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--- services:system_and_service_managers [2016/07/06 13:45] – peter
+++ services:system_and_service_managers [2020/07/26 13:10] (current) – old revision restored (2016/07/06 14:52) 173.249.63.71
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 ====== Services - System and service managers ======
+Linux provides many System and service managers.
+A good init system should start only what is needed, and that on-demand. Either lazily or in parallel and in advance.  However it should not start more than necessary, particularly not everything installed that could use that service.
 ===== init =====
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 **Disadvantages of init**
-  The traditional System V init system had limitations.  For example, some services need to start after other services (for example, you can't mount NFS filesystems until the network is running), but the only way in System V to handle that is to set the links in the rc#.d directory such that one is before the other.  You might need to re-number everything later when dependencies are added or changed.
+  * The traditional System V init system had limitations.  For example, some services need to start after other services (for example, you can't mount NFS filesystems until the network is running), but the only way in System V to handle that is to set the links in the rc#.d directory such that one is before the other.  You might need to re-number everything later when dependencies are added or changed.
+  * Could not start services in parallel.
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 **Advantages of systemd**
-  * Every process started gets its own cgroup or a particular cgroup.
+  * Every process started gets its own cgroup or a particular cgroup.  This makes it more efficient to identify malicious users/processes.
   * Pre-creation of sockets and file handles for services, similar to how xinetd does for it's services, allowing dependent services to start faster.  For example, systemd will hold open the filehandle for /dev/log for syslog, and subsequent services that send to /dev/log will have their messages buffered until syslogd is ready to take over.
   * Fewer processes run to actually start a service.  This means you aren't writing a shell script to start up your service.  This can be a speed improvement, and (IMO) something easier to set up in the first place.
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-** References **
+**Disadvantages of systemd**
+  * All startup scripts need to be rewritten.
+  * There's way less compatibility with non-linux OSs (like BSDs, for example).
+**References**
   * http://en.wikipedia.org/wiki/Systemd
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 Upstart jobs start as soon as they can.