auditd - The Linux Audit daemon
auditd [-f] [-l] [-n] [-s disable|enable|nochange]
auditd is the userspace component to the Linux Auditing System. It's responsible for writing audit records to the disk. Viewing the logs is done with the ausearch or aureport utilities. Configuring the audit system or loading rules is done with the auditctl utility. During startup, the rules in /etc/audit/audit.rules are read by auditctl and loaded into the kernel. Alternately, there is also an augenrules program that reads rules located in /etc/audit/rules.d/ and compiles them into an audit.rules file. The audit daemon itself has some configuration options that the admin may wish to customize. They are found in the auditd.conf file.
-f leave the audit daemon in the foreground for debugging. Messages also go to stderr rather than the audit log. -l allow the audit daemon to follow symlinks for config files. -n no fork. This is useful for running off of inittab or systemd. -s=ENABLE_STATE specify when starting if auditd should change the current value for the kernel enabled flag. Valid values for ENABLE_STATE are "disable", "enable" or "nochange". The default is to enable (and disable when auditd terminates). The value of the enabled flag may be changed during the lifetime of auditd using 'auditctl -e'.
SIGHUP causes auditd to reconfigure. This means that auditd re-reads the configuration file. If there are no syntax errors, it will proceed to implement the requested changes. If the reconfigure is successful, a DAEMON_CONFIG event is recorded in the logs. If not successful, error handling is controlled by space_left_action, admin_space_left_action, disk_full_action, and disk_error_action parameters in auditd.conf. SIGTERM caused auditd to discontinue processing audit events, write a shutdown audit event, and exit. SIGUSR1 causes auditd to immediately rotate the logs. It will consult the max_log_size_action to see if it should keep the logs or not. SIGUSR2 causes auditd to attempt to resume logging. This is usually needed after logging has been suspended.
/etc/audit/auditd.conf - configuration file for audit daemon /etc/audit/audit.rules - audit rules to be loaded at startup /etc/audit/rules.d/ - directory holding individual sets of rules to be compiled into one file by augenrules.
A boot param of audit=1 should be added to ensure that all processes that run before the audit daemon starts is marked as auditable by the kernel. Not doing that will make a few processes impossible to properly audit. The audit daemon can receive audit events from other audit daemons via the audisp-remote audispd plugin. The audit daemon may be linked with tcp_wrappers to control which machines can connect. If this is the case, you can add an entry to hosts.allow and deny.
auditd.conf(5), audispd(8), ausearch(8), aureport(8), auditctl(8), augenrules(8), audit.rules(7).
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