1z0-106 Oracle Linux 8 Advanced System Administration Questions and Answers

Thednf infocommand provides detailed information about an installed package. When used with the path of a binary (such as/usr/bin/gzip), it shows the package that provides the binary along with detailed information like the version, release, architecture, size, source, repository, summary, URL, and license.

Explanation of Answer A:Consistent network device naming is enabled by default in Oracle Linux 8. This feature ensures that network interfaces retain their names across reboots, which is important for maintaining network configuration consistency. This is managed through the Predictable Network Interface Names feature, which is part of thesystemdproject and is implemented inudev.

Explanation of Answer B:Theudevdevice manager is responsible for dynamically managing device nodes in the/devdirectory. It generates network interface names based on several naming schemes, such as the interface’s physical location on the bus (likeenp0s3), MAC address, or other attributes. These schemes are used to provide consistent and predictable names for network interfaces.

Option C (Correct):Theall-squashoption in the/etc/exportsfile maps all user and group requests from remote systems to the anonymous user (nfsnobody) on the NFS server. However, because theanonuidandanongidoptions are specified with501, all incoming requests are explicitly mapped to the UID and GID of the unprivileged local user with UID 501 and GID 501. Thero(read-only) option allows all clients to mount/usr/shared/toolsas read-only.

Option A (Incorrect):This is incorrect because all clients can mount the directory, but all users' requests are squashed to UID 501. There is no exception for local 501 users.

Option B (Incorrect):The answer is incorrect because it incorrectly states "privileged local 501 user." The UID 501 is typically an unprivileged user.

Option D (Incorrect):Theall-squashoption does not override the UID and GID explicitly defined byanonuidandanongid. Instead, it maps all remote requests to these values.

Option E (Incorrect):Theanonuidandanongiddirectives are not ignored; they are explicitly used to map all requests to the specified UID and GID.

Oracle Linux Reference:For more information on NFS exports and options, refer to:

Oracle® Linux 8: Managing NFS and NIS

man exportsfor details on export options.

Explanation of Answer A:Thesysctl -wcommand is used to modify kernel parameters at runtime. It allows you to set the value of a specific parameter in the/proc/sysdirectory. For example,sysctl -w net.ipv4.ip_forward=1will enable IP forwarding by writing the value directly to the corresponding file in/proc/sys.

Explanation of Answer B:Using theechocommand to write values directly to specific files in the/proc/sysdirectory is another method to change kernel parameters dynamically for the running system. For instance,echo 1 > /proc/sys/net/ipv4/ip_forwardachieves the same effect as thesysctl -wcommand.

Option A (Correct):/lib64/securityis a common directory where PAM (Pluggable Authentication Module) libraries are stored for 64-bit systems.

Option D (Correct):/lib/securityis another directory where PAM libraries are stored, usually on 32-bit systems or as a fallback for 64-bit systems.

Option B (Incorrect):/etc/pam.dcontains configuration files for PAM modules but does not store the modules themselves.

Option C (Incorrect):/usr/libis a general directory for libraries but does not specifically store PAM modules.

Option E (Incorrect):/var/libis typically used for variable state information and is not relevant for storing PAM modules.

Oracle Linux Reference:Refer to:

Oracle® Linux 8: Managing Authentication

Explanation of Answer B:The commandssh -L 5011:127.0.0.1:80 bob@10.10.2.20 -f sleep 30creates a local port forward. This means port5011on the client machine is forwarded to port80on the remote machine (10.10.2.20) using the SSH connection.

Explanation of Answer E:The-foption of thesshcommand causes the SSH connection process to fork to the background after authentication is complete. Thesleep 30command keeps the SSH connection alive for 30 seconds.

Option A (Correct):A user private group (UPG) ensures that each user has their own unique group created with the same name and ID as the user.

Option E (Correct):The UPG model helps prevent other users from modifying files by default, as newly created files are assigned to the user’s unique group and not to a shared group.

Option B (Incorrect):UPG does not give the capability to create new group users; this is related to group management commands.

Option C (Incorrect):UPG does not providesudocapabilities;sudoconfiguration is managed separately.

Option D (Incorrect):UPGs do not limit reading files to group users by default; it depends on specific file permissions.

