systemd for Administrators, Part II

Post Syndicated from Lennart Poettering original http://0pointer.net/blog/projects/systemd-for-admins-2.html

Here’s the second installment of my ongoing series about systemd for administrators.

Which Service Owns Which Processes?

On most Linux systems the number of processes that are running by
default is substantial. Knowing which process does what and where it
belongs to becomes increasingly difficult. Some services even maintain
a couple of worker processes which clutter the “ps” output with
many additional processes that are often not easy to recognize. This is
further complicated if daemons spawn arbitrary 3rd-party processes, as
Apache does with CGI processes, or cron does with user jobs.

A slight remedy for this is often the process inheritance tree, as
shown by “ps xaf“. However this is usually not reliable, as processes
whose parents die get reparented to PID 1, and hence all information
about inheritance gets lost. If a process “double forks” it hence loses
its relationships to the processes that started it. (This actually is
supposed to be a feature and is relied on for the traditional Unix
daemonizing logic.) Furthermore processes can freely change their names
with PR_SETNAME or by patching argv[0], thus making
it harder to recognize them. In fact they can play hide-and-seek with
the administrator pretty nicely this way.

In systemd we place every process that is spawned in a control
group
named after its service. Control groups (or cgroups)
at their most basic are simply groups of processes that can be
arranged in a hierarchy and labelled individually. When processes
spawn other processes these children are automatically made members of
the parents cgroup. Leaving a cgroup is not possible for unprivileged
processes. Thus, cgroups can be used as an effective way to label
processes after the service they belong to and be sure that the
service cannot escape from the label, regardless how often it forks or
renames itself. Furthermore this can be used to safely kill a service
and all processes it created, again with no chance of escaping.

In today’s installment I want to introduce you to two commands you
may use to relate systemd services and processes. The first one, is
the well known ps command which has been updated to show
cgroup information along the other process details. And this is how it
looks:

