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Q: How to create linux account with useradd without creating mail spool Summary
Can I create a new user without creating mail spool and without modification of /etc/default/useradd ?
Explaination
I want to create a user that has a home directory and skeletion, but I dont want the useradd script to add a mail spool file to the unix system.
My /etc/default/useradd file states that
CREATE_MAIL_SPOOL=yes

but I dont want to modify the default behaviour.
For now Im using
useradd nomailuser
rm /var/spool/mail/nomailuser

Also I know about -d but it seems that I cant find an option for not creating a mail spool.
Im thinking about is there an option to use custom /etc/default/useradd file.

A: man useradd
   -K, --key KEY=VALUE
       Overrides /etc/login.defs defaults (UID_MIN, UID_MAX, UMASK, PASS_MAX_DAYS and others).

       Example: -K PASS_MAX_DAYS=-1 can be used when creating system account to turn off password ageing, even though
       system account has no password at all. Multiple -K options can be specified, e.g.: -K UID_MIN=100 -K UID_MAX=499

So, try this:
# useradd -K MAIL_DIR=/dev/null nomailuser

A warning would appear (Creating mailbox file: Not a directory), but you can ignore.

A: Im setting up a Docker image with Alpine and shadow package and got the same error.  
To avoid this Creating mailbox file: No such file or directory error I had to add the following inline replacement before trying to add user: 
RUN sed -i s/^CREATE_MAIL_SPOOL=yes/CREATE_MAIL_SPOOL=no/ /etc/default/useradd

This is a Dockerfile directive. If you are struggling with an already running host, just edit the /etc/default/useradd file and change the setting accordingly. This change would prevent any other user creation from getting its mailbox created.
It that is not the desired behavior, you can just create the /var/mail folder with 
[ -d /var/mail ] || mkdir /var/mail

Or in the Dockerfile: 
RUN mkdir /var/mail 

Hope this helped. 

A: Oddly enough, the answer is no. I just read the sourcecode and there is no option for this, though there is a workaround (sort of): maildirs dont get created for system accounts.
So you can do useradd -r -m. Youll have to specify a UID/GID manually as well though, as theyre picked from different ranges.

user
I counted one hundred and seventy-six "e"s in that text.
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