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 /etc/init.d/apparmor SysV
initscript (on Ubuntu, also see UBUNTU POLICY LOAD, below), which is
used like this:
# /etc/init.d/apparmor start
# /etc/init.d/apparmor stop
# /etc/init.d/apparmor restart
AppArmor can operate in two modes: enforcement, and complain or
o 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.
o 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
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); an already running process cannot be confined.
However, once a profile is loaded for a program, that program will be
confined on the next exec(3).
AppArmor supports the Linux kernel's securityfs filesystem, and makes
available the list of the profiles currently loaded; to mount the
# mount -tsecurityfs securityfs /sys/kernel/security
$ cat /sys/kernel/security/apparmor/profiles
Normally, the initscript will mount securityfs if it has not already
AppArmor also restricts what privileged operations a confined process
Because Upstart is an event-driven init system and understanding that
policy must be loaded before execution, Ubuntu loads policy in two
stages: first via upstart jobs for binaries that are started in early
boot, and then via a SysV initscript that starts in S37 for all
remaining policy. When developing policy it is important to know how
your application is started and if policy load should be handled
In general, nothing extra has to be done for applications without an
initscript or with an initscript that starts after AppArmor's second
If the confined application has an Upstart job, adjust the job to call
/lib/init/apparmor-profile-load with the filename of the policy file
(relative to /etc/apparmor.d/). For example:
If the confined application does not have an Upstart job but it starts
before AppArmor's second stage initscript, then add a symlink from the
policy file in /etc/apparmor.d to
/etc/apparmor/init/network-interface-security/. For example:
# cd /etc/apparmor/init/network-interface-security/
# ln -s /etc/apparmor.d/usr.bin.foo .
The network-interface-security Upstart job will load all the symlinked
policy files in /etc/apparmor/init/network-interface-security/ before
any network interfaces come up. Because network interfaces come up very
early in the boot process, this will help ensure that AppArmor policy
is loaded before the confined application starts.
When a confined process tries to access a file it does not have
permission to access, the kernel will report a message through audit,
audit(1148420912.879:96): REJECTING x access to /bin/uname
(sh(6646) profile /tmp/sh active /tmp/sh)
audit(1148420912.879:97): REJECTING r access to /bin/uname
(sh(6646) profile /tmp/sh active /tmp/sh)
audit(1148420944.837:98): REJECTING access to capability
'dac_override' (sh(6641) profile /tmp/sh active /tmp/sh)
The permissions requested by the process are immediately after
REJECTING. The "name" and process id of the running program are
reported, as well as the profile name and any "hat" that may be active.
("Name" is in quotes, because the process name is limited to 15 bytes;
it is the same as reported through the Berkeley process accounting.) If
no hat is active (see aa_change_hat(2)) then the profile name is
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.
apparmor_parser(8), aa_change_hat(2), apparmor.d(5), subdomain.conf(5),
aa-autodep(1), clean(1), auditd(8), aa-unconfined(8), aa-enforce(1),
aa-complain(1), and <http://wiki.apparmor.net>.
AppArmor 2.7.102 2017-03-16 APPARMOR(7)
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