.\" Copyright (c) 2004-2009 Apple Inc.
.\" Copyright (c) 2006, 2016 Robert N. M. Watson
.\" All rights reserved.
.\"
.\" Portions of this software were developed by BAE Systems, the University of
.\" Cambridge Computer Laboratory, and Memorial University under DARPA/AFRL
.\" contract FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent
.\" Computing (TC) research program.
.\"
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.Dd August 19, 2016
.Dt AUDIT_CONTROL 5
.Os
.Sh NAME
.Nm audit_control
.Nd "audit system parameters"
.Sh DESCRIPTION
The
.Nm
file contains several audit system parameters.
Each line of this file is of the form:
.Pp
.D1 Ar parameter Ns : Ns Ar value
.Pp
The parameters are:
.Bl -tag -width indent
.It Va dir
The directory where audit log files are stored.
There may be more than one of these entries.
Changes to this entry can only be enacted by restarting the
audit system.
See
.Xr audit 8
for a description of how to restart the audit system.
.It Va dist
When set to
.Va on
or
.Va yes ,
.Xr auditd 8
will be creating hardlinks to all trail files in
.Pa /var/audit/dist
directory.
Those hardlinks will be consumed by the
.Xr auditdistd 8
daemon.
.It Va flags
Specifies which audit event classes are audited for all users.
.Xr audit_user 5
describes how to audit events for individual users.
See the information below for the format of the audit flags.
.It Va host
Specify the hostname or IP address to be used when setting the local
systems's audit host information.
This hostname will be converted into an IP or IPv6 address and will
be included in the header of each audit record.
Due to the possibility of transient errors coupled with the
security issues in the DNS protocol itself, the use of DNS
should be avoided.
Instead, it is strongly recommended that the hostname be
specified in the /etc/hosts file.
For more information see
.Xr hosts 5 .
.It Va naflags
Contains the audit flags that define what classes of events are audited when
an action cannot be attributed to a specific user.
.It Va minfree
The minimum free space required on the file system audit logs are being written to.
When the free space falls below this limit a warning will be issued.
If no value for the minimum free space is set, the default of 20 percent is
applied by the kernel.
.It Va policy
A list of global audit policy flags specifying various behaviors, such as
fail stop, auditing of paths and arguments, etc.
.It Va filesz
Maximum trail size in bytes; if set to a non-0 value, the audit daemon will
rotate the audit trail file at around this size.
Sizes less than the minimum trail size (default of 512K) will be rejected as
invalid.
If 0, trail files will not be automatically rotated based on file size.
For convenience, the trail size may be expressed with suffix letters:
B (Bytes), K (Kilobytes), M (Megabytes), or G (Gigabytes).
For example, 2M is the same as 2097152.
.It Va expire-after
Specifies when audit log files will expire and be removed.
This may be after a time period has passed since the file was last
written to or when the aggregate of all the trail files have reached a
specified size or a combination of both.
If no expire-after parameter is given then audit log files will not
expire and be removed by the audit control system.
See the information below for the format of the expiration
specification.
.It Va qsize
Specifies the maximum number of outstanding committed audit records that can
be in the kernel's post-commit queue pending write to disk.
If this number has been reached, user threads performing an auditable event
will be suspended until the queue has fallen below the limit.
Depending on the underlying kernel implementation, the number of in-flight
records can exceed this number, as it does not constrain uncommitted records
(e.g., those associated with incomplete auditable system calls), and may also
exclude the set of records extracted from the queue and currently being
prepared for or undergoing I/O.
Other operational limits may be affected by this parameter, such as the
minimum free space on disk required to continue system operation, estimated as
the maximum number of allowable in-flight records multiplied by the maximum
audit record size.
.El
.Sh AUDIT FLAGS
Audit flags are a comma-delimited list of audit classes as defined in the
.Xr audit_class 5
file.
Event classes may be preceded by a prefix which changes their interpretation.
The following prefixes may be used for each class:
.Pp
.Bl -tag -width indent -compact -offset indent
.It (none)
Record both successful and failed events.
.It Li +
Record successful events.
.It Li -
Record failed events.
.It Li ^
Record neither successful nor failed events.
.It Li ^+
Do not record successful events.
.It Li ^-
Do not record failed events.
.El
.Sh AUDIT POLICY FLAGS
The policy flags field is a comma-delimited list of policy flags from the
following list:
.Pp
.Bl -tag -width ".Cm zonename" -compact -offset indent
.It Cm cnt
Allow processes to continue running even though events are not being audited.
