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.\"
.IX Title "APPARMOR 7"
.TH APPARMOR 7 2025-04-08 "AppArmor 4.1.0" AppArmor
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH NAME
AppArmor \- kernel enhancement to confine programs to a limited set of resources.
.SH DESCRIPTION
.IX Header "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.
.PP
AppArmor confinement is provided via \fIprofiles\fR loaded into the kernel
via \fBapparmor_parser\fR\|(8), typically through the \fIapparmor.service\fR
systemd unit, which is used like this:
.PP
.Vb 2
\&        # systemctl start apparmor
\&        # systemctl reload apparmor
.Ve
.PP
AppArmor can operate in two modes: \fIenforcement\fR, and \fIcomplain or learning\fR:
.IP \(bu 4
\&\fIenforcement\fR \-  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.
.IP \(bu 4
\&\fIcomplain\fR \- Profiles loaded in  \f(CW\*(C`complain\*(C'\fR 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 \fBaa\-complain\fR\|(8) and \fBaa\-enforce\fR\|(8) can be used. 
These utilities take a program name as an argument.
.PP
Profiles are traditionally stored in files in \fI/etc/apparmor.d/\fR
under filenames with the convention of replacing the \fB/\fR in pathnames
with \fB.\fR (except for the root \fB/\fR) so profiles are easier to manage
(e.g. the \fI/usr/sbin/nscd\fR profile would be named \fIusr.sbin.nscd\fR).
.PP
Profiles are applied to a process at \fBexec\fR\|(3) time (as seen through the
\&\fBexecve\fR\|(2) system call): once a profile is loaded for a program, that
program will be confined on the next \fBexec\fR\|(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.
.PP
AppArmor supports the Linux kernel's securityfs filesystem, and makes
available the list of the profiles currently loaded; to mount the
filesystem:
.PP
.Vb 5
\&        # mount \-tsecurityfs securityfs /sys/kernel/security
\&        $ cat /sys/kernel/security/apparmor/profiles
\&        /usr/bin/mutt
\&        /usr/bin/gpg
\&           ...
.Ve
.PP
Normally, the initscript will mount securityfs if it has not already
been done.
.PP
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:
.PP
.Vb 3
\&        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)
.Ve
.SS "Complain mode"
.IX Subsection "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 \fIcomplain mode\fR. 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
\&\fITurn off deny audit quieting\fR if this is a problem).
.PP
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 exercised 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.
.PP
\&\fBWarning\fR 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.
.PP
\&\fBNote\fR 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 \fIAudit Rate Limiting\fR if
complain mode is generating too many log messages.
.PP
To set a profile and any children or hat profiles the profile may contain
into complain mode use
.PP
.Vb 1
\&        aa\-complain /etc/apparmor.d/<the\-application>
.Ve
.PP
To manually set a specific profile in complain mode, add the
\&\f(CW\*(C`complain\*(C'\fR flag, and then manually reload the profile:
.PP
.Vb 1
\&        profile foo flags=(complain) { ... }
.Ve
.PP
Note that the \f(CW\*(C`complain\*(C'\fR flag must also be added manually to any
hats or children profiles of the profile or they will continue to
use the previous mode.
.PP
To enable complain mode globally, run:
.PP
.Vb 1
\&        echo \-n complain > /sys/module/apparmor/parameters/mode
.Ve
.PP
or to set it on boot add:
.PP
.Vb 1
\&        apparmor.mode=complain
.Ve
.PP
as a kernel boot parameter.
.PP
\&\fBWarning\fR Setting complain mode globally 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.
.SH ERRORS
.IX Header "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:
.PP
.Vb 3
\&        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"
.Ve
.PP
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.)
.PP
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:
.PP
.Vb 3
\&        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
.Ve
.PP
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 \fI/var/log/audit/audit.log\fR or \fI/var/log/messages\fR,
depending upon local configuration.
.SH DEBUGGING
.IX Header "DEBUGGING"
AppArmor provides a few facilities to log more information,
which can help debugging profiles.
.SS "Enable debug mode"
.IX Subsection "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.
.PP
To enable debug mode, run:
.PP
.Vb 1
\&        echo 1 > /sys/module/apparmor/parameters/debug
.Ve
.PP
or to set it on boot add:
.PP
.Vb 1
\&        apparmor.debug=1
.Ve
.PP
as a kernel boot parameter.
.SS "Turn off deny audit quieting"
.IX Subsection "Turn off deny audit quieting"
By default, operations that trigger \f(CW\*(C`deny\*(C'\fR rules are not logged.
This is called \fIdeny audit quieting\fR.
.PP
To turn off deny audit quieting, run:
.PP
.Vb 1
\&        echo \-n noquiet >/sys/module/apparmor/parameters/audit
.Ve
.PP
or to set it on boot add:
.PP
.Vb 1
\&        apparmor.audit=noquiet
.Ve
.PP
as a kernel boot parameter.
.SS "Force audit mode"
.IX Subsection "Force audit mode"
AppArmor can log a message for every operation that triggers a rule
configured in the policy. This is called \fIforce audit mode\fR.
.PP
\&\fBWarning!\fR Force audit mode can be extremely noisy even for a single profile,
let alone when enabled globally.
.PP
To set a specific profile in force audit mode, add the \f(CW\*(C`audit\*(C'\fR flag:
.PP
.Vb 1
\&        profile foo flags=(audit) { ... }
.Ve
.PP
To enable force audit mode globally, run:
.PP
.Vb 1
\&        echo \-n all > /sys/module/apparmor/parameters/audit
.Ve
.PP
or to set it on boot add:
.PP
.Vb 1
\&        apparmor.audit=all
.Ve
.PP
as a kernel boot parameter.
.PP
\&\fBAudit Rate Limiting\fR
.PP
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:
.PP
.Vb 1
\&        echo 0 > /proc/sys/kernel/printk_ratelimit
.Ve
.PP
But even then the kernel ring buffer may overflow and you might
lose messages.
.PP
Else, if auditd is running, see \fBauditd\fR\|(8) and \fBauditd.conf\fR\|(5).
.SH FILES
.IX Header "FILES"
.IP \fI/etc/apparmor.d/\fR 4
.IX Item "/etc/apparmor.d/"
.PD 0
.IP \fI/var/cache/apparmor/\fR 4
.IX Item "/var/cache/apparmor/"
.IP \fI/var/log/audit/audit.log\fR 4
.IX Item "/var/log/audit/audit.log"
.IP \fI/var/log/messages\fR 4
.IX Item "/var/log/messages"
.PD
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBapparmor_parser\fR\|(8), \fBaa_change_hat\fR\|(2), \fBapparmor.d\fR\|(5),
\&\fBaa\-autodep\fR\|(1), \fBclean\fR\|(1),
\&\fBauditd\fR\|(8),
\&\fBaa\-unconfined\fR\|(8), \fBaa\-enforce\fR\|(1), \fBaa\-complain\fR\|(1), and
<https://wiki.apparmor.net>.