Useradd hangs while trying to add a system user

Issue

• Red Hat Enterprise Linux 6:

  • While trying to add a system user using useradd with -r or --system option, the command never terminates until Ctrl-C is pressed.
  • Installation of some packages using yum may hang on useradd.

• Red Hat Enterprise Linux 7:

  • While trying to add a system user using useradd with -r or --system option, the command takes long to complete and show the following error:

    useradd: Can't get unique system UID (Numerical result out of range). Suppressing additional messages.
    

  • The system user is added to /etc/passwd, and /etc/shadow or remote database correctly.