What is nm Linux command?

The Linux nm command is a powerful tool used to display symbol information from object files. It helps users examine binary files and libraries to understand the symbols present within them. This command is commonly used in debugging and analyzing compiled programs.

nm Syntax:

nm [options] [object-file]

nm Options:

Option	Description
-A, —print-file-name	Print the name of the file before its symbols.
-C, —demangle	Decode (demangle) low-level symbol names into user-level names.
-D, —dynamic	Display dynamic symbols instead of normal symbols.
-f , —format=	Specify the output format for the symbols.
-l, —line-numbers	Show line numbers where symbols were found.
-n, —numeric-sort	Sort symbols numerically.
-p, —no-sort	Do not sort the symbols.
-t , —radix-sort=	Sort symbols on the specified column.
-S, —print-size	Show the size of the symbols.
-u, —undefined-only	Show only undefined symbols.

Parameters:

Parameter	Description
object-file	The object file to examine for symbols.

nm Command Usage Examples:

Display Symbols in a Binary File

nm /usr/bin/ls

Displays the symbols (functions and variables) in the binary file “ls”.

Display Only External Symbols

nm -g /usr/bin/ls

Displays only the external symbols in the binary file “ls”.

Display Symbols in a Shared Library

nm /usr/lib/libc.so

Displays the symbols in the shared library “libc.so”.

Display Demangled C++ Symbols

nm -C /usr/bin/program

Displays demangled C++ symbols in the binary file “program”.

Filter Symbols by Name

nm /usr/bin/program | grep my_function

Filters and displays symbols with the name “my_function” in the binary file “program”.

Tip

When using the nm command in Linux, make sure to provide the appropriate options and arguments to get the desired output. Understanding the different options and flags available with nm can help you extract valuable information about object files and binaries.

How do I use nm in Linux?

To use the nm command in bash, execute the following command:

nm /path/to/your/file

What are the common options used with nm in Linux?

To display the symbol table of an object file using nm in Linux, you can use the -S option. Here’s an example:

nm -S /path/to/your/file

How can I filter the output of nm in Linux?

You can filter the output of nm in Linux by using grep to search for specific symbols. For example:

nm /path/to/your/file | grep main

How do I show only undefined symbols with nm in Linux?

To display only undefined symbols using nm in Linux, you can use the -u option. Here’s how you can do it:

nm -u /path/to/your/file

How can I demangle C++ symbol names with nm in Linux?

To demangle C++ symbol names when using nm in Linux, you can use the --demangle option. Here’s an example:

nm --demangle /path/to/your/file

How do I display the size of symbols with nm in Linux?

You can display the size of symbols using nm in Linux by using the -S and -l options together. Here’s how you can do it:

nm -S -l /path/to/your/file

How can I get the full path for symbols with nm in Linux?

To show the full path for each symbol when using nm in Linux, you can use the -A option. Here’s an example:

nm -A /path/to/your/file

How do I list only external defined symbols with nm in Linux?

To list only external defined symbols using nm in Linux, you can use the -g and -D options together. Here’s an example:

nm -g -D /path/to/your/file

Applications of the nm command

• Display symbols from object files
• List shared library dependencies
• Show the type of symbols (e.g., function, object, etc.)
• Check for the presence of specific symbols in binary files
• Identify undefined symbols in an object file