AUDIT.LOG(5) File Formats Manual AUDIT.LOG(5)

auditBasic Security Module (BSM) file format

The audit(4) subsystem has been deprecated since macOS 11.0, disabled since macOS 14.0, and WILL BE REMOVED in a future version of macOS. Applications that require a security event stream should use the EndpointSecurity(7) API instead.

On this version of macOS, you can re-enable audit(4) by renaming or copying /etc/security/audit_control.example to /etc/security/audit_control, re-enabling the system/com.apple.auditd service by running launchctl enable system/com.apple.auditd as root, and rebooting.

The audit file format is based on Sun's Basic Security Module (BSM) file format, a token-based record stream to represent system audit data. This file format is both flexible and extensible, able to describe a broad range of data types, and easily extended to describe new data types in a moderately backward and forward compatible way.

BSM token streams typically begin and end with a “file” token, which provides time stamp and file name information for the stream; when processing a BSM token stream from a stream as opposed to a single file source, file tokens may be seen at any point between ordinary records identifying when particular parts of the stream begin and end. All other tokens will appear in the context of a complete BSM audit record, which begins with a “header” token, and ends with a “trailer” token, which describe the audit record. Between these two tokens will appear a variety of data tokens, such as process information, file path names, IPC object information, MAC labels, socket information, and so on.

The BSM file format defines specific token orders for each record event type; however, some variation may occur depending on the operating system in use, what system options, such as mandatory access control, are present.

This manual page documents the common token types and their binary format, and is intended for reference purposes only. It is recommended that application programmers use the libbsm(3) interface to read and write tokens, rather than parsing or constructing records by hand.

The “file” token is used at the beginning and end of an audit log file to indicate when the audit log begins and ends. It includes a pathname so that, if concatenated together, original file boundaries are still observable, and gaps in the audit log can be identified. A “file” token can be created using au_to_file(3).

Bytes Description
Token ID 1 byte Token ID
Seconds 4 bytes File time stamp
Microseconds 4 bytes File time stamp
File name lengh 2 bytes File name of audit trail
File pathname N bytes + 1 NUL File name of audit trail

The “header” token is used to mark the beginning of a complete audit record, and includes the length of the total record in bytes, a version number for the record layout, the event type and subtype, and the time at which the event occurred. A 32-bit “header” token can be created using au_to_header32(3); a 64-bit “header” token can be created using au_to_header64(3).

Bytes Description
Token ID 1 byte Token ID
Record Byte Count 4 bytes Number of bytes in record
Version Number 2 bytes Record version number
Event Type 2 bytes Event type
Event Modifier 2 bytes Event sub-type
Seconds 4/8 bytes Record time stamp (32/64-bits)
Nanoseconds 4/8 bytes Record time stamp (32/64-bits)

The “expanded header” token is an expanded version of the “header” token, with the addition of a machine IPv4 or IPv6 address. A 32-bit extended “header” token can be created using au_to_header32_ex(3); a 64-bit extended “header” token can be created using au_to_header64_ex(3).

Bytes Description
Token ID 1 byte Token ID
Record Byte Count 4 bytes Number of bytes in record
Version Number 2 bytes Record version number
Event Type 2 bytes Event type
Event Modifier 2 bytes Event sub-type
Address Type/Length 1 byte Host address type and length
Machine Address 4/16 bytes IPv4 or IPv6 address
Seconds 4/8 bytes Record time stamp (32/64-bits)
Nanoseconds 4/8 bytes Record time stamp (32/64-bits)

The “trailer” terminates a BSM audit record, and contains a magic number, AUT_TRAILER_MAGIC and length that can be used to validate that the record was read properly. A “trailer” token can be created using au_to_trailer(3).

Bytes Description
Token ID 1 byte Token ID
Trailer Magic 2 bytes Trailer magic number
Record Byte Count 4 bytes Number of bytes in record

The “identity” token contains information about the process that triggered the audit record to be created. An “identity” token can be created using au_to_identity(3).

