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Paul Cobbaut
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several systemd updates
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‎modules/systemd/030_systemd_theory.xml

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@@ -21,17 +21,15 @@ root@debian8:~#</screen>
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<?hard-pagebreak?>
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<section><title>systemd targets</title>
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<para>The first command to learn is <command>systemctl list-units --type=target</command> (or the shorter version <command>systemctl -t target</command>). It will show you the different targets on the system.</para>
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<screen>[root@rhel7 ~]# systemctl list-units --type=target
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<screen>[root@rhel71 ~]# <command>systemctl -t target</command>
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UNIT LOAD ACTIVE SUB DESCRIPTION
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basic.target loaded active active Basic System
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cryptsetup.target loaded active active Encrypted Volumes
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getty.target loaded active active Login Prompts
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graphical.target loaded active active Graphical Interface
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local-fs-pre.target loaded active active Local File Systems (Pre)
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local-fs.target loaded active active Local File Systems
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multi-user.target loaded active active Multi-User System
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network.target loaded active active Network
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nfs.target loaded active active Network File System Server
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paths.target loaded active active Paths
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remote-fs.target loaded active active Remote File Systems
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slices.target loaded active active Slices
@@ -44,19 +42,20 @@ LOAD = Reflects whether the unit definition was properly loaded.
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ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
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SUB = The low-level unit activation state, values depend on unit type.
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16 loaded units listed. Pass --all to see loaded but inactive units, too.
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14 loaded units listed. Pass --all to see loaded but inactive units, too.
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To show all installed unit files use 'systemctl list-unit-files'.
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[root@rhel7 ~]#</screen>
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[root@rhel71 ~]#</screen>
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<para>Targets are the replacement of runlevels and define specific points to reach when booting the system. For example the <command>graphical.target</command> is reached when you get a graphical interface, and the <command>nfs.target</command> requires a running nfs server.</para>
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<para>To switch to a target (for example <command>multi-user.target</command>), we now use <command>systemctl isolate</command> (instead of the equivalent <command>init 3</command> to change the runlevel).</para>
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<screen>[root@rhel7 ~]# ps fax | wc -l
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<para>This screenshot shows a <command>Red Hat Enterprise Linux 7</command> server switching from a graphical interface to command line (decreasing the number of running processes).</para>
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<screen>[root@rhel7 ~]# <command>ps fax | wc -l</command>
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[root@rhel7 ~]# systemctl isolate multi-user.target
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[root@rhel7 ~]# ps fax | wc -l
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[root@rhel7 ~]# <command>systemctl isolate multi-user.target</command>
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[root@rhel7 ~]# <command>ps fax | wc -l</command>
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[root@rhel7 ~]#</screen>
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<para>To change the default target, we again use this <command>systemctl</command> command (instead of editing the <command>/etc/inittab</command> file).</para>
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<screen>[root@rhel7 ~]# systemctl enable multi-user.target --force
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<screen>[root@rhel7 ~]# <command>systemctl enable multi-user.target --force</command>
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rm '/etc/systemd/system/default.target'
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ln -s '/usr/lib/systemd/system/multi-user.target' '/etc/systemd/system/default\
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.target'
@@ -65,80 +64,103 @@ ln -s '/usr/lib/systemd/system/multi-user.target' '/etc/systemd/system/default\
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</section>
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<?hard-pagebreak?>
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<section><title>systemd dependencies</title>
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<para>Dependencies are no longer defined by alfabetical order of running scripts, but by configuration in <command>/etc/systemd/system/</command>. For example here are the required services for the <command>multi-user.target</command> on Red Hat Enterprise 7.</para>
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<screen>[root@rhel7 ~]# ls /etc/systemd/system/multi-user.target.wants/
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abrt-ccpp.service hypervkvpd.service postfix.service
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abrtd.service hypervvssd.service remote-fs.target
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abrt-oops.service irqbalance.service rhsmcertd.service
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abrt-vmcore.service ksm.service rngd.service
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abrt-xorg.service ksmtuned.service rpcbind.service
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atd.service libstoragemgmt.service rsyslog.service
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auditd.service libvirtd.service smartd.service
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avahi-daemon.service mdmonitor.service sshd.service
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chronyd.service ModemManager.service sysstat.service
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crond.service NetworkManager.service tuned.service
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cups.path nfs.target vmtoolsd.service
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[root@rhel7 ~]#</screen>
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<para>Debian8 is not fully migrated yet.</para>
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<screen>root@debian8:~# ls /etc/systemd/system/multi-user.target.wants/
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anacron.service binfmt-support.service pppd-dns.service ssh.service
