--- /dev/null
+<!--
+
+lxc: linux Container library
+
+(C) Copyright Canonical Inc. 2019
+
+Authors:
+Venkata Harshavardhan Reddy Allu <venkataharshavardhan_ven@srmuniv.edu.in>
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public
+License as published by the Free Software Foundation; either
+version 2.1 of the License, or (at your option) any later version.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with this library; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+-->
+
+<!DOCTYPE refentry PUBLIC @docdtd@ [
+
+<!ENTITY seealso SYSTEM "@builddir@/see_also.sgml">
+]>
+
+<refentry>
+
+ <docinfo><date>@LXC_GENERATE_DATE@</date></docinfo>
+
+ <refmeta>
+ <refentrytitle>pam_cgfs</refentrytitle>
+ <manvolnum>8</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>pam_cgfs</refname>
+
+ <refpurpose>
+ cgroup management for unprivileged LXC containers.
+ </refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <cmdsynopsis>
+ <command>pam_cgfs.so</command>
+ <arg choice="req">-c <replaceable>kernel_controller,name=named_controller</replaceable></arg>
+ </cmdsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>
+ LXC has supported fully unprivileged containers since LXC 1.0.
+ Fully unprivileged containers are the safest containers and are run by
+ normal (non-root) users. This is achieved by using user namespaces by
+ mapping between a range of UIDs and GIDs on the host to a different
+ (unprivileged) range of UIDs and GIDs in the container. That means the uid
+ 0 (root) in the container is mapped to an unprivileged user id (something
+ like 1000000) outside of the container and only has rights on resources
+ that it owns itself.
+ </para>
+ <para>
+ Cgroup management of fully unprivileged containers means restricting the
+ resources used by these containers like limiting the CPU usage of a
+ container, or the number of processes it is allowed to spawn, or the
+ memory it is allowed to consume. It is clear that the fully
+ unprivileged containers are run by normal users and there is a need to
+ limit and manage resource consumption among the containers.
+ But unprivileged cgroup management is not easy with most init systems.
+ So, the pam_cgfs.so came into existence.
+ </para>
+
+ <para>
+ The <command>pam_cgfs.so</command> module can handle both pure cgroupfs v1
+ (<filename>/sys/fs/cgroup/$controller</filename>) and pure cgroupfs
+ v2 (<filename>/sys/fs/cgroup</filename>), as well as mixed mounts,
+ where some controllers are mounted in a standard cgroupfs v1 hierarchy
+ (<filename>/sys/fs/cgroup/$controller</filename>) and others in
+ cgroupfs v2 hierarchy (<filename>/sys/fs/cgroup/unified</filename>).
+ Writeable cgroups are either created for all controllers or, if specified,
+ for only controllers listed as arguments on the command line.
+ </para>
+
+ <para>
+ The cgroup created <filename>user/$user/n</filename> will be for the nth
+ session under cgroup kernel controller hierarchy.
+ </para>
+
+ <para>
+ Systems with a systemd init system are treated specifically, both with
+ respect to cgroupfs v1 and cgroupfs v2. For both, cgroupfs v1 and
+ cgroupfs v2, the module checks whether systemd already placed the user in
+ a cgroup it created <filename>user.slice/user-$uid/session-n.scope
+ </filename> by checking whether $uid == login uid. If so, the login
+ user chown the <filename>session-n.scope</filename>, else a cgroup is
+ created as outlined above (<filename>user/$user/n</filename>) and chown it
+ to login uid. If the init system has already placed the login user inside
+ a session specific group, the <command>pam_cgfs.so</command> module is
+ smart enough to detect it and re-use the cgroup.
+ </para>
+
+ <para>
+ In essence, the <command>pam_cgfs.so</command> module takes care of
+ placing unprivileged (non-root) users into writable cgroups at login
+ and also cleaning up these cgroup hierarchies on logout, so they are free
+ to delegate resources to containers as needed that have been provided to
+ them.
+ </para>
+
+ </refsect1>
+
+ <refsect1>
+
+ <title>Options</title>
+
+ <variablelist>
+
+ <varlistentry>
+ <term> <option>-c <replaceable>controller-list</replaceable></option> </term>
+ <listitem>
+ <para>
+ Takes a string argument which sets the list of kernel controllers and
+ named controllers delimited by commas in-between “,”. Named controllers
+ need to be specified in the form “name=$namedcontroller”. Can use “all”
+ enable all cgroup resource controller hierarchies. Specifying “all” and
+ other controllers explicitly returns PAM_SESSION_ERR.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ </refsect1>
+
+ <refsect1>
+ <title>Module types provided</title>
+ <para>
+ Only <option>session</option> module type is provided (and needed).
+ </para>
+ </refsect1>
+
+ <refsect1>
+
+ <title>Return Values</title>
+
+ <variablelist>
+
+ <varlistentry>
+ <term>PAM_SUCCESS</term>
+ <listitem>
+ <para>
+ Writeable cgroups have been created for the user.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>PAM_SESSION_ERR</term>
+ <listitem>
+ <para>
+ Failed to create writable cgroups for the user.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ </refsect1>
+
+ <refsect1>
+
+ <title>Files</title>
+
+ <variablelist>
+
+ <varlistentry>
+ <term>/etc/pam.d/common-session{,-noninteractive}</term>
+ <listitem>
+ <para>
+ Default configuration is added at the end of these files.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ </refsect1>
+
+ <refsect1>
+ <title>EXAMPLE</title>
+ <programlisting>
+session optional pam_cgfs.so -c freezer,memory,named=systemd
+# default configuration
+# user writable cgroups are created under freezer, memory and named cgroup systemd hierarchies.
+# /sys/fs/cgroup/$controller/user/$user/n for freezer,memory.
+# /sys/fs/cgroup/systemd/user.slice/user-$uid/session-n.scope for systemd.
+
+session optional pam_cgfs.so -c all
+# user writable cgroups are created under all cgroup controllers.
+
+session optional pam_cgfs.so -c all,memory,freezer
+# invalid argument and returns PAM_SESSION_ERR
+ </programlisting>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+
+ <simpara>
+ <citerefentry>
+ <refentrytitle><command>lxc-cgroup</command></refentrytitle>
+ <manvolnum>1</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle><command>cgroups</command></refentrytitle>
+ <manvolnum>7</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle><command>user_namespaces</command></refentrytitle>
+ <manvolnum>7</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle><command>namespaces</command></refentrytitle>
+ <manvolnum>7</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle><command>pam</command></refentrytitle>
+ <manvolnum>8</manvolnum>
+ </citerefentry>
+ </simpara>
+
+
+ </refsect1>
+
+
+ <refsect1>
+ <title>Author</title>
+ <para>Venkata Harshavardhan Reddy Allu <email>venkataharshavardhan_ven@srmuniv.edu.in</email></para>
+ </refsect1>
+
+</refentry>
+
+<!-- Keep this comment at the end of the file
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+mode: sgml
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+End:
+-->
projects / thirdparty / lxc.git / commitdiff
