Strip Command in Linux with Examples

In the world of Linux system administration and software development, optimizing file sizes and enhancing security are crucial tasks. One powerful tool that aids in these endeavors is the strip command. This article delves deep into the strip command, exploring its functionality, usage, and practical applications in Linux environments.

What is the Strip Command?

The strip command is a utility found in Unix-like operating systems, including Linux. Its primary function is to remove symbols and debugging information from object files, executables, and shared libraries. Developed as part of the GNU Binutils package, strip has been an essential tool for system administrators and developers for decades.

Originally conceived in the early days of Unix, the strip command has evolved to become a versatile tool for optimizing binaries. It operates by analyzing the structure of object files and selectively removing non-essential information, thereby reducing file size and potentially improving load times.

Why Use the Strip Command?

The strip command offers several benefits that make it an indispensable tool in the Linux ecosystem. Let’s explore the primary reasons for using this powerful utility:

File Size Reduction

One of the most significant advantages of using the strip command is its ability to reduce file sizes. When compiling programs, especially in debug mode, the resulting binaries often contain a wealth of debugging information and symbols. While this information is crucial during development, it’s typically unnecessary for end-users and production environments.

By removing these symbols and debugging details, strip can significantly decrease the size of executables and shared libraries. This reduction in file size can lead to several benefits:

• Reduced disk space usage
• Faster file transfers and downloads
• Improved system performance, especially on resource-constrained devices

Security Enhancement

Security is a paramount concern in software development and deployment. The strip command plays a role in enhancing the security of binaries by making reverse engineering more challenging. When symbols and debugging information are removed, it becomes more difficult for potential attackers to analyze and understand the internal workings of a program.

This added layer of obscurity can deter casual attempts at reverse engineering and provide an extra barrier against malicious actors seeking to exploit vulnerabilities in the software.

Performance Improvement

Stripped binaries often exhibit improved performance characteristics compared to their unstripped counterparts. This performance boost is primarily due to two factors:

1. Reduced file size leads to faster loading times, as less data needs to be read from disk into memory.
2. The absence of debugging information means the system doesn’t need to process this extra data during program execution.

While the performance gains may be minimal for small programs, they can become significant for larger applications or systems with limited resources.

Basic Syntax and Options of Strip Command

To effectively use the strip command, it’s essential to understand its basic syntax and common options. The general syntax for the strip command is as follows:

strip [options] objfile

Here, objfile represents the file or files you want to strip. The strip command supports various options that allow you to customize its behavior. Let’s explore some of the most commonly used options:

-s or –strip-all

This option removes all symbols from the object file. It’s the most aggressive stripping option and results in the smallest file size. However, it also removes information that might be necessary for debugging or linking.

strip -s myprogram

–strip-debug

This option removes debugging symbols and sections from the object file while preserving other symbols. It’s a good compromise between file size reduction and maintaining some useful information.

strip --strip-debug myprogram

–strip-unneeded

This option removes all symbols that are not needed for relocations. It’s less aggressive than --strip-all but more thorough than --strip-debug.

strip --strip-unneeded myprogram

Using Strip Command with Examples

To better understand how the strip command works in practice, let’s walk through some real-world examples. These examples will demonstrate the impact of stripping on file size and provide insights into different stripping techniques.

Example 1: Basic Stripping

Let’s start with a simple C program and observe how stripping affects its size. First, we’ll create a basic “Hello, World!” program:

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

Now, let’s compile this program and examine its size:

gcc -o hello hello.c
ls -l hello

You might see output similar to this:

-rwxr-xr-x 1 user user 16696 Oct 10 10:00 hello

Now, let’s strip the binary and check its size again:

strip -s hello
ls -l hello

The output might now look like this:

-rwxr-xr-x 1 user user 14528 Oct 10 10:01 hello

As you can see, the file size has been reduced significantly after stripping.

Example 2: Selective Stripping

Sometimes, you may want to remove only debugging symbols while preserving other information. This can be achieved using the --strip-debug option. Let’s compile our program with debugging symbols and then selectively strip it:

gcc -g -o hello_debug hello.c
ls -l hello_debug
strip --strip-debug hello_debug
ls -l hello_debug

You’ll notice that the file size decreases, but not as dramatically as with -s. This is because we’ve only removed debugging information while preserving other symbols.

Example 3: Output to a New File

In some cases, you might want to preserve the original binary while creating a stripped version. The strip command allows you to specify an output file using the -o option:

gcc -o hello hello.c
strip -o hello_stripped hello
ls -l hello hello_stripped

This command creates a new file called hello_stripped that contains the stripped version of the original hello binary. This approach is useful when you need to maintain both debug and release versions of your software.

Advanced Usage of Strip Command

While the basic usage of strip is straightforward, the command offers advanced features for more specific use cases. Let’s explore some of these advanced techniques:

Keeping Specific Symbols

In some situations, you may want to strip most symbols but retain a few specific ones. The -K option allows you to keep named symbols:

strip -K symbolname myprogram

This command will strip all symbols except for symbolname. You can use this option multiple times to keep several symbols:

strip -K symbol1 -K symbol2 myprogram

Removing Specific Sections

The strip command also allows you to remove specific sections from the binary using the -R option. This can be useful for fine-tuning the stripping process:

strip -R .comment myprogram

This command removes the .comment section from the binary. You can use objdump -h to view the sections in a binary before deciding which ones to remove.

Comparison with Other Tools and Methods

While the strip command is a powerful tool for reducing binary sizes, it’s not the only method available. Let’s compare it with some alternatives:

GCC’s -s Option

GCC (GNU Compiler Collection) provides a -s option that strips symbols during the compilation process:

gcc -s -o myprogram myprogram.c

While this approach is convenient, it offers less flexibility compared to using the strip command separately. The strip command allows for more fine-grained control over which symbols and sections to remove.

UPX (Ultimate Packer for eXecutables)

UPX is a compression tool for executables that can significantly reduce file sizes. While it’s very effective, it works differently from strip:

• UPX compresses the entire executable, while strip removes specific information.
• UPX-packed executables decompress at runtime, which can impact startup time.
• Strip is generally considered safer and more widely compatible.