[chef] Re: Re: Re: Re: How to detect user does exist?

[Matthew Moretti < >]

Documentation for Ruby’s ‘Etc’ module is here. You could use it in place of your shell guard like so:

group "sensu" do
  action :modify
  members "vagrant"
  append true
  only_if { Etc.getpwnam('vagrant') rescue false }
end

The “rescue” is required because .getpwnam raises an exception if the user can’t be found. If you want to avoid the sin of in-line “rescue”, this is a bit better:

group "sensu" do
  action :modify
  members "vagrant"
  append true
  only_if do
    begin
      Etc.getpwnam('vagrant')
    rescue ArgumentError
      false
    end
  end
end

I’ll be honest, I prefer the “getent passwd vagrant” solution more. It’s easier to read, and isn’t any less efficient or more platform dependent than the Ruby solution as far as I can tell.

Matt Moretti

​

On Sun, Mar 1, 2015 at 8:47 PM, Anthony Kong < " target="_blank"> > wrote:

Hi Mark,

Can you shed more light on it? Do you have a url to the documentation or some example?

Cheers,

Tony Kong

blog: www.ahwkong.com

linkedin: www.linkedin.com/in/anthonykong

Don’t EVER make the mistake that you can design something better than what you get from ruthless massively parallel trial-and-error with a feedback cycle. That’s giving your intelligence much too much credit.

- Linus Torvalds

On Mon, Mar 2, 2015 at 4:12 AM, Mark Pimentel < " target="_blank"> > wrote:

For a more ruby-esque way you can use the built-in method Etc.

On Feb 28, 2015 5:56 PM, "Eric Helgeson" < " target="_blank"> > wrote:

Hey Anthony,

You can use a guard in this case to check and execute the resource 'only_if' the condition is true. You can use ruby or specify a command.

```
$ cat test.rb
group "sensu" do

  action :modify

  members "vagrant"

  append true

  only_if "getent passwd vagrant"
end

$ chef-apply test.rb
Recipe: (chef-apply cookbook)::(chef-apply recipe)
  * group[sensu] action modify (skipped due to only_if)
```

More info on Guards - https://docs.chef.io/resource_common.html#guards

Grabbed the guard form this post - http://stackoverflow.com/questions/24856339/chef-initialize-new-linux-user-if-it-doesnt-already-exist

​

HTH​

-Eric Helgeson

@nulleric

http://usingchef.com

On Sat, Feb 28, 2015 at 4:42 PM, Anthony Kong < " target="_blank"> > wrote:

Hi 

I have this definition on my cookbook

group "sensu" do

  action :modify

  members "vagrant"

  append true

end

it will throw an exception when I run it on ec2 because there is no user vagrant

How can I avoid the exception? Is there any way to detect the user exist? I have checked the doc https://docs.chef.io/resource_group.html but there is nothing obvious

Cheers,