NAME
auditctl - a utility to assist controlling the kernel's audit system
SYNOPSIS
auditctl [options]
DESCRIPTION
The auditctl program is used to control the behavior, get status, and
add or delete rules into the 2.6 kernel's audit system.
OPTIONS
-b backlog
Set max number of outstanding audit buffers allowed (Kernel
Default=64) If all buffers are full, the failure flag is
consulted by the kernel for action.
-e [0..2]
Set enabled flag. When 0 is passed, this can be used to
temporarily 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 configuration in this mode will be audited and
denied. The configuration can only be changed by rebooting the
machine.
-f [0..2]
Set failure flag 0=silent 1=printk 2=panic. This option lets you
determine how you want the kernel to handle critical errors.
Example conditions where this flag is consulted 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 Ignore errors when reading rules from a file
-l List all rules 1 per line. This can take a key option (-k), too.
-k 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
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
audispd plugin that uses a key to aid its analysis.
-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.
-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.
-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
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
action. The default value is 0.
-R file
Read rules from a file. The rules must be 1 per line and in the
order that they are to be executed in. The rule file must be
owned by root and not readable by other users or it will be
rejected. The rule file may have comments embedded by starting
the line with a '#' character. Rules that are read from a file
are identical to what you would type on a command line except
they are not preceded by auditctl (since auditctl is the one
executing the file).
-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.
-t Trim the subtrees after a mount command.
-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
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, and
subj_clr. All other fields will be treated as non-
matching.
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. The message type that you do not wish
to see is given with the msgtype field.
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.
-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.
-D Delete all rules and watches. This can take a key option (-k),
too.
-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. 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, for
example, the open 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.
-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 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
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
subtree. 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.
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.
fsuid Filesystem User ID. May be numeric or the user
account name.
filetype The target file's type. Can be either file, dir,
socket, symlink, char, 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 filter list.
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
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.
-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
performance 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 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 exit,always -S open -F success=0
auditctl -a exit,always -S truncate -F success=0
could be re-written as one rule:
auditctl -a exit,always -S open -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 exit,always -S open -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:
auditctl -a exit,always -S all -F pid=1005
To see files opened by a specific user:
auditctl -a exit,always -S open -F auid=510
To see unsuccessful open calls:
auditctl -a exit,always -S open -F success=0
To watch a file for changes (2 ways to express):
auditctl -w /etc/shadow -p wa
auditctl -a exit,always -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 exit,always -F dir=/etc/ -F perm=wa
FILES
/etc/audit/audit.rules
SEE ALSO
audit.rules(7), auditd(8).
AUTHOR
Steve Grubb