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Figure 3-12 To set the auto login for an account or to delete an account, highlight the account and click the appropriate button. To create a new user, just click the New User button. Linux Linux offers many ways to manage accounts with a GUI. Every distribution has its own method of user administration. Here s a list of the commands that start the various graphical administration tools on the major distributions of Linux: Distribution Command SUSE /sbin/yast2 Red Hat (Fedora Core) /usr/bin/system-config-users Mandrakelinux /usr/sbin/userdrake All webmin The webmin command enables remote administration, typically with a graphic interface for users and other types of administrative tasks. It is available at http://webmin.com and works on most Unix systems, including Solaris s. Webmin is not installed by default on most versions of Unix. The Linux tools vary in functionality, but generally provide all the capabilities of the command-line equivalents. 45 Understanding Users and Groups
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User Management with Graphical User Interface Tools There are many graphical user interface (GUI) tools available on the various Unix systems, and although space prohibits covering them in depth in this book, you should be aware of their existence. The use of GUI tools makes management much easier for new administrators, but a good understanding of the command line interface tools is necessary before you use them primarily. Let s take a look at a few of the GUI tools; refer to your own documentation for more information on the many tools available. Mac OS X Mac OS X has very straightforward user management tools. To access them, click the Apple icon in the upper-right corner of the screen and select System Preferences. Then choose Account in the section labeled System (bottom left). Figure 3-11 shows the screen that appears. Figure 3-11 Two accounts User and Beginning Unix (both of which are admin type accounts, meaning they can run system administrator commands on the system) can be seen in Figure 3-11. From this screen, you can add, edit or modify, and delete an account. You can also set the account to log in automatically upon boot-up. To edit an existing account, simply highlight the account and click the Edit User button. Figure 3-12 shows an example of the account screen that displays. 44 Chapter 3
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The userdel command is extremely easy to use and can therefore be dangerous if not used with caution. There is only one argument or option available for the command: r, for removing the account s home directory and mail spool (mail file). Here s how to remove the saraht account: userdel -r saraht If you want to keep her home directory for backup purposes, omit the -r option. You can remove the home directory as needed at a later time. The useradd, usermod, and userdel commands work similarly in most Unix systems (Solaris, Linux, BSD, and so on) but not in Mac OS X. If you want to modify accounts with the command line, you need to use niutil with the -create, -createprop, and -appendprop arguments. niutil is a Mac OS X specific command; refer to your man pages for more information if you are using Mac OS X and need to add users at the command line. Group Management Managing groups is accomplished with the groupadd, groupmod, and groupdel commands on most Unix systems. groupadd has this syntax: groupadd -g group_id group_name To create a new group for the finance department called finance_2 and assign it a unique GID of 535, for example, you d use: groupadd -g 535 finance_2 This command makes the appropriate entry in the /etc/group file. To modify a group, use the groupmod syntax: groupmod -n new_modified_group_name old_group_name To change the finance_2 group name to financial, type: groupmod -n financial finance_2 You can also use the -g option with groupmod to change the GID of the group. Here s how you d change the financial GID to 545: groupmod -g 545 financial To delete an existing group, all you need are the groupdel command and the group name. To delete the financial group, the command is: groupdel financial This removes only the group, not any files associated with that group. (The files are still accessible by their owners.) 43 Understanding Users and Groups
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After this command runs, a password to the account must be set using the passwd accountname command. To create the password for Jane Doe s account, root would type: passwd unixnewbie The new account owner should change the password immediately. Try It Out Create an Account with useradd A new temporary employee, Sarah Torvalds, has joined your company today (5/01/05). Sarah s manager has requested that you create an account for Sarah. She has joined the company to assist in some end-of-the-year human resources work, so she needs access to the default user group and to the hr group. Her contract with the company ends 120 days from her start day (the same day the account is created). Standard users are created with an inactive account timeout of 30 days, are assigned to the employees group by default, and are assigned the c shell. Usernames are created using the first initial and last name (no more than eight characters total for the account name, in this case for compatibility with other Unix systems). You need to create an account for Sarah using the useradd command because you do not have access to any graphical tools. First log in as root, then run the following commands: # useradd -c Sarah Torvalds -d /home/storvald -e 05/01/05 -f 30 -g employees -G hr -m -s /bin/csh -u 1005 storvald # passwd storvald Changing password for user storvald. New UNIX password: