Question

Is there a ruby method to get process start time? Something like the following in shell:

 $ ps -p $$ -o lstart
 STARTED
 Thu Oct 18 11:49:22 2012

I was hoping to avoid parsing ps output. Also, I know how to parse /proc/self/status on linux to get at the info, but I was hoping for a more portable solution.

Update:
A portable way to do this is exactly what I wanted. I used sys/proctable and use the following line to get what I wanted:

ProcTable.ps($$).starttime

Thanks, Koen.

Update:
I was playing around a bit with this and found that it’s not as portable as I thought. On Darwin, a Time object is returned. On Linux, an integer is returned that corresponds to the number of jiffies since boot. Unfortunately, you need to use the sysconf syscall to get the number of ms/jiffy. This syscall is not available directly on ruby. I used the following to get the proc start time on Linux:

module LinuxCLib
  extend FFI::Library
  ffi_lib 'c'

  @@cg = FFI::ConstGenerator.new(nil, :required => true) do |gen|
    gen.include('unistd.h')
    gen.const(:_SC_CLK_TCK)
  end

  attach_function :sysconf, [:int], :long

  def self.hz
    self.sysconf(@@cg["_SC_CLK_TCK"].to_i)
  end
end

def self.get_proc_starttime
  proc_jiffies_since_boot_starttime = Sys::ProcTable.ps($$).starttime
  stat_lines = File.open("/proc/stat").readlines
  system_s_since_epoch_boottime = catch(:boottime) do
    stat_lines.each do |line|
      split_line = line.split
      throw :boottime, split_line[1].to_i if split_line[0] == "btime"
    end
    nil
  end
  proc_s_since_epoch_starttime = (
      proc_jiffies_since_boot_starttime/LinuxCLib::hz + system_s_since_epoch_boottime)
  Time.at(proc_s_since_epoch_starttime)
end

Answer 1

There is a gem that could do that: sys-proctable

It parses the files in /proc

Install the gem

gem install sys-proctable

Require the gem

require 'sys/proctable'
include Sys

For all processes

ProcTable.ps{ |p|
    puts p.comm
    puts p.starttime
}

For just a single process (like in your example)

p = ProcTable.ps($$)
puts p.inspect

And if you don’t want to use the gem, maybe you can extract the part of how they parse the /proc files from the source

EDIT:

I misread the part that you do know how to parse the /proc files. But maybe the gem still can be of use to you, making it portable and so.