systemd-analyse: add "critical-chain" command

"critical-chain" prints a tree of the critical chain of units

$ ./systemd-analyze critical-chain
graphical.target @1.226s
└─multi-user.target @1.226s
  └─nfs-lock.service @961ms +265ms
    └─rpcbind.service @958ms +1ms
      └─network.target @957ms
        └─NetworkManager.service @434ms +522ms
          └─basic.target @428ms
            └─sockets.target @428ms
              └─dbus.socket @428ms
                └─sysinit.target @427ms
                  └─systemd-tmpfiles-setup.service @411ms +15ms
                    └─local-fs.target @410ms
                      └─boot-efi.automount @410ms
                        └─boot.mount @397ms +9ms
                          └─local-fs-pre.target @192ms
                            └─systemd-udevd.service @187ms +5ms
                              └─systemd-udevd-control.socket @140ms
                                └─-.mount

With the "--fuzz=<ms>" parameter one can display more units around
the critical units.

$ ./systemd-analyze --fuzz=10ms critical-chain
└─multi-user.target @1.226s
  └─nfs-lock.service @961ms +265ms
    ├─rpcbind.service @958ms +1ms
    │ └─network.target @957ms
    │   └─NetworkManager.service @434ms +522ms
    │     ├─basic.target @428ms
    │     │ ├─sockets.target @428ms
    │     │ │ ├─dbus.socket @428ms
    │     │ │ │ └─sysinit.target @427ms
    │     │ │ │   ├─systemd-tmpfiles-setup.service @411ms +15ms
    │     │ │ │   │ └─local-fs.target @410ms
    │     │ │ │   │   └─boot-efi.automount @410ms
    │     │ │ │   │     └─boot.mount @397ms +9ms
    │     │ │ │   │       └─local-fs-pre.target @192ms
    │     │ │ │   │         └─systemd-udevd.service @187ms +5ms
    │     │ │ │   │           ├─systemd-udevd-control.socket @140ms
    │     │ │ │   │           │ └─-.mount
    │     │ │ │   │           └─systemd-udevd-kernel.socket @140ms
    │     │ │ │   └─swap.target @421ms
    │     │ │ │     └─dev-disk-by\x2duuid-....swap @414ms +6ms
    │     │ │ │       └─systemd-journald.socket
    │     │ │ ├─rpcbind.socket @428ms
    │     │ │ └─cups.socket @428ms
    │     │ ├─paths.target @428ms
    │     │ │ └─cups.path @428ms
    │     │ ├─timers.target @427ms
    │     │ │ └─systemd-tmpfiles-clean.timer @427ms
    │     │ └─sysinit.target @427ms
    │     │   └─...
    │     └─dbus.socket @428ms
    │       └─...
    └─network.target @957ms
      └─...

1 files changed, 32 insertions, 0 deletions

diff --git a/man/systemd-analyze.xml b/man/systemd-analyze.xml
index 9f313d76f1..ae45bfcf31 100644
--- a/man/systemd-analyze.xml
+++ b/man/systemd-analyze.xml
@@ -34,6 +34,12 @@
                                 <surname>Poettering</surname>
                                 <email>lennart@poettering.net</email>
                         </author>
+                        <author>
+                                <contrib>Developer</contrib>
+                                <firstname>Harald</firstname>
+                                <surname>Hoyer</surname>
+                                <email>harald@redhat.com</email>
+                        </author>
                 </authorgroup>
         </refentryinfo>
 
@@ -55,6 +61,9 @@
                         <command>systemd-analyze <arg choice="opt" rep="repeat">OPTIONS</arg> blame </command>
                 </cmdsynopsis>
                 <cmdsynopsis>
+                        <command>systemd-analyze <arg choice="opt" rep="repeat">OPTIONS</arg> critical-chain </command>
+                </cmdsynopsis>
+                <cmdsynopsis>
                         <command>systemd-analyze <arg choice="opt" rep="repeat">OPTIONS</arg> plot <arg choice="opt">&gt; file.svg</arg></command>
                 </cmdsynopsis>
                 <cmdsynopsis>
@@ -88,6 +97,16 @@
                 be slow simply because it waits for the initialization
                 of another service to complete.</para>
 
+                <para><command>systemd-analyze critical-chain</command>
+                prints a tree of the time critical chain of units.
+                The time after the unit is active or started is printed
+                after the "@" character. The time the unit takes to
+                start is printed after the "+" character.
+                Note that the output might be misleading as the
+                initialization of one service might depend on socket
+                activation and because of the parallel execution
+                of units.</para>
+
                 <para><command>systemd-analyze plot</command> prints
                 an SVG graphic detailing which system services have
                 been started at what time, highlighting the time they
@@ -181,6 +200,19 @@
                                 unit name must match one of given
                                 values.</para></listitem>
                         </varlistentry>
+
+                        <varlistentry>
+                                <term><option>--fuzz=</option><replaceable>timespan</replaceable></term>
+
+                                <listitem><para>When used in conjunction
+                                with the <command>critical-chain</command>
+                                command (see above), also show units, which
+                                finished <replaceable>timespan</replaceable> earlier, than the
+                                latest unit in the same level. The unit of
+                                <replaceable>timespan</replaceable> is seconds
+                                unless specified with a different unit,
+                                i.e. "50ms".</para></listitem>
+                        </varlistentry>
                 </variablelist>
 
         </refsect1>