Debian package will fail to create mongodb user if another user exists with the word "mongodb" as part of its name

The postinst script for mongodb 2.4.9 has the following:

case "$1" in

    configure)

        # create a mongodb group and user

        if ! grep -q mongodb /etc/passwd; then

                adduser --system --no-create-home mongodb

                addgroup --system mongodb

                adduser mongodb mongodb

        fi

grep -q mongodb will succeed if any user exists that has "mongodb" as part of its name. In regex parlance, the grep is not anchored.

In particular, if the mongodb-mms-backup-agent package is installed first, it will create a mongodb-mms-agent user. Then if mongodb is installed after, it will fail to create a mongodb user as grep -q mongodb will match on mongodb-mms-agent.

You might consider running /usr/bin/id mongodb >/dev/null 2>&1 and checking the return code.