Systemd. The giant monster that ate Linux

Transcription

1 Systemd The giant monster that ate Linux

2

3 SysV Init is comfy Dates back to AT&T System III from 1982 Modified up until AT&T Sys V in 1983

4 systemd is Easy

5 Systemd Managing The System

6 System Service Management Unified System Management Tab completion for commands Aggressive parallelization Transactional activation logic Power management Backward compatibility

7 Unified System Management Multiple non-integrated tools System management by committee Can hinder forward progress X11? -> Wayland & Mir

8 Unified System Management (cont.) One system to start them all, One system to stop them, One system to log them all and with ease manage them.

9 Tab Completion Makes life easier First tab adds a space Subsequent tabs work like BASH tab completion

10 Tab Completion Example ~]$ systemd-<tab><tab><tab> systemd-analyze systemd-machine-id-setup systemd-ask-password systemd-notify systemd-cat systemd-nspawn systemd-cgls systemd-path systemd-cgtop systemd-run systemd-delta systemd-stdio-bridge systemd-detect-virt systemd-sysusers systemd-escape systemd-tmpfiles systemd-firstboot systemd-tty-ask-password-agent systemd-inhibit

11 Can Be Overwhelming ~]$ sysctl<tab><tab><tab> Display all 745 possibilities? (y or n)

12 Power Management systemctl reboot systemctl poweroff systemctl suspend systemctl hibernate systemctl hybrid-sleep

13 Aggressive parallelization SysV init: inherently serial Upstart: parallelization using a dependency graph Systemd: socket activation can make all service startup parallel

14 Transactional activation Before activating or deactivating a unit, systemd calculates its dependencies, creates a temporary transaction, and verifies that this transaction is consistent. If a transaction is inconsistent, systemd automatically attempts to correct it and remove non-essential jobs from it before reporting an error. systemd performs dependency checking and attempts to handle dependencies before reporting an error

15 Backward compatibility systemd processes the scripts in /etc/init.d legacy commands telinit, init, halt, shutdown, reboot, runlevel

16 Unit Files Defining Services

17 Types of Unit Files systemctl -t help service socket target device mount automount snapshot timer swap path slice scope

18 Locations - System Mode /usr/lib/systemd/system/ - Installed Packages /etc/systemd/system/ - System Administrator

19 Locations - User Mode /usr/lib/systemd/user/ - Provided by installed packages /etc/systemd/user/ - System-wide user services ~/.config/systemd/user/ - User specific services

20 Writing org/software/systemd/man/systemd.unit.html systemd.service(5), systemd.socket(5), systemd.device(5), systemd.mount(5), systemd.automount(5), systemd.swap(5), systemd.target(5), systemd.path(5), systemd.timer(5), systemd.snapshot(5). systemd.slice(5). systemd.scope(5)

21 Example Service Unit File [Unit] Description=OpenSSH server daemon After=syslog.target network.target auditd.service jaybrown]# cat /etc/init.d/sshd wc -l 236 [Service] EnvironmentFile=/etc/sysconfig/sshd ExecStartPre=/usr/sbin/sshd-keygen ExecStart=/usr/sbin/sshd -D $OPTIONS ExecReload=/bin/kill -HUP $MAINPID KillMode=process Restart=on-failure RestartSec=42s [Install] WantedBy=multi-user.target

22 Socket Units listens on a IP port or UNIX socket queues request until the service is available

23 Example.socket file [Unit] Description=OpenSSH Server Socket Conflicts=sshd.service [Socket] ListenStream=22 Accept=yes [Install] WantedBy=sockets.target

24 Service Units listens for D-Bus communication and activate services uses D-Bus service files for bus-based activation

25 Example D-Bus.service file [Unit] Description=Bluetooth service [Service] Type=dbus BusName=org.bluez ExecStart=/usr/sbin/bluetoothd -n [Install] WantedBy=bluetooth.target Alias=dbus-org.bluez.service

26 Device Units enables services based on device connection or activation named after the device paths they control dev-sda5.device = /dev/sda5 configured directly from the udev database

27 Example.device file Documents]$ systemctl status dev-sda1.device dev-sda1.device - KINGSTON_SNS4151S316G 1 Follow: unit currently follows state of sys-devices-pci0000: :00:1f.2-ata1-host0- target0:0:0-0:0:0:0-block-sda-sda1.device Loaded: loaded Active: active (plugged) since Sat :16:37 CST; 1h 14min ago Device: /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/sda1

