why I have lost messages on boot even with very big backlog while I hunting only 2 syscalls?

[Steve Grubb]

On Wednesday, September 27, 2017 4:41:29 PM EDT Lev Olshvang wrote:
> Hello list !
> 
> A very technical question
> I have Ubuntu 16.10 Virtual Box , auditd 2.7.8
> I have audit=1 parameter in grub.cfg
> I see that /proc/cmdline indeed sees it
> 
> I see that auditd is started with PID 564
> 
> root       312     2  0 23:12 ?        00:00:00 [kauditd]
> root       564     1  0 23:12 ?        00:00:00 /sbin/auditd
> 
> And I have 15 lost messages   ???
> auditctl -s
> enabled 1
> failure 1
> pid 564
> rate_limit 0
> backlog_limit 16384
> lost 15
> backlog 0
> backlog_wait_time 30
> loginuid_immutable 0 unlocked
> 
> auditctl -l
> -a always,exit -F arch=b64 -S execve,execveat -F key=exec
> 
> Do I understand correctly that auiditd is indeed started by systemd  before
> other services, except 2 that is listed in auditd.service dependencuies -
> local-fs and some temp setup of systemd ?

Yes, it is started before most services. However. systemd-journal for some 
reason feels obligated to enable auditing. And sometimes people put audit=1 on 
the kernel command line. Either way, auditing is on way before auditd starts. 
The audit logs have a 64 entry buffer by default. So, as the system boots 
events pile up and eventually overflows the 64 entry limit.

The fix is to add another boot command option audit_backlog_limit=8192 or some 
other suitable number. The test to check for this is to boot your system, 
login and run auditctl -s. If you have just booted and lost events during 
boot, this should fix it.

-Steve