/etc/adduser.conf

sudo cat /etc/adduser.conf
# /etc/adduser.conf: `adduser' configuration.
# See adduser(8) and adduser.conf(5) for full documentation.

# A commented out setting indicates that this is the default in the
# code. If you need to change those settings, remove the comment and
# make your intended change.

# STDERRMSGLEVEL, STDOUTMSGLEVEL, and LOGMSGLEVEL set the minimum
# priority for messages logged to syslog/journal and the console,
# respectively.
# Values are trace, debug, info, warn, err, and fatal.
# Messages with the set priority or higher get logged to the
# respective medium.
#STDOUTMSGLEVEL=warn
#STDERRMSGLEVEL=warn
#LOGMSGLEVEL=info

# The login shell to be used for all new users.
# Default: DSHELL=/bin/bash
#DSHELL=/bin/bash

# The directory in which new home directories should  be  created.
# Default: DHOME=/home
# DHOME=/home

# The directory from which skeletal user configuration files
# will be copied.
# Default: SKEL=/etc/skel
#SKEL=/etc/skel

# Specify inclusive ranges of UIDs and GIDs from which UIDs and GIDs
# for system users, system groups, non-system users and non-system groups
# can be dynamically allocated.
# Default: FIRST_SYSTEM_UID=100, LAST_SYSTEM_UID=999
#FIRST_SYSTEM_UID=100
#LAST_SYSTEM_UID=999

# Default: FIRST_SYSTEM_GID=100, LAST_SYSTEM_GID=999
#FIRST_SYSTEM_GID=100
#LAST_SYSTEM_GID=999

# Default: FIRST_UID=1000, LAST_UID=59999
#FIRST_UID=1000
#LAST_UID=59999

# Default: FIRST_GID=1000, LAST_GID=59999
#FIRST_GID=1000
#LAST_GID=59999

# Specify a file or a directory containing UID and GID pool.
#UID_POOL=/etc/adduser-pool.conf
#UID_POOL=/etc/adduser-pool.d/
#GID_POOL=/etc/adduser-pool.conf
#GID_POOL=/etc/adduser-pool.d/
#RESERVE_UID_POOL=yes
#RESERVE_GID_POOL=yes

# Specify whether each created non-system user will be
# given their own group to use.
# Default: USERGROUPS=yes
#USERGROUPS=yes

# Defines the groupname or GID of the group all newly-created
# non-system users are placed into.
# It is a configuration error to define both variables
# even if the values are consistent.
# Default: USERS_GID=undefined, USERS_GROUP=users
#USERS_GID=100
#USERS_GROUP=users

# The permissions mode for home directories of non-system users.
# Default: DIR_MODE=0700
#DIR_MODE=0700

# The permissions mode for home directories of system users.
# Default: SYS_DIR_MODE=0755
#SYS_DIR_MODE=0755

# If set to a nonempty value, new users will have quotas copied
# from that user with `edquota -p QUOTAUSER newuser'
# Default: QUOTAUSER=""
#QUOTAUSER=""

# Non-system user- and groupnames are checked against this regular
# expression. RFC8265 would allow all codepoints U+0021 through U+007E
# meaning: !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~ plus digits, lower case and
# capital letters. ., / and : clash with special file names, path separator
# and /etc/passwd format, many other characters might cause issues in shell
# scripts. Therefore, the default is more restrictive than RFC8265 would
# allow. Local administrators might relax this regexp as far as useradd
# will allow.
# Default: NAME_REGEX="^[a-zA-Z][a-zA-Z0-9_-]*\$?$"
#NAME_REGEX="^[a-zA-Z][a-zA-Z0-9_-]*\$?$"

# System user- and groupnames are checked against this regular
# expression. Comments from above apply as well, but changes here may
# affect package installation.
# Default: SYS_NAME_REGEX="^[a-zA-Z_][a-zA-Z0-9_-]*\$?$"
#SYS_NAME_REGEX="^[a-zA-Z_][a-zA-Z0-9_-]*\$?$"

# When populating the newly created home directory of a non-system user,
# files in SKEL matching this regex are not copied.
# Default: SKEL_IGNORE_REGEX="\.(dpkg|ucf)-(old|new|dist|save)$"
#SKEL_IGNORE_REGEX="\.(dpkg|ucf)-(old|new|dist|save)$"

# list of groups that new non-system users will be added to
# if ADD_EXTRA_GROUPS is non-zero or set on the command line.
# Default: EXTRA_GROUPS="users"
#EXTRA_GROUPS="users"

# Setting this to something other than 0 will cause adduser to add
# newly created non-system users to the list of groups defined by
# EXTRA_GROUPS.
# Default: ADD_EXTRA_GROUPS=0
#ADD_EXTRA_GROUPS=0