Module: Daemons

Module | Daemons
In: | lib/daemons/application.rb lib/daemons/application_group.rb lib/daemons/cmdline.rb lib/daemons/controller.rb lib/daemons/exceptions.rb lib/daemons/monitor.rb lib/daemons/pid.rb lib/daemons/pidfile.rb lib/daemons/pidmem.rb lib/daemons.rb

All functions and classes that Daemons provides reside in this module.

Daemons is normally invoked by one of the following four ways:

1. `Daemons.run(script, options)`: This is used in wrapper-scripts that are supposed to control other ruby scripts or external applications. Control is completely passed to the daemons library. Such wrapper script need to be invoked with command line options like ‘start’ or ‘stop’ to do anything useful.
2. `Daemons.run_proc(app_name, options) { (…) }`: This is used in wrapper-scripts that are supposed to control a proc. Control is completely passed to the daemons library. Such wrapper script need to be invoked with command line options like ‘start’ or ‘stop’ to do anything useful.
3. `Daemons.call(options) { block }`: Execute the block in a new daemon. `Daemons.call` will return immediately after spawning the daemon with the new Application object as a return value.
4. `Daemons.daemonize(options)`: Daemonize the currently runnig process, i.e. the calling process will become a daemon.

## What does daemons internally do with my daemons?

or: | why do my daemons crash when they try to open a file?
or: | why can I not see any output from the daemon on the console (when using for example `puts`)?

From a technical aspect of view, daemons does the following when creating a daemon:

1. Forks a child (and exits the parent process, if needed)
2. Becomes a session leader (which detaches the program from the controlling terminal).
3. Forks another child process and exits first child. This prevents the potential of acquiring a controlling terminal.
4. Changes the current working directory to "/".
5. Clears the file creation mask (sets `umask` to 0000).
6. Closes file descriptors (reopens `STDOUT` and `STDERR` to point to a logfile if possible).

So what does this mean for your daemons:

- the current directory is ’/’
- you cannot receive any input from the console (for example no `gets`)
- you cannot output anything from the daemons with `puts`/`print` unless a logfile is used

## How do PidFiles work? Where are they stored?

Also, you are maybe interested in reading the documentation for the class PidFile. There you can find out about how Daemons works internally and how and where the so called PidFiles are stored.

### Methods

call controller daemonize group run run_proc

### Classes and Modules

Class Daemons::Application
Class Daemons::ApplicationGroup
Class Daemons::CmdException
Class Daemons::Controller
Class Daemons::Error
Class Daemons::Exception
Class Daemons::Monitor
Class Daemons::Optparse
Class Daemons::Pid
Class Daemons::PidFile
Class Daemons::PidMem
Class Daemons::RuntimeException
Class Daemons::SystemError

### Constants

VERSION | = | "1.0.10"

### Public Instance methods

call(options = {}, &block)

Execute the block in a new daemon. `Daemons.call` will return immediately after spawning the daemon with the new Application object as a return value.

`options`: | A hash that may contain one or more of the options listed below
`block`: | The block to call in the daemon.

### Options:

`:multiple`: | Specifies whether multiple instances of the same script are allowed to run at the same time
`:ontop`: | When given, stay on top, i.e. do not daemonize the application
`:backtrace`: | Write a backtrace of the last exceptions to the file ’[app_name].log’ in the pid-file directory if the application exits due to an uncaught exception

### Example:

      options = {
        :backtrace  => true,
        :monitor    => true,
        :ontop      => true
      }

      Daemons.call(options) begin
        # Server loop:
        loop {
          conn = accept_conn()
          serve(conn)
        }
      end

controller()

Return the internal Controller instance.

daemonize(options = {})

Daemonize the currently runnig process, i.e. the calling process will become a daemon.

`options`: | A hash that may contain one or more of the options listed below

### Options:

`:ontop`: | When given, stay on top, i.e. do not daemonize the application
`:backtrace`: | Write a backtrace of the last exceptions to the file ’[app_name].log’ in the pid-file directory if the application exits due to an uncaught exception

### Example:

      options = {
        :backtrace  => true,
        :ontop      => true
      }

      Daemons.daemonize(options)

      # Server loop:
      loop {
        conn = accept_conn()
        serve(conn)
      }

group()

Return the internal ApplicationGroup instance.

run(script, options = {})

Passes control to Daemons. This is used in wrapper-scripts that are supposed to control other ruby scripts or external applications. Control is completely passed to the daemons library. Such wrapper script should be invoked with command line options like ‘start’ or ‘stop’ to do anything useful.

`script`: | This is the path to the script that should be run as a daemon. Please note that Daemons runs this script with `load <script>`. Also note that Daemons cannot detect the directory in which the controlling script resides, so this has to be either an absolute path or you have to run the controlling script from the appropriate directory.
`options`: | A hash that may contain one or more of the options listed below

### Options:

`:app_name`: | The name of the application. This will be used to contruct the name of the pid files and log files. Defaults to the basename of the script.
`:ARGV`: | An array of strings containing parameters and switches for Daemons. This includes both parameters for Daemons itself and the controlled scripted. These are assumed to be separated by an array element ’—’, .e.g. [‘start’, ‘f’, ’—’, ‘param1_for_script’, ‘param2_for_script’]. If not given, ARGV (the parameters given to the Ruby process) will be used.
`:dir_mode`: | Either `:script` (the directory for writing the pid files to given by `:dir` is interpreted relative to the script location given by `script`) or `:normal` (the directory given by `:dir` is interpreted as a (absolute or relative) path) or `:system` (`/var/run` is used as the pid file directory)
`:dir`: | Used in combination with `:dir_mode` (description above)
`:multiple`: | Specifies whether multiple instances of the same script are allowed to run at the same time
`:ontop`: | When given (i.e. set to true), stay on top, i.e. do not daemonize the application (but the pid-file and other things are written as usual)
`:mode`: | `:load` Load the script with `Kernel.load`; `:exec` Execute the script file with `Kernel.exec`
`:backtrace`: | Write a backtrace of the last exceptions to the file ’[app_name].log’ in the pid-file directory if the application exits due to an uncaught exception
`:monitor`: | Monitor the programs and restart crashed instances
`:log_output`: | When given (i.e. set to true), redirect both STDOUT and STDERR to a logfile named ’[app_name].output’ in the pid-file directory
`:keep_pid_files`: | When given do not delete lingering pid-files (files for which the process is no longer running).
`:hard_exit`: | When given use exit! to end a daemons instead of exit (this will for example not call at_exit handlers).

### Example:

      options = {
        :app_name   => "my_app",
        :ARGV       => ['start', '-f', '--', 'param_for_myscript']
        :dir_mode   => :script,
        :dir        => 'pids',
        :multiple   => true,
        :ontop      => true,
        :mode       => :exec,
        :backtrace  => true,
        :monitor    => true
      }

      Daemons.run(File.join(File.dirname(__FILE__), 'myscript.rb'), options)

run_proc(app_name, options = {}, &block)

Passes control to Daemons. This function does the same as Daemons.run except that not a script but a proc will be run as a daemon while this script provides command line options like ‘start’ or ‘stop’ and the whole pid-file management to control the proc.

`app_name`: | The name of the application. This will be used to contruct the name of the pid files and log files. Defaults to the basename of the script.
`options`: | A hash that may contain one or more of the options listed in the documentation for Daemons.run

A block must be given to this function. The block will be used as the :proc entry in the options hash.

### Example:

      Daemons.run_proc('myproc.rb') do
        loop do
          accept_connection()
          read_request()
          send_response()
          close_connection()
        end
      end

[Validate]