$ ps xawf -eo pid,user,cgroup,args
  PID USER     CGROUP                              COMMAND
    2 root     -                                   [kthreadd]
    3 root     -                                    \_ [ksoftirqd/0]
[...]
 4281 root     -                                    \_ [flush-8:0]
    1 root     name=systemd:/systemd-1             /sbin/init
  455 root     name=systemd:/systemd-1/sysinit.service /sbin/udevd -d
28188 root     name=systemd:/systemd-1/sysinit.service  \_ /sbin/udevd -d
28191 root     name=systemd:/systemd-1/sysinit.service  \_ /sbin/udevd -d
 1096 dbus     name=systemd:/systemd-1/dbus.service /bin/dbus-daemon --system --address=systemd: --nofork --systemd-activation
 1131 root     name=systemd:/systemd-1/auditd.service auditd
 1133 root     name=systemd:/systemd-1/auditd.service  \_ /sbin/audispd
 1135 root     name=systemd:/systemd-1/auditd.service      \_ /usr/sbin/sedispatch
 1171 root     name=systemd:/systemd-1/NetworkManager.service /usr/sbin/NetworkManager --no-daemon
 4028 root     name=systemd:/systemd-1/NetworkManager.service  \_ /sbin/dhclient -d -4 -sf /usr/libexec/nm-dhcp-client.action -pf /var/run/dhclient-wlan0.pid -lf /var/lib/dhclient/dhclient-7d32a784-ede9-4cf6-9ee3-60edc0bce5ff-wlan0.lease -
 1175 avahi    name=systemd:/systemd-1/avahi-daemon.service avahi-daemon: running [epsilon.local]
 1194 avahi    name=systemd:/systemd-1/avahi-daemon.service  \_ avahi-daemon: chroot helper
 1193 root     name=systemd:/systemd-1/rsyslog.service /sbin/rsyslogd -c 4
 1195 root     name=systemd:/systemd-1/cups.service cupsd -C /etc/cups/cupsd.conf
 1207 root     name=systemd:/systemd-1/mdmonitor.service mdadm --monitor --scan -f --pid-file=/var/run/mdadm/mdadm.pid
 1210 root     name=systemd:/systemd-1/irqbalance.service irqbalance
 1216 root     name=systemd:/systemd-1/dbus.service /usr/sbin/modem-manager
 1219 root     name=systemd:/systemd-1/dbus.service /usr/libexec/polkit-1/polkitd
 1242 root     name=systemd:/systemd-1/dbus.service /usr/sbin/wpa_supplicant -c /etc/wpa_supplicant/wpa_supplicant.conf -B -u -f /var/log/wpa_supplicant.log -P /var/run/wpa_supplicant.pid
 1249 68       name=systemd:/systemd-1/haldaemon.service hald
 1250 root     name=systemd:/systemd-1/haldaemon.service  \_ hald-runner
 1273 root     name=systemd:/systemd-1/haldaemon.service      \_ hald-addon-input: Listening on /dev/input/event3 /dev/input/event9 /dev/input/event1 /dev/input/event7 /dev/input/event2 /dev/input/event0 /dev/input/event8
 1275 root     name=systemd:/systemd-1/haldaemon.service      \_ /usr/libexec/hald-addon-rfkill-killswitch
 1284 root     name=systemd:/systemd-1/haldaemon.service      \_ /usr/libexec/hald-addon-leds
 1285 root     name=systemd:/systemd-1/haldaemon.service      \_ /usr/libexec/hald-addon-generic-backlight
 1287 68       name=systemd:/systemd-1/haldaemon.service      \_ /usr/libexec/hald-addon-acpi
 1317 root     name=systemd:/systemd-1/abrtd.service /usr/sbin/abrtd -d -s
 1332 root     name=systemd:/systemd-1/[email protected]/tty2 /sbin/mingetty tty2
 1339 root     name=systemd:/systemd-1/[email protected]/tty3 /sbin/mingetty tty3
 1342 root     name=systemd:/systemd-1/[email protected]/tty5 /sbin/mingetty tty5
 1343 root     name=systemd:/systemd-1/[email protected]/tty4 /sbin/mingetty tty4
 1344 root     name=systemd:/systemd-1/crond.service crond
 1346 root     name=systemd:/systemd-1/[email protected]/tty6 /sbin/mingetty tty6
 1362 root     name=systemd:/systemd-1/sshd.service /usr/sbin/sshd
 1376 root     name=systemd:/systemd-1/prefdm.service /usr/sbin/gdm-binary -nodaemon
