A tool to determine what a process is doing
Ruby Perl
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A tool to determine what I/O a Linux process is doing by interpreting the output of strace. When attaching to an existing process it also uses lsof to determine which file handles are currently open.

The codebase also includes an Apache module (Apache2::Procview) that can be used to trigger a trace on individual web requests.

It is a linux-only GEM as it requires the following Linux programs:

  • lsof at version 4.82 or higher
  • strace at version 4.5.19


This tool is published to RubyGems so you can simply do:

gem install procview


This tool can be used in one of three ways:

  • To analyze a currently running process in realtime (using the -p option)
  • To run a command while performing the analysis (by supplying a command)
  • To post-process trace files produced by Apache2::Procview or a raw strace

To get a summary of the options type procview -?

Manual strace

Create a trace file for later analysis using the following command:

strace -Tfq -e desc,network,file,process -o trace.file [either -p or command+args]


The output of procview lists the I/O endpoints and the total time recorded against them in four categories: read, write, wait and other. The read and write times mean the obvious. The wait time is time spent in calls like poll and select. Other time is any time that doesn't belong to that. For example the duration of a chdir('/directory') call accumulates into the 'other' category for the '/directory' path.

Summarization Options

The summary options all create 'buckets' for the accumulation of statistics. Each bucket has a patternset that is used to match against the name associated with each I/O. The statistics are accumulated in the first bucket found. The sequence of buckets is as they appear on the command line.

  • -F: Summarize all disk file activity in one line.
  • -s: Summarize all activity to the LSB 'system' directories
  • --sum: Create a bucket using a regular expression. The bucket can optionally be named by included name= prior to the regular expression. The RE syntax is that of Ruby.


There are certain calls which cannot be allocated against any IO handles. Examples would be stat() or close() calls for non-existant handles. These are accumulated into a special bucket called 'dregs' and displayed as Unassigned in the output. This time is accounted for in the call level summary, but cannot be placed into an I/O bucket.


Optionally the breakdown of time per call can be displayed. If this total doesn't match the breakdown by name plus the 'unassigned' time then that's a bug and should be reported!

Problems and Known Issues

There are many potential calls produced by strace and procview is not guaranteed to handle them all. In such cases the utility will print an error message to stderr and continue. Record the output and create an Issue on GitHub.