EX200 Manage security — 20 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

Question 11

Match each networking term to its definition.

Accepted Answer

IP address: A unique identifier assigned to each device on a network.. The correct matches are: IP address (unique identifier), Subnet mask (network/host division), Default gateway (router to external networks), DNS server (name resolution). Common confusions include swapping definitions between IP address and subnet mask, or between default gateway and DNS server.

Answer

IP address: A 32-bit number used to divide an IP address into network and host portions.

Answer

Default gateway: A server that resolves domain names to IP addresses.

Question 12

A sysadmin wants to allow user 'alice' to run all commands as root via sudo. Which line should be added to /etc/sudoers?

Accepted Answer

alice ALL=(root) ALL. The sudoers entry 'alice ALL=(root) ALL' grants user alice permission to run any command as root on any host, exactly matching the requirement. Option C ('alice ALL=(ALL) ALL') allows running commands as any user, which is more permissive than needed. Option B restricts the host to 'localhost' and allows running as any user, so it is not the best fit. Option D uses '%alice' which refers to a group, not a user, and is therefore incorrect.

Answer

alice localhost=(ALL) ALL

Answer

alice ALL=(ALL) ALL

Answer

%alice ALL=(ALL) ALL

Question 13

An administrator wants newly created files to be readable and writable only by the owner, and readable by group and others. Which umask value should be set?

Accepted Answer

022. The umask value 022 removes write permissions for group and others, while leaving read and execute permissions intact. Since the default base permissions for files are 666 (rw-rw-rw-), applying umask 022 results in 644 (rw-r--r--), which gives the owner read/write access and group/others read-only access — exactly matching the requirement.

Answer

027

Answer

002

Answer

077

Question 14

A user reports that SSH key-based authentication fails, but password authentication works. The admin checks /etc/ssh/sshd_config: PubkeyAuthentication yes, PasswordAuthentication no (contrary to the report). Which is the most likely reason key-based auth fails?

Accepted Answer

The .ssh directory has permissions 755.. SSH key-based authentication requires that the ~/.ssh directory and its contents have restrictive permissions. If the .ssh directory has permissions 755, it is world-readable, which violates SSH's security model. SSH daemon (sshd) will refuse to use the authorized_keys file if the directory permissions are too permissive, causing key-based authentication to fail even though PubkeyAuthentication is enabled.

Answer

SELinux is blocking SSH from reading the key.

Answer

The public key is not in ~/.ssh/authorized_keys.

Answer

SSH is configured to use a different port.

Question 15

Which file contains the hashed passwords for local user accounts?

Accepted Answer

/etc/shadow. The /etc/shadow file stores hashed passwords for local user accounts, along with password aging and expiration information. It is readable only by root (or privileged processes) to prevent unauthorized access to password hashes, unlike /etc/passwd which is world-readable.

Answer

/etc/security/passwd

Answer

/etc/passwd

Answer

/etc/gshadow

Question 16

An administrator needs to grant user 'dev' the ability to execute /usr/local/bin/deploy.sh as root without a password, but no other commands. Which sudoers entry accomplishes this?

Accepted Answer

dev ALL=(root) NOPASSWD: /usr/local/bin/deploy.sh. The correct syntax is 'dev ALL=(root) NOPASSWD: /usr/local/bin/deploy.sh'. This allows dev to run that specific command as root without a password.

Answer

dev ALL=(root) PASSWD: /usr/local/bin/deploy.sh

Answer

dev ALL=(ALL) NOPASSWD: /usr/local/bin/deploy.sh

Answer

%dev ALL=(root) NOPASSWD: /usr/local/bin/deploy.sh

Question 17

Refer to the exhibit. What is the primary security concern with this sudo configuration?

Accepted Answer

The less command allows executing shell commands via !, enabling privilege escalation.. The `less` command, when executed with sudo, allows the user to escape to a shell by typing `!command` from within the pager. This bypasses the intended restriction of only running `/usr/bin/less` as root, enabling arbitrary command execution with elevated privileges. The NOPASSWD directive further compounds the risk by removing the password prompt, making the escalation trivial.

Answer

The NOPASSWD option eliminates the need for a password.

Answer

The entry uses (ALL) instead of (root), allowing jane to run as any user.

Answer

The command /usr/bin/less can be used to read any file.

Question 18

Refer to the exhibit. A CGI script located at /var/www/cgi-bin/test.cgi fails to execute. What is the most likely cause?

Accepted Answer

The SELinux context should be httpd_sys_script_exec_t.. SELinux contexts control which processes can access files and directories. The CGI script at /var/www/cgi-bin/test.cgi requires the httpd_sys_script_exec_t context to allow the Apache HTTP server (httpd) to execute it. Without this context, SELinux will deny execution even if file permissions and ownership are correct.

Answer

The script is in the wrong directory.

Answer

The script is not marked as executable.

Answer

The file permissions are incorrect.

Question 19

Refer to the exhibit. An administrator wants to add the HTTP service (port 80) to the internal zone permanently. Which sequence of commands should be used?

Accepted Answer

firewall-cmd --zone=internal --add-service=http --permanent; firewall-cmd --reload. It uses the --permanent flag to make the rule persistent across reboots, and then runs firewall-cmd --reload to apply the permanent configuration to the running runtime environment without restarting the firewalld service. This sequence ensures the HTTP service is added to the internal zone permanently while maintaining active connections.

Answer

firewall-cmd --add-service=http --zone=internal; firewall-cmd --reload

Answer

firewall-cmd --permanent --add-service=http --zone=internal; systemctl restart firewalld

Answer

firewall-cmd --zone=internal --add-service=http; firewall-cmd --runtime-to-permanent

Question 20

Which TWO statements about the /etc/shadow file are true? (Select exactly two.)

Accepted Answer

Contains hashed passwords for local users.. The /etc/shadow file stores hashed user passwords using algorithms like SHA-512 or yescrypt, as defined by the pam_unix module. It also contains password aging fields (e.g., minimum days, maximum days, warning period) that enforce password expiration policies. These two functions make options A and E correct.

Answer

Contains the user's UID.

Answer

Is used to store encrypted group passwords.

Answer

Is readable by all users.