Using command line commands for group administration in AIX

Now that you are familiar with the files behind the commands, take a look at the commands themselves. You'll learn how to create a user as well as modify a user after it has been created.

Like user administration, it's important that you know the configuration files behind the commands that modify them.

/etc/group

The /etc/group file contains the basics of a group. For example:

	
system:!:0:root,pconsole,esaadmin
staff:!:1:ipsec,esaadmin,sshd,xander
bin:!:2:root,bin
sys:!:3:root,bin,sys
adm:!:4:bin,adm
uucp:!:5:uucp,nuucp
mail:!:6:
security:!:7:root
cron:!:8:root
printq:!:9:lp
audit:!:10:root
ecs:!:28:
nobody:!:4294967294:nobody,lpd
perf:!:20:
shutdown:!:21:
lp:!:11:root,lp
invscout:!:12:invscout
snapp:!:13:snapp
ipsec:!:200:
pconsole:!:14:pconsole
sshd:!:201:sshd

 

As you can see, the file is colon delimited like the /etc/passwd file, and each entry contains only four fields in the following format (with spaces added before and after the delimiter to ease reading):

Group Name : Password Flag : GID : User(s)

Here's the line-by-line breakdown:

• Group Name. The group name associated with the group.
• Password Flag. This field is not used in AIX. Instead, AIX uses the /etc/security/group file for group administrators.
• GID. The GID associated with the group.
• User(s). The list of users who are members of the group.

  Note: This field is comma delimited.

/etc/security/group

The /etc/security/group file is much like /etc/security/user for users: It contains extended attributes to the specified group:

For more attributes, read the man page for /etc/security/group (man group), or visit http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.files/doc/aixfiles/group.htm.

The file is broken down into stanzas like the other configuration files in /etc/security, with the group name as the identifier. A nice feature of this file is that it allows you to set administrator rights to a standard user for a group. The administrators of that group can then modify the group as they see fit by adding members to or removing members from the group. Listing 18 provides an example of what an /etc/security/group looks like. In this example, the group jradmin has admin set to False and standard users pac and xander defined as administrators of the group.

	
system:
        admin = true

staff:
        admin = false

bin:
        admin = true

sys:
        admin = true

jradmin:
        admin = false
        adms = pac,xander

A few more commands

You've read enough about the files behind the commands. Now, let's look at the commands themselves. You'll see how to create a group as well as modify it after it has been created.

mkgroup

Creating a group in AIX is simple and straightforward. The same restrictions for creating a user pertain to creating a group:

• Groups cannot start with the:
  • Dash or minus sign (-).
  • Plus sign (+)
  • At symbol (@)
  • Tilde (~)
• Groups cannot be named ALL or default, as these names are reserved to the operating system.
• Group names cannot include:
  • Colon (:)
  • Quotation marks—single or double (' or ")
  • Pound or hash sign (#)
  • Comma (,)
  • Equal sign (=)
  • Slashes—back or forward (\ or /)
  • Question mark (?)
  • Back quote or tick (`)
  • White space (space or tab)
  • New-line characters
• Group names can only be eight characters or less in AIX version 5.2 and earlier. Starting with AIX version 5.3, IBM increased the maximum number of characters to 255.

Both user and group name lengths are handled by the same parameter: v_max_logname. To view or change the value, follow the instructions provided for viewing and changing the user name length in mkuser, earlier in this article.

To create a group, simply execute the mkgroup command with the group name as an argument, as shown in in example:

	
# mkgroup atctest

# grep atctest /etc/group
atctest:!:202:

# grep -p atctest /etc/security/group
atctest:
        admin = false

To create an admin group, add the -a switch, as shown in example:

	
# mkgroup -a atcadmin

# grep atcadmin /etc/group
atcadmin:!:15:

# grep -p atcadmin /etc/security/group
atcadmin:
        admin = true

To create a group and add Xander as the administrator of the group, add the adm section of the /etc/security/group stanza to the command line, as shown in example below:

	
# mkgroup adms=xander xangroup

# grep xangroup /etc/group
xangroup:!:203:

# grep -p xangroup /etc/security/group
xangroup:
        admin = false
        adms = xander

Like mkuser, mkgroup follows the same attributes as chgroup. For a full list of the attributes, read chgroup's man page (man chgroup).

chgroup

The chgroup command works just like chuser, and its man page contains all the attributes you can change on a group. Listing 22 provides an example of how to change the group's xangroup GID from 203 to 204. Add a few users to the group, as well.

	
# grep xangroup /etc/group
xangroup:!:203:

# chgroup id=204 users=xander,atc,amdc xangroup

# grep xangroup /etc/group
xangroup:!:204:xander,atc,amdc

chgrpmem

Another way to modify a group's members is with chgrpmem. The chgrpmem command allows you to list, add, and remove users from a group as well as modify the administrators of the group.

For example, the group xangroup has xander and atc as members and xander as an administrator of the group. Remove atc from the group:

	
# chgrpmem xangroup
xangroup:
        members = xander,atc
        adms = xander

# chgrpmem -m - atc xangroup

# chgrpmem xangroup
xangroup:
        members = xander
        adms = xander

Suppose there was a mistake and user atc was not supposed to be removed. Instead, user atc was supposed to become the administrator of the group, while xander's administrative rights were to be removed. Listing 24 shows the code to make the correction.

	
# chgrpmem -m + atc xangroup

# chgrpmem -a + atc xangroup

# chgrpmem -a - xander xangroup

# chgrpmem xangroup
xangroup:
        members = xander,atc
        adms = atc

lsgroup

With such a nice command for users as lsuser, shouldn't there be one for groups, as well? There is: lsgroup. To continue with the standard format of commands and their options in AIX, lsgroup follows the same structure as lsuser.

# lsgroup xangroup
xangroup id=204 admin=false users=xander,cormany adms=cormany registry=files

# lsgroup -f xangroup
xangroup:
        id=204
        admin=false
        users=xander,cormany
        adms=cormany
        registry=files

# lsgroup -c xangroup,atcadmin
#name:id:admin:users:adms:registry
xangroup:204:false:xander,cormany:cormany:files
#name:id:admin:registry
atcadmin:15:true:files

# lsgroup -c -a id xangroup,atcadmin
#name:id
xangroup:204
#name:id
atcadmin:15

rmgroup

Throughout this article, you've been creating sample groups. Now, it's time to clean up the AIX system you're using. To remove a group from the system, simply execute rmgroup with the group's name as the argument:

# rmgroup atctest

The rmgroup command does not allow you to remove the group until you have moved all users that have the group as their primary group to another group.

Recommended Links

AIX user and group administration by Adam Cormany

• getconf: See IBM's man page for the getconf command.
• /etc/security/limits: See IBM's System Information Center Web page for /etc/security/limits.
• /etc/security/user: See IBM's System Information Center Web page for /etc/security/user.
• /usr/lib/security/mkuser.default: See IBM's System Information Center Web page for /usr/lib/security/mkuser.default.
   
• chuser: See IBM's System Information Center Web page for the chuser command.
• /etc/group: See IBM's System Information Center Web page for /etc/group.
• /etc/security/group: See IBM's System Information Center Web page for /etc/security/group.
• The AIX and UNIX developerWorks zone provides a wealth of information relating to all aspects of AIX systems administration and expanding your UNIX skills.New to AIX and UNIX? Visit the New to AIX and UNIX page to learn more.
• Browse the technology bookstore for books on this and other technical topics.

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