実際にシステムを管理する現場管理者としては、initからsystemdに変わったことで「実運用で、何が変わるのか」が最も気になる部分だと思います。具体例で説明します。
systemdでは、これまでサービス起動スクリプトで定義されていたものがUnitという形で定義されます。initでいう「サービスの管理」は、「Unitの管理」を意味します。
CentOS 7で有効化されているUnitをsystemctl list-unitsコマンドで一覧表示します。
表示項目のうち、UNITはUnit名、LOADはSystemdへの設定読み込み状況、ACTIVEおよびSUBがUnitの実行状態(ACTIVEは起動しているか否か、SUBは稼働中や待ち受け中などの各Unitの状態)、DESCRIPTIONがUnitの概要を表しています。起動対象ながら、起動に失敗した場合はACTIVEやSUBの値がfailedといった表示になります。
# systemctl list-units UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys...t_misc.automount loaded active waiting Arbitrary Executable File Fo sys-devi...block-sr0.device loaded active plugged QEMU_DVD-ROM sys-devi...block-sr1.device loaded active plugged QEMU_DVD-ROM sys-devi...-net-eth0.device loaded active plugged Virtio network device sys-devi...-vda-vda1.device loaded active plugged /sys/devices/pci0000:00/0000 sys-devi...-vda-vda2.device loaded active plugged /sys/devices/pci0000:00/0000 sys-devi...-vda-vda3.device loaded active plugged /sys/devices/pci0000:00/0000 sys-devi...block-vda.device loaded active plugged /sys/devices/pci0000:00/0000 sys-devi...block-fd0.device loaded active plugged /sys/devices/platform/floppy sys-devi...tty-ttyS1.device loaded active plugged /sys/devices/platform/serial sys-devi...tty-ttyS2.device loaded active plugged /sys/devices/platform/serial sys-devi...tty-ttyS3.device loaded active plugged /sys/devices/platform/serial sys-devi...tty-ttyS0.device loaded active plugged /sys/devices/pnp0/00:04/tty/ sys-module-configfs.device loaded active plugged /sys/module/configfs sys-subs...ices-eth0.device loaded active plugged Virtio network device -.mount loaded active mounted / dev-hugepages.mount loaded active mounted Huge Pages File System dev-mqueue.mount loaded active mounted POSIX Message Queue File Sys sys-kernel-config.mount loaded active mounted Configuration File System sys-kernel-debug.mount loaded active mounted Debug File System brandbot.path loaded active waiting Flexible branding systemd-...rd-plymouth.path loaded active waiting Forward Password Requests to systemd-...ssword-wall.path loaded active waiting Forward Password Requests to chronyd.service loaded active running NTP client/server crond.service loaded active running Command Scheduler dbus.service loaded active running D-Bus System Message Bus fail2ban.service loaded active running Fail2Ban Service firewalld.service loaded active running firewalld - dynamic firewall getty@tty1.service loaded active running Getty on tty1 kmod-static-nodes.service loaded active exited Create list of required stat network.service loaded failed failed LSB: Bring up/down networkin NetworkManager.service loaded active running Network Manager polkit.service loaded active running Authorization Manager postfix.service loaded active running Postfix Mail Transport Agent rhel-aut...bel-mark.service loaded active exited Mark the need to relabel aft rhel-dmesg.service loaded active exited Dump dmesg to /var/log/dmesg rhel-import-state.service loaded active exited Import network configuration rhel-readonly.service loaded active exited Configure read-only root sup rsyslog.service loaded active running System Logging Service sshd-keygen.service loaded active exited OpenSSH Server Key Generatio sshd.service loaded active running OpenSSH server daemon systemd-fsck-root.service loaded active exited File System Check on Root De systemd-journald.service loaded active running Journal Service systemd-logind.service loaded active running Login Service systemd-random-seed.service loaded active exited Load/Save Random Seed systemd-remount-fs.service loaded active exited Remount Root and Kernel File systemd-sysctl.service loaded active exited Apply Kernel Variables systemd-...etup-dev.service loaded active exited Create static device nodes i systemd-...es-setup.service loaded active exited Create Volatile Files and Di systemd-...