 1391 root     name=systemd:/systemd-1/prefdm.service  \_ /usr/libexec/gdm-simple-slave --display-id /org/gnome/DisplayManager/Display1 --force-active-vt
 1394 root     name=systemd:/systemd-1/prefdm.service      \_ /usr/bin/Xorg :0 -nr -verbose -auth /var/run/gdm/auth-for-gdm-f2KUOh/database -nolisten tcp vt1
 1495 root     name=systemd:/user/lennart/1             \_ pam: gdm-password
 1521 lennart  name=systemd:/user/lennart/1                 \_ gnome-session
 1621 lennart  name=systemd:/user/lennart/1                     \_ metacity
 1635 lennart  name=systemd:/user/lennart/1                     \_ gnome-panel
 1638 lennart  name=systemd:/user/lennart/1                     \_ nautilus
 1640 lennart  name=systemd:/user/lennart/1                     \_ /usr/libexec/polkit-gnome-authentication-agent-1
 1641 lennart  name=systemd:/user/lennart/1                     \_ /usr/bin/seapplet
 1644 lennart  name=systemd:/user/lennart/1                     \_ gnome-volume-control-applet
 1646 lennart  name=systemd:/user/lennart/1                     \_ /usr/sbin/restorecond -u
 1652 lennart  name=systemd:/user/lennart/1                     \_ /usr/bin/devilspie
 1662 lennart  name=systemd:/user/lennart/1                     \_ nm-applet --sm-disable
 1664 lennart  name=systemd:/user/lennart/1                     \_ gnome-power-manager
 1665 lennart  name=systemd:/user/lennart/1                     \_ /usr/libexec/gdu-notification-daemon
 1670 lennart  name=systemd:/user/lennart/1                     \_ /usr/libexec/evolution/2.32/evolution-alarm-notify
 1672 lennart  name=systemd:/user/lennart/1                     \_ /usr/bin/python /usr/share/system-config-printer/applet.py
 1674 lennart  name=systemd:/user/lennart/1                     \_ /usr/lib64/deja-dup/deja-dup-monitor
 1675 lennart  name=systemd:/user/lennart/1                     \_ abrt-applet
 1677 lennart  name=systemd:/user/lennart/1                     \_ bluetooth-applet
 1678 lennart  name=systemd:/user/lennart/1                     \_ gpk-update-icon
 1408 root     name=systemd:/systemd-1/console-kit-daemon.service /usr/sbin/console-kit-daemon --no-daemon
 1419 gdm      name=systemd:/systemd-1/prefdm.service /usr/bin/dbus-launch --exit-with-session
 1453 root     name=systemd:/systemd-1/dbus.service /usr/libexec/upowerd
 1473 rtkit    name=systemd:/systemd-1/rtkit-daemon.service /usr/libexec/rtkit-daemon
 1496 root     name=systemd:/systemd-1/accounts-daemon.service /usr/libexec/accounts-daemon
 1499 root     name=systemd:/systemd-1/systemd-logger.service /lib/systemd/systemd-logger
 1511 lennart  name=systemd:/systemd-1/prefdm.service /usr/bin/gnome-keyring-daemon --daemonize --login
 1534 lennart  name=systemd:/user/lennart/1        dbus-launch --sh-syntax --exit-with-session
 1535 lennart  name=systemd:/user/lennart/1        /bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session
 1603 lennart  name=systemd:/user/lennart/1        /usr/libexec/gconfd-2
 1612 lennart  name=systemd:/user/lennart/1        /usr/libexec/gnome-settings-daemon
 1615 lennart  name=systemd:/user/lennart/1        /usr/libexec/gvfsd
 1626 lennart  name=systemd:/user/lennart/1        /usr/libexec//gvfs-fuse-daemon /home/lennart/.gvfs
 1634 lennart  name=systemd:/user/lennart/1        /usr/bin/pulseaudio --start --log-target=syslog
 1649 lennart  name=systemd:/user/lennart/1         \_ /usr/libexec/pulse/gconf-helper
 1645 lennart  name=systemd:/user/lennart/1        /usr/libexec/bonobo-activation-server --ac-activate --ior-output-fd=24
