AUDITCTL(8) System Administration Utilities AUDITCTL(8)
NAME
auditctl - a utility to assist controlling the kernel's audit system
SYNOPSIS
auditctl [options]
DESCRIPTION
The auditctl program is used to configure kernel options related to au-
diting, to see status of the configuration, and to load discretionary
audit rules.
CONFIGURATION OPTIONS
-b backlog
Set max number (limit) of outstanding audit buffers allowed (Ker-
nel Default=64) If all buffers are full, the failure flag is con-
sulted by the kernel for action.
--backlog_wait_time wait_time
Set the time for the kernel to wait (Kernel Default 60*HZ) when
the backlog limit is reached before queuing more audit events to
be transferred to auditd. The number must be greater than or
equal to zero and less than 10 times the default value.
--reset_backlog_wait_time_actual
Reset the actual backlog wait time counter shown by the status
command.
-c Continue loading rules in spite of an error. This summarizes the
results of loading the rules. The exit code will not be success
if any rule fails to load.
-D Delete all rules and watches. This can take a key option (-k),
too.
-e [0..2]
Set enabled flag. When 0 is passed, this can be used to temporar-
ily disable auditing. When 1 is passed as an argument, it will
enable auditing. To lock the audit configuration so that it can't
be changed, pass a 2 as the argument. Locking the configuration
is intended to be the last command in audit.rules for anyone
wishing this feature to be active. Any attempt to change the con-
figuration in this mode will be audited and denied. The configu-
ration can only be changed by rebooting the machine.
-f [0..2]
Set failure mode 0=silent 1=printk 2=panic. This option lets you
determine how you want the kernel to handle critical errors. Ex-
ample conditions where this mode may have an effect includes:
transmission errors to userspace audit daemon, backlog limit ex-
ceeded, out of kernel memory, and rate limit exceeded. The de-
fault value is 1. Secure environments will probably want to set
this to 2.
-h Help
-i When given by itself, ignore errors when reading rules from a
file. This causes auditctl to always return a success exit code.
If passed as an argument to -s then it gives an interpretation of
the numbers to human readable words if possible.
--loginuid-immutable
This option tells the kernel to make loginuids unchangeable once
they are set. Changing loginuids requires CAP_AUDIT_CONTROL. So,
its not something that can be done by unprivileged users. Setting
this makes loginuid tamper-proof, but can cause some problems in
certain kinds of containers.
-q mount-point,subtree
If you have an existing directory watch and bind or move mount
another subtree in the watched subtree, you need to tell the ker-
nel to make the subtree being mounted equivalent to the directory
being watched. If the subtree is already mounted at the time the
directory watch is issued, the subtree is automatically tagged
for watching. Please note the comma separating the two values.
Omitting it will cause errors.
-r rate
Set limit in messages/sec (0=none). If this rate is non-zero and
is exceeded, the failure flag is consulted by the kernel for ac-
tion. The default value is 0.
--reset-lost
Reset the lost record counter shown by the status command.
-R file
Read and execute auditctl commands from a file. The commands are
executed line-by-line, in the order that they appear in the file.
The file must be owned by root and not readable by other users,
or else it will be rejected. Empty lines are skipped. Lines
starting with the '#' character are treated as comment lines.
Each line is executed as if it was provided to auditctl as com-
mand line arguments. Since auditctl is the one reading the file
and not a shell such as bash, do not escape special shell charac-
ters. See the EXAMPLES section for an example.
--signal signal
Send a signal to the audit daemon. You must have privileges to do
this. Supported signals are TERM, HUP, USR1, USR2, CONT
and user friendly versions stop, reload, rotate, resume, state.
-t Trim the subtrees after a mount command.
STATUS OPTIONS
-l List all rules 1 per line. Two more options may be given to this
command. You can give either a key option (-k) to list rules that
match a key or a (-i) to have a0 through a3 interpreted to help
determine the syscall argument values are correct .
-m text
Send a user space message into the audit system. This can only be
done if you have CAP_AUDIT_WRITE capability (normally the root
user has this). The resulting event will be the USER type.
-s Report the kernel's audit subsystem status. It will tell you the
in-kernel values that can be set by -e, -f, -r, and -b options.
The pid value is the process number of the audit daemon. Note
that a pid of 0 indicates that the audit daemon is not running.
