Generate a user-generation script

README.md

Generate User Creation

Sometimes it is nice to have a simple way to "reproduce users" on a system

i.e. my server is connected to LDAP and has users / groups defined. I want to be able to create the same UIDs/GIDs without joining to the LDAP server.

This script is designed to help.

• Run it on the server where users are defined.
• It loops through users, code-generating a shell script that can "recreate" those users with proper UID/GID
• Save the output script and transport it to where you need it (docker containers, etc.)

Disclaimer

Ok. In an ideal world, we probably wouldn't need this. But in all cases ( 😉 ), "ideal world" != "real world"

Example usage:

# make script executable
chmod +x generate_user_creation.sh

# basic usage
# ./generate_user_creation.sh << space delimited usernames >>
./generate_user_creation.sh colearendt other-user

# to see only the script output
./generate_user_creation.sh colearendt other-user 2>/dev/null

# to build the generation script and see logs in the terminal
./generate_user_creation.sh colearendt other-user > my_script.sh

Notes

• Users who do not exist / have an error will be skipped
• useradd / groupadd commands for existing users / groups will error, but set -e is not in use, so the output script will continue
• stdout is for the script, stderr is for logging
• I have not tested thorougly with invalid user / group names. Add parameters / customize as needed for your own case!

generate_user_creation.sh

#!/bin/bash

# all stdout is used for creating a script
# all stderr is used for messages / logging

# output script setup
cat <<$HERE$
#!/bin/bash
# script for user creation output

$HERE$

for usr in $@; do
	echo "Setting up user: $usr" >&2;
	id_output=$(id $usr)
	id_code=$?

	grplist=$(echo "$id_output" | sed 's/.*groups=//')
	grplist_code=$?
	if [[ $id_code != 0 ]] || [[ $grplist_code != 0 ]]; then
		echo "---> Error code $id_code, $grplist_code finding groups for user: $usr" >&2
		continue
	# else
	# 	echo "Got error code: $id_code, $grplist_code"
	fi

	usr_id=$(echo "$id_output" | sed 's/.*uid=//' | sed 's/(.*//')
	usr_gid=$(echo "$id_output" | sed 's/.*gid=//' | sed 's/(.*//' | sed 's/ groups=.*//')

# set up user provisioning and group membership
cat <<$HERE$
# ------------------------------
# $usr
# ------------------------------

  # (possibly redundant) group creation
$HERE$

	usr_grps=''
	for grp in $(echo "$grplist" | sed 's/,/ /g'); do
		echo "---> Setting up group: $grp" >&2
		grpid=$(echo "$grp" | sed 's/(.*//')
		echo "---> groupid: $grpid" >&2
		grpname=$(echo "$grp" | sed 's/.*(//' | sed 's/)$//')
		echo "---> groupname: $grpname" >&2

# make sure these commands are idempotent
cat <<$HERE$
  groupadd $grpname -g $grpid
$HERE$

		# build up group add command for user membership
		usr_grps=${usr_grps},${grpid}
	done
	usr_grps=$(echo "$usr_grps" | sed 's/^,//')
	echo "---> Using user group membership string: $usr_grps" >&2

	# set up user provisioning and group membership
cat <<$HERE$

  # user creation
  useradd -m -u $usr_id -g $usr_gid -G $usr_grps $usr

$HERE$
done