If not set, processes will be suspended when the audit store space is
exhausted.
Currently, this is not a recoverable state.
.It Cm ahlt
Fail stop the system if unable to audit an event\[em]this consists of first
draining pending records to disk, and then halting the operating system.
.It Cm argv
Audit command line arguments to
.Xr execve 2 .
.It Cm arge
Audit environmental variable arguments to
.Xr execve 2 .
.It Cm seq
Include a unique audit sequence number token in generated audit records (not
implemented on
.Fx
or Darwin).
.It Cm group
Include supplementary groups list in generated audit records (not implemented
on
.Fx
or Darwin; supplementary groups are never included in records on
these systems).
.It Cm trail
Append a trailer token to each audit record (not implemented on
.Fx
or
Darwin; trailers are always included in records on these systems).
.It Cm path
Include secondary file paths in audit records (not implemented on
.Fx
or
Darwin; secondary paths are never included in records on these systems).
.It Cm zonename
Include a zone ID token with each audit record (not implemented on
.Fx
or
Darwin;
.Fx
audit records do not currently include the jail ID or name).
.It Cm perzone
Enable auditing for each local zone (not implemented on
.Fx
or Darwin; on
.Fx ,
audit records are collected from all jails and placed in a single
global trail, and only limited audit controls are permitted within a jail).
.El
.Pp
It is recommended that installations set the
.Cm cnt
flag but not
.Cm ahlt
flag unless it is intended that audit logs exceeding available disk space
halt the system.
.Sh AUDIT LOG EXPIRATION SPECIFICATION
The expiration specification can be one value or two values with the
logical conjunction of AND/OR between them.
Values for the audit log file age are numbers with the following
suffixes:
.Pp
.Bl -tag -width "(space) or" -compact -offset indent
.It Li s
Log file age in seconds.
.It Li h
Log file age in hours.
.It Li d
Log file age in days.
.It Li y
Log file age in years.
.El
.Pp
Values for the disk space used are numbers with the following suffixes:
.Pp
.Bl -tag -width "(space) or" -compact -offset indent
.It (space) or
.It Li B
Disk space used in Bytes.
.It Li K
Disk space used in Kilobytes.
.It Li M
Disk space used in Megabytes.
.It Li G
Disk space used in Gigabytes.
.El
.Pp
The suffixes on the values are case sensitive.
If both an age and disk space value are used they are separated by
AND or OR and both values are used to determine when audit
log files expire.
In the case of AND, both the age and disk space conditions must be met
before the log file is removed.
In the case of OR, either condition may expire the log file.
For example:
.Bd -literal -offset indent
expire-after: 60d AND 1G
.Ed
.Pp
will expire files that are older than 60 days but only if 1
gigabyte of disk space total is being used by the audit logs.
.Sh DEFAULT
The following settings appear in the default
.Nm
file:
.Bd -literal -offset indent
dir:/var/audit
flags:lo,aa
minfree:5
naflags:lo,aa
policy:cnt,argv
filesz:2M
expire-after:10M
.Ed
.Pp
The
.Va flags
parameter above specifies the system-wide mask corresponding to login/logout
as well as authentication and authorization events.
The
.Va policy
parameter specifies that the system should neither fail stop nor suspend
processes when the audit store fills and that command line arguments should
be audited for
.Dv AUE_EXECVE
events.
The trail file will be automatically rotated by the audit daemon when the
file size reaches approximately 2MB.
Trail files will expire when their aggregate size exceeds 10MB.
.Sh FILES
.Bl -tag -width ".Pa /etc/security/audit_control" -compact
.It Pa /etc/security/audit_control
.El
.Sh SEE ALSO
.Xr auditon 2 ,
.Xr audit 4 ,
.Xr audit_class 5 ,
.Xr audit_event 5 ,
.Xr audit_user 5 ,
.Xr audit 8 ,
.Xr auditd 8
.Sh HISTORY
The OpenBSM implementation was created by McAfee Research, the security
division of McAfee Inc., under contract to Apple Computer Inc.\& in 2004.
It was subsequently adopted by the TrustedBSD Project as the foundation for
the OpenBSM distribution.
.Sh AUTHORS
.An -nosplit
This software was created by McAfee Research, the security research division
of McAfee, Inc., under contract to Apple Computer Inc.
Additional authors include
.An Wayne Salamon ,
.An Robert Watson ,
and SPARTA Inc.
.Pp
The Basic Security Module (BSM) interface to audit records and audit event
stream format were defined by Sun Microsystems.