varlogauthlog

varlogauthlog commonly refers to the system authentication log file typically located at /var/log/auth.log on Debian-based Unix and Linux distributions. It records authentication-related events generated by system services such as sshd, PAM modules, sudo, su, gdm/login managers, and other components that perform user authentication or authorization checks. Similar logs may appear under different names on other distributions (for example /var/log/secure on Red Hat–based systems) or be retained in the systemd journal.

Entries in the authentication log usually include a timestamp, the originating process name and PID, the username or account involved, and a brief description of the event (successful or failed logins, sudo invocations, password changes, session openings and closings). The format is determined by the system logger (syslogd/rsyslog/syslog-ng) that forwards messages to the file.

Access to the authentication log is typically restricted to privileged users to protect sensitive information; default permissions often allow root and administrative groups to read the file. Log rotation and retention are managed by utilities such as logrotate to prevent uncontrolled growth and to implement archival policies.

Administrators use the authentication log for troubleshooting login problems, auditing access, and forensic analysis after security incidents. Because it contains sensitive data and indicators of compromise, proper protection, monitoring, and integration with centralized logging or intrusion detection systems are recommended.