Package: passwd Version: 1:4.4-4.1 Severity: minor File: /usr/share/man/man1/chsh.1.gz
We read
-s, --shell SHELL
The name of the user's new login shell. Setting this field to blank
causes the system to select the default login shell.
However, trying it gives
# chsh -s '' nobody
chsh: Warning: does not exist