 1668 lennart  name=systemd:/user/lennart/1        /usr/libexec/im-settings-daemon
 1701 lennart  name=systemd:/user/lennart/1        /usr/libexec/gvfs-gdu-volume-monitor
 1707 lennart  name=systemd:/user/lennart/1        /usr/bin/gnote --panel-applet --oaf-activate-iid=OAFIID:GnoteApplet_Factory --oaf-ior-fd=22
 1725 lennart  name=systemd:/user/lennart/1        /usr/libexec/clock-applet
 1727 lennart  name=systemd:/user/lennart/1        /usr/libexec/wnck-applet
 1729 lennart  name=systemd:/user/lennart/1        /usr/libexec/notification-area-applet
 1733 root     name=systemd:/systemd-1/dbus.service /usr/libexec/udisks-daemon
 1747 root     name=systemd:/systemd-1/dbus.service  \_ udisks-daemon: polling /dev/sr0
 1759 lennart  name=systemd:/user/lennart/1        gnome-screensaver
 1780 lennart  name=systemd:/user/lennart/1        /usr/libexec/gvfsd-trash --spawner :1.9 /org/gtk/gvfs/exec_spaw/0
 1864 lennart  name=systemd:/user/lennart/1        /usr/libexec/gvfs-afc-volume-monitor
 1874 lennart  name=systemd:/user/lennart/1        /usr/libexec/gconf-im-settings-daemon
 1903 lennart  name=systemd:/user/lennart/1        /usr/libexec/gvfsd-burn --spawner :1.9 /org/gtk/gvfs/exec_spaw/1
 1909 lennart  name=systemd:/user/lennart/1        gnome-terminal
 1913 lennart  name=systemd:/user/lennart/1         \_ gnome-pty-helper
 1914 lennart  name=systemd:/user/lennart/1         \_ bash
29231 lennart  name=systemd:/user/lennart/1         |   \_ ssh tango
 2221 lennart  name=systemd:/user/lennart/1         \_ bash
 4193 lennart  name=systemd:/user/lennart/1         |   \_ ssh tango
 2461 lennart  name=systemd:/user/lennart/1         \_ bash
29219 lennart  name=systemd:/user/lennart/1         |   \_ emacs systemd-for-admins-1.txt
15113 lennart  name=systemd:/user/lennart/1         \_ bash
27251 lennart  name=systemd:/user/lennart/1             \_ empathy
29504 lennart  name=systemd:/user/lennart/1             \_ ps xawf -eo pid,user,cgroup,args
 1968 lennart  name=systemd:/user/lennart/1        ssh-agent
 1994 lennart  name=systemd:/user/lennart/1        gpg-agent --daemon --write-env-file
18679 lennart  name=systemd:/user/lennart/1        /bin/sh /usr/lib64/firefox-3.6/run-mozilla.sh /usr/lib64/firefox-3.6/firefox
18741 lennart  name=systemd:/user/lennart/1         \_ /usr/lib64/firefox-3.6/firefox
28900 lennart  name=systemd:/user/lennart/1             \_ /usr/lib64/nspluginwrapper/npviewer.bin --plugin /usr/lib64/mozilla/plugins/libflashplayer.so --connection /org/wrapper/NSPlugins/libflashplayer.so/18741-6
 4016 root     name=systemd:/systemd-1/sysinit.service /usr/sbin/bluetoothd --udev
 4094 smmsp    name=systemd:/systemd-1/sendmail.service sendmail: Queue [email protected]:00:00 for /var/spool/clientmqueue
 4096 root     name=systemd:/systemd-1/sendmail.service sendmail: accepting connections
 4112 ntp      name=systemd:/systemd-1/ntpd.service /usr/sbin/ntpd -n -u ntp:ntp -g
27262 lennart  name=systemd:/user/lennart/1        /usr/libexec/mission-control-5
27265 lennart  name=systemd:/user/lennart/1        /usr/libexec/telepathy-haze
27268 lennart  name=systemd:/user/lennart/1        /usr/libexec/telepathy-logger
27270 lennart  name=systemd:/user/lennart/1        /usr/libexec/dconf-service
27280 lennart  name=systemd:/user/lennart/1        /usr/libexec/notification-daemon
27284 lennart  name=systemd:/user/lennart/1        /usr/libexec/telepathy-gabble
27285 lennart  name=systemd:/user/lennart/1        /usr/libexec/telepathy-salut
27297 lennart  name=systemd:/user/lennart/1        /usr/libexec/geoclue-yahoo