Bytes Description
1 byte Token ID
4 bytes Code signing signer type
2 bytes Length of code signing identifier
N bytes + 1 NUL Code signing identifier
1 byte Whether or not the Signing ID field was truncated
2 bytes Length of team identifier
N bytes + 1 NUL Team identifier
1 byte Whether or not the Team ID field was truncated
CDHash Length 2 bytes Length of the CDHash
N bytes CDHash

The “arbitrary data” token contains a byte stream of opaque (untyped) data. The size of the data is calculated as the size of each unit of data multipled by the number of units of data. A “How to print” field is present to specify how to print the data, but interpretation of that field is not currently defined. An “arbitrary data” token can be created using au_to_data(3).

Bytes Description
Token ID 1 byte Token ID
How to Print 1 byte User-defined printing information
Basic Unit 1 byte Size of a unit in bytes
Unit Count 1 byte Number of units of data present
Data Items Variable User data

The “in_addr” token holds a network byte order IPv4 address. An “in_addr” token can be created using au_to_in_addr(3) for an IPv4 address.

Bytes Description
Token ID 1 byte Token ID
IP Address 4 bytes IPv4 address

The “in_addr_ex” token holds a network byte order IPv4 or IPv6 address. An “in_addr_ex” token can be created using au_to_in_addr_ex(3) for an IPv6 address.

See the BUGS section for information on the storage of this token.

Bytes Description
Token ID 1 byte Token ID
IP Address Type 1 byte Type of address
IP Address 4/16 bytes IPv4 or IPv6 address

The “ip” token contains an IP packet header in network byte order. An “ip” token can be created using au_to_ip(3).

Bytes Description
Token ID 1 byte Token ID
Version and IHL 1 byte Version and IP header length
Type of Service 1 byte IP TOS field
Length 2 bytes IP packet length in network byte order
ID 2 bytes IP header ID for reassembly
Offset 2 bytes IP fragment offset and flags, network byte order
TTL 1 byte IP Time-to-Live
Protocol 1 byte IP protocol number
Checksum 2 bytes IP header checksum, network byte order
Source Address 4 bytes IPv4 source address
Destination Address 4 bytes IPv4 destination address

The “iport” token stores an IP port number in network byte order. An “iport” token can be created using au_to_iport(3).

Bytes Description
Token ID 1 byte Token ID
Port Number 2 bytes Port number in network byte order

The “path” token contains a pathname. A “path” token can be created using au_to_path(3).

Bytes Description
Token ID 1 byte Token ID
Path Length 2 bytes Length of path in bytes
Path N bytes + 1 NUL Path name

The “path_attr” token contains a set of NUL-terminated path names. The libbsm(3) API cannot currently create a “path_attr” token.

Bytes Description
Token ID 1 byte Token ID
Count 2 bytes Number of NUL-terminated string(s) in token
Path Variable count NUL-terminated string(s)

The “process” token contains a description of the security properties of a process involved as the target of an auditable event, such as the destination for signal delivery. It should not be confused with the “subject” token, which describes the subject performing an auditable event. This includes both the traditional UNIX security properties, such as user IDs and group IDs, but also audit information such as the audit user ID and session. A “process” token can be created using au_to_process32(3) or au_to_process64(3).

Bytes Description
Token ID 1 byte Token ID
Audit ID 4 bytes Audit user ID
Effective User ID 4 bytes Effective user ID
Effective Group ID 4 bytes Effective group ID
Real User ID 4 bytes Real user ID
Real Group ID 4 bytes Real group ID
Process ID 4 bytes Process ID
Session ID 4 bytes Audit session ID
Terminal Port ID 4/8 bytes Terminal port ID (32/64-bits)
Terminal Machine Address 4 bytes IP address of machine

The “expanded process” token contains the contents of the “process” token, with the addition of a machine address type and variable length address storage capable of containing IPv6 addresses. An “expanded process” token can be created using au_to_process32_ex(3) or au_to_process64_ex(3).

