Mixed Deck — All LCA Topics Flashcards

Which command displays real-time per-CPU statistics including user, system, and idle percentages?

Answer: mpstat

mpstat from the sysstat package shows per-processor statistics in real time.

What does `set -o pipefail` change about pipeline exit status?

Answer: The pipeline returns the exit status of the last failed command, not just the last command

Without `pipefail`, a pipeline's exit status is the last command's status; with it, any failure in the pipeline propagates.

What does the `du` command do in Linux?

Answer: Shows disk usage per file/directory

The `du` command (disk usage) estimates file space usage, specifically showing the amount of disk space consumed by files or directories. When run without arguments, it displays the usage for the current directory and its subdirectories. This is useful for identifying large files or directories that are consuming significant disk space.

Which file contains the persistent mount information in Linux?

Answer: /etc/fstab

The `/etc/fstab` file stores persistent mount information, meaning it defines file systems that should be mounted automatically every time the system boots. Each entry in this file specifies a device, its mount point, file system type, and various options. This ensures that critical partitions and devices are always available.

In Bacula, which daemon manages job scheduling, client catalog, and coordinates the overall backup/restore process?

Answer: Director (bacula-dir)

The Bacula Director (bacula-dir) is the central control daemon that schedules jobs, maintains the catalog, and coordinates all backup and restore operations.

Which configuration file sets the DNS resolver search domain and nameserver addresses on a traditional (non-NetworkManager) Linux system?

Answer: /etc/resolv.conf

/etc/resolv.conf contains 'nameserver' and 'search' directives that configure the system's DNS resolver library.

Which command pins a process or command to specific CPU cores using a CPU affinity mask?

Answer: taskset

taskset sets or retrieves a process's CPU affinity, controlling which cores it may run on.

When building an RPM package, which directory structure is expected under the RPM build root?

Answer: BUILD, RPMS, SOURCES, SPECS, SRPMS

The rpmbuild process expects the standard directory structure: SOURCES for tarballs, SPECS for spec files, BUILD for compilation, RPMS for binary RPMs, and SRPMS for source RPMs.

Which SSH configuration directive restricts login to specific users?

Answer: AllowUsers

The AllowUsers directive in sshd_config accepts a space-separated list of usernames permitted to authenticate via SSH.

What is the purpose of the `mount` command in Linux?

Answer: To make a file system accessible at a specific directory

The `mount` command in Linux is used to attach a file system from a storage device to a specific directory in the existing file system hierarchy. This makes the files and directories on that device accessible through the specified mount point. Without mounting, the contents of the device cannot be accessed by the operating system.

What is the effect of running 'chmod 4755' on an executable?

Answer: Sets the SUID bit so the file runs with the owner's privileges

The leading '4' in octal notation sets the Set-UID bit, causing execution under the file owner's UID.

Which command compiles and installs software from source code using the traditional UNIX build method?

Answer: ./configure && make && make install

The classic source install sequence runs configure to check dependencies, make to compile, and make install to copy binaries to the system.

You need to capture only TCP traffic on port 443 on interface eth0 using tcpdump. Which command is correct?

Answer: tcpdump -i eth0 tcp and port 443

tcpdump uses BPF filter syntax; 'tcp and port 443' captures only TCP packets on port 443.

When a LCA professional encounters an unfamiliar challenge in virtualization & container management, what is the recommended first course of action?

Answer: Research applicable standards, consult with subject matter experts, and document the approach

Professional practice requires a methodical approach to unfamiliar challenges: research the applicable standards, consult experts when needed, and document the reasoning for the chosen approach.

In Nginx, which directive configures the path to the error log and its severity level?

Answer: error_log /var/log/nginx/error.log warn

The error_log directive sets the file path and minimum severity level (debug, info, notice, warn, error, crit, alert, emerg) for Nginx error logging.

Which Nginx directive sets the maximum allowed size of the client request body?

Answer: client_max_body_size

client_max_body_size limits the size of the request body; exceeding it returns a 413 Request Entity Too Large error.

Which operator is used for arithmetic expansion in bash?

Answer: $(( ))

The `$(( ))` syntax performs arithmetic expansion and is the preferred POSIX-compatible method.

What is the purpose of a GPG key in the context of YUM/DNF repositories?

Answer: To verify the authenticity and integrity of downloaded packages

GPG keys allow the package manager to verify that packages come from the claimed publisher and haven't been tampered with.

Which command is used to create a new ext4 file system in Linux?

Answer: mkfs.ext4

The `mkfs.ext4` command is specifically used to create an Ext4 file system on a specified partition or device. `mkfs` stands for "make filesystem," and the `.ext4` suffix indicates the type of file system to be created. This command initializes the file system structure, making the partition ready to store data.

What does the `set -e` option do in a bash script?

Answer: Exits the script immediately if any command returns a non-zero exit status

`set -e` causes the shell to exit immediately when a command exits with a non-zero status.