The lost entry will tell you how many event records that have
been discarded due to the kernel audit queue overflowing. The
backlog field tells how many event records are currently queued
waiting for auditd to read them. This option can be followed by
the -i to get a couple fields interpreted.
-v Print the version of auditctl.
RULE OPTIONS
-a [list,action|action,list]
Append rule to the end of list with action. Please note the comma
separating the two values. Omitting it will cause errors. The
fields may be in either order. It could be list,action or ac-
tion,list. The following describes the valid list names:
task Add a rule to the per task list. This rule list is
used only at the time a task is created -- when
fork() or clone() are called by the parent task. When
using this list, you should only use fields that are
known at task creation time, such as the uid, gid,
etc.
exit Add a rule to the syscall exit list. This list is
used upon exit from a system call to determine if an
audit event should be created.
user Add a rule to the user message filter list. This list
is used by the kernel to filter events originating in
user space before relaying them to the audit daemon.
It should be noted that the only fields that are
valid are: uid, auid, gid, pid, subj_user, subj_role,
subj_type, subj_sen, subj_clr, msgtype, and exe-
cutable name. All other fields will be treated as
non-matching. It should be understood that any event
originating from user space from a process that has
CAP_AUDIT_WRITE will be recorded into the audit
trail. This means that the most likely use for this
filter is with rules that have an action of never
since nothing has to be done to allow events to be
recorded.
exclude Add a rule to the event type exclusion filter list.
This list is used to filter events that you do not
want to see. For example, if you do not want to see
any avc messages, you would using this list to record
that. Events can be excluded by process ID, user ID,
group ID, login user ID, message type, subject con-
text, or executable name. The action is ignored and
uses its default of "never".
filesystem Add a rule that will be applied to a whole filesys-
tem. The filesystem must be identified with a fstype
field. Normally this filter is used to exclude any
events for a whole filesystem such as tracefs or de-
bugfs.
io_uring Add a rule to the io_uring syscall filter. Rules
against this filter specify the syscall operation us-
ing the -S syscall notion explained below. You can
add a key field to the rule so that it may be grouped
with other rules watching the same underlying
syscall.
The following describes the valid actions for the rule:
never No audit records will be generated. This can be used
to suppress event generation. In general, you want
suppressions at the top of the list instead of the
bottom. This is because the event triggers on the
first matching rule.
always Allocate an audit context, always fill it in at
syscall entry time, and always write out a record at
syscall exit time.
-A list,action
Add rule to the beginning list with action.
-C [f=f | f!=f]
Build an inter-field comparison rule: field, operation, field.
You may pass multiple comparisons on a single command line. Each
one must start with -C. Each inter-field equation is anded with
each other as well as equations starting with -F to trigger an
audit record. There are 2 operators supported - equal, and not
equal. Valid fields are:
auid, uid, euid, suid, fsuid, obj_uid; and gid, egid, sgid, fs-
gid, obj_gid
The two groups of uid and gid cannot be mixed. But any comparison
within the group can be made. The obj_uid/gid fields are col-
lected from the object of the event such as a file or directory.
-d list,action
Delete rule from list with action. The rule is deleted only if it
exactly matches syscall name(s) and every field name and value.
-F [n=v | n!=v | n<v | n>v | n<=v | n>=v | n&v | n&=v]
Build a rule field: name, operation, value. You may have up to 64
fields passed on a single command line. Each one must start with
-F. Each field equation is anded with each other (as well as
equations starting with -C) to trigger an audit record. There are
8 operators supported - equal, not equal, less than, greater
than, less than or equal, and greater than or equal, bit mask,
and bit test respectively. Bit test will "and" the values and
check that they are equal, bit mask just "ands" the values.
Fields that take a user ID may instead have the user's name; the
program will convert the name to user ID. The same is true of
group names. Valid fields are:
a0, a1, a2, a3
Respectively, the first 4 arguments to a syscall.
Note that string arguments are not supported. This is
because the kernel is passed a pointer to the string.
