---
name: "audit.log"
section: "5"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/audit.log"
---

# audit.log(5)

Basic Security Module (BSM) file format

## NAME

**audit** – Basic Security Module (BSM) file format

## DESCRIPTION

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)](/libbsm/3.md) interface to read and write tokens, rather than parsing or constructing records by hand.

### File Token

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)](/au_to_file/3.md).

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Seconds | 4 bytes | File time stamp |
| Microseconds | 4 bytes | File time stamp |
| File name length | 2 bytes | File name of audit trail |
| File pathname | N bytes + 1 NUL | File name of audit trail |

### Header Token

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)](/au_to_header32/3.md); a 64-bit “header” token can be created using [au\_to\_header64(3)](/au_to_header64/3.md).

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Record Byte Count | 4 bytes | Number of bytes in record |
| Version Number | 1 byte | 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) |

### Expanded Header Token

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)](/au_to_header32_ex/3.md); a 64-bit extended “header” token can be created using au\_to\_header64\_ex(3).

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Record Byte Count | 4 bytes | Number of bytes in record |
| Version Number | 1 byte | 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) |

### Trailer Token

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)](/au_to_trailer/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### Arbitrary Data Token

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 multiplied 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)](/au_to_data/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### in\_addr Token

The “in\_addr” token holds a network byte order IPv4 address. An “in\_addr” token can be created using [au\_to\_in\_addr(3)](/au_to_in_addr/3.md) for an IPv4 address.

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| IP Address | 4 bytes | IPv4 address |

### Expanded in\_addr Token

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)](/au_to_in_addr_ex/3.md) for an IPv6 address.

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

| | | |
| --- | --- | --- |
| **Field** | 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 |

### ip Token

The “ip” token contains an IP packet header in network byte order. An “ip” token can be created using [au\_to\_ip(3)](/au_to_ip/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### iport Token

The “iport” token stores an IP port number in network byte order. An “iport” token can be created using [au\_to\_iport(3)](/au_to_iport/3.md).

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Port Number | 2 bytes | Port number in network byte order |

### Path Token

The “path” token contains a pathname. A “path” token can be created using [au\_to\_path(3)](/au_to_path/3.md).

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

### path\_attr Token

The “path\_attr” token contains a set of NUL-terminated path names. The [libbsm(3)](/libbsm/3.md) API cannot currently create a “path\_attr” token.

| | | |
| --- | --- | --- |
| **Field** | 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) |

### Process Token

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)](/au_to_process32/3.md) or [au\_to\_process64(3)](/au_to_process64/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### Expanded Process Token

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)](/au_to_process32_ex/3.md) or [au\_to\_process64\_ex(3)](/au_to_process64_ex/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 | 4 bytes | Length of machine address |
| Terminal Machine Address | 4 bytes | IPv4 or IPv6 address of machine |

### Return Token

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)](/au_to_return32/3.md) or [au\_to\_return64(3)](/au_to_return64/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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) |

### Subject Token

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)](/au_to_subject32/3.md) and [au\_to\_subject64(3)](/au_to_subject64/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### Expanded Subject Token

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)](/au_to_subject32_ex/3.md) or [au\_to\_subject64\_ex(3)](/au_to_subject64_ex/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### System V IPC Token

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 .

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Object ID type | 1 byte | Object ID |
| Object ID | 4 bytes | Object ID |

### Text Token

The “text” token contains a single NUL-terminated text string. A “text” token may be created using [au\_to\_text(3)](/au_to_text/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### Attribute Token

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)](/au_to_attr32/3.md) or [au\_to\_attr64(3)](/au_to_attr64/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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) |

### Groups Token

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)](/au_to_groups/3.md).

| | | |
| --- | --- | --- |
| **Field** | 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 |

### System V IPC Permission Token

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)](/au_to_ipc_perm/3.md).

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Owner user ID | 4 bytes | User ID of IPC owner |
| Owner group ID | 4 bytes | Group ID of IPC owner |
| Creator user ID | 4 bytes | User ID of IPC creator |
| Creator group ID | 4 bytes | Group ID of IPC creator |
| Access mode | 4 bytes | Access mode |
| Sequence number | 4 bytes | Sequence number |
| Key | 4 bytes | IPC key |

### Arg Token

The “arg” token contains information 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)](/au_to_arg32/3.md) or [au\_to\_arg64(3)](/au_to_arg64/3.md).

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Argument ID | 1 byte | Argument ID |
| Argument value | 4/8 bytes | Argument value |
| Length | 2 bytes | Length of the text |
| Text | N bytes + 1 nul | The string including nul |

### exec\_args Token

The “exec\_args” token contains information about arguments of the exec() system call. An exec\_args token may be created using [au\_to\_exec\_args(3)](/au_to_exec_args/3.md).

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

### exec\_env Token

The “exec\_env” token contains current environment variables to an exec() system call. An exec\_args token may be created using [au\_to\_exec\_env(3)](/au_to_exec_env/3.md).

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

### Exit Token

The “exit” token contains process exit/return code information. An “exit” token can be created using [au\_to\_exit(3)](/au_to_exit/3.md).

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

### Socket Token

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)](/au_to_sock_inet32/3.md) or [au\_to\_sock\_inet128(3)](/au_to_sock_inet128/3.md).

| | | |
| --- | --- | --- |
| **Field** | **Bytes** | **Description** |
| Token ID | 1 byte | Token ID |
| Socket family | 2 bytes | Socket family |
| Local port | 2 bytes | Local port |
| Socket address | 4 bytes | Socket address |

### Expanded Socket Token

The “expanded socket” token contains information about IPv4 and IPv6 sockets. A “expanded socket” token can be created using [au\_to\_socket\_ex(3)](/au_to_socket_ex/3.md).

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

### Seq Token

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.

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |
| Sequence Number | 4 bytes | Audit event sequence number |

### privilege Token

The “privilege” token ...

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |

### Use-of-auth Token

The “use-of-auth” token ...

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |

### Command Token

The “command” token ...

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |

### ACL Token

The “ACL” token ...

| | | |
| --- | --- | --- |
| **Field** | Bytes | Description |
| Token ID | 1 byte | Token ID |

### Zonename Token

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

| | | |
| --- | --- | --- |
| **Field** | 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 |

## SEE ALSO

[auditreduce(1)](/auditreduce/1.md), [praudit(1)](/praudit/1.md), [libbsm(3)](/libbsm/3.md), [audit(4)](/audit/4.md), [auditpipe(4)](/auditpipe/4.md), [audit(8)](/audit/8.md)

## 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.

## AUTHORS

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⟩.

## BUGS

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)](/libbsm/3.md) implementation of [au\_to\_in\_addr\_ex(3)](/au_to_in_addr_ex/3.md).