EX200 Manage security — 10 Questions

Question 1

A junior admin needs to ensure that the 'apache' user (UID 48) cannot log in via SSH or console. Which command achieves this?

Accepted Answer

usermod -s /sbin/nologin apache. Setting the user's login shell to `/sbin/nologin` prevents the user from obtaining an interactive shell via SSH or console login. When the user attempts to log in, the system executes `/sbin/nologin`, which prints a polite message and exits immediately, effectively denying shell access while leaving other services (e.g., Apache) functional.

Answer

passwd -l apache

Answer

chage -l apache

Answer

usermod -e 1 apache

Question 2

An administrator runs 'getenforce' and sees 'Enforcing'. They then run 'setenforce 0' but SELinux still denies access to a custom application. What is the most likely reason?

Accepted Answer

The issue is due to file permissions or ACLs, not SELinux.. `setenforce 0` switches SELinux to permissive mode, which logs but does not enforce denials. If access is still denied after this command, the issue is not caused by SELinux enforcement but by traditional Linux file permissions (DAC) or ACLs. The administrator should check `ls -l` and `getfacl` to verify the file's ownership and permissions.

Answer

SELinux is in enforcing mode and the policy is misconfigured.

Answer

The application's SELinux context is incorrect and needs relabeling.

Answer

The change requires a reboot to take effect.

Question 3

A system administrator wants to allow user 'jdoe' to execute any command as root via sudo without being prompted for a password, but only from the host 'client1.example.com'. Which sudoers rule achieves this?

Accepted Answer

jdoe client1.example.com=(root) NOPASSWD: ALL. The sudoers rule 'jdoe client1.example.com=(root) NOPASSWD: ALL' specifies the user 'jdoe', the host 'client1.example.com' as the source host from which the command is run, the target user '(root)', the NOPASSWD tag to skip password authentication, and the command 'ALL' to allow any command. This matches the requirement exactly: passwordless root access restricted to a specific client host.

Answer

jdoe client1.example.com=(root) ALL

Answer

jdoe ALL=(root) NOPASSWD: ALL

Answer

jdoe ALL=(root) ALL

Question 4

Which TWO commands can be used to display SELinux contexts of files? (Choose two.)

Accepted Answer

stat -c %C. The `stat -c %C` command displays the SELinux security context of a file by using the `%C` format specifier, which outputs the security context string. The `ls -Z` command also shows SELinux contexts for files in a directory listing, with the `-Z` flag specifically requesting security context information. Both commands are standard tools for viewing SELinux labels on files.

Answer

chcon -l

Answer

id -Z

Answer

getenforce

Question 5

Which THREE factors determine whether a local user can SSH into a Red Hat Enterprise Linux 9 system? (Choose three.)

Accepted Answer

The user's shell is listed in /etc/shells.. SSHd validates that the user's login shell is listed in /etc/shells before allowing authentication. If the shell is not present in /etc/shells (e.g., /sbin/nologin or a custom script), SSHd will deny the connection, even if the user has valid credentials. This check is controlled by the 'AllowUsers' and 'DenyUsers' directives but is a fundamental security measure to prevent users with non-standard shells from gaining interactive access.

Answer

The /etc/nologin file exists.

Answer

The user has sudo privileges.

Question 6

Refer to the exhibit. A web server (httpd) is unable to serve files from a user's home directory. What is the most appropriate single command to resolve the issue?

Accepted Answer

setsebool -P httpd_enable_homedirs on. SELinux policy by default blocks httpd from reading user home directories via the httpd_enable_homedirs boolean, which is off. The command 'setsebool -P httpd_enable_homedirs on' enables this boolean and directly allows httpd to serve files from user home directories. Option C only sets the file context to httpd_sys_content_t, which is insufficient without the boolean because httpd still cannot traverse the user home directory path.

Answer

chcon -u system_u /home/user/www/index.html

Answer

semanage fcontext -a -t httpd_sys_content_t '/home/user/www(/.*)?' && restorecon -Rv /home/user/www

Answer

chcon -r object_r /home/user/www/index.html

Question 7

You are the system administrator for a small company. A developer, Alice, needs to restart the web server (httpd.service) on server 'web1.example.com' without being prompted for a password. She should also be able to run any command as root on that server, but only from the server itself (not remotely). Currently, Alice can SSH into the server using her SSH key, but when she runs 'sudo systemctl restart httpd', she is prompted for her password. You have verified that Alice is in the 'wheel' group. The sudoers file currently has the line '%wheel ALL=(ALL) ALL'. You want to modify sudoers to satisfy the requirement with minimal privilege. Which action should you take?

