Logs, scheduled tasks, host names, System time

1. Log

The process and operating system cores need to be able to log the events that occur, which can be used for system audits and troubleshooting problems. By management, these logs are permanently stored in the/var/log

In the red HAT7 version, there are two log services, namely Rsyslog and systemd-journal

Systemd-journal is an improved log management service that collects messages from the kernel, early stages of the boot process, standard output, system logs, and errors during daemon startup and operation. It writes these messages to a structured event, where the log is not persisted by default, and the previous log is lost after each reboot. In addition, some rsyslog logs that cannot be collected are also written to systemd-journal.

(1). Rsyslog logs that are collected are recorded in each log file in the/var/log directory.

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Systemctl status Rsyslog See if Rsyalog service is running

Its configuration file is in/etc/rsyslog.conf

For each log type, log a class of logs into a file.

(2). Log level

Number	Priority level	Severity
0	Emerg	System not available
1	Alert	Immediate measures must be taken
2	Crit	Critical condition
3	Err	A very serious error condition.
4	Warning	Warning
5	Notice	A normal but important event
6	Info	Informational Events
7	Debug	Debug level messages

View Rsyslog configuration file: vim/etc/rsyslog.conf

Any configuration files that have been modified must be restarted.

(3). View SYSTEMD log Entry specific commands Journalctl

Journalctl used to view all the logs

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Journalctl-n [NUM] Displays the last 10 log entries by default

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Journalctl-p Err filtering log level output

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You can also output a specific time range, two options-since and-until, the accepted time format is YYY-MM-DD hh:mm:ss, if the date is omitted, the command is assumed to be the date of the day, and if the time is omitted, it is assumed to be 00:00:00, except for the specific date time. These two options also accept yesterday,today,tomorrow.

(4). Save SYSTEMD Log

Typically saved in/etc/log/journal, this allows you to persist the SYSTEMD log, but only one months of log information is saved by default, which can be adjusted in the configuration file/etc/systemd/journald.conf

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2. Check the system time in Red HAT7

Command	Explain
Timedatectl	View system time
Timedatectl List-timezones	List Time zone information
Timedatectl Set-timezone Asia/shanghai	Setting the time zone
Timedatectl set-time 22:19:00[yyy-mm-dd Hh:mm:ss]	Set time and date
Timedatectl Set-ntp[true|false]	To start or disable NTP (Network Time Protocol) synchronization

The configuration file is in/ETC/CHRONY.CONFZ.

3. Scheduled Tasks

(1). Perform a task at some point in the future

Related command: At is relatively simple, not much to say

(2). Perform a task periodically

Cron: Self is a service that runs uninterrupted

For cron tasks, there are two categories: System cron task, user-independent, System periodic maintenance, format: minutes and hours of the day and month user tasks

User Cron task: usually defined in the/var/spool/cron/username directory

Format: minutes hours Sun Moon Week task

Valid values for TIME:

Minutes 0-59 Hours 0-23 Day 1-31 Month 1-12 Weeks 0-7, 0, and 7 mean Sunday.

Time wildcard characters:

* All valid values corresponding to

, discrete-time point values

-Continuous point in time

/how often in the corresponding value range

Management of user cron tasks:

Crontab This command enables the detection of syntax:

Options	Explain
-L	List the cron tasks for the current user
-E	Edit the cron task for the current user
-R	Remove all cron tasks
-U USERNAME	Manage cron for other users, only root is available

4. Host Name

Hostname Viewing host names

Hostname "hostname" temporarily modifies host name

The static hostname is saved in the/etc/hostname file, and Hostnamectl can modify the file

HOSTNAMECTL set-hostname hostname permanently Modify host name

There is a name resolution: used to convert the host name to an IP address, or vice versa.

Logs, scheduled tasks, host names, System time