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NAME | OVERVIEW | LEXICAL STRUCTURE | EXPRESSION SYNTAX | VIRTUAL FIELDS | SEMANTICS | EXAMPLES | FUTURE DIRECTIONS | AUTHOR | COLOPHON |
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AUSEARCH-EXPRESSION(5) Linux Audit AUSEARCH-EXPRESSION(5)
ausearch-expression - audit search expression format
This man page describes the format of "ausearch expressions".
Parsing and evaluation of these expressions is provided by
libauparse and is common to applications that use this library.
White space (ASCII space, tab and new-line characters) between
tokens is ignored. The following tokens are recognized:
Punctuation
( ) \
Logical operators
! && ||
Comparison operators
< <= == > >= !== i= i!= r= r!=
Unquoted strings
Any non-empty sequence of ASCII letters, digits, and the _
symbol.
Quoted strings
A sequence of characters surrounded by the " quotes. The \
character starts an escape sequence. The only defined
escape sequences are \\ and \". The semantics of other
escape sequences is undefined.
Regexps
A sequence of characters surrounded by the / characters.
The \ character starts an escape sequence. The only
defined escape sequences are \\ and \/. The semantics of
other escape sequences is undefined.
Anywhere an unquoted string is valid, a quoted string is valid as
well, and vice versa. In particular, field names may be specified
using quoted strings, and field values may be specified using
unquoted strings.
The primary expression has one of the following forms:
field comparison-operator value
\regexp string-or-regexp
field is either a string, which specifies the first field with
that name within the current audit record, or the \ escape
character followed by a string, which specifies a virtual field
with the specified name (virtual fields are defined in a later
section).
field is a string. operator specifies the comparison to perform
r= r!= Get the "raw" string of field, and compare it to value.
For fields in audit records, the "raw" string is the exact
string stored in the audit record (with all escaping and
unprintable character encoding left alone); applications
can read the "raw" string using auparse_get_field_str(3).
Each virtual field may define a "raw" string. If field is
not present or does not define a "raw" string, the result
of the comparison is false (regardless of the operator).
i= i!= Get the "interpreted" string of field, and compare it to
value. For fields in audit records, the "interpreted"
string is an "user-readable" interpretation of the field
value; applications can read the "interpreted" string using
auparse_interpret_field(3). Each virtual field may define
an "interpreted" string. If field is not present or does
not define an "interpreted" string, the result of the
comparison is false (regardless of the operator).
< <= == > >= !==
Evaluate the "value" of field, and compare it to value. A
"value" may be defined for any field or virtual field, but
no "value" is currently defined for any audit record field.
The rules of parsing value for comparing it with the
"value" of field are specific for each field. If field is
not present, the result of the comparison is false
(regardless of the operator). If field does not define a
"value", an error is reported when parsing the expression.
In the special case of \regexp regexp-or-string, the current audit
record is taken as a string (without interpreting field values),
and matched against regexp-or-string. regexp-or-string is an
extended regular expression, using a string or regexp token (in
other words, delimited by " or /).
If E1 and E2 are valid expressions, then ! E1, E1 && E2, and E1
|| E2 are valid expressions as well, with the usual C semantics
and evaluation priorities. Note that ! field op value is
interpreted as !(field op value), not as (!field) op value.
The following virtual fields are defined:
\timestamp
The value is the timestamp of the current event. value
must be formatted as:
ts:seconds.milli
where seconds and milli are decimal numbers specifying the
seconds and milliseconds part of the timestamp,
respectively.
\timestamp_ex
This is similar to \timestamp but also includes the event's
serial number. value must be formatted as:
ts:seconds.milli:serial
where serial is a decimal number specifying the event's
serial number.
\record_type
The value is the type of the current record. value is
either the record type name, or a decimal number specifying
the type.
The expression as a whole applies to a single record. The
expression is true for a specified event if it is true for any
record associated with the event.
As a demonstration of the semantics of handling missing fields,
the following expression is true if field is present:
(field r= "") || (field r!= "")
and the same expression surrounded by !( and ) is true if field is
not present.
New escape sequences for quoted strings may be defined.
For currently defined virtual fields that do not define a "raw" or
"interpreted" string, the definition may be added. Therefore,
don't rely on the fact that comparing the "raw" or "interpreted"
string of the field with any value is false.
New formats of value constants for the \timestamp virtual field
may be added.
Miloslav Trmac
This page is part of the audit (Linux Audit) project. Information
about the project can be found at
⟨http://people.redhat.com/sgrubb/audit/⟩. If you have a bug report
for this manual page, send it to linux-audit@redhat.com. This
page was obtained from the project's upstream Git repository
⟨https://github.com/linux-audit/audit-userspace.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-09.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
Red Hat Feb 2008 AUSEARCH-EXPRESSION(5)
Pages that refer to this page: ausearch_add_expression(3), ausearch_add_interpreted_item(3), ausearch_add_item(3), ausearch_add_timestamp_item(3), ausearch_add_timestamp_item_ex(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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