Bytes Description
Token ID 1 byte Token ID
Audit ID 4 bytes Audit user ID
Effective User ID 4 bytes Effective user ID
Effective Group ID 4 bytes Effective group ID
Real User ID 4 bytes Real user ID
Real Group ID 4 bytes Real group ID
Process ID 4 bytes Process ID
Session ID 4 bytes Audit session ID
Terminal Port ID 4/8 bytes Terminal port ID (32/64-bits)
Terminal Address Type/Length 1 byte Length of machine address
Terminal Machine Address 4 bytes IPv4 or IPv6 address of machine

The “return” token contains a system call or library function return condition, including return value and error number associated with the global variable errno. A “return” token can be created using au_to_return32(3) or au_to_return64(3).

Bytes Description
Token ID 1 byte Token ID
Error Number 1 byte Errno value, or 0 if undefined
Return Value 4/8 bytes Return value (32/64-bits)

The “subject” token contains information on the subject performing the operation described by an audit record, and includes similar information to that found in the “process” and “expanded process” tokens. However, those tokens are used where the process being described is the target of the operation, not the authorizing party. A “subject” token can be created using au_to_subject32(3) and au_to_subject64(3).

Bytes Description
Token ID 1 byte Token ID
Audit ID 4 bytes Audit user ID
Effective User ID 4 bytes Effective user ID
Effective Group ID 4 bytes Effective group ID
Real User ID 4 bytes Real user ID
Real Group ID 4 bytes Real group ID
Process ID 4 bytes Process ID
Session ID 4 bytes Audit session ID
Terminal Port ID 4/8 bytes Terminal port ID (32/64-bits)
Terminal Machine Address 4 bytes IP address of machine

The “expanded subject” token consists of the same elements as the “subject” token, with the addition of type/length and variable size machine address information in the terminal ID. An “expanded subject” token can be created using au_to_subject32_ex(3) or au_to_subject64_ex(3).

Bytes Description
Token ID 1 byte Token ID
Audit ID 4 bytes Audit user ID
Effective User ID 4 bytes Effective user ID
Effective Group ID 4 bytes Effective group ID
Real User ID 4 bytes Real user ID
Real Group ID 4 bytes Real group ID
Process ID 4 bytes Process ID
Session ID 4 bytes Audit session ID
Terminal Port ID 4/8 bytes Terminal port ID (32/64-bits)
Terminal Address Type/Length 1 byte Length of machine address
Terminal Machine Address 4 bytes IPv4 or IPv6 address of machine

The “System V IPC” token contains the System V IPC message handle, semaphore handle or shared memory handle. A System V IPC token may be created using +.Xr au_to_ipc 3 .

Bytes Description
Token ID 1 byte Token ID
Object ID type 1 byte Object ID
Object ID 4 bytes Object ID

The “text” token contains a single NUL-terminated text string. A “text” token may be created using au_to_text(3).

Bytes Description
Token ID 1 byte Token ID
Text Length 2 bytes Length of text string including NUL
Text N bytes + 1 NUL Text string including NUL

The “attribute” token describes the attributes of a file associated with the audit event. As files may be identified by 0, 1, or many path names, a path name is not included with the attribute block for a file; optional “path” tokens may also be present in an audit record indicating which path, if any, was used to reach the object. An “attribute” token can be created using au_to_attr32(3) or au_to_attr64(3).

Bytes Description
Token ID 1 byte Token ID
File Access Mode 1 byte mode_t associated with file
Owner User ID 4 bytes uid_t associated with file
Owner Group ID 4 bytes gid_t associated with file
File System ID 4 bytes fsid_t associated with file
File System Node ID 8 bytes ino_t associated with file
Device 4/8 bytes Device major/minor number (32/64-bit)

The “groups” token contains a list of group IDs associated with the audit event. A “groups” token can be created using au_to_groups(3).

