Fix: Docker user warning UID is greater than SYS_UID_MAX

[z017]

Description

Currently docker entrypoints create users as system users by using the -r flag of useradd:

polar/docker/bitcoind/docker-entrypoint.sh

Line 13 in 52dc3c3

useradd -r -u $USERID -g $GROUPID bitcoin

The default user uid is 1000 greater than SYS_UID_MAX resulting in the following warning:

useradd warning: bitcoin's uid 1000 is greater than SYS_UID_MAX 999

To fix the warning:

• The -r flag was removed.
  • That flag also avoid home directory creation and password aging information in /etc/shadow.
• The -M flag was added to avoid home directory creation.
• And the password aging information is not necessary because the user has no password.

References

• https://linux.die.net/man/8/useradd
• Remove --system flag from non-root user and group creation dotnet/dotnet-docker#4676
  • Another project with the same issue.