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This may have more to do with detecting operating systems, but I specifically need the init system currently in use on the system.

Fedora 15 now uses systemd, Ubuntu uses Upstart, while others use variations of System V.

I have an application that I am writing to be a cross-platform daemon. The init scripts are being dynamically generated based on parameters that can be passed in on configure.

What I'd like to do is only generate the script for the particular init system that they are using. This way the install script can be run reasonably without parameters as root and the daemon can be "installed" automagically.

This is what I've come up with:

  • Search for systemd, upstart, etc in /bin
  • Compare /proc/1/comm to the systemd, upstart, etc
  • Ask the user

What would be the best cross/platform way of doing this?

Kind of related, Can I depend on bash to be on the majority of *nix or is it distribution/OS dependent?

Target platforms:

  • Mac OS
  • Linux (all distributions)
  • BSD (all versions)
  • Solaris, Minix, and other *nix
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Just to add my two cents, bash isn't installed by default on FreeBSD. – Chinmay Kanchi Aug 7 '11 at 3:27

2 Answers

up vote 3 down vote accepted

For the second question, the answer is no and you should have a look at Resources for portable shell programming.

As for the first part - first of all, you certainly have to be careful. I'd say perform several tests to make sure - because the fact that someone does have systemd (for ex.) installed, does not mean it is actually used as the default init. Also, looking at /proc/1/comm can be misleading, because some installations of various init programs can automatically make /sbin/init a symlink hardlink or even a renamed version of their main program.

Maybe the most useful thing could be to look at the init scripts type - because those are what you'll actually be creating, no matter what runs them.

As a side note, you might also have a look at OpenRC which aims to provide a structure of init scripts that is compatible with both Linux and BSD systems.

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What do you mean by "look at the init scripts type"? Often different init systems put their scripts/files somewhere besides /etc/init, like systemd puts them in /etc/systemd. If I was to have my script grok these, it could take a little while. Oh, and thanks for the link BTW for portable shell programming. – tjameson Aug 7 '11 at 0:23
I meant to say that some init implementations can be adjusted to make use of different init scripts' types and locations (like /etc/rc.d/ or /etc/init.d/). And you should properly adjust your program at installation time to utilize the structure that is used on the given system. – rozcietrzewiacz Aug 7 '11 at 1:08
So, are you saying that there is no reliable way to detect the init system programmatically? Having the user pass in parameters is certainly safer, but if the user does not pass anything in, what would be the best way to guess? – tjameson Aug 7 '11 at 1:27
I've no idea what will be the best way for your program - it all depends on what systems will the program end up running. I haven't used too many distributions, but I was trying to share my observations to help you. It is a tough piece of scripting you are about to try and I tried to give you some view on the field - you must come to the final answer yourself or wait for more hints. – rozcietrzewiacz Aug 7 '11 at 1:40
Cool, thanks for all your help. You definitely have pointed me in the right direction. – tjameson Aug 7 '11 at 1:47
up vote 2 down vote

  1. This is what distro-specific packages are for. There is much more to installing software properly than just detecting the init system. Many distros use SysVinit but not all of them write their init scripts the same way. The proper way to solve this is to include all the different variants and then bundle it up using spec files with distro-specific dependency names for rpm distros, deb files for apt based systems, etc. Almost all distros have some sort of package specification you can write that includes dependencies, scripts, init scripts, etc. Don't re-invent the wheel here.

  2. No. Which brings us back to 1. If you need bash it should be a dependency. You can specify this check as part of your configure scripts, but it should also be in the package descriptions.

Edit: Use flags on your configure script such as --with upstart or --without sysvinit. Pick a sane default, then the scripts that package your software for other distros can choose to run this with other options.

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Hmph, so it's looking like I can't have a 'one script to rule them all' solution. I've seen a lot of programs that use autoconf or similar to handle cross-platform stuff, but it doesn't seem like it's the right tool for my application. Is maintaining versions for each platform really the only reliable solution? – tjameson Aug 7 '11 at 7:27
One installation script to rule them all is a BadIdea. It ends up failing more places than it works. Autoconf is good as far as it goes. Work hard on keeping your end of the software as generic as possible and include alternate init scripts in your package. Setup package specifications for several major distros. If your software is good you can get other people to help you out with getting it packaged for other systems. – Caleb Aug 7 '11 at 7:34
@tjameson: I just realized I forgot the most important bit. This sort of thing is usually done with switches passed to the configure script. Each distro's build/package routines can call different switches, and your configure/make only has to know what switch it was passed, not detect all the possible software configurations. – Caleb Aug 7 '11 at 7:38
@Caleb- Yeah, I already have that logic in there, but good catch. I was hoping for a way to sniff the init system to use an intelligent guess than a sane default. – tjameson Aug 7 '11 at 7:40

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