System Administration Guide: Basic Administration

What Are User Accounts and Groups?

One basic system administration task is to set up a user account for each user at a site. A typical user account includes the information a user needs to log in and use a system, without having the system's root password. The components of user account information are described in User Account Components.

When you set up a user account, you can add the user to predefined groups of users. A typical use of groups is to set up group permissions on a file and directory, which allows access only to users who are part of that group.

For example, you might have a directory containing confidential files that only a few users should be able to access. You could set up a group called topsecret that includes the users working on the topsecret project. And, you could set up the topsecret files with read permission for the topsecret group. That way, only the users in the topsecret group would be able to read the files.

A special type of user account, called a role, is used to give selected users special privileges. For more information, see Role-Based Access Control (Overview) in System Administration Guide: Security Services.

User Account Components

The following sections describe the specific components of a user account.

User (Login) Names

User names, also called login names, let users access their own systems and remote systems that have the appropriate access privileges. You must choose a user name for each user account that you create.

Consider establishing a standard way of assigning user names so that they are easier for you to track. Also, names should be easy for users to remember. A simple scheme when selecting a user name is to use the first name initial and first seven letters of the user's last name. For example, Ziggy Ignatz becomes zignatz. If this scheme results in duplicate names, you can use the first initial, middle initial, and the first six characters of the user's last name. For example, Ziggy Top Ignatz becomes ztignatz.

If this scheme still results in duplicate names, consider using the following scheme to create a user name:

Note –

Each new user name must be distinct from any mail aliases that are known to the system or to a NIS domain. Otherwise, mail might be delivered to the alias rather than to the actual user.

For detailed guidelines on setting up user (login) names, see Guidelines for Using User Names, User IDs, and Group IDs.

User ID Numbers

Associated with each user name is a user identification number (UID). The UID number identifies the user name to any system on which the user attempts to log in. And, the UID number is used by systems to identify the owners of files and directories. If you create user accounts for a single individual on a number of different systems, always use the same user name and ID number. In that way, the user can easily move files between systems without ownership problems.

UID numbers must be a whole number that is less than or equal to 2147483647. UID numbers are required for both regular user accounts and special system accounts. The following table lists the UID numbers that are reserved for user accounts and system accounts.

Table 4–3 Reserved UID Numbers

UID Numbers 

User or Login Accounts 


0 – 99 

root, daemon, bin, sys, and so on

Reserved for use by OracleSolaris  

100 – 2147483647 

Regular users 

General purpose accounts 

60001 and 65534 

nobody and nobody4

Anonymous users 



Non trusted users 

Do not assign UIDs 0 through 99. These UIDs are reserved for allocation by Oracle Solaris. By definition, root always has UID 0, daemon has UID 1, and pseudo-user bin has UID 2. In addition, you should give uucp logins and pseudo user logins, such as who, tty, and ttytype, low UIDs so that they fall at the beginning of the passwd file.

For additional guidelines on setting up UIDs, see Guidelines for Using User Names, User IDs, and Group IDs.

As with user (login) names, you should adopt a scheme for assigning unique UID numbers. Some companies assign unique employee numbers. Then, administrators add a number to the employee number to create a unique UID number for each employee.

To minimize security risks, you should avoid reusing the UIDs from deleted accounts. If you must reuse a UID, “wipe the slate clean” so that the new user is not affected by attributes set for a former user. For example, a former user might have been denied access to a printer by being included in a printer deny list. However, that attribute might be inappropriate for the new user.

Using Large User IDs and Group IDs

UIDs and group IDs (GIDs) can be assigned up to the maximum value of a signed integer, or 2147483647.

However, UIDs and GIDs over 60000 do not have full functionality and are incompatible with many Oracle Solaris features. So, avoid using UIDs or GIDs over 60000.

The following table describes interoperability issues with Oracle Solaris products and previous releases.

Table 4–4 Interoperability Issues for UIDs or GIDs Over 60000


Product or Command 


NFS interoperability 

SunOS 4.0 NFS software and compatible releases 

NFS server and client code truncates large UIDs and GIDs to 16 bits. This situation can create security problems, if systems running SunOS 4.0 and compatible releases are used in an environment where large UIDs and GIDs are being used. Systems running SunOS 4.0 and compatible releases require a patch to avoid this problem. 

Name service interoperability 

NIS name service and file-based name service 

Users with UIDs greater than 60000 can log in or use the su command on systems running the Solaris 2.5 (and compatible releases). However, their UIDs and GIDs will be set to 60001 (nobody).


NIS+ name service 

Users with UIDs greater than 60000 are denied access on systems running Solaris 2.5 (and compatible releases) and the NIS+ name service. 

The following table describes UID and GUI limitations.

Table 4–5 Large UID and GID Limitation Summary



60003 or greater 

Users who log in to systems running Solaris 2.5 (and compatible releases) and the NIS or files name service get a UID and GID of nobody.

65535 or greater 

  • Systems running Solaris 2.5 (and compatible releases) with the NFS version 2 software truncate UIDs to 16 bits, creating possible security problems.

  • Users who use the cpio command with the default archive format to copy a file see an error message for each file. And, the UIDs and GIDs are set to nobody in the archive.

  • x86 based systems: Users that run SVR3-compatible applications will probably see EOVERFLOW return codes from system calls.

  • x86 based systems: If users attempt to create a file or directory on a mounted System V file system, the System V file system returns an EOVERFLOW error.

