How to implement a Linux daemon in bash that can be start/stop by `sudo service`?

[Robert Heller]

At Sun, 11 Feb 2018 18:16:02 -0600 "Ubuntu user technical support,  not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> Hi,
> 
> There are a lot of resource about creating Linux daemon. But I am not
> sure which is one is the most correct and provide the essential things
> for a Linux daemon in bash that can be start/stop by `sudo service`?
> Would anybody point me the best resource to learn how to create such a
> daemon? Thanks.

There are actually two parts to this.

One part is the daemon itself.  Nomially, this is just a program that does 
something in an endless loop, eg it could be waiting for network and/or UNIX 
socket connections and processing them.  Or it could be doing some periodic 
task.   In any case, it needs to do this "quietly" -- eg without doing I/O to 
std in, out, or err (unless stderr is your log file).  There are some "rules" 
and tips about closing off stdin/stdout/stderr and "fading" into the 
background (disassociating itself from a controlling terminal and becoming its 
own process group head, etc.).

The second part has to do with what flavor of /bin/init is in use: SysV,
Upstart, or SystemD. Each of these has a different mechanism for dealing with
getting deamons started or stopped during boot up and shutdown. There are man
pages for that.

One of the best resources is to just pick a favored deamon see how someone 
else did it.  Find the source package and, to misquote Obiwan Kenobe, "Use the 
Source, Luke"... :-)  In many cases you can copy someone else's start/stop 
script (or whatever) and make a small number of changes and there you are.


> 

-- 
Robert Heller             -- 978-544-6933
Deepwoods Software        -- Custom Software Services
http://www.deepsoft.com/  -- Linux Administration Services
heller at deepsoft.com       -- Webhosting Services