Como o Arch Wiki deixa claro :
Warning: In order to be able to log in, the login shell must be one of those listed in /etc/shells, otherwise the PAM module pam_shell will deny the login request. In particular, do not use the /usr/bin/bash path instead of /bin/bash, unless it is properly configured in /etc/shells.
cat /etc/shells
#
# /etc/shells
#
/bin/sh
/bin/bash