Bytes Description
Token ID 1 byte Token ID
Number of Groups 2 bytes Number of groups in token
Group List N * 4 bytes List of N group IDs

The “System V IPC permission” token contains a System V IPC access permissions. A System V IPC permission token may be created using au_to_ipc_perm(3).

Bytes Description
Token ID 1 byte Token ID
4 bytes User ID of IPC owner
4 bytes Group ID of IPC owner
4 bytes User ID of IPC creator
4 bytes Group ID of IPC creator
4 bytes Access mode
4 bytes Sequnce number
4 bytes IPC key

The “arg” token contains informations about arguments of the system call. Depending on the size of the desired argument value, an Arg token may be created using au_to_arg32(3) or au_to_arg64(3).

Bytes Description
Token ID 1 byte Token ID
1 byte Argument ID
4/8 bytes Argument value
2 bytes Length of the text
N bytes + 1 NUL The string including nul

The “exec_args” token contains informations about arguements of the exec() system call. An exec_args token may be created using au_to_exec_args(3).

Bytes Description
Token ID 1 byte Token ID
4 bytes Number of arguments
* bytes Count nul-terminated strings

The “exec_env” token contains current eviroment variables to an exec() system call. An exec_args token may be created using au_to_exec_env(3).

Bytes Description
Token ID 1 byte Token ID
Count ID 4 bytes Number of variables
* bytes Count nul-terminated strings

The “exit” token contains process exit/return code information. An “exit” token can be created using au_to_exit(3).

Bytes Description
Token ID 1 byte Token ID
Status 4 bytes Process status on exit
Return Value 4 bytes Process return value on exit

The “socket” token contains information about UNIX domain and Internet sockets. Each token has four or eight fields. Depending on the type of socket, a socket token may be created using au_to_sock_unix(3), au_to_sock_inet32(3) or au_to_sock_inet128(3).

1 byte Token ID
2 bytes Socket family
2 bytes Local port
4 bytes Socket address

The “expanded socket” token contains information about IPv4 and IPv6 sockets. A “expanded socket” token can be created using au_to_socket_ex(3).

Bytes Description
1 byte Token ID
2 bytes Socket domain
2 bytes Socket type
2 byte Address type (IPv4/IPv6)
2 bytes Local port
4/16 bytes Local IP address
2 bytes Remote port
4/16 bytes Remote IP address

The “seq” token contains a unique and monotonically increasing audit event sequence ID. Due to the limited range of 32 bits, serial number arithmetic and caution should be used when comparing sequence numbers.

Bytes Description
Token ID 1 byte Token ID
Sequence Number 4 bytes Audit event sequence number

The “privilege” token ...

Bytes Description
Token ID 1 byte Token ID
XXXXX

The “use-of-auth” token ...

Bytes Description
Token ID 1 byte Token ID
XXXXX

The “command” token ...

Bytes Description
Token ID 1 byte Token ID
XXXXX

The “ACL” token ...

Bytes Description
Token ID 1 byte Token ID
XXXXX

The “zonename” token holds a NUL-terminated string with the name of the zone or jail from which the record originated. A token can be created using au_to_zonename(3).

Bytes Description
Token ID 1 byte Token ID
Zonename length 2 bytes Length of zonename string including NUL
Zonename N bytes + 1 NUL Zonename string including NUL

auditreduce(1), praudit(1), libbsm(3), audit(4), auditpipe(4), audit(8)

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.

The Basic Security Module (BSM) interface to audit records and audit event stream format were defined by Sun Microsystems.

This manual page was written by Robert Watson ⟨rwatson@FreeBSD.org⟩.

The “How to print” field in the “arbitrary data” token has undefined values.

The “in_addr” and “in_addr_ex” token layout documented here appears to be in conflict with the libbsm(3) implementation of au_to_in_addr_ex(3).

November 5, 2006 macOS 14.4