Retype UNIX password: passwd: all authentication tokens updated successfully. # How It Works The useradd command modifies the /etc/passwd, /etc/shadow, and /etc/group files and creates a home directory. Just think how much easier this is than having to manually edit all three files and create the home directory! useradd works quickly because the format for the files is standardized and can be easily used. You can also create scripts using this command to make the process even easier. You can use the -D option to assign default values to some of the useradd values, making the commands easier to run. Refer to the useradd man pages for more information. The usermod command enables you to make changes to an existing account from the command line (instead of modifying system files). It uses the same arguments as the useradd command, plus the -l argument, which allows you to change the account name. For instance, to change Sarah Torvalds account name to saraht and provide her with a home directory, you d issue the following command: usermod -d /home/saraht -m -l saraht storvald This command changes Sarah Torvalds current account (storvald) and makes the new home directory /home/saraht (-d /home/saraht -m) and the new account name saraht (-l saraht). The -m creates the home directory that hadn t previously existed. 42 Chapter 3
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You can avoid these steps by using the commands. You ll also reduce the risk of introducing a typo into one of the files, which could make your system unusable. To run these commands, you must be logged in as root (superuser). Account Management The useradd command enables you to add a user in a single command line. The following table describes some of the options to the useradd command. Option Description File and Field Affected -c Comment for the GCOS or comment field (use /etc/passwd; Field 5 quotes if you have a space in the comments). -d Account s home directory. /etc/passwd; Field 6 -e Expiration date of the account in yyyy-mm-dd /etc/shadow; Field 8 or mm/dd/yy format, depending on the Unix version. (The account is not valid after this date.) -f Number of days the account can be inactive /etc/shadow; Field 7 before being disabled or the number of days after the password has expired that the account will be disabled. -g Initial group (default group). /etc/passwd; Field 4 -G Comma-separated list of supplementary or /etc/group; Field 4 of secondary groups to which the user belongs. groups identified in the command line -m Creates the home directory if it doesn t exist. Not applicable -s The user s shell for interactive logins. /etc/passwd; Field 7 -u Assigns user ID (unique unless -o option, which /etc/passwd; Field 3 allows duplicate UIDs, is used). UIDs 0 99 are generally reserved for system accounts. The structure of the command is: useradd -c comment -d home directory -e expiration date -f inactive days -g primary (default) group -G secondary groups -m -s shell -u user id accountname The last item is the account name. It is not optional. It s field 1 in the /etc/passwd file. Here s an example that creates an account for a user named unixnewbie, whose real name is Jane Doe. Jane needs the account until July 4, 2006. Her primary group is users, and authors is her secondary group. She has requested the Bourne shell for her default shell. She isn t sure she will be using this system, so let s disable her account if she hasn t used it within 60 days. The useradd command to create this account is: useradd -c Jane Doe -d /home/unixnewbie -e 040406 -f 60 -g users -G authors -m -s /bin/ksh -u 1000 unixnewbie 41 Understanding Users and Groups
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Figure 3-10 Managing Accounts and Groups Some Unix systems use different commands or command structures (options to the command), but using the command line to create, modify, and delete accounts and groups is fairly standardized among them. Following are commands available on the majority of Unix systems and their descriptions: Command Description useradd Adds accounts to the system. usermod Modifies account attributes. userdel Deletes accounts from the system. groupadd Adds groups to the system. groupmod Modifies group attributes. groupdel Removes groups from the system. To add or delete an account manually (without using the preceding commands), you would have to: . Modify /etc/passwd to add or remove the account line. . Modify /etc/shadow to add or remove the account line. . Modify /etc/group to add or remove the account references. . Add or remove the account s home directory (if not shared, which by default it should not be). 40 Chapter 3
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Mac OS X Differences The preceding are primary user administration files on almost all Unix systems. Mac OS X is a notable exception to this. The /etc/passwd, /etc/shadow, and /etc/group files exist, but are used by the system only for single-user mode (discussed in Chapter 20). The primary repository for this information is the NetInfo database, which can be viewed and modified with the niutil command. Here s how to view a list of the current databases: niutil -list . / This command generates output similar to that shown in Figure 3-9. Figure 3-9 To view one of the databases, such as a listing of current users, you can type the following: niutil -read . /groups The output of this command is shown in Figure 3-10. For more information about NetInfo on Mac OS X, see Chapter 20. The Mac OS X graphical user interface (GUI) makes it easy to manage user accounts because it was built with ease of use in mind from the start. This is an advantage over some of the other Unix systems. 39 Understanding Users and Groups
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