Author: tadmin

Linux ionice: set I/O priority for command

~ tadmin

In Linux, when operating with root administrator privileges, you have the ability to adjust the I/O priority of processes. This is particularly useful when you need to manage system resources more effectively. The tool for this task is the `ionice` command.

Here’s how you can utilize `ionice`:

  1. Running a Command with Highest I/O Priority:

    To execute a command with the highest I/O priority, use the following syntax:

       ionice -c1 -n0 /bin/some-command

    In this example, `-c1` sets the class to ‘real time’, and `-n0` assigns the highest priority within that class.

  2. Applying to an Existing Process:

    Alternatively, if you want to set the I/O priority for an already running process, use its Process ID (PID):

       ionice -c1 -n0 -p PID

    You can find the PID of a process using commands like `ps`, `top`, or `htop`. These tools provide a snapshot of current processes and their respective PIDs.

  3. Setting Lowest I/O Priority:

    To assign the lowest I/O priority to a process or command, you would adjust the parameters to `-c3 -n7`. For example:

       ionice -c3 -n7 /bin/some-command

    Here, `-c3` places the process in the ‘Idle’ class, ensuring it only uses I/O when no other process needs it, while `-n7` is the lowest priority within this class.

Understanding and manipulating process priorities can be crucial for optimal system performance, especially on servers or in environments where resource allocation is key. Remember, modifying I/O priorities should be done with care, as it can significantly affect system performance and behavior.

Linux find: search files by name

~ tadmin

Efficiently Finding and Archiving Specific File Types in Linux

In the world of Linux, the `find` command is an incredibly powerful tool, especially when you need to locate files of different types by their names. Let’s dive into a common scenario: You need to find all `*.php`, `*.js`, and `*.css` files in a folder for archiving, regardless of the case sensitivity of the file names.

Locating the Files

Firstly, navigate to the target directory:

cd /home/taras/public_html

Then, execute the following `find` command:

find . -type f \( -iname '*.php' -o -iname '*.js' -o -iname '*.css' \) -print > /home/taras/list-to-archive.txt

This command breaks down as follows:

  • `find .` starts the search in the current directory.
  • `-type f` looks for files (not directories).
  • `\( -iname ‘*.php’ -o -iname ‘*.js’ -o -iname ‘*.css’ \)` searches for files ending in `.php`, `.js`, or `.css`, using `-iname` for case-insensitive matching.
  • `-print` outputs the found file names.
  • `> /home/taras/list-to-archive.txt` redirects the output to a file.

Archiving the Files

The file `/home/taras/list-to-archive.txt` now contains a list of the files you’ve found. To archive them, use the `tar` utility:

tar -cpjf /home/taras/archive.tar.bz2 -T /home/taras/list-to-archive.txt

Case-Sensitive Search

If you prefer a case-sensitive search, simply replace `-iname` with `-name` in the find command.

Conclusion

Using the `find` command in Linux for locating specific file types and archiving them can greatly simplify file management tasks. Whether you’re dealing with case-sensitive or case-insensitive requirements, this method is both efficient and effective.

Converting Space-Separated Strings to Arrays in Bash Scripts

~ tadmin

Introduction:

In bash scripting, there are times when you need to process a string of space-separated values. A common scenario is when a script receives a string as an argument and needs to handle each word separately. Let’s explore how to convert a space-separated string into an array.

The Solution:

Here’s a simple bash script to do this:

#!/bin/bash

# Convert the first argument into an array
declare -a PARAMS="( $1 )"

# Accessing elements from the array
# The first element is at index 0
PARAM1="${PARAMS[0]}"
# The second element, if present, is at index 1
PARAM2="${PARAMS[1]}"

# Add more elements as needed

Explanation:

  • `declare -a PARAMS=”( $1 )”`: This line declares an array named `PARAMS` and initializes it with the words from the first script argument (`$1`).
  • `PARAM1=”${PARAMS[0]}”` and `PARAM2=”${PARAMS[1]}”`: These lines assign the first and second elements of the array to `PARAM1` and `PARAM2` respectively.

Example Usage:

Suppose you call your script like this: `./yourscript.sh “apple orange banana”`. The `PARAM1` will be ‘apple’, and `PARAM2` will be ‘orange’.

Handling Errors and Edge Cases:

What happens if the script is run without any arguments or with a single word? It’s important to handle such cases to prevent unexpected behavior.

Conclusion and Further Reading:

This simple technique is handy for numerous scenarios in bash scripting. For more advanced bash scripting techniques, consider exploring other bash related articles in our blog.

