The /sbin/nologin shell is a special shell that prevents the user from logging into an interactive session. It is commonly used for system accounts that are not meant to be accessed by users, such as daemon or service accounts. When a user tries to log in with this shell, they will see a message like "This account is currently not available" and the login will fail.
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The /sbin/nologin shell is listed as one of the valid shells in the /etc/shells file1.
The CompTIA Linux+ Certification Exam Objectives mention that the candidate should be able to "configure and manage system accounts and groups, including password aging and restricted shells" as part of the Hardware and System Configuration domain2.
The usermod command can be used to change the user's login shell with the -s or --shell option3. For example, to change the shell of a user named daemon to /sbin/nologin, the command would be: sudo usermod
-s /sbin/nologin daemon

When antivirus software is configured to scan files in real time, and it includes the web root directory (e.g., /var/www/html), every time a user requests a page, image, or script, the antivirus scans that file before it's served. This introduces latency, especially on high-traffic servers, even when CPU, RAM, and network usage appear normal.
By excluding the web root from real-time scanning, the server can deliver files faster, improving website performance without adding hardware or changing the infrastructure.

The apt update command updates the package lists for repositories but does not upgrade installed packages.
After apt update, the administrator should run apt upgrade to install the latest versions of all packages.

The snap list command is used to display the installed snaps on the system1. Snaps are self-contained software packages that can be installed and updated across different Linux distributions2. The snap list command shows the name, version, revision, developer and notes of each snap1.
The snap find command is used to search for snaps in the Snap Store, which is an online repository of snaps2. The snap install command is used to install snaps from the Snap Store or from a local file2. The snap try command is used to test a snap without installing it, by mounting a directory that contains the snap files2.
These commands are not useful for verifying if a package was installed using a snap.

The command chattr +a /opt/app/logs will ensure the log file can only be written into without removing previous entries. The chattr command is a tool for changing file attributes on Linux file systems.
The +a option sets the append-only attribute, which means that the file can only be opened in append mode for writing. This prevents the file from being modified, deleted, or renamed. This is the best command to use to accomplish the task. The other options are incorrect because they either set the wrong attributes (+d, +i, or +c) or do not affect the file at all (-a). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 11: Managing Files and Directories, page 357.