28 Path Units encodes information about a path monitored by systemd takes action on filesystem activity in path

29 Example.path file [Unit] Description=Forward Password Requests to Wall Directory Watch Documentation=man:systemd-ask-password-console.service(8) DefaultDependencies=no Conflicts=shutdown.target Before=paths.target shutdown.target [Path] DirectoryNotEmpty=/run/systemd/ask-password MakeDirectory=yes

30 Mount and automount point management reads /etc/fstab and dynamically generates native units /etc/fstab is preferred over static mount units must be named for its mountpoint /home/user file is home-user.mount

31 Example.automount file [Unit] Description=Arbitrary Executable File Formats File System Automount Point Documentation= org/doc/documentation/binfmt_misc.txt Documentation= org/wiki/software/systemd/apifilesystems DefaultDependencies=no Before=sysinit.target ConditionPathExists=/proc/sys/fs/binfmt_misc/ ConditionPathIsReadWrite=/proc/sys/ [Automount] Where=/proc/sys/fs/binfmt_misc

32 Example.mount file [Unit] Description=Debug File System Documentation= org/doc/documentation/filesystems/debugfs.txt Documentation= org/wiki/software/systemd/apifilesystems DefaultDependencies=no ConditionPathExists=/sys/kernel/debug Before=sysinit.target [Mount] What=debugfs Where=/sys/kernel/debug Type=debugfs

33 Managing Units New Commands

34 Listing Units In Specific State or States ~]$ systemctl list-unit-files --state=failed UNIT FILE STATE 0 unit files listed. [jaybrown@localhost ~]$ systemctl list-unit-files --state=disabled,enabled UNIT FILE cups.path abrt-ccpp.service abrt-oops.service abrt-pstoreoops.service STATE enabled enabled enabled disabled

35 Listing Only Enabled Socket Units ~]$ systemctl list-unit-files -t socket --state=enabled UNIT FILE STATE avahi-daemon.socket enabled cups.socket dm-event.socket iscsid.socket iscsiuio.socket enabled enabled enabled enabled lvm2-lvmetad.socket enabled rpcbind.socket enabled

36 Disabling a Unit [jaybrown@localhost ~]$ systemctl disable cups Removed symlink /etc/systemd/system/printer.target.wants/cups.service. Removed symlink /etc/systemd/system/multi-user.target.wants/cups.path. Removed symlink /etc/systemd/system/sockets.target.wants/cups.socket.

37 Enabling a Unit [jaybrown@localhost ~]$ systemctl enable cups Created symlink from /etc/systemd/system/printer.target.wants/cups.service to /usr/lib/systemd/system/cups.service. Created symlink from /etc/systemd/system/sockets.target.wants/cups.socket to /usr/lib/systemd/system/cups.socket. Created symlink from /etc/systemd/system/multi-user.target.wants/cups.path to /usr/lib/systemd/system/cups.path.

38 systemd Journal journalctl provides the ability to work with the systemd journal as written by systemd-journal.service Without any parameters it displays the full contents of the journal journalctl --since "20 min ago" Can use / to search within results

39 System state snapshots Save the state of the system configuration in a snapshot systemctl <snapshot name> creates a snapshot of the current state under the name <snapshot name> systemctl isolate <snapshot name>.service restores the system state to the state saved in the snapshot <snapshot name> systemctl delete <snapshot name> deletes a previously saved snapshot man 5 systemd.snapshot & man systemctl

40 Reference Where to get more detailed information

41 Commands Full man page index at /usr/bin/busctl /usr/bin/coredumpctl /usr/sbin/halt /usr/bin/hostname /usr/bin/hostnamectl /usr/sbin/init /usr/bin/journalctl /usr/bin/localectl /usr/bin/loginctl /usr/bin/machinectl /usr/sbin/reboot /usr/sbin/runlevel /usr/sbin/shutdown /usr/sbin/sysctl /usr/bin/systemctl /usr/sbin/telinit /usr/bin/timedatectl /usr/bin/udevadm

42 Good Pages Beyond init: systemd RedHat 7 Documentation systemd man pages