Linux whereis Command: File and Command Finding

Introduction

Welcome to TechCorp's System Administration department! As a new junior system administrator, your task is to master the whereis command. This powerful tool will help you locate binary, source, and manual page files for various commands in the Linux system. By the end of this lab, you'll be able to efficiently navigate the file system and locate critical system components.

Skills Graph

Understanding the Basics of 'whereis'

Your first task at TechCorp is to familiarize yourself with the whereis command. This command is used to locate the binary, source, and manual page files for a specified command.

Let's start by using whereis to find information about the ls command:

whereis ls

You should see output similar to this:

ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz

This output provides two pieces of information:

1. /usr/bin/ls: This is the location of the ls binary executable. When you type ls in the terminal, this is the actual program that runs.
2. /usr/share/man/man1/ls.1.gz: This is the location of the manual page for ls. Manual pages contain detailed information about how to use commands.

The whereis command searches for files in a restricted set of locations, including standard binary directories, library directories, and man page directories. This makes it faster than searching the entire file system.

If you're curious about what these paths mean:

• /usr/bin is a common location for user commands.
• /usr/share/man is where manual pages are typically stored.
• man1 indicates this is a user command manual (as opposed to system calls or library functions).
• The .gz extension means the file is compressed to save space.

Finding Binary Files

Your team lead asks you to locate the binary file for the grep command. The -b option of whereis is perfect for this task as it specifically searches for binary files.

Try the following command:

whereis -b grep

You might see output like this:

grep: /usr/bin/grep

This output shows the location of the grep binary file. Binary files are the executable programs that run when you type a command. In this case, when you use the grep command, you're actually running the program located at /usr/bin/grep.

Now, let's try to find the binary for a command that might not exist on the system. Use whereis -b to search for a fictional command called nonexistent:

whereis -b nonexistent

You should see:

nonexistent:

This empty output indicates that no binary was found for the nonexistent command. This is useful when you're unsure if a particular command is installed on your system.

Locating Manual Pages

Your next task is to find the manual pages for the ssh command. Manual pages are essential for understanding how to use various commands.

Use the -m option with whereis to locate manual pages:

whereis -m ssh

You might see output similar to this:

ssh: /usr/share/man/man1/ssh.1.gz

This output shows the location of the manual page for the ssh command. The .gz extension indicates that the file is compressed to save space.

To view the contents of a manual page, you would typically use the man command. However, as we haven't covered that command yet, let's just confirm that the file exists:

ls /usr/share/man/man1/ssh.1.gz

If the file exists, you'll see its name in the output. This confirms that the manual page is indeed present on your system.

Understanding manual page locations is crucial for system administrators. It allows you to verify if documentation is available for a particular command, which can be invaluable when you need to understand how to use a tool or troubleshoot issues.

Combining Options

As you become more comfortable with whereis, your team lead challenges you to find both the binary and the manual page for the python3 command in one go.

You can combine the -b and -m options to achieve this:

whereis -bm python3

You might see output like this:

python3: /usr/bin/python3 /usr/lib/python3 /etc/python3 /usr/share/python3 /usr/share/man/man1/python3.1.gz

This output provides a wealth of information:

• /usr/bin/python3: The location of the Python 3 binary (the executable program)
• /usr/lib/python3: The directory containing Python 3 libraries (reusable code used by Python programs)
• /etc/python3: A directory containing Python 3 configuration files
• /usr/share/python3: A directory containing shared Python 3 data
• /usr/share/man/man1/python3.1.gz: The location of the Python 3 manual page

This comprehensive view is particularly useful when you're working with complex software that has multiple components spread across the file system. It gives you a quick overview of where everything is located.

Exploring Source Files

For the final task, your team lead wants you to check if the source files for the bash shell are available on the system. Source files can be useful for understanding how a program works or for compiling custom versions.

Use the -s option to search for source files:

whereis -s bash

The output might be empty, as source files are not typically installed by default on most systems. If you do see output, it would indicate the location of bash source files on your system.

Now, let's combine all options to get a complete picture of the bash command:

whereis bash

This command without any options will show all available information about bash, which might look like this:

bash: /usr/bin/bash /etc/bash.bashrc /usr/share/man/man1/bash.1.gz

This output shows:

• /usr/bin/bash: The binary executable for bash
• /etc/bash.bashrc: A system-wide configuration file for bash
• /usr/share/man/man1/bash.1.gz: The manual page for bash

Understanding the locations of these files is crucial for system administration tasks. For example, if you need to modify the default behavior of bash for all users, you'd know to look in /etc/bash.bashrc.

Summary

In this lab, you've learned how to use the whereis command to locate binary, source, and manual page files for various commands in the Linux system. You've discovered how to:

1. Find basic information about commands
2. Locate binary files using the -b option
3. Find manual pages using the -m option
4. Combine options to get more comprehensive information
5. Search for source files using the -s option

These skills will prove invaluable in your role as a system administrator, allowing you to quickly locate important files and understand the structure of your Linux system.

Additional whereis command options not covered in this lab include:

• -u: Search for unusual entries (files that do not follow the usual naming pattern)
• -B: Change or restrict the places where whereis searches for binaries
• -M: Change or restrict the places where whereis searches for manual pages
• -S: Change or restrict the places where whereis searches for sources

As you continue your journey in system administration, remember that whereis is just one of many tools at your disposal. It's particularly useful for quick lookups, but for more comprehensive file searches, you might want to explore commands like find or locate in the future.