(Note that this output is shortened, I have removed most of the
kernel threads here, since they are not relevant in the context of
this blog story)

In the third column you see the cgroup systemd assigned to each
process. You’ll find that the udev processes are in the
name=systemd:/systemd-1/sysinit.service cgroup, which is
where systemd places all processes started by the
sysinit.service service, which covers early boot.

My personal recommendation is to set the shell alias psc
to the ps command line shown above:

alias psc='ps xawf -eo pid,user,cgroup,args'

With this service information of processes is just four keypresses
away!

A different way to present the same information is the
systemd-cgls tool we ship with systemd. It shows the cgroup
hierarchy in a pretty tree. Its output looks like this:

$ systemd-cgls
+    2 [kthreadd]
[...]
+ 4281 [flush-8:0]
+ user
| \ lennart
|   \ 1
|     +  1495 pam: gdm-password
|     +  1521 gnome-session
|     +  1534 dbus-launch --sh-syntax --exit-with-session
|     +  1535 /bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session
|     +  1603 /usr/libexec/gconfd-2
|     +  1612 /usr/libexec/gnome-settings-daemon
|     +  1615 /ushr/libexec/gvfsd
|     +  1621 metacity
|     +  1626 /usr/libexec//gvfs-fuse-daemon /home/lennart/.gvfs
|     +  1634 /usr/bin/pulseaudio --start --log-target=syslog
|     +  1635 gnome-panel
|     +  1638 nautilus
|     +  1640 /usr/libexec/polkit-gnome-authentication-agent-1
|     +  1641 /usr/bin/seapplet
|     +  1644 gnome-volume-control-applet
|     +  1645 /usr/libexec/bonobo-activation-server --ac-activate --ior-output-fd=24
|     +  1646 /usr/sbin/restorecond -u
|     +  1649 /usr/libexec/pulse/gconf-helper
|     +  1652 /usr/bin/devilspie
|     +  1662 nm-applet --sm-disable
|     +  1664 gnome-power-manager
|     +  1665 /usr/libexec/gdu-notification-daemon
|     +  1668 /usr/libexec/im-settings-daemon
|     +  1670 /usr/libexec/evolution/2.32/evolution-alarm-notify
|     +  1672 /usr/bin/python /usr/share/system-config-printer/applet.py
|     +  1674 /usr/lib64/deja-dup/deja-dup-monitor
|     +  1675 abrt-applet
|     +  1677 bluetooth-applet
|     +  1678 gpk-update-icon
|     +  1701 /usr/libexec/gvfs-gdu-volume-monitor
|     +  1707 /usr/bin/gnote --panel-applet --oaf-activate-iid=OAFIID:GnoteApplet_Factory --oaf-ior-fd=22
|     +  1725 /usr/libexec/clock-applet
|     +  1727 /usr/libexec/wnck-applet
|     +  1729 /usr/libexec/notification-area-applet
|     +  1759 gnome-screensaver
|     +  1780 /usr/libexec/gvfsd-trash --spawner :1.9 /org/gtk/gvfs/exec_spaw/0
|     +  1864 /usr/libexec/gvfs-afc-volume-monitor
|     +  1874 /usr/libexec/gconf-im-settings-daemon
|     +  1882 /usr/libexec/gvfs-gphoto2-volume-monitor
|     +  1903 /usr/libexec/gvfsd-burn --spawner :1.9 /org/gtk/gvfs/exec_spaw/1
|     +  1909 gnome-terminal
|     +  1913 gnome-pty-helper
|     +  1914 bash
|     +  1968 ssh-agent
|     +  1994 gpg-agent --daemon --write-env-file
|     +  2221 bash
|     +  2461 bash
|     +  4193 ssh tango
|     + 15113 bash
|     + 18679 /bin/sh /usr/lib64/firefox-3.6/run-mozilla.sh /usr/lib64/firefox-3.6/firefox
|     + 18741 /usr/lib64/firefox-3.6/firefox
|     + 27251 empathy
|     + 27262 /usr/libexec/mission-control-5
|     + 27265 /usr/libexec/telepathy-haze
|     + 27268 /usr/libexec/telepathy-logger
|     + 27270 /usr/libexec/dconf-service
|     + 27280 /usr/libexec/notification-daemon
|     + 27284 /usr/libexec/telepathy-gabble
|     + 27285 /usr/libexec/telepathy-salut
|     + 27297 /usr/libexec/geoclue-yahoo
|     + 28900 /usr/lib64/nspluginwrapper/npviewer.bin --plugin /usr/lib64/mozilla/plugins/libflashplayer.so --connection /org/wrapper/NSPlugins/libflashplayer.so/18741-6
|     + 29219 emacs systemd-for-admins-1.txt