Oracle Linux Reference:Refer to:

Oracle® Linux 8: Managing Users and Groups

Explanation of Answer D:Theinitramfs(initial RAM filesystem) is a temporary filesystem loaded into memory during the boot process, containing essential drivers and utilities. The kernel usesinitramfsto load necessary drivers and modules required to access the root file system, particularly if it resides on a disk that requires special drivers.

Explanation of Answer E:Both thevmlinuz(the compressed Linux kernel image) and theinitramfsfile are located in the/bootdirectory. The bootloader, such as GRUB, reads these files from/bootto start the system.

Option C (Correct):If a device named/dev/hdbwith theide-diskdriver is discovered, a symbolic link/dev/sparediskwill be created, pointing to/dev/hdb.

Option D (Correct):TheKERNEL=="hdb"match specifies that the device will have the kernel device name/dev/hdb.

Option A (Incorrect):This is incorrect because existing symbolic links are not overwritten unless explicitly defined.

Option B (Incorrect):The device itself is not renamed to/dev/sparedisk; rather, a symbolic link is created.

Option E (Incorrect):The rule specifically requires bothKERNEL=="hdb"andDRIVER=="ide-disk"to match; it is not an either/or condition.

Option B: journalctl -p err shows only error log level.

Explanation:

The -p or --priority option in journalctl filters messages by their priority level.

When specifying asingle priority level, journalctl shows messagesonlyat that level.

The priority levels, as per syslog standards, are:

0: emerg

1: alert

2: crit

3: err

4: warning

5: notice

6: info

7: debug

Therefore, journalctl -p err displays messages with priorityerr (3)only.

Oracle Linux Reference:

Oracle® Linux 8: Managing Log Files- Section onFiltering Output withjournalctl:

"Use the -p option to display messages from the journal that have a specific priority level."

Example:

# journalctl -p err

Option D: journalctl -k shows kernel logs since the last boot.

Explanation:

The -k or --dmesg option filters messages from the kernel, equivalent to the output of the dmesg command.

This option implies -b, which limits the output to messages from the current boot.

Therefore, journalctl -k displays kernel messages since the last boot.

Oracle Linux Reference:

Oracle® Linux 8: Managing Log Files- Section onViewing Kernel Messages:

"Use the journalctl -k command to display kernel messages since the last system boot."

Example:

# journalctl -k

Option E: journalctl -p 6 shows all info log level messages and above.

Explanation:

When specifying a single numeric priority, journalctl displays messages withthat priority level and higher priority levels(i.e., lower severity).

Priority levels are ordered from 0 (highest severity) to 7 (lowest severity).

Therefore, journalctl -p 6 shows messages with priorities:

0 (emerg)

1 (alert)

2 (crit)

3 (err)

4 (warning)

5 (notice)

6 (info)

This includesinfo level messages (6)and all higher priority messages.

Oracle Linux Reference:

Oracle® Linux 8: Managing Log Files- Section onFiltering Output with journalctl:

"When you specify a single priority level, journalctl shows messages at that level and higher severity."

Example:

# journalctl -p 6

Why Other Options Are Not Correct:

Option A:journalctl -bl -p err fails if journal persistence is not configured.

Explanation:

The -b option displays messages from the current boot. This works even if journal persistence isnotconfigured because the logs from the current boot are stored in volatile memory (/run/log/journal).

Therefore, the command doesnot failif journal persistence is not configured.

Oracle Linux Reference:

Oracle® Linux 8: Managing Log Files- Section onJournal Volatility:

"By default, the journal stores logs in volatile memory and does not persist logs across reboots unless persistent storage is configured."

Option C:journalctl -p notice..warning shows all messages from notice to warning log level since the last boot.

Explanation:

The -p option allows specifying arangeof priorities. However, the correct order for the range should be from thehigher priority (lower number)to thelower priority (higher number).

Also, the priorities should be specified in the correct sequence, and ranges are inclusive.

Moreover, journalctl by default shows messages from all boots unless limited by the -b option.

Therefore, without -b, it does not limit messages to "since the last boot," making the statement incorrect.

Correct Command:

To display messages fromwarning (4)tonotice (5), the command should be:

# journalctl -p warning..notice -b

But even then, the priorities need to be specified correctly, and the command in Option C is incorrect.

Conclusion:

OptionsB,D, andEare correct because they accurately describe the behavior of the journalctl command in filtering and displaying log messages based on priority levels and sources.

