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:
"Use the -p option to display messages from the journal that have a specific priority level."
# 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:
"Use the journalctl -k command to display kernel messages since the last system boot."
# 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:
"When you specify a single priority level, journalctl shows messages at that level and higher severity."
# journalctl -p 6
Why Other Options Are Not Correct:
"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
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.