Linux log Files utmp, wtmp, Lastlog, messages

1. Information about the current logged-in user is recorded in file utmp; ==who command

2. Login entry and exit record in document WTMP; ==W command

3, the last login file can be viewed with lastlog command;

4. messages====== log information from the Syslog

Note: Wtmp and utmp files are binary files and they cannot be clipped or merged (using the Cat command) such as the tail command. User

The information contained in these two files needs to be used by WHO, W, users, last, and AC.

Example:
Last command search wtmp to show users who have logged in since the first time the file was created

Users print out a separate line for the currently logged-on user with a login session for each displayed user name

The W command queries the utmp file and displays information about each user in the current system and the process it is running

The WHO command queries the utmp file and reports each user who is currently logged on

The AC command reports the user's link time (in hours) based on login entry and exit in the current/var/log/wtmp file.

Utmp file, which records the current login into the system of the various users;

A binary record containing the following structures is written to these two files:
struct UTMP {
Char Ut_line[8]; /* TTY line: "Ttyh0", "ttyd0", "ttyp0", ... * *
Char Ut_name[8]; /* Login Name */
Long Ut_time; /* seconds since Epoch * *
};

When logged in, the login program fills in such a structure and writes it to the Utmp file, and also adds it to the wtmp file. When logging off, the INIT process erases the corresponding records in the Utmp file (each byte is filled with 0) and adds a new record to the Wtmp file. Read the logout record in the Wtmp file, and its Ut_name field is cleared to 0. Special record entries are added to the Wtmp file when the system restarts, and before and after changes to the system time and date. The WHO (1) program reads the Utmp file and prints its contents in a readable format. Later versions of Unix provide the last (1) command, which reads the wtmp file and prints the selected record. The Wtmp file, which tracks individual logon and logoff events.

wted
Wtmp/utmp Log editing program. You can use this tool to edit all wtmp or utmp types of files.

Z2
Utmp/wtmp/lastlog Log Cleanup Tool. You can delete all entries for a user name in the Utmp/wtmp/lastlog log file. However, if the Linux system needs to manually modify its source code, set the location of the log file.

Linux log Files utmp, wtmp, Lastlog, messages