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atd.service fancontrol.service remote-fs.target
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avahi-daemon.service lm-sensors.service rsyslog.service</screen>
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<para>Dependencies are no longer defined by alfabetical order of running scripts, but by configuration in <command>/etc/systemd/system/</command>. For example here are the required services for the <command>multi-user.target</command> on Red Hat Enterprise 7.1.</para>
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<screen>[root@rhel71 ~]# <command>cat /etc/redhat-release</command>
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Red Hat Enterprise Linux Server release 7.1 (Maipo)
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[root@rhel71 ~]# <command>ls /etc/systemd/system/multi-user.target.wants/</command>
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abrt-ccpp.service auditd.service postfix.service sysstat.service
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abrtd.service chronyd.service remote-fs.target tuned.service
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abrt-oops.service crond.service rhsmcertd.service
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abrt-vmcore.service irqbalance.service rsyslog.service
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abrt-xorg.service NetworkManager.service sshd.service
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[root@rhel71 ~]#</screen>
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<para>Below a screenshot from Debian (stretch/sid is Debian 9). There is already a lot of <command>systemd</command> in Debian 8 and 9 (less than in RHEL7).</para>
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<screen>root@debian9:~# <command>cat /etc/debian_version</command>
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stretch/sid
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root@debian9:~# <command>ls /etc/systemd/system/multi-user.target.wants/</command>
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anacron.service binfmt-support.service lm-sensors.service rsyslog.service
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atd.service cron.service pppd-dns.service ssh.service
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avahi-daemon.service fancontrol.service remote-fs.target
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root@debian9:~#</screen>
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<para>Typical <command>rc scripts</command> are replaced with services. Issue the <command>systemctl list-units -t service --all</command> (or <command>systemctl -at service</command>) to get a list of all services on your system.</para>
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<screen>[root@rhel7 ~]# systemctl -at service | head -5 | column -t | cut -c1-78
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<screen>[root@rhel7 ~]# <command>systemctl -at service | head -5 | column -t | cut -c1-78</command>
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UNIT LOAD ACTIVE SUB DESCRIPTION
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abrt-ccpp.service loaded active exited Install ABRT coredump
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abrt-oops.service loaded active running ABRT kernel log
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abrt-vmcore.service loaded inactive dead Harvest vmcores for
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abrt-xorg.service loaded active running ABRT Xorg log
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[root@rhel7 ~]#</screen>
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<para>And here an example on how to see the status of the <command>sshd</command> service.</para>
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<screen>[root@rhel7 ~]# systemctl status sshd.service
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</section>
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<?hard-pagebreak?>
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<section><title>service status</title>
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<para>Below is a (truncated) screenshot showing how to see the status of the <command>sshd</command> service. (This RHEL server was attacked using brute force ssh on 2 August 2015.)</para>
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<screen>[root@rhel71 ~]# <command>systemctl status sshd.service</command>
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sshd.service - OpenSSH server daemon
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Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)
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Active: active (running) since Wed 2014-09-10 13:42:21 CEST; 55min ago
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Main PID: 1400 (sshd)
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CGroup: /system.slice/sshd.service
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--1400 /usr/sbin/sshd -D
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Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)
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Active: active (running) since Wed 2015-07-29 12:00:10 CEST; 1 weeks 0 days ago
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Main PID: 1123 (sshd)
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CGroup: /system.slice/sshd.service
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└─1123 /usr/sbin/sshd -D
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Sep 10 13:42:21 rhel7 systemd[1]: Started OpenSSH server daemon.
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Sep 10 13:42:21 rhel7 sshd[1400]: Server listening on 0.0.0.0 port 22.
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Sep 10 13:42:21 rhel7 sshd[1400]: Server listening on :: port 22.
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[root@rhel7 ~]#</screen>
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Aug 02 16:45:24 rhel71 sshd[12704]: Failed password for root from 43.229.53.79
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Aug 02 18:15:28 rhel71 sshd[12872]: pam_unix(sshd:auth): authentication failur
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Aug 02 18:15:28 rhel71 sshd[12872]: pam_succeed_if(sshd:auth): requirement "ui
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Aug 02 18:15:30 rhel71 sshd[12872]: Failed password for root from 43.229.53.79
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Aug 02 18:15:30 rhel71 sshd[12872]: pam_succeed_if(sshd:auth): requirement "ui
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Aug 02 18:15:32 rhel71 sshd[12872]: Failed password for root from 43.229.53.79
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Aug 02 18:15:32 rhel71 sshd[12872]: pam_succeed_if(sshd:auth): requirement "ui
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Aug 02 18:15:34 rhel71 sshd[12872]: Failed password for root from 43.229.53.79
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Aug 02 18:15:34 rhel71 sshd[12872]: Received disconnect from 43.229.53.79: 11:
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Aug 03 10:21:11 rhel71 sshd[14616]: pam_unix(sshd:auth): authentication failur
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Aug 03 10:21:11 rhel71 sshd[14616]: pam_succeed_if(sshd:auth): requirement "ui
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Aug 03 10:21:13 rhel71 sshd[14616]: Failed password for root from 119.188.7.14
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Aug 03 10:21:13 rhel71 sshd[14616]: Received disconnect from 119.188.7.143: 11
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Aug 03 14:20:03 rhel71 sshd[15083]: Accepted password for root from 192.168.1.
