journald: introduce new "systemd-journal" group and make it own the journal files

Previously all journal files were owned by "adm". In order to allow
specific users to read the journal files without granting it access to
the full "adm" powers, introduce a new specific group for this.

"systemd-journal" has to be created by the packaging scripts manually at
installation time. It's a good idea to assign a static UID/GID to this
group, since /var/log/journal might be shared across machines via NFS.

This commit also grants read access to the journal files by default to
members of the "wheel" and "adm" groups via file system ACLs, since
these "almost-root" groups should be able to see what's going on on the
system. These ACLs are created by "make install". Packagers probably
need to duplicate this logic in their postinst scripts.

This also adds documentation how to grant access to the journal to
additional users or groups via fs ACLs.

1 files changed, 34 insertions, 1 deletions

diff --git a/man/systemd-journald.service.xml b/man/systemd-journald.service.xml
index 4969ab19c..bc32c8e38 100644
--- a/man/systemd-journald.service.xml
+++ b/man/systemd-journald.service.xml
@@ -158,6 +158,38 @@
                 </variablelist>
         </refsect1>
 
+        <refsect1>
+                <title>Access Control</title>
+
+                <para>Journal files are by default owned and readable
+                by the <literal>systemd-journal</literal> system group
+                (but not writable). Adding a user to this group thus
+                enables her/him to read the journal files.</para>
+
+                <para>By default, each logged in user will get her/his
+                own set of journal files in
+                <filename>/var/log/journal/</filename>. These files
+                will not be owned by the user however, in order to
+                avoid that the user can write to them
+                directly. Instead, file system ACLs are used to ensure
+                the user gets read access only.</para>
+
+                <para>Additional users and groups may be granted
+                access to journal files via file system access control
+                lists (ACL). Distributions and administrators may
+                choose to grant read access to all members of the
+                <literal>wheel</literal> and <literal>adm</literal>
+                system groups with a command such as the
+                following:</para>
+
+                <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
+
+                <para>Note that this command will update the ACLs both
+                for existing journal files and for future journal
+                files created in the
+                <filename>/var/log/journal/</filename>
+                directory.</para>
+        </refsect1>
 
         <refsect1>
                 <title>See Also</title>
@@ -166,7 +198,8 @@
                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
-                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                 </para>
         </refsect1>