APPARMOR(7) AppArmor APPARMOR(7)
NAME
AppArmor - kernel enhancement to confine programs to a limited set of
resources.
DESCRIPTION
AppArmor is a kernel enhancement to confine programs to a limited set
of resources. AppArmor's unique security model is to bind access
control attributes to programs rather than to users.
AppArmor confinement is provided via profiles loaded into the kernel
via apparmor_parser(8), typically through the apparmor.service systemd
unit, which is used like this:
# systemctl start apparmor
# systemctl reload apparmor
AppArmor can operate in two modes: enforcement, and complain or
learning:
• enforcement - Profiles loaded in enforcement mode will result in
enforcement of the policy defined in the profile as well as
reporting policy violation attempts to syslogd.
• complain - Profiles loaded in "complain" mode will not enforce
policy. Instead, it will report policy violation attempts. This
mode is convenient for developing profiles. To manage complain mode
for individual profiles the utilities aa-complain(8) and
aa-enforce(8) can be used. These utilities take a program name as
an argument.
Profiles are traditionally stored in files in /etc/apparmor.d/ under
filenames with the convention of replacing the / in pathnames with .
(except for the root /) so profiles are easier to manage (e.g. the
/usr/sbin/nscd profile would be named usr.sbin.nscd).
Profiles are applied to a process at exec(3) time (as seen through the
execve(2) system call): once a profile is loaded for a program, that
program will be confined on the next exec(3). If a process is already
running under a profile, when one replaces that profile in the kernel,
the updated profile is applied immediately to that process. On the
other hand, a process that is already running unconfined cannot be
confined.
AppArmor supports the Linux kernel's securityfs filesystem, and makes
available the list of the profiles currently loaded; to mount the
filesystem:
# mount -tsecurityfs securityfs /sys/kernel/security
$ cat /sys/kernel/security/apparmor/profiles
/usr/bin/mutt
/usr/bin/gpg
...
Normally, the initscript will mount securityfs if it has not already
been done.
AppArmor also restricts what privileged operations a confined process
may execute, even if the process is running as root. A confined process
cannot call the following system calls:
create_module(2) delete_module(2) init_module(2) ioperm(2)
iopl(2) ptrace(2) reboot(2) setdomainname(2)
sethostname(2) swapoff(2) swapon(2) sysctl(2)
Complain mode
Instead of denying access to resources the profile does not have a rule
for AppArmor can "allow" the access and log a message for the operation
that triggers it. This is called complain mode. It is important to note
that rules that are present in the profile are still applied, so allow
rules will still quiet or force audit messages, and deny rules will
still result in denials and quieting of denial messages (see Turn off
deny audit quieting if this is a problem).
Complain mode can be used to develop profiles incrementally as an
application is exercised. The logged accesses can be added to the
profile and then can the application further excercised to discover
further additions that are needed. Because AppArmor allows the accesses
the application will behave as it would if AppArmor was not confining
it.
Warning complain mode does not provide any security, only auditing,
while it is enabled. It should not be used in a hostile environment or
bad behaviors may be logged and added to the profile as if they are
resource accesses that should be used by the application.
Note complain mode can be very noisy with new or empty profiles, but
with developed profiles might not log anything if the profile covers
the application behavior well. See Audit Rate Limiting if complain mode
is generating too many log messages.
To set a profile and any children or hat profiles the profile may
contain into complain mode use
aa-complain /etc/apparmor.d/<the-application>
To manually set a specific profile in complain mode, add the "complain"
flag, and then manually reload the profile:
profile foo flags=(complain) { ... }
Note that the "complain" flag must also be added manually to any hats
or children profiles of the profile or they will continue to use the
previous mode.
To enable complain mode globally, run:
echo -n complain > /sys/module/apparmor/parameters/mode
or to set it on boot add:
apparmor.mode=complain
as a kernel boot paramenter.
Warning Setting complain mode gloabally disables all apparmor security
protections. It can be useful during debugging or profile development,
but setting it selectively on a per profile basis is safer.
