Home > Articles > Operating Systems, Server

This chapter is from the book

4.14 Module Access Control

It is possible to grant a Webmin user or group access to only a subset of features in the Users and Groups module. This is most commonly used to allow a subadministrator the right to edit only selected users and groups on the system, and to change their attributes in only limited ways. In a virtual hosting environment, for example, you may want to give a Webmin user the ability to create and edit up to 10 users with UIDs in a limited range, and home directories under a fixed directory. These privileges give the user no way to gain root access and affect users that do not belong to him.

Table 4.3. Environment Variables for Before and After Commands


Indicates which action is being taken. Possible values are:



The username of the user being created, modified, or deleted. Not set when a group action is being performed.


The user ID of the user being created, modified, or deleted.


The group ID of the user.


The real name of the user, including any office and phone information.


The shell of the user.


The home directory of the user.


The plain text password of the user, if available.


A comma-separated list of any secondary groups to which the user belongs.


The name of the group being added, modified, or deleted. Not set when a user action is being performed.

Chapter 52 explains how to create additional Webmin users and edit their module access control in more detail. The following steps cover just the parts of the process that grant the kind of limited access that is specific to the Users and Groups module:

  1. In the Webmin Users module, click on Users and Groups next to the name of the user that you want to edit. This will take you to the access control form shown in Figure 52.3.

  2. Change the Can edit module configuration? field to No.

  3. The UNIX users who can be edited field controls the users that can be changed by this Webmin user. You would typically set it to Users with UIDs in range and enter maximum and minimum UIDs into the fields next to it, such as 5000 and 5010.

  4. To allow the addition of new UNIX users, set the Can create new users? field to Yes.

  5. Set the Can view batch file form? option to No. This will prevent the Webmin user from creating and editing users from a batch script, which is not normally necessary. Allowing it, however, does not grant the user any additional privileges and is not a security risk.

  6. For the UIDs for new and modified users fields, enter the same UIDs as in Step 4.

  7. Deselect the More than one user can have the same UID option, but leave the UIDs of existing users can be changed option selected. An untrusted subadministrator should not normally be allowed to create multiple users with the same UID due to the problems that this can cause.

    When UID clashes are prevented, the Webmin user will not be able to create any more UNIX users than fit in his allowed UID range.

  8. In the Allowed groups for new or modified users field, you would typically select the Only groups option and enter the names of any groups of which new users can be primary or secondary members. Normally you would just enter a single group like users. Leaving this field set to All groups is a very bad idea, because it would allow the creation of users who are members of the root or bin groups, and who can thus edit important system files and executables. The Groups with GIDs in range option can be useful if this Webmin user is allowed to create multiple groups of his own within the same GID range.

  9. To restrict the shells that a new user can be assigned, set the Allowed shells for new or modifed users to Listed and enter their paths into the text box below. This can be useful to allow the creation of only mail-only users who always have the shell /bin/false.

  10. Set the Home directories must be under field to a directory that will only be used for accounts created by this Webmin user. Setting it to /home is a bad idea, because this would allow the subadministrator to rename or delete directories belonging to other users that are under /home. Instead, enter something like /home/subadmin.

    To force every user's home directory to be based on his username (such as /home/subadmin/username), check the Home directory is always same as username box.

  11. To stop the Webmin user from deselecting some of the options at the bottom of the user creation, editing and deletion forms, deselect the matching Allowed on save options. Any that are not chosen will effectively always be turned on.

  12. Assuming you just want the Webmin user to create and edit UNIX users, set the UNIX groups who can be edited field to No groups.

  13. If you want to restrict the user from viewing recent logins, change the Can display logins by field. Any user who can login with telnet or SSH can run the last command anyway to display logins, so setting this option to No users does not usually make your system any more secure.

  14. Finally, click Save. You will be returned to the module's main page and the new access control restrictions will be immediately applied to the Webmin user.

Be careful when granting a Webmin user access to certain UNIX users, as a mistake may allow him to edit the root user or create a new user who is equivalent to root. There are also many other users like bin, uucp, and httpd that own important system files or are used for running server and daemon processes. Someone who can edit or login as one of these users could gain root privileges on your system or access files that he is not supposed to.

Often the access control in the Disk Quotas and Scheduled Cron Jobs module is set up to allow editing of the quotas and Cron jobs of the same UNIX users as those that can be edited and created in this module. All modules support the UID range and primary group access control options, which can be set in the same way.

It is also possible to use the Users and Groups access control form to allow a user to edit or create selected UNIX groups, though this is not generally as useful. Granting an untrusted user the rights to edit all groups on the system is a bad idea, as he would make himself a member of the root or bin group and so be able to read or write critical files.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020