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
auditing, 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
(Kernel Default=64) If all buffers are full, the failure flag is
consulted 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 tempo-
rarily 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 configu-
ration is intended to be the last command in audit.rules for
anyone wishing this feature to be active. Any attempt to change
the configuration in this mode will be audited and denied. The
configuration 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.
Example conditions where this mode may have an effect includes:
transmission errors to userspace audit daemon, backlog limit
exceeded, out of kernel memory, and rate limit exceeded. The
default 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. Set-
ting this makes loginuid tamper-proof, but can cause some prob-
lems 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
kernel 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 automati-
cally 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
action. 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 command line arguments. Since auditctl is the one reading the
file and not a shell such as bash, do not escape special shell
characters. 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
action,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 origi-
nating 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 executable 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, sub-
ject context, 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
debugfs.
io_uring Add a rule to the io_uring syscall filter. Rules
against this filter specify the syscall operation
using 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 underly-
ing 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,
fsgid, obj_gid
The two groups of uid and gid cannot be mixed. But any compari-
son within the group can be made. The obj_uid/gid fields are
collected from the object of the event such as a file or direc-
tory.
-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 oper-
ations.
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
independent because the family type will be auto
detected. 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
abbreviation 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
errno, 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
account 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 This is another way of setting a filter key. See
discussion above for -k option.
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 Full Path of File to watch. It can only be used on
exit list.
perm Permission filter for file operations. See "-p". It
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 permissions
being requested.
pers OS Personality Number
pid Process ID
ppid Parent's Process ID
saddr_fam Address family number as found in
/usr/include/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. The filter key is an arbi-
trary 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
security 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 select 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.
-p [r|w|x|a]
Describe the permission access 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.
-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
specified, it will default to all syscalls. You may also specify
multiple 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
separated 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 undesirable 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
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
internally. If you place a watch on a file, its the same as
using the -F path option on a syscall rule. If you place a watch
on a directory, its the same as using the -F dir option on a
syscall rule. The -w form of writing watches is for backwards
compatibility and the syscall based form is more expressive.
Unlike most syscall auditing rules, watches do not impact per-
formance based on the number of rules sent to the kernel. The
only valid options when using a watch are the -p and -k. If you
need to do anything fancy like audit a specific user accessing a
file, then use the syscall auditing form with the path or dir
fields. See the EXAMPLES section for an example of converting
one form to another.
-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 -S openat -S 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
auditctl -a always,exit -F path=/etc/shadow -F perm=wa
To recursively watch a directory for changes (2 ways to express):
auditctl -w /etc/ -p wa
auditctl -a always,exit -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
processing. This is usually done to avoid a small performance overhead
imposed 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-con-
fig.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 Feb 2023 AUDITCTL(8)
Linux-Distributionen
Huschi als Linux-Admin