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Hint: Some lines were ellipsized, use -l to show in full.
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[root@rhel71 ~]#</screen>
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<para>This <command>systemd</command> feature does not work by default on <command>Debian 8/9</command> because <command>init</command> has pid 1. It only works when the system is booted with <command>systemd</command> as pid 1.</para>
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<screen>root@debian8:~# <command>systemctl status sshd</command>
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Failed to get D-Bus connection: Operation not permitted
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root@debian8:~# <command>systemctl status ssh</command>
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Failed to get D-Bus connection: Operation not permitted
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root@debian8:~# <command>service ssh status</command>
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sshd is running.
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root@debian8:~#</screen>
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</section>
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<?hard-pagebreak?>
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<section><title>systemd services</title>
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<section><title>systemd services configuration</title>
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<para>The <command>chkconfig</command> and <command>service</command> commands are considered 'legacy'. They are replaced with <command>systemctl</command>.</para>
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<para>This screenshot shows the new way to start and stop a service.</para>
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<screen>[root@rhel7 ~]# systemctl start crond.service
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[root@rhel7 ~]# systemctl show crond.service | grep State
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<screen>[root@rhel7 ~]# <command>systemctl start crond.service</command>
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[root@rhel7 ~]# <command>systemctl show crond.service | grep State</command>
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LoadState=loaded
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ActiveState=active
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SubState=running
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UnitFileState=enabled
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[root@rhel7 ~]# systemctl stop crond.service
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[root@rhel7 ~]# systemctl show crond.service | grep State
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[root@rhel7 ~]# <command>systemctl stop crond.service</command>
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[root@rhel7 ~]# <command>systemctl show crond.service | grep State</command>
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LoadState=loaded
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ActiveState=inactive
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SubState=dead
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UnitFileState=enabled
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[root@rhel7 ~]#</screen>
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<para>And here is the new way to stop and disable a service.</para>
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<screen>[root@rhel7 ~]# systemctl stop crond.service
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[root@rhel7 ~]# systemctl disable crond.service
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<screen>[root@rhel7 ~]# <command>systemctl stop crond.service</command>
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[root@rhel7 ~]# <command>systemctl disable crond.service</command>
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rm '/etc/systemd/system/multi-user.target.wants/crond.service'
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[root@rhel7 ~]# systemctl show crond.service | grep State
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[root@rhel7 ~]# <command>systemctl show crond.service | grep State</command>
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LoadState=loaded
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ActiveState=inactive
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SubState=dead
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UnitFileState=disabled
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[root@rhel7 ~]#</screen>
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<para>This screenshot shows how to enable and start the service again.</para>
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<screen>[root@rhel7 ~]# systemctl enable crond.service
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<screen>[root@rhel7 ~]# <command>systemctl enable crond.service</command>
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ln -s '/usr/lib/systemd/system/crond.service' '/etc/systemd/system/multi-user.\
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target.wants/crond.service'
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[root@rhel7 ~]# systemctl start crond.service
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[root@rhel7 ~]# systemctl show crond.service | grep State
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[root@rhel7 ~]# <command>systemctl start crond.service</command>
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[root@rhel7 ~]# <command>systemctl show crond.service | grep State</command>
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LoadState=loaded
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ActiveState=active
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SubState=running
@@ -148,13 +170,13 @@ UnitFileState=enabled
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<?hard-pagebreak?>
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<section><title>systemd signalling</title>
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<para>You can also use <command>systemd</command> to <command>kill</command> problematic services.</para>
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<screen>[root@rhel7 ~]# systemctl show crond.service | grep State
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<screen>[root@rhel7 ~]# <command>systemctl show crond.service | grep State</command>
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LoadState=loaded
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ActiveState=active
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SubState=running
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UnitFileState=enabled
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[root@rhel7 ~]# systemctl kill -s SIGKILL crond.service
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[root@rhel7 ~]# systemctl show crond.service | grep State
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[root@rhel7 ~]# <command>systemctl kill -s SIGKILL crond.service</command>
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[root@rhel7 ~]# <command>systemctl show crond.service | grep State</command>
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LoadState=loaded
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ActiveState=failed
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SubState=failed

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