Shulou(Shulou.com)06/02 Report--

The function of log

Used to record all kinds of events that occur during the operation of the system and the program.

By reading the log, it is helpful to diagnose and solve the system failure.

Classification of log files

Kernel and Syslog:

It is managed by the system service syslog, and the log format is basically similar.

User log:

Record information about system users logging in and logging out of the system

Program log:

Log files independently managed by various applications with inconsistent recording format

Log save location

By default, it is located in: / var/log directory

Main log file log file directory log file introduction / var/log/messages kernel messages and various applications / var/log/cron records crond scheduled task production information / var/log/dmesg records various event information of the Linux system during boot / var/log/maillog records enter or send out system email activity / var/log/lastlog records each user's most recent login event / var / log/secure records security event information related to user authentication / var/log/wtmp records each user login, Logout and system startup and downtime events / var/log/btmq logging failed, erroneous login attempts and authentication event log messages warning level warning content 0EMERG (urgent) will cause the host system to be unavailable 1ALERT (warning) problems that must be addressed immediately 2CRIT (serious) more serious cases 3ERR (error) running error 4WARING (reminder) may affect system function Need to provide the user's important event 5NOTICE (note) will not affect the normal function, but need to pay attention to the event 6INFO (information) general information 7DEBUG (debugging) program or system debugging information user log file

In wtmp, btmp, lastlog and other log files, the system user login, logout and other related event messages are saved. However, these files are binary data files, which can not be browsed directly by text viewing tools such as tail and less, but need to use user query commands such as who, w, users, last and lastb to obtain log information.

(1)-- query the status of current users logged in-- users, users, w commands

Users: simply output the name of the user currently logged in, with each displayed user name corresponding to a login session

Who: used to report each user information in the currently logged-in system

W: used to display each user in the current system and the process information they are running, which is richer than the output of users and who commands.

(2) query the history of user login-last, lastb commands

Lastb: used to query the records of users who failed to log in, such as incorrect user name and incorrect password.

Last: used to query the records of users who successfully logged in to the system. The most recent login will be displayed at the top.

Program log

In the Linux operating system, there are still a considerable number of applications that do not use rsyslog services to manage logs, but rather maintain their own log records. For example, the httpd Web Service uses two log files, access_log and error_log, to record customer access events and error events, respectively.

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