UNIX for Dummies Questions & Answers

Hi Expert,

I am newbies here.

When I do cat /etc/group

it will list example:

cdrom:x:24
floppy:x:19
postfix:!:51
avahi:!:105

I can see the following:

My question are as below:

1. why there is x sign, what is the meaning of that?

2. why there is ! sign, what is the meaning of that?

Thank you in advance.

cdrom:x:24:vivek,student13,raj
_____ _ _ _____
| | | |
| | | |
1 2 3 4
1-->group name
2-->Generally password is not used, hence it is empty/blank.or 'x' if the password hash is stored in /etc/shadow
3-->User ID, uid - number for this user
4-->Group List: It is a list of user names of users who are members of the group. The user names, must be separated by commas.

Thanks vidyadhar85.

But what about the ! sign?

/etc/shadow is associated with /etc/passwd. Some systems support an /etc/gshadow but it is rarely used. Putting an x or a * in that field is common. Putting a ! is something I haven't seen before. The exact character chosen means nothing to the software. Maybe I will will use a P the next time I do one. That won't mean anything either. The important thing is to not leave the field blank. Leaving it blank allows anyone to set themselves to that group by using the old newgrp command.