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AIX User and Group Administration


See also

Redbooks IBM Links Recommended Links Reference
Using Smit for user administration Using Smit for group administration User administration via command line Group administration via command line    
Useful AIX commands smit sudo Tips Humor Etc

There are three ways to administer users and groups in AIX

Before going into the commands to create, modify, and maintain users and groups in AIX, it is important that you know what is happening behind the scenes. For example, you should understand the files and what they mean.

Look at the some of the files that affect the user itself:


The file /etc/passwd contains the basics of a user and is probably the best-known file to UNIX® and Linux® users for user administration.

snapp:*:200:13:snapp login user:/usr/sbin/snapp:/usr/sbin/snappd
nuucp:*:7:5:uucp login user:/var/spool/uucppublic:/usr/sbin/uucp/uucico
atc:!:8000:400:Adam Cormany,Sr UNIX Admin:/home/atc:/bin/ksh
pac:!:8002:400:PAC,Jr UNIX Admin:/home/pac:/bin/ksh
As you can see, the file is colon (:) delimited, and each entry contains seven fields in the following format (with spaces added before and after delimiter to ease reading):
Username : Password Flag : UID : GID : GECOS : Home : Shell/Command
Here's the line-by-line breakdown:


The file /etc/security/.profile can really save you some valuable time and ease frustration. When you create a user using the mkuser command, the script /usr/lib/security/mkuser.sys is executed. This script creates the user's directory, sets the correct permissions, and "creates" the user's .profile. The mkuser.sys script actually copies the /etc/security/.profile file into the user's new home directory.

If you are building a new system, or maybe a new division of 100 people needs accounts on a system, make sure you make your changes to the /etc/security/.profile file before creating all the users' accounts. If you create the accounts and then realize that you need to make a simple change in a variable or modify another setting, you're going to have to manually make the change to everyone's profile. It could be scripted out easily, but life would have been much simpler if you would have just changed the /etc/security/.profile.


export PATH

if [ -s "$MAIL" ]           # This is at Shell startup.  In normal
then echo "$MAILMSG"        # operation, the Shell checks
fi                          # periodically.


The /etc/security/limits file contains all the ulimits, or users' system resource limitations. The fields in the /etc/security/limits file: 

Soft limit Hard limit Description
fsize fsize_hard Size of file a user can create
core core_hard Size of core file a user can create
cpu cpu_hard The amount of system time allowed
data data_hard Size of the process data segment
stack stack_hard Size of the process stack segment
rss rss_hard Physical memory allowed
nofiles nofiles_hard Number of open file descriptors at one time
nproc nproc_hard Number of running processes at one time

What's the difference between soft and hard limits? A soft limit is a value that a user or application can change on the fly up to the maximum (the hard limit). The hard limit is just that -- the maximum value a parameter can be set to. If setting the parameter to a numeric value is too difficult (for example, if a developer has no idea how much memory his or her program is going to take or the number of files it will need to open), you can set the parameter to -1, which translates to unlimited.

It isn't imperative that you set individual ulimits for each and every user, however. The /etc/security/limits file contains a section called default that defines a template of standard values for each user unless that user has set custom values. If the default section doesn't exist, IBM kindly set predetermined limits just in case.

The IBM default values are:

*   Attribute        Value
*   ==========    ============
*   fsize_hard    set to fsize
*   cpu_hard      set to cpu
*   core_hard         -1
*   data_hard         -1
*   stack_hard      8388608
*   rss_hard          -1
*   nofiles_hard      -1

An example of a /etc/security/limits file.
        fsize = 4194303
        core = 16384
        cpu = -1
        data = 262144
        rss = 65536
        stack = 65536

        fsize = 131072
        fsize_hard = 262144
        core = 262144


Considering that user "pac" is a junior UNIX administrator, his fsize soft value was reduced from the default section's 4,194,303 to 131,072; however, you were nice enough to allow the user to increase his value to 262,144, if needed. Also, pac is notorious for finding ways to break his own programs. As a result, you've increased his core ulimit to 262,144.


The /etc/security/passwd file contains the AIX user's password information. The file contains three fields per user:

Listing 4 provides an example of a /etc/security/password file.

Listing 4. Example /etc/security/password file
        password = oBQaUkPkUryCY
        lastupdate = 1243972006
        flags = ADMCHG


In this example, user "amdc" has a password that was set on Tue. Jun. 2 15:46:46 EDT 2009. The next time the user logs in or sus to amdc, he or she will be prompted to change the password.

To convert the seconds from epoch to timestamp you can use Perl one-kliner:

# perl -e 'use POSIX; print strftime("%c\n", localtime(1243972006));'
Tue Jun  2 15:46:46 EDT 2009


Now you're getting into the meat of AIX user administration. The /etc/security/user file contains the most important settings, outside of the basics in /etc/passwd, for a user:

Parameter Format Description
account_locked TRUE | FALSE Lock out the account; the user is unable to log in if set to True.
admin TRUE | FALSE If True, the user has administrative rights.
expires MMDDHHYY If the date has been reached, the account has expired and is locked.
histexpire 0-260 Number of weeks the user can't reuse a password.
histsize 0-50 Number of passwords previously used that can't be reused.
login TRUE | FALSE User can log in if True.
maxage 0-52 Number of weeks a password is valid.
minage 0-52 Number of weeks a user must wait before changing his or her password.
rlogin TRUE | FALSE The account can be accessed remotely if set to True.
su TRUE | FALSE Others can use su to access this account if set to True.

For a full listing of all parameters, look in your AIX system under /etc/security/user, or see AIX Information Center. Like /etc/security/limits, a default section sets all the fields if not specified by the individual account.


The /usr/lib/security/mkuser.default file contains values used when creating a new AIX user through mkuser.

        pgrp = staff
        groups = staff
        shell = /usr/bin/ksh
        home = /home/$USER

        pgrp = system
        groups = system
        shell = /usr/bin/ksh
        home = /home/$USER

More parameters can be defined in this file. To view the full list, look at man chuser.

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AIX user and group administration by Adam Cormany




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