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How to Write Suse Init Scripts

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Creating your own init scripts for Red Hat

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Essentially, here’s what we need to do:

  1. We put an executable script into /etc/init.d
  2. We follow the LSB standard to ensure:
    1. the script works with LSB-compliant distros.
    2. dependant services are started/shutdown in the proper order.
  3. use chkconfig to register the service.

This will create symlinks to our script in /etc/rc.d/rcX.d (where X is each runlevel we specified). One will be prefixed with an S, indicating a startup script, and another will be prefixed with K, for the kill or shutdown script.

The links will also be prefixed with numbers so that they can be sorted by the init system. This ensures they will start or shutdown in the proper order.

Script Requirements

Because of common convention, LSB standards, and the nuance of the chkconfig command, any init script we write will have to meet the following requirements:

  1. It must be executable on the command-line.
  2. It must support the following command-line options (actions):

    And optionally support the following actions:

  3. It must be placed into /etc/init.d
  4. It must contain 2 comments indicating the requested start/shutdown order and the description (these are specified by the chkconfig man page):

             # chkconfig: 345 20 70
             # description: My service that rocks \
             # socks
             

    There must be a space between the hash mark and the chkconfig/description field name.

    The chkconfig: field indicates 3 space-separated values:

    1. what runlevels you want the service to run at (no spaces; a single dash means “don’t start by default in any runlevels”)
    2. What order you’d like the service to start
    3. What order you’d like the service to shut down

    Note the orders are just requests, the LSB block (defined below) and other dependencies will dictate the final start/shutdown order.

    The description: field describes what the service is. It can span multiple lines if you add a backslash before the carriage return, as illustrated above.

  5. It must contain an LSB info block, with at least the Description, and Provides fields.
     

     

             ### BEGIN INIT INFO
             # Provides: myservice
             # Description: A service of mine that rocks socks 
             ### END INIT INFO
             

    The Description serves the same purpose as the chkconfig description (and they can be the same text).

    The Provides field lists all of the “boot facilities” that this service provides. This is used to set dependencies.

    Listing more than one can be useful if you are controlling multiple services, or replacing the standard init scripts (so you can specify cluster ocfs2 drbd, and any other drbd or ocfs2-dependant services will not need to be altered).

    However, it’s most likely you’ll want to also add the Required-Start and Required-Stop fields as well. These fields list “boot facilities” that your service requires during startup and shutdown.

             ### BEGIN INIT INFO
             # Provides: myservice
             # Description: A service of mine that rocks socks
             # Required-Start: nfs ntpd
             # Required-Stop: nfs
             ### END INIT INFO
             

    In this example, we’re telling chkconfig that our service mustn’t start before nfs and ntpd have started.

    There are also some “facilities” that are in-specific, and prefixed with a dollar sign. These include $network and $local_fs,
    which represent “the network is up” and “all local file systems are mounted”, respectively.

  6. The script must write a file with the same name as the service to /var/lock/subsys.

    I’m having trouble finding concrete explanation as to why this is a requirement. All I’ve been able to find is a Red Hat “tips and tricks” entry (scroll down).

    So I’m not sure if this is a hard requirement, a Red Hat requirement, or what, but it was part of Coraid’s init script shell, and I don’t see any harm, so I’ve included it here.

Some other things to keep in mind:

 

Code Skeleton

The LSB specs call for a “library” of sorts that contains useful functions that help simplify init script creation. Most Linux distributions (or, at least the ones I’m dealing with here) include a variant, installed at /etc/init.d/functions.

At some point I’d like to emulate that entire library in python (or see if someone else already has), but there’s one bit in there that I really like, which would make these python-based init scripts look much more authentic.

When you send a command via /sbin/service servicename, or call the script using /etc/init.d/servicename, most distributions print a little colorized [ OK ] once a task has completed successfully (or [FAILED] upon failure). I think its worth the trouble to emulate that idea.

This is accomplished with a couple of new functions, named after shell functions I found in /etc/init.d/functions (on a RHEL5 machine).

 


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Last modified: March 12, 2019