Network Information Service Overview NIS

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Tracing Linux Processes Dr. B. Thangaraju
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Agenda

• Execution Trace
• Different Ways of Tracing
• proc file system
• Linux Trace Toolkit (LTT)

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Introduction

• Debuggers (gdb, kdb and kgdb) are used for
  finding and correcting program errors.
• Debuggers offers little help in finding any sort
  of problem that involves an applications
  interaction with other applications or with the
  kernel.
• Execution Trace - tracing execution of processes
  over a certain period of time.

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Process Tracing

• A simplest form of tracing involves monitoring
  the interactions between a single application and
  the Linux kernel.
• The main tool for tracing a single process is
  strace.
• strace uses the ptrace( ) system call to
  intercept all system calls made by an
  application.
• It can extract all the system call information
  and present the result in text form.

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Proc File System

• proc file system is not stored on the hard disk.
• It is a virtual filesystem that the kernel
  creates in memory.
• It is used as an interface to the kernel data
  structures.
• /proc maintains highly dynamic data on the state
  of the system.
• mount
• none on /proc type proc (rw)

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iostat

• Report Central Processing Unit (CPU) statistics
  and input/output statistics for devices and
  partitions.
• The iostat command generates two types of
  reports, the CPU Utilization report and the
  Device Utilization report.
• Example
• iostat -d -x 1 1 (for device utilization report)
• iostat -c 1 1 (for CPU utilization report)

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sar

• Collect, Report, or save system activity
  information.
• sar A
• It gives statistics about
• Total number of read/write requests per second
  issued to the physical disk.
• Number of active/inactive (dirty) pages in memory
• Number of processes created per second
• Total number of packets received/transmitted per
  second
• Number of TCP/UDP/RAW sockets currently in use
• Run queue length (number of processes waiting for
  run time)
• Memory statistics
• etc.,

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Linux Trace Toolkit

• strace will trace only one process and present
  the result in text form.
• To trace many processes in a given period of
  time, Linux Trace Toolkit (LTT) is a better
  choice.
• LTT is distributed as free software under GPL.
• Applying an LTT-patch to the corresponding kernel
  enable us to create a module to trace many events.

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Linux Trace Toolkit

• LTT is useful for systems administrators for
  analyzing the performance of the system.
• It is useful for programmers for getting details
  of the interaction between kernel and user-level
  applications.
• For embedded/real-time programmers for getting
  information about real and non-real-time tasks
  behavior.

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Trace Points

• File Systems
• System call
• Trap
• Interrupt
• Scheduling change
• Timer
• Process
• Memory
• IPC
• Socket

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LTT -components

• The trace toolkit provides a daemon, which will
  capture the events and write it to disk.
• To achieve this, LTTs operation is subdivided
  into four software components
• Kernel Instrumentation
• Tracing Subsystem
• Trace Daemon
• Visualization Tool

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Data Analysis

• The provided trace visualizer is used to analyze
  the tracing data in three different forms
• event graph
• process analysis
• raw event descriptions

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Real and non-real time
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References

• http//www.opersys.com/LTT/
• Examining Process Information, Linux For You,
  January 2004, pp. 84-87.
• Mastering Linux Debugging Techniques
  (http//www-128.ibm.com/developerworks/linux/libra
  ry/l-debug/?dwzonelinux).
• Debugging Tools, Chapter 11, Building Embedded
  Linux Systems by Karim Yaghmour
• Process Tracing with the Linux Trace Toolkit
  (http//www.opersys.com/ftp/pub/LTT/Documentation/
  sys-admin-mag-ltt-2004-11.pdf).
• Debugging code with strace (http//www.redhat.com/
  magazine/010aug05/features/strace/)

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• Thank You
• balat.raju _at_ wipro.com