A colleague recently told me that he’d heard that you could create some file that would change the default parameters that “useradd” used, such as change the default shell. I hadn’t heard of this before and answered, “Ya, you just specify it as an argument to useradd!” Never the less, he was insistent that there was a way and wanted to know what it was. So our journey began.
If there was a way, we had two options. First, we could run “useradd” with truss and look at any files its trying to open and then search Google. But thats not very educational. So I opted for the second method, that is to go to src.opensolaris.org, search for the useradd.c code and read through it. Within about 2 minutes we had our answer.
Turns out he was absolutely right, useradd look at /usr/sadm/defadduser and if it exists reads default values from it. You can see the default parameters its looking for and the format in userdefs.h line 47. So from that we created the following file (/usr/sadm/defadduser):
## Ben's test defuseradd file: /usr/sadm/defadduser ## http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/head/userdefs.h#89 defrid=99 defgroup=99 defgname=other defparent=/home defskel=/etc/skel defshell=/usr/bin/bash definact=0 defexpire= defauthorization= defprofile= defrole= defproj=3 defprojname=default deflimitpriv= defdefaultpriv= deflock_after_retries=
Now test it, and sure enough its working. In this case we’re only overriding the default shell, changing from /bin/sh to /usr/bin/bash:
$ useradd alex $ tail -1 /etc/passwd alex:x:501:99::/home/alex:/usr/bin/bash
One word of caution is that you will want to specify all the values in the defaults file (/usr/sadm/defadduser)… if the value is empty it will use no value.
So this was a fun problem which not only showed a new flexibility that I was unaware of but showcased the awesome power of open source and accessibility via OpenGrok. Viva la code!
great new information .. would you please tell us what is the default values so if we want to use them in conjunction with new specific parameters .. it would be easier
Surely the man page includes all this information… ?
useradd -D [-A authorization [,authorization...]]
[-b base_dir] [-s shell [-k skel_dir]] [-e expire]
[-f inactive] [-g group] [-K key=value] [-p projname]
[-P profile [,profile...]] [-R role [,role...]]
modifies the said default user settings file.
useradd -D
displays it’s contents.
You don’t really need to edit it manually.
Cheers.
You can user ‘useradd -D’ to show and set defaults too.
It is documented in the man page.
Man pages and arguments; pfffft, digging code is way more fun.
thanks for you code!
like you site
A good article which i was also unaware..
Thanks, this is useful.
I already knew about changing the defaults and had done so successfully for the home directory but I could not change the default shell via the ‘useradd -D’ method.
Editing the file directly did the trick.
I’ve also added that file to my jumpstart finish script.
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“defshell=/usr/bin/bash”
Oh geez. Ben, what is happening to you?
You’re giving in and melding with all the clueless Linux “me toos”? Are you really going to let them brainwash you?
Come on buddy, pick yourself up. We’re oldskool. Don’t give up who and what you are for a fashion fad that’ll go away.
Hey man…sorry I missed the party.
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Wow, thanks for the insightful post. I look forward to reading more from you.
Have you filed a bug yet?
The canonical place for this info would be “/etc/default/adduser”…
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