These fields must not contain any colons. Except for the other field, they should not contain any comma or equal sign. It is also recommended to avoid non-US-ASCII characters, but this is only enforced for the phone numbers. The other field is used to store accounting information used by other applications.
The options which apply to the chfn command are:
-f, --full-name FULL_NAME
-h, --home-phone HOME_PHONE
-o, --other OTHER
-r, --room ROOM_NUMBER
-R, --root CHROOT_DIR
-w, --work-phone WORK_PHONE
If none of the options are selected, chfn operates in an interactive fashion, prompting the user with the current values for all of the fields. Enter the new value to change the field, or leave the line blank to use the current value. The current value is displayed between a pair of [ ] marks. Without options, chfn prompts for the current user account.
The following configuration variables in /etc/login.defs change the behavior of this tool:
chsh(1), login.defs(5), passwd(5).