Accepted Answer

Add 'alice web1.example.com=(root) NOPASSWD: /usr/bin/systemctl restart httpd' to /etc/sudoers.d/alice.. It grants Alice passwordless sudo access specifically to the command `/usr/bin/systemctl restart httpd` on the host `web1.example.com` as root, meeting the requirement with minimal privilege. The `NOPASSWD:` tag is essential to bypass the password prompt, and the host restriction ensures the rule applies only when Alice is on that server.

Answer

Add 'alice web1.example.com=(root) NOPASSWD: ALL' to /etc/sudoers.d/alice.

Answer

Add 'alice web1.example.com=(root) /usr/bin/systemctl restart httpd' to /etc/sudoers.d/alice.

Answer

Change '%wheel ALL=(ALL) ALL' to '%wheel ALL=(ALL) NOPASSWD: ALL' in /etc/sudoers.

Question 8

A system administrator needs to configure a firewall using firewalld to allow incoming HTTPS traffic and deny incoming SSH traffic from a specific source IP 192.168.1.100. Which two commands should be run? (Choose two.)

Accepted Answer

firewall-cmd --add-service=https --permanent. `firewall-cmd --add-service=https --permanent` adds the HTTPS service (TCP port 443) to the permanent firewall configuration, which is required to allow incoming HTTPS traffic persistently across reboots. The `--permanent` flag ensures the rule survives a reload or restart, and the `--add-service` option uses predefined service definitions from firewalld to simplify rule creation.

Answer

firewall-cmd --runtime-to-permanent

Answer

firewall-cmd --add-rich-rule='rule family=ipv4 source address=192.168.1.100 service name=ssh reject' --permanent

Answer

firewall-cmd --add-service=http --permanent

Question 9

A junior administrator is tasked with setting up SELinux contexts on a Red Hat Enterprise Linux 9 server to allow Apache HTTPD to read and write to a custom directory /var/www/customcontent. The directory already exists and contains several files. The administrator has confirmed that the httpd service is running and SELinux is in enforcing mode. After changing the context to httpd_sys_content_t using chcon, the web server can read files but cannot write to the directory. The administrator needs to fix this without disabling SELinux or changing the mode to permissive. Which of the following is the correct next step?

Accepted Answer

Run restorecon -R -v /var/www/customcontent after setting the default context with semanage fcontext -a -t httpd_sys_rw_content_t '/var/www/customcontent(/.*)?'. The directory already has the httpd_sys_content_t type, which allows reading but not writing. To enable write access, the correct type is httpd_sys_rw_content_t. Option B correctly uses semanage fcontext to set the default context to this type and then runs restorecon to apply it persistently, ensuring Apache can both read and write.

Answer

Set the SELinux boolean httpd_enable_homedirs to on using setsebool.

Answer

Change the context to httpd_sys_content_t using chcon -R -t httpd_sys_content_t /var/www/customcontent

Answer

Run semanage fcontext -a -t httpd_sys_rw_content_t '/var/www/customcontent(/.*)?' without running restorecon.

Question 10

Order the steps to configure firewall rules to allow HTTP and HTTPS traffic using firewalld.

Accepted Answer

1. Add HTTP service: firewall-cmd --permanent --add-service=http
2. Add HTTPS service: firewall-cmd --permanent --add-service=https
3. Reload firewall: firewall-cmd --reload
4. Verify: firewall-cmd --list-services. Firewalld rules are added with --permanent flag and then reloaded to take effect.

Answer

1. Reload firewall: firewall-cmd --reload
2. Add HTTP service: firewall-cmd --permanent --add-service=http
3. Add HTTPS service: firewall-cmd --permanent --add-service=https
4. Verify: firewall-cmd --list-services

Answer

1. Add HTTP service: firewall-cmd --add-service=http (without --permanent)
2. Add HTTPS service: firewall-cmd --add-service=https (without --permanent)
3. Reload firewall: firewall-cmd --reload
4. Verify: firewall-cmd --list-services

Answer

1. Add HTTP service: firewall-cmd --permanent --add-service=http
2. Reload firewall: firewall-cmd --reload
3. Add HTTPS service: firewall-cmd --permanent --add-service=https
4. Verify: firewall-cmd --list-services