Refer to crypt(3) for details on how this string is interpreted.
If the password field contains some string that is not a valid result of crypt(3), for instance ! or *, users will not be able to use a unix password to access the group (but group members do not need the password).
The password is used when an user who is not a member of the group wants to gain the permissions of this group。
This field may be empty, in which case only the group members can gain the group permissions.
A password field which starts with a exclamation mark means that the password is locked. The remaining characters on the line represent the password field before the password was locked.
This password supersedes any password specified in /etc/group.