Here is a proposed file for /etc/default/adduser. It barely comments the variables and their values and just forces a default shell which actually would solve this issue.
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# Default values for useradd(8) # # The SHELL variable specifies the default login shell on your # system. # Similar to DHSELL in adduser. We however use "sh" here because # useradd being a low level utility should rather be as widely opened # as possible SHELL=/bin/sh # # The default group for users # 1000=users on Debian systems # same then USERS_GID in adduser # Please be aware that Debian's adduser defaults to "user groups" # which means that one group is created for each user # There is no way to achieve this with useradd which must remains a low # level utility # GROUP=100 # # The default home directory. Same than DHOME for adduser # HOME=/home # # The number of days after a password expires until the account # is permanently disabled # INACTIVE=-1 # # The default expire date # EXPIRE= # # The SKEL variable specifies the directory containing "skeletal" user # files; in other words, files such as a sample .profile that will be # copied to the new user's home directory when it is created. # SKEL=/etc/skel # # Defines whether the mail spool should be created while # creating the account # CREATE_MAIL_SPOOL=yes