How to use the nice command to change process priority in Linux

~ tadmin

Introduction

In the world of Linux, managing process priorities is crucial for optimal system performance. The ‘nice’ command is a built-in utility in Linux that allows you to execute commands with altered priorities. Understanding how to use this tool effectively can significantly enhance your system management skills.

Understanding the ‘nice’ Command

The ‘nice’ command in Linux is used to run a program with modified scheduling priority. This is particularly useful when you want to allocate more or less CPU resources to a specific process.

How to Use the ‘nice’ Command

The basic syntax of the ‘nice’ command is as follows:

nice -n N command

Here, `N` represents the niceness level, ranging from -20 (highest priority) to 19 (lowest priority). By default, if you don’t specify the niceness level, the process is set to priority 10.

Example of ‘nice’ Command in Action

Let’s say you want to start a backup process with a lower priority. You could use:

nice -n 15 backup_script.sh

This command will start `backup_script.sh` with a lower CPU priority, allowing other critical tasks to take precedence.

Tips for Using ‘nice’

  • Use positive values for less critical tasks.
  • System administrators may use negative values for high-priority system processes.
  • Be cautious with setting very high or low priorities, as it might affect system stability.

Conclusion

The ‘nice’ command is a powerful tool in Linux for process priority management. By understanding its usage, you can effectively control how your system allocates resources to different processes.

Have you used the ‘nice’ command in your Linux experience? Share your thoughts and tips in the comments below!

How to Extract MP3 Audio from AVI or WebM Videos Using FFmpeg

~ tadmin

Introduction:

What You Will Need: a computer with FFmpeg installed. I’m providing you with a link with instructions on how to install FFmpeg on Linux, Windows or MacOS just in case if it’s not already installed.

Step-by-Step Guide:

  1. Open the Terminal or Command Prompt:
    – I think there is no need to explain you on how to open Terminal on macOS/Linux or Command Prompt on Windows if you visit my website. ;) I believe in your solid technical skills.
  2. Navigate to the Video File’s Directory:
    – Use `cd` command to navigate to the folder containing the video file you need.
  3. Run the FFmpeg Command:
    – We are presenting the command:

    ffmpeg -i sample.avi -q:a 0 -map a sample.mp3

    – The command options description goes below:
    – `-i sample.avi`: Specifies the input file.
    – `-q:a 0`: Sets the audio quality. 0 is the highest quality.
    – `-map a`: Maps only the audio tracks.
    – `sample.mp3`: The name of the output MP3 file.

  4. Execute the Command:
    – Do not forget to replace `sample.avi` and `sample.mp3` with file name and extensions you need.
    – You should see in the Terminal or Command Prompt as the command runs the example output as it shown below:
ffmpeg version 4.4.2-0ubuntu0.22.04.1 Copyright (c) 2000-2021 the FFmpeg developers
...
Stream mapping:
  Stream #0:1 -> #0:0 (opus (native) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
Output #0, mp3, to 'sample.mp3':
  Metadata:
    COMPATIBLE_BRANDS: iso6mp41
    MAJOR_BRAND     : dash
    MINOR_VERSION   : 0
    TSSE            : Lavf58.76.100
  Stream #0:0(eng): Audio: mp3, 48000 Hz, stereo, fltp (default)
    Metadata:
      DURATION        : 01:04:10.261000000
      encoder         : Lavc58.134.100 libmp3lame
size=  117368kB time=01:04:10.25 bitrate= 249.7kbits/s speed=69.9x    
video:0kB audio:117367kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000275%

What string set -Eeuo pipefail in shell script does mean?

~ tadmin

The string `set -Eeuo pipefail` is a command used in shell scripts, particularly in Bash, to modify the behavior of the script for better error handling and debugging. Here’s what each component means:

  1. `set`: This is a shell builtin command that sets or unsets shell options and positional parameters.
  2. `-E`: This option ensures that the `ERR` trap is inherited by shell functions, command substitutions, and commands executed in a subshell environment. This enhances the error handling capabilities of the script.
  3. `-e`: The `-e` option causes the script to exit immediately if any command it runs exits with a non-zero status (i.e., it encounters an error). This prevents errors from snowballing and makes it easier to pinpoint where a script is failing.
  4. `-u`: This option treats unset variables and parameters other than the special parameters “@” and “*” as an error when performing parameter expansion. If you try to use a variable that hasn’t been set, the script will exit, which helps catch typos and other mistakes.
  5. `-o pipefail`: The `-o` option sets various shell attributes. `pipefail` is an option that affects pipelines, which are sequences of commands connected by pipes (`|`). With `pipefail` enabled, the return value of a pipeline is the status of the last command to exit with a non-zero status, or zero if no command exited with a non-zero status. This makes it easier to detect failures in any part of a pipeline and is particularly useful for debugging and ensuring correct script behavior.