100000 or greater 

The ps -l command displays a maximum five-digit UID. So, the printed column won't be aligned when it includes a UID or GID larger than 99999.

262144 or greater 

Users who use the cpio command with the -H odc format or the pax -x cpio command to copy files see an error message returned for each file. And, the UIDs and GIDs are set to nobody in the archive.

1000000 or greater 

Users who use the ar command have their UIDs and GIDs set to nobody in the archive.

2097152 or greater 

Users who use the tar command, the cpio -H ustar command, or the pax -x tar command have their UIDs and GIDs set to nobody.

UNIX Groups

A group is a collection of users who can share files and other system resources. For example, users who working on the same project could be formed into a group. A group is traditionally known as a UNIX group.

Each group must have a name, a group identification (GID) number, and a list of user names that belong to the group. A GID number identifies the group internally to the system.

The two types of groups that a user can belong to are as follows:

For detailed guidelines on setting up group names, see Guidelines for Using User Names, User IDs, and Group IDs.

Sometimes, a user's secondary group is not important. For example, ownership of files reflect the primary group, not any secondary groups. Other applications, however, might rely on a user's secondary group memberships. For example, a user has to be a member of the sysadmin group (group 14) to use the Admintool software in previous Solaris releases. However, it doesn't matter if group 14 is his or her current primary group.

The groups command lists the groups that a user belongs to. A user can have only one primary group at a time. However, a user can temporarily change the user's primary group, with the newgrp command, to any other group in which the user is a member.

When adding a user account, you must assign a primary group for a user or accept the default group, staff (group 10). The primary group should already exist. If the primary group does not exist, specify the group by a GID number. User names are not added to primary groups. If user names were added to primary groups, the list might become too long. Before you can assign users to a new secondary group, you must create the group and assign it a GID number.

Groups can be local to a system or managed through a name service. To simplify group administration, you should use a name service such as NIS or a directory service such as LDAP. These services enable you to centrally manage group memberships.

User Passwords

You can specify a password for a user when you add the user. Or, you can force the user to specify a password when the user first logs in.

User passwords must comply with the following syntax:

Although user names are publicly known, passwords must be kept secret and known only to users. Each user account should be assigned a password. The password can be a combination of six to eight letters, numbers, or special characters.

To make your computer systems more secure, users should change their passwords periodically. For a high level of security, you should require users to change their passwords every six weeks. Once every three months is adequate for lower levels of security. System administration logins (such as root and sys) should be changed monthly, or whenever a person who knows the root password leaves the company or is reassigned.

Many breaches of computer security involve guessing a legitimate user's password. You should make sure that users avoid using proper nouns, names, login names, and other passwords that a person might guess just by knowing something about the user.

Good choices for passwords include the following:

Do not use these choices for passwords:

Home Directories

The home directory is the portion of a file system allocated to a user for storing private files. The amount of space you allocate for a home directory depends on the kinds of files the user creates, their size, and the number of files that are created.

A home directory can be located either on the user's local system or on a remote file server. In either case, by convention the home directory should be created as /export/home/username. For a large site, you should store home directories on a server. Use a separate file system for each /export/homen directory to facilitate backing up and restoring home directories. For example, /export/home1, /export/home2.

Regardless of where their home directory is located, users usually access their home directories through a mount point named /home/username. When AutoFS is used to mount home directories, you are not permitted to create any directories under the /home mount point on any system. The system recognizes the special status of /home when AutoFS is active. For more information about automounting home directories, see Task Overview for Autofs Administration in System Administration Guide: Network Services.

To use the home directory anywhere on the network, you should always refer to the home directory as $HOME, not as /export/home/username. The latter is machine-specific. In addition, any symbolic links created in a user's home directory should use relative paths (for example, ../../../x/y/x) so that the links are valid no matter where the home directory is mounted.

Name Services

If you are managing user accounts for a large site, you might want to consider using a name or directory service such as LDAP, or NIS or NIS+. A name or directory service enables you to store user account information in a centralized manner instead of storing user account information in every system's /etc files. When you use a name or directory service for user accounts, users can move from system to system using the same user account without having site-wide user account information duplicated on every system. Using a name or directory service also promotes centralized and consistent user account information.

User's Work Environment

Besides having a home directory to create and store files, users need an environment that gives them access to the tools and resources they need to do their work. When a user logs in to a system, the user's work environment is determined by initialization files. These files are defined by the user's startup shell, which can vary, depending on the release.

A good strategy for managing the user's work environment is to provide customized user initialization files, such as, .login, .cshrc, or .profile, in the user's home directory.

Note –

Do not use system initialization files, such as /etc/profile or /etc/.login, to manage a user's work environment. These files reside locally on systems and are not centrally administered. For example, if AutoFS is used to mount the user's home directory from any system on the network, you would have to modify the system initialization files on each system to ensure a consistent environment whenever a user moved from system to system.

For detailed information about customizing user initialization files for users, see Customizing a User's Work Environment.

Another way to customize user accounts is through role-based access control (RBAC). See Role-Based Access Control (Overview) in System Administration Guide: Security Services for more information.

Guidelines for Using User Names, User IDs, and Group IDs

User names, UIDs, and GIDs should be unique within your organization, which might span multiple domains.

Keep the following guidelines in mind when creating user or role names, UIDs, and GIDs: