tree-wide: add SD_ID128_MAKE_STR, remove LOG_MESSAGE_ID

[elogind.git] / README

diff --git a/README b/README
index 928bd7d0c4447d6b3ed1a98cf2cf311069867d4d..0cd868ade28b70e40163bbb3ddfca44f0e536b8c 100644 (file)
--- a/README
+++ b/README
@@ -29,7 +29,7 @@ provide a subset of the interfaces of systemd 219.
 
 To contribute to elogind, fork the current source code from github:
 
-  https://github.com/andywingo/elogind
+  https://github.com/elogind/elogind
 
 Send a pull request for the changes you like.
 
@@ -39,7 +39,7 @@ To chat about elogind:
 
 Finally, bug reports:
 
-  https://github.com/andywingo/elogind/issues
+  https://github.com/elogind/elogind/issues
 
 Why bother?
 -----------
@@ -77,27 +77,32 @@ of <systemd/sd-login.h>.
 Libelogind just implements login-related functionality.  It also
 provides the sd-bus API.
 
-Unlike systemd, whose logind arranges to run user sessions in cgroups
-via RPC calls to systemd, in elogind there is no systemd so there are
-no cgroups.  This has a few implications:
+Unlike systemd, whose logind arranges to manage resources for user
+sessions via RPC calls to systemd, in elogind there is no systemd so
+there is no global cgroup-based resource management.  This has a few
+implications:
 
   * Elogind does not create "slices" for users.  Elogind will not
     record that users are associated with slices.
 
-  * Systemd's logind waits for all user jobs to stop before recording
-    that a user's session has gone away.  Since we have no cgroups,
-    elogind just removes the session directly when pam_elogind.so
-    indicates the user has logged out.
-
   * The /run/systemd/slices directory will always be empty.
 
-  * Support for lingering is not so great.
+  * Elogind does not have the concept of a "scope", internally, as
+    it's the same as a session.  Any API that refers to scopes will
+    always return an error code.
+
+On the other hand, elogind does use a similar strategy to systemd in
+that it places processes in a private cgroup for organizational
+purposes, without installing any controllers (see
+http://0pointer.de/blog/projects/cgroups-vs-cgroups.html).  This
+allows elogind to map arbitrary processes to sessions, even if the
+process does the usual double-fork to be reparented to PID 1.
 
 Elogind does not manage virtual terminals.
 
 Elogind does monitor power button and the lid switch, like systemd,
 but instead of doing RPC to systemd to suspend, poweroff, or restart
-the machine, elogind just does this directly.  For suspend, hybernate,
+the machine, elogind just does this directly.  For suspend, hibernate,
 and hybrid-sleep, elogind uses the same code as systemd-sleep.
 Instead of using a separate sleep.conf file to configure the sleep
 behavior, this is included in the [Sleep] section of
@@ -111,6 +116,32 @@ flag.
 
 The PAM module is called pam_elogind.so, not pam_systemd.so.
 
+Elogind and the running cgroup controller
+-----------------------------------------
+While 'configure' runs, it will detect which controller is in place.
+If no controller is in place, configure will determine, that elogind
+should be its own controller, which will be a very limited one.
+
+This approach should generally work, but if you just have no cgroup
+controller in place, yet, or if you are currently switching to
+another one, this approach will fail.
+
+In this case you can do one of the two following things:
+
+ 1) Boot your system with the target init system and cgroup
+    controller, before configuring and building elogind, or
+ 2) Use the --with-cgroup-controller=name option.
+
+Example: If you plan to use openrc, but openrc has not yet booted
+         the machine, you can use
+         --with-cgroup-controller=openrc
+         to let elogind know that openrc will be the controller
+         in charge.
+
+However, if you set the controller at configure time to something
+different than what is in place, elogind will not start until that
+controller is actively used as the primary controller.
+
 License
 -------