readelf command in Linux with Examples
When we compile source code, an object file is generated of the program and with the help of linker, this object files gets converted to a binary file which, only the machine can understand. This kind of file follows some structures one of which is ELF(Executable and Linkable Format). And to get the information of these ELF files ‘readelf’ command is used.
Here, we will explore how to effectively use the ‘readelf' command to work with ELF files in Linux.
What is the ‘readelf’ Command?
‘readelf’ is a command-line tool that allows you to view detailed information about ELF files. ELF is a common file format for executables, object code, shared libraries, and core dumps in Unix-based systems. The ‘readelf’ command provides insights into the structure of these files, displaying headers, sections, symbols, and other critical information needed for understanding and debugging ELF binaries.
Syntax:
readelf [options] elf_file
where,
- ‘[options]’: Various command-line options that determine the output and level of detail displayed by ‘readelf’.
- ‘elf_file’: The ELF file to be analyzed.
Common Options for the ‘readelf’ Command
The ‘readelf’ command offers a variety of options to explore different aspects of ELF files. Here are some commonly used options:
| Option | Description |
|---|---|
-h |
Displays the ELF header, which contains key information about the file’s structure. |
-S |
Lists all the sections in the ELF file, showing details about each section’s address, size, type, and attributes. |
-l |
Displays the program headers, which describe the segments used at runtime. |
-s |
Shows the symbol table, including symbols defined and used in the ELF file. |
-r |
Displays the relocation sections, showing how the binary modifies itself at runtime. |
-d |
Displays the dynamic section, which contains information about dynamic linking. |
-n |
Displays core notes, which include metadata such as the build ID. |
-V |
Displays the version information of the ‘readelf’ command. |
--help |
Provides a help message listing all available options for the ‘readelf’ command. |
Working with readelf command and ELF files
Let’s look into the practical examples of how to use the ‘readelf’ command to extract information from ELF files.
1. To display help of readelf command.
$readelf
This displays the help section of the command containing all its parameters and their uses.
2. To check whether a file is ELF file.
$file elf_file
If it prints ELF in the output then the file is an ELF file. Note: In our case, file name is ‘elf_file’.
3. To generate a elf file using gcc compiler.
$gcc filename.c -o elf_file
The above command will generate an executable elffile. Note: In our case, the name of file is filename.c and the name of elf file is ‘elf_file’.
4. To display file headers of a elf file.
$readelf -h elf_file
This will display the top-level headers of the elf file.
Note: In our case, the name of elf file is ‘elf_file’.
5. To display information about the different sections of the process’ address space.
$readelf -S elf_file
This will display the different sections of the process’ address space.
Note: In our case, the name of elf file is ‘elf_file’.
6. To display symbols table.
$readelf -s elf_file
This will display the symbols table of the file.
Note: In our case, the name of elf file is ‘elf_file’.
7. To display core notes.
$readelf -n elf_files
This will display the core notes related to the file.
Note: In our case, the name of elf file is ‘elf_file’.
8. To display relocation section.
$readelf -r elf_file
This will display the relocks(if present).
Note: In our case, the name of elf file is ‘elf_file’.
9. To display the dynamic section.
$readelf -d elf_file
This will display the dynamic section of the file.
Note: In our case, the name of elf file is elf_file.
10. To get the version of the readelf command.
$readelf -v
This will display the version information of the ‘readelf’ command.
Conclusion
The ‘readelf’ command is a powerful tool for working with ELF files in Linux, providing deep insights into the structure and contents of executable binaries. Mastering ‘readelf’ is an essential skill for a developer debugging an application, a security professional conducting binary analysis, or a system administrator verifying software configurations.