Explanation of Answer C:Bothatandbatchcan accept commands from standard input or from a file specified using the-foption. This allows scheduling of tasks by providing the commands directly or reading them from a file.

Explanation of Answer E:Theatcommand schedules a one-time task to run at a specified time. It is used to execute commands once at a particular time in the future.

Explanation of Answer C:Thesscommand can be used to display all available internal TCP information, including established connections with detailed TCP metrics, which matches the output in Answer C.

Explanation of Answer D:Thesscommand can display listening ports (TCP in this case) with details like congestion control algorithms (cubic), which aligns with Answer D. The output indicates a listening TCP socket on port 80.

Option D: anacron jobs may run only once a day.

Explanation:

Anacronis designed for systems that are not running continuously (e.g., desktops or laptops that may be powered off at night). It ensures that scheduled tasks are executed at the specified intervals.

Anacron jobs are defined with periods indays. The minimal unit of time for scheduling in Anacron isone day. Therefore, Anacron can schedule jobs to runonce a dayat most.

It is not intended for tasks that need to run multiple times per day.

Oracle Linux Reference:

Oracle® Linux 8: Scheduling Tasks- Section onAnacron Configuration Files:

"Anacron is used to run commands periodically with a frequency specified in days."

Option E: anacron jobs are used to run cron jobs if the system was powered off when they were scheduled to run.

Explanation:

Anacron complements Cron by ensuring thatscheduled jobs are not missedif the system is powered off or in standby mode at the time they were supposed to run.

When the system boots up, Anacron checks for any scheduled jobs that did not run and executes them accordingly.

This is particularly useful for laptops or desktops that are not always on.

Oracle Linux Reference:

Oracle® Linux 8: Scheduling Tasks- Section onUnderstanding Anacron:

"Anacron is designed to run commands periodically with specified frequency, but unlike cron, it does not assume that the system is running continuously."

Why Other Options Are Not Correct:

Option A:cron jobs may run only once a minute.

Explanation:

Cron allows scheduling tasks with a minimum granularity ofone minute. However, this means that tasks can be scheduled to runevery minute, not limited to only once a minute.

Multiple cron jobs can be scheduled to run at the same minute.

Therefore, the statement is misleading; cron jobs can runas frequently as every minute, but notonly once a minute.

Option B:All crontabs are held in the /etc/cron.d directory.

Explanation:

The /etc/cron.d directory is used for system-wide cron jobs provided by packages or administrators.

User-specific cron jobs are stored in /var/spool/cron/ or managed via the crontab command and not placed in /etc/cron.d.

Additionally, the system crontab file is /etc/crontab, and there are also directories like /etc/cron.hourly, /etc/cron.daily, etc.

Option C:The crond daemon looks for jobs only in /etc/crontab.

Explanation:

The crond daemon checks multiple locations for scheduled jobs:

User crontabs managed via the crontab -e command (stored in /var/spool/cron/).

System-wide crontab file (/etc/crontab).

The /etc/cron.d/ directory.

The /etc/cron.hourly/, /etc/cron.daily/, /etc/cron.weekly/, and /etc/cron.monthly/ directories.

Therefore, crond does not look for jobsonlyin /etc/crontab.

Conclusion:

OptionsDandEare correct because they accurately describe the characteristics and purposes of Anacron in the context of scheduling tasks on an Oracle Linux system.

Option A (Correct):Boot parameters are set in/etc/default/grubunder theGRUB_CMDLINE_LINUXdirective. After modifying this file, thegrub2-mkconfigcommand must be run to apply changes.

Option C (Correct):The/boot/loader/entries/directory contains configuration files for each kernel version, which store the boot parameters separately.

Option B (Incorrect):Boot parameters specified at the GRUB command line are not persistent across reboots unless added to the configuration file.

Option D (Incorrect):Parameters set from the GRUB menu are temporary and do not apply to subsequent reboots.

Oracle Linux Reference:Refer to:

Oracle® Linux 8: Configuring GRUB2

Explanation of Answer D:The entrypool pool.ntp.org offlinein the/etc/chrony.conffile specifies that thechronydservice should not automatically poll the NTP pool servers atpool.ntp.orguntil it is explicitly enabled by thechronyccommand. This setting is typically used in environments where the network is not always available (e.g., laptops or isolated systems) to avoid unnecessary polling.