utmpx

The utmpx file is a system file found on Unix-like operating systems that logs information about user logins and logouts. It is a binary file that contains records of current users, their terminal devices, login times, and hostnames. This information is essential for system administration tasks such as tracking user activity, managing resources, and identifying potential security issues.

The utmpx file is typically located in the /var/run directory. Its contents can be accessed using the `who` and `w` commands, which display information about logged-in users. The `last` command, on the other hand, reads the related utmp file to show historical login and logout information. The format of the utmpx file is defined by the `utmpx` structure in the system's header files, such as `<utmpx.h>`.

Entries in the utmpx file include fields for the user's name, the terminal device they are using, their process ID, the time of login, and the IP address or hostname of the remote host if they logged in remotely. When a user logs in, a new record is created in the utmpx file. When they log out, the record is updated to reflect the logout time. System processes also create entries in utmpx to indicate their startup and termination.

The utmpx file is crucial for maintaining an accurate record of system access. It helps administrators understand who is using the system, when, and from where, which is vital for auditing and troubleshooting.