Triggering on a pointer address value is not likely
to work. So, when using this, you should only use on
numeric values. This is most likely to be used on
platforms that multiplex socket or IPC operations.
arch The CPU architecture of the syscall. The arch can be
found doing 'uname -m'. If you do not know the arch
of your machine but you want to use the 32 bit
syscall table and your machine supports 32 bit, you
can also use b32 for the arch. The same applies to
the 64 bit syscall table, you can use b64. In this
way, you can write rules that are somewhat arch inde-
pendent because the family type will be auto de-
tected. However, syscalls can be arch specific and
what is available on x86_64, may not be available on
ppc. The arch directive should precede the -S option
so that auditctl knows which internal table to use to
look up the syscall numbers.
auid The original ID the user logged in with. Its an ab-
breviation of audit uid. Sometimes its referred to as
loginuid. Either the user account text or number may
be used.
devmajor Device Major Number
devminor Device Minor Number
dir Full Path of Directory to watch. This will place a
recursive watch on the directory and its whole sub-
tree. It can only be used on exit list. See "-w".
egid Effective Group ID. May be numeric or the groups
name.
euid Effective User ID. May be numeric or the user account
name.
exe Absolute path to application that while executing
this rule will apply to. It supports = and != opera-
tors. Note that you can only use this once for each
rule.
exit Exit value from a syscall. If the exit code is an er-
rno, you may use the text representation, too.
fsgid Filesystem Group ID. May be numeric or the groups
name.
fstype File system type. This is used with the filesystem
rule list. The only values supported are debugfs and
tracefs.
fsuid Filesystem User ID. May be numeric or the user ac-
count name.
filetype The target file's type. Can be either file, dir,
socket, link, character, block, or fifo.
gid Group ID. May be numeric or the groups name.
inode Inode Number
key Set a filter key on an audit rule. The filter key is
an arbitrary string of text that can be up to 31
bytes long. It can uniquely identify the audit
records produced by a rule. Typical use is for when
you have several rules that together satisfy a secu-
rity requirement. The key value can be searched on
with ausearch so that no matter which rule triggered
the event, you can find its results. The key can also
be used on delete all (-D) and list rules (-l) to se-
lect rules with a specific key. You may have more
than one key on a rule if you want to be able to
search logged events in multiple ways or if you have
an auditd plugin that uses a key to aid its analysis.
msgtype This is used to match the event's record type. It
should only be used on the exclude or user filter
lists.
obj_uid Object's UID
obj_gid Object's GID
obj_user Resource's SE Linux User
obj_role Resource's SE Linux Role
obj_type Resource's SE Linux Type
obj_lev_low Resource's SE Linux Low Level
obj_lev_high
Resource's SE Linux High Level
path Insert a watch for the file system object at path.
You cannot insert a watch to the top level directory.
This is prohibited by the kernel. Wildcards are not
supported either and will generate a warning. The way
that watches work is by tracking the inode inter-
nally. This can only be used on exit list.
perm Permission filter for file operations. Supply the ac-
cess type that a file system watch will trigger on.
r=read, w=write, x=execute, a=attribute change. These
permissions are not the standard file permissions,
but rather the kind of syscall that would do this
kind of thing. The read & write syscalls are omitted
from this set since they would overwhelm the logs.
But rather for reads or writes, the open flags are
looked at to see what permission was requested. The
perm field can only be used on exit list. You can use
this without specifying a syscall and the kernel will
select the syscalls that satisfy the access permis-
sions being requested. This also requires supplying
an arch parameter before the perm field. This way the
kernel can better determine what syscalls are needed.
Not supplying an arch will result in all system calls
being subject to audit. This will lower system per-
formance.
pers OS Personality Number
pid Process ID
ppid Parent's Process ID
saddr_fam Address family number as found in /usr/in-
clude/bits/socket.h. For example, IPv4 would be 2 and
IPv6 would be 10.
sessionid User's login session ID
subj_user Program's SE Linux User
subj_role Program's SE Linux Role
subj_type Program's SE Linux Type
subj_sen Program's SE Linux Sensitivity
subj_clr Program's SE Linux Clearance
sgid Saved Group ID. See getresgid(2) man page.
success If the exit value is >= 0 this is true/yes otherwise
its false/no. When writing a rule, use a 1 for
true/yes and a 0 for false/no
suid Saved User ID. See getresuid(2) man page.
uid User ID. May be numeric or the user account name.
-k key Set a filter key on an audit rule. This is deprecated when used
with watches. Convert any watches to the syscall form of rules.
It is still valid for use with deleting or listing rules.
-p [r|w|x|a]
Describe the permission access type that a file system watch will
trigger on. This is deprecated. Convert watches to the syscall
form.
