: lftp -u user,…
Extracting a file extension from a filename is a common task. Here are the main approaches, with modern best practices. Simple Method with lastIndexOf() The most straightforward approach uses lastIndexOf() to find the last dot: function getExtension(filename) { const lastDotIndex = filename.lastIndexOf(‘.’); return (lastDotIndex < 1) ? ” : filename.substring(lastDotIndex + 1); } console.log(getExtension(‘file.txt’)); //…
Python provides several ways to check if files or directories exist, with different trade-offs depending on your use case. Using pathlib (recommended) The modern approach uses pathlib.Path, which is cleaner and more object-oriented: from pathlib import Path path = Path(‘/etc/passwd’) # Check if path exists (file or directory) if path.exists(): print(“Path exists”) # Check if…
When running scripts as root, you often need to execute commands with the environment of a different user. The most reliable way to retrieve another user’s PATH is by spawning a login shell under that user’s context. Basic Approach user1path=$(su – user1 -c ‘echo $PATH’) This spawns a login shell (-) as user1 and outputs…
The scp command handles multiple files efficiently, whether you’re pushing to a remote server or pulling from one. Here are the practical approaches for copying multiple files from remote to local. Brace Expansion Use brace expansion to specify discrete files: scp user@remote:file{1,2,3} ./ This works well when you have a known set of files with…
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…
When you source a script using . script.sh or source script.sh, the $0 variable doesn’t point to the sourced script—it stays as the path of the parent shell or calling script. This creates a problem if you need the sourced script to know its own location. The solution: use ${BASH_SOURCE[0]} The ${BASH_SOURCE[0]} variable holds the…
When writing system administration scripts, you often need to check if a user account exists before taking action. There are several reliable methods to accomplish this. Using id command The id command retrieves user information and returns a non-zero exit code if the user doesn’t exist. This makes it ideal for conditional testing: user=”hello” if…
If you need to jump to a particular byte position in a file, Vim provides the goto command. This is useful when debugging binary files, working with hex editors, or when error messages reference byte offsets. Using the goto command In normal mode, press go followed by the byte number: 20go This moves the cursor…