In summary, `set -Eeuo pipefail` is a common set of options used in shell scripts to make them more robust and less prone to common errors. It’s especially useful in scripts where correct error handling and script behavior are critical.

Converting Adobe Photoshop PSD Files with CMYK color scheme to RGB for best compatibility for GIMP in Linux

~ tadmin

Recently, I encountered a challenging issue while working with graphic files: I was unable to open files created in Adobe Photoshop (with a CMYK color scheme) using the GIMP editor on Linux. This compatibility problem is not uncommon for graphic designers and developers who work across different operating systems and software.

To overcome this hurdle, I discovered a practical solution that involved converting the Photoshop PSD files to a more universally compatible format. I achieved this by utilizing the powerful ImageMagick’s convert utility. The process is straightforward and efficient. Here’s how I did it:

  1. Open your terminal in Linux.
  2. Use the following command:
convert file.psd -colorspace rgb file.png

This command effectively changes the color space from CMYK (used in Photoshop) to RGB, which is more compatible with a wide range of software, including GIMP. The conversion to PNG format ensures that the file retains its quality and is readily accessible in GIMP.

It’s a simple yet effective workaround for those who frequently work with graphic files across different platforms. This method has significantly eased my workflow, and I hope it helps others facing similar challenges.

How to Exclude Files from Git Tracking Without Using .gitignore

Git
~ tadmin

How to Exclude Files from Git Tracking Without Using .gitignore

Introduction:

In certain scenarios, you might find yourself needing to stop Git from tracking changes in specific files without adding them to `.gitignore`. This situation often arises with local configuration files, which you do not wish to share with others but still need to keep in your repository. In this post, we’ll explore how to achieve this using the `git update-index` command.

The Command:

To tell Git to ignore changes to a specific file, you can use the `–assume-unchanged` flag with `git update-index`. This command is helpful when you want to keep a file in your repository but stop tracking any changes to it. Here’s how you do it:

git update-index --assume-unchanged path/to/file

Replace `path/to/file` with the actual path to the file you want to ignore. Once you run this command, Git will no longer track changes to the file.

Reverting Back:

If, at some point, you decide you want to start tracking changes to the file again, you can reverse the process. Use the `–no-assume-unchanged` flag to tell Git to resume tracking changes:

git update-index --no-assume-unchanged path/to/file

Again, replace `path/to/file` with the relevant file path.

Conclusion:

Using `git update-index` with the `–assume-unchanged` and `–no-assume-unchanged` flags provides a flexible way to manage file tracking in Git. It’s particularly useful for files like local configurations, where you need them in your repository but don’t want their changes to be constantly tracked. Remember, this is a local operation, and these changes are specific to your repository and do not impact other collaborators.

What is the difference between print in echo in PHP?

~ tadmin

In PHP, both `print` and `echo` are used for outputting data to the screen, but there are some differences between them:

  1. Type:
    • `echo` is a language construct, not really a function, so you can use it without parentheses. It can take multiple arguments.
    • `print` is also a construct but behaves more like a function and always returns 1. It can take only one argument.
  2. Return Value:
    • `echo` does not return any value. It just outputs the arguments.
    • `print` always returns 1, so it can be used in expressions.
  3. Performance: `echo` is marginally faster than `print` because it doesn’t have a return value to check. However, this speed difference is extremely negligible and usually not a factor in choosing one over the other.
  4. Usage in Expressions:
    • Since `echo` does not return a value, it cannot be used in expressions. For example, you cannot use `echo` within a complex expression or inside a function expecting a value.
    • `print`, with its return value of 1, can be used in expressions.
  5. Argument Handling:
    • `echo` can take multiple parameters, separated by commas, to output. For example, `echo $str1, $str2;`.
    • `print` can only take one argument. To output multiple strings, you would need to concatenate them first.

In practical terms, the differences are quite minor, and choosing between `echo` and `print` usually comes down to personal preference or specific needs in certain situations (like needing a return value or handling multiple arguments). In most cases, they are interchangeable.

Merging MP3 Files Seamlessly with FFmpeg

~ tadmin

It could be useful to merge a number of mp3 files into one using the following command:

ffmpeg -i "concat:file1.mp3|file2.mp3|file3.mp3|file4.mp3|file5.mp3|file6.mp3|file7.mp3|file8.mp3" -acodec copy _all_files_combined.mp3

The command above will combine mp3 files listed in -i option into one large audio file called _all_files_combined.mp3.

Check out video tutorial version located on my Youtube channel Linux Tutorials at: https://youtu.be/1YM_G7nPQo4