ERRORS
When a confined process tries to access a file it does not have
permission to access, the kernel will report a message through audit,
similar to:
audit(1386511672.612:238): apparmor="DENIED" operation="exec"
parent=7589 profile="/tmp/sh" name="/bin/uname" pid=7605
comm="sh" requested_mask="x" denied_mask="x" fsuid=0 ouid=0
audit(1386511672.613:239): apparmor="DENIED" operation="open"
parent=7589 profile="/tmp/sh" name="/bin/uname" pid=7605
comm="sh" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
audit(1386511772.804:246): apparmor="DENIED" operation="capable"
parent=7246 profile="/tmp/sh" pid=7589 comm="sh" pid=7589
comm="sh" capability=2 capname="dac_override"
The permissions requested by the process are described in the
operation= and denied_mask= (for files - capabilities etc. use a
slightly different log format). The "name" and process id of the
running program are reported, as well as the profile name including any
"hat" that may be active, separated by "//". ("Name" is in quotes,
because the process name is limited to 15 bytes; it is the same as
reported through the Berkeley process accounting.)
For confined processes running under a profile that has been loaded in
complain mode, enforcement will not take place and the log messages
reported to audit will be of the form:
audit(1386512577.017:275): apparmor="ALLOWED" operation="open"
parent=8012 profile="/usr/bin/du" name="/etc/apparmor.d/tunables/"
pid=8049 comm="du" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
audit(1386512577.017:276): apparmor="ALLOWED" operation="open"
parent=8012 profile="/usr/bin/du" name="/etc/apparmor.d/tunables/"
pid=8049 comm="du" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
If the userland auditd is not running, the kernel will send audit
events to klogd; klogd will send the messages to syslog, which will log
the messages with the KERN facility. Thus, REJECTING and PERMITTING
messages may go to either /var/log/audit/audit.log or
/var/log/messages, depending upon local configuration.
DEBUGGING
AppArmor provides a few facilities to log more information, which can
help debugging profiles.
Enable debug mode
When debug mode is enabled, AppArmor will log a few extra messages to
dmesg (not via the audit subsystem). For example, the logs will tell
whether environment scrubbing has been applied.
To enable debug mode, run:
echo 1 > /sys/module/apparmor/parameters/debug
or to set it on boot add:
apparmor.debug=1
as a kernel boot paramenter.
Turn off deny audit quieting
By default, operations that trigger "deny" rules are not logged. This
is called deny audit quieting.
To turn off deny audit quieting, run:
echo -n noquiet >/sys/module/apparmor/parameters/audit
or to set it on boot add:
apparmor.audit=noquiet
as a kernel boot paramenter.
Force audit mode
AppArmor can log a message for every operation that triggers a rule
configured in the policy. This is called force audit mode.
Warning! Force audit mode can be extremely noisy even for a single
profile, let alone when enabled globally.
To set a specific profile in force audit mode, add the "audit" flag:
profile foo flags=(audit) { ... }
To enable force audit mode globally, run:
echo -n all > /sys/module/apparmor/parameters/audit
or to set it on boot add:
apparmor.audit=all
as a kernel boot paramenter.
Audit Rate Limiting
If auditd is not running, to avoid losing too many of the extra log
messages, you will likely have to turn off rate limiting by doing:
echo 0 > /proc/sys/kernel/printk_ratelimit
But even then the kernel ring buffer may overflow and you might lose
messages.
Else, if auditd is running, see auditd(8) and auditd.conf(5).
FILES
/etc/apparmor.d/
/var/cache/apparmor/
/var/log/audit/audit.log
/var/log/messages
SEE ALSO
apparmor_parser(8), aa_change_hat(2), apparmor.d(5), aa-autodep(1),
clean(1), auditd(8), aa-unconfined(8), aa-enforce(1), aa-complain(1),
and <https://wiki.apparmor.net>.
AppArmor 4.0.1 2025-03-19 APPARMOR(7)
Generated by dwww version 1.16 on Tue Dec 16 15:19:51 CET 2025.