|     + 29231 ssh tango
|     \ 29519 systemd-cgls
\ systemd-1
  + 1 /sbin/init
  + ntpd.service
  | \ 4112 /usr/sbin/ntpd -n -u ntp:ntp -g
  + systemd-logger.service
  | \ 1499 /lib/systemd/systemd-logger
  + accounts-daemon.service
  | \ 1496 /usr/libexec/accounts-daemon
  + rtkit-daemon.service
  | \ 1473 /usr/libexec/rtkit-daemon
  + console-kit-daemon.service
  | \ 1408 /usr/sbin/console-kit-daemon --no-daemon
  + prefdm.service
  | + 1376 /usr/sbin/gdm-binary -nodaemon
  | + 1391 /usr/libexec/gdm-simple-slave --display-id /org/gnome/DisplayManager/Display1 --force-active-vt
  | + 1394 /usr/bin/Xorg :0 -nr -verbose -auth /var/run/gdm/auth-for-gdm-f2KUOh/database -nolisten tcp vt1
  | + 1419 /usr/bin/dbus-launch --exit-with-session
  | \ 1511 /usr/bin/gnome-keyring-daemon --daemonize --login
  + [email protected]
  | + tty6
  | | \ 1346 /sbin/mingetty tty6
  | + tty4
  | | \ 1343 /sbin/mingetty tty4
  | + tty5
  | | \ 1342 /sbin/mingetty tty5
  | + tty3
  | | \ 1339 /sbin/mingetty tty3
  | \ tty2
  |   \ 1332 /sbin/mingetty tty2
  + abrtd.service
  | \ 1317 /usr/sbin/abrtd -d -s
  + crond.service
  | \ 1344 crond
  + sshd.service
  | \ 1362 /usr/sbin/sshd
  + sendmail.service
  | + 4094 sendmail: Queue [email protected]:00:00 for /var/spool/clientmqueue
  | \ 4096 sendmail: accepting connections
  + haldaemon.service
  | + 1249 hald
  | + 1250 hald-runner
  | + 1273 hald-addon-input: Listening on /dev/input/event3 /dev/input/event9 /dev/input/event1 /dev/input/event7 /dev/input/event2 /dev/input/event0 /dev/input/event8
  | + 1275 /usr/libexec/hald-addon-rfkill-killswitch
  | + 1284 /usr/libexec/hald-addon-leds
  | + 1285 /usr/libexec/hald-addon-generic-backlight
  | \ 1287 /usr/libexec/hald-addon-acpi
  + irqbalance.service
  | \ 1210 irqbalance
  + avahi-daemon.service
  | + 1175 avahi-daemon: running [epsilon.local]
  + NetworkManager.service
  | + 1171 /usr/sbin/NetworkManager --no-daemon
  | \ 4028 /sbin/dhclient -d -4 -sf /usr/libexec/nm-dhcp-client.action -pf /var/run/dhclient-wlan0.pid -lf /var/lib/dhclient/dhclient-7d32a784-ede9-4cf6-9ee3-60edc0bce5ff-wlan0.lease -cf /var/run/nm-dhclient-wlan0.conf wlan0
  + rsyslog.service
  | \ 1193 /sbin/rsyslogd -c 4
  + mdmonitor.service
  | \ 1207 mdadm --monitor --scan -f --pid-file=/var/run/mdadm/mdadm.pid
  + cups.service
  | \ 1195 cupsd -C /etc/cups/cupsd.conf
  + auditd.service
  | + 1131 auditd
  | + 1133 /sbin/audispd
  | \ 1135 /usr/sbin/sedispatch
  + dbus.service
  | +  1096 /bin/dbus-daemon --system --address=systemd: --nofork --systemd-activation
  | +  1216 /usr/sbin/modem-manager
  | +  1219 /usr/libexec/polkit-1/polkitd
  | +  1242 /usr/sbin/wpa_supplicant -c /etc/wpa_supplicant/wpa_supplicant.conf -B -u -f /var/log/wpa_supplicant.log -P /var/run/wpa_supplicant.pid
  | +  1453 /usr/libexec/upowerd
  | +  1733 /usr/libexec/udisks-daemon
  | +  1747 udisks-daemon: polling /dev/sr0
  | \ 29509 /usr/libexec/packagekitd
  + dev-mqueue.mount
  + dev-hugepages.mount
  \ sysinit.service
    +   455 /sbin/udevd -d
    +  4016 /usr/sbin/bluetoothd --udev
    + 28188 /sbin/udevd -d
    \ 28191 /sbin/udevd -d

(This too is shortened, the same way)

As you can see, this command shows the processes by their cgroup
and hence service, as systemd labels the cgroups after the
services. For example, you can easily see that the auditing service
auditd.service spawns three individual processes,
auditd, audisp and sedispatch.

If you look closely you will notice that a number of processes have
been assigned to the cgroup /user/1. At this point let’s
simply leave it at that systemd not only maintains services in cgroups,
but user session processes as well. In a later installment we’ll discuss in
more detail what this about.

So much for now, come back soon for the next installment!