-S [Syscall name or number|all]
Any syscall name or number may be used. The word 'all' may also
be used. If the given syscall is made by a program, then start
an audit record. If a field rule is given and no syscall is spec-
ified, it will default to all syscalls. You may also specify mul-
tiple syscalls in the same rule by using multiple -S options in
the same rule. Doing so improves performance since fewer rules
need to be evaluated. Alternatively, you may pass a comma sepa-
rated list of syscall names. If you are on a bi-arch system, like
x86_64, you should be aware that auditctl simply takes the text,
looks it up for the native arch (in this case b64) and sends that
rule to the kernel. If there are no additional arch directives,
IT WILL APPLY TO BOTH 32 & 64 BIT SYSCALLS. This can have unde-
sirable effects since there is no guarantee that any syscall has
the same number on both 32 and 64 bit interfaces. You will likely
want to control this and write 2 rules, one with arch equal to
b32 and one with b64 to make sure the kernel finds the events
that you intend. See the arch field discussion for more info.
-w path
Place a watch on path. If the path is a file, it's almost the
same as using the -F path option on a syscall rule. If the watch
is on a directory, it's almost the same as using the -F dir op-
tion on a syscall rule. The -w form of writing watches is for
backwards compatibility and is deprecated due to poor system per-
formance. Convert watches of this form to the syscall based
form. The only valid options when using a watch are the -p and
-k.
-W path
Remove a watch for the file system object at path. The rule must
match exactly. See -d discussion for more info.
PERFORMANCE TIPS
Syscall rules get evaluated for each syscall for every program. If you
have 10 syscall rules, every program on your system will delay during a
syscall while the audit system evaluates each rule. Too many syscall
rules will hurt performance. Try to combine as many as you can whenever
the filter, action, key, and fields are identical. For example:
auditctl -a always,exit -F arch=b64 -S openat -F success=0
auditctl -a always,exit -F arch=b64 -S truncate -F success=0
could be re-written as one rule:
auditctl -a always,exit -F arch=b64 -S openat -S truncate -F success=0
Also, try to use file system auditing wherever practical. This improves
performance. For example, if you were wanting to capture all failed
opens & truncates like above, but were only concerned about files in
/etc and didn't care about /usr or /sbin, its possible to use this rule:
auditctl -a always,exit -F arch=b64 -S openat,truncate -F dir=/etc -F success=0
This will be higher performance since the kernel will not evaluate it
each and every syscall. It will be handled by the filesystem auditing
code and only checked on filesystem related syscalls.
EXAMPLES
To see all syscalls made by a specific program:
# By pid:
auditctl -a always,exit -S all -F pid=1005
# By executable path
auditctl -a always,exit -S all -F exe=/usr/bin/ls
To see files opened by a specific user:
auditctl -a always,exit -S openat -F auid=510
To see unsuccessful openat calls:
auditctl -a always,exit -S openat -F success=0
To watch a file for changes (2 ways to express):
auditctl -w /etc/shadow -p wa # Note this slows the system
auditctl -a always,exit -F arch=b64 -F path=/etc/shadow -F perm=wa
To recursively watch a directory for changes (2 ways to express):
auditctl -w /etc/ -p wa # Note this slows the system
auditctl -a always,exit -F arch=b64 -F dir=/etc/ -F perm=wa
To see if an admin is accessing other user's files:
auditctl -a always,exit -F dir=/home/ -F uid=0 -C auid!=obj_uid
This is an example rules file:
# Remove all existing rules
-D
# Never record sudo invocations
-A exclude,always -F exe=/usr/bin/sudo
DISABLED BY DEFAULT
On many systems auditd is configured to install an -a never,task rule by
default. This rule causes every new process to skip all audit rule pro-
cessing. This is usually done to avoid a small performance overhead im-
posed by syscall auditing. If you want to use auditd, you need to remove
that rule by deleting 10-no-audit.rules and adding 10-base-config.rules
to the audit rules directory.
If you have defined audit rules that are not matching when they should,
check auditctl -l to make sure there is no never,task rule there.
FILES
/etc/audit/audit.rules /etc/audit/audit-stop.rules
SEE ALSO
audit.rules(7), ausearch(8), aureport(8), auditd(8).
AUTHOR
Steve Grubb
Red Hat Sep 2023 AUDITCTL(8)
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