How to Use the Command 'dtrace' (with examples)

The ‘dtrace’ command is a powerful tool used in Unix-based operating systems to trace and analyze system behavior and performance. It provides a simple interface to invoke the D language compiler, retrieve buffered trace data, and print traced data from the DTrace kernel facility. This article illustrates different use cases of the ‘dtrace’ command with examples.

Use case 1: Set target data model for a specific architecture

Code:

dtrace -arch arch_name

Motivation: The ‘-arch’ option allows you to specify the target data model for a specific architecture. This is useful when you want to trace and analyze the behavior of a particular architecture.

Explanation:

• ‘-arch’: Specify the target data model.
• ‘arch_name’: The name of the specific architecture.

Example output:

dtrace: invalid probe specifier arch_name

Use case 2: Claim anonymous tracing state and display the traced data

Code:

dtrace -a

Motivation: The ‘-a’ option allows you to claim anonymous tracing state and display the traced data. This is useful when you want to monitor system-wide activity without specifying any particular probes.

Explanation:

• ‘-a’: Claim anonymous tracing state.

Example output:

CPU     ID                    FUNCTION:NAME
  0      3                          :dt_printf:entry 
 ...

Use case 3: Set principal trace buffer size

Code:

dtrace -b 2g

Motivation: The ‘-b’ option allows you to set the principal trace buffer size. This is useful when you want to increase or decrease the size of the trace buffer according to your requirements.

Explanation:

• ‘-b’: Set the principal trace buffer size.
• ‘2g’: Specifies a trace buffer size of 2 gigabytes.

Example output: No output will be displayed for this command.

Use case 4: Compile the specified D Program source file

Code:

dtrace -s D_script

Motivation: The ‘-s’ option allows you to compile a specified D program source file. This is useful when you want to create custom D scripts to trace specific activities or events.

Explanation:

• ‘-s’: Compile the specified D program source file.
• ‘D_script’: The path to the D program source file.

Example output: No output will be displayed for this command.

Use case 5: Run the specified command and exit upon its completion

Code:

dtrace -c command

Motivation: The ‘-c’ option allows you to run a specified command and exit upon its completion. This is useful when you want to trace the behavior of a particular command or application.

Explanation:

• ‘-c’: Run the specified command.
• ‘command’: The command to be traced.

Example output:

dtrace: pid 12345 exited with status 0

Use case 6: Specify function name to trace or list

Code:

dtrace -f function

Motivation: The ‘-f’ option allows you to specify a function name to trace or list. This is useful when you want to trace a specific function or a list of functions.

Explanation:

• ‘-f’: Specify the function name to trace or list.
• ‘function’: The name of the function to be traced or listed.

Example output: No output will be displayed for this command.

Use case 7: Grab the specified process ID, cache its symbol table, and exit upon completion

Code:

dtrace -p pid

Motivation: The ‘-p’ option allows you to grab the specified process ID, cache its symbol table, and exit upon completion. This is useful when you want to trace the behavior of a specific process.

Explanation:

• ‘-p’: Grab the specified process ID.
• ‘pid’: The process ID of the target process.

Example output:

...

Use case 8: Combine different options for tracing functions in a process

Code:

dtrace -a -b buffer_size -f function -p pid

Motivation: Combining multiple options allows you to trace specific functions in a process while customizing the trace buffer size. This is useful when you want to have finer-grained control over the tracing process.

Explanation:

• ‘-a’: Claim anonymous tracing state.
• ‘-b’: Set the principal trace buffer size.
• ‘buffer_size’: The desired trace buffer size.
• ‘-f’: Specify the function name to trace or list.
• ‘function’: The name of the function to be traced or listed.
• ‘-p’: Grab the specified process ID.
• ‘pid’: The process ID of the target process.

Example output:

...

Conclusion:

The ‘dtrace’ command is a versatile tool for tracing and analyzing system behavior and performance. By understanding and utilizing the various options available, you can have precise control over the tracing process and gather valuable insights into the workings of your system. Experiment with these use cases and explore the full potential of the ‘dtrace’ command to enhance your system analysis capabilities.