-trigger.service loaded active exited udev Coldplug all Devices systemd-udevd.service loaded active running udev Kernel Device Manager systemd-update-utmp.service loaded active exited Update UTMP about System Reb systemd-...sessions.service loaded active exited Permit User Sessions systemd-...le-setup.service loaded active exited Setup Virtual Console tuned.service loaded active running Dynamic System Tuning Daemon -.slice loaded active active Root Slice system-getty.slice loaded active active system-getty.slice system.slice loaded active active System Slice user.slice loaded active active User and Session Slice dbus.socket loaded active running D-Bus System Message Bus Soc systemd-initctl.socket loaded active listening /dev/initctl Compatibility N systemd-journald.socket loaded active running Journal Socket systemd-shutdownd.socket loaded active listening Delayed Shutdown Socket systemd-...d-control.socket loaded active running udev Control Socket systemd-udevd-kernel.socket loaded active running udev Kernel Socket dev-vda2.swap loaded active active /dev/vda2 basic.target loaded active active Basic System cryptsetup.target loaded active active Encrypted Volumes getty.target loaded active active Login Prompts local-fs-pre.target loaded active active Local File Systems (Pre) local-fs.target loaded active active Local File Systems multi-user.target loaded active active Multi-User System network.target loaded active active Network paths.target loaded active active Paths remote-fs.target loaded active active Remote File Systems slices.target loaded active active Slices sockets.target loaded active active Sockets swap.target loaded active active Swap sysinit.target loaded active active System Initialization timers.target loaded active active Timers systemd-...iles-clean.timer loaded active waiting Daily Cleanup of Temporary D LOAD = Reflects whether the unit definition was properly loaded. ACTIVE = The high-level unit activation state, i.e. generalization of SUB. SUB = The low-level unit activation state, values depend on unit type. 81 loaded units listed. Pass --all to see loaded but inactive units, too. To show all installed unit files use 'systemctl list-unit-files'.
続いて、インストールされているUnitファイルをsystemctl list-unit-filesコマンドで一覧表示してみます。
STATE列の表示を見ることで、現在の設定状況を確認できます。「enable」は自動起動設定が有効になっているUnit、「disable」は自動起動設定が無効になっているUnit、「static」は単体では自動起動できないUnitを表します。
# systemctl list-unit-files UNIT FILE STATE proc-sys-fs-binfmt_misc.automount static dev-hugepages.mount static dev-mqueue.mount static proc-sys-fs-binfmt_misc.mount static sys-fs-fuse-connections.mount static sys-kernel-config.mount static sys-kernel-debug.mount static tmp.mount disabled brandbot.path disabled systemd-ask-password-console.path static systemd-ask-password-plymouth.path static systemd-ask-password-wall.path static auditd.service disabled autovt@.service disabled brandbot.service static chrony-wait.service disabled chronyd.service enabled console-getty.service disabled console-shell.service disabled cpupower.service disabled crond.service enabled dbus-org.fedoraproject.FirewallD1.service enabled dbus-org.freedesktop.hostname1.service static dbus-org.freedesktop.locale1.service static dbus-org.freedesktop.login1.service static dbus-org.freedesktop.machine1.service static dbus-org.freedesktop.NetworkManager.service enabled dbus-org.freedesktop.nm-dispatcher.service enabled dbus-org.freedesktop.timedate1.service static dbus.service static debug-shell.service disabled dnsmasq.service disabled dracut-cmdline.service static dracut-initqueue.service static dracut-mount.service static dracut-pre-mount.service static dracut-pre-pivot.service static dracut-pre-trigger.service static dracut-pre-udev.service static dracut-shutdown.service static ebtables.service disabled emergency.service static fail2ban.service enabled firewalld.service enabled getty@.service enabled halt-local.service static initrd-cleanup.service static initrd-parse-etc.service static initrd-switch-root.service static initrd-udevadm-cleanup-db.service static iprdump.service disabled iprinit.service disabled iprupdate.service disabled irqbalance.service enabled kdump.service disabled kmod-static-nodes.service static messagebus.service static NetworkManager-dispatcher.service enabled NetworkManager-wait-online.service disabled NetworkManager.service enabled plymouth-halt.service disabled plymouth-kexec.service disabled plymouth-poweroff.service disabled plymouth-quit-wait.service disabled plymouth-quit.service disabled plymouth-read-write.service disabled plymouth-reboot.service disabled plymouth-start.service disabled plymouth-switch-root.service static polkit.service static postfix.service enabled quotaon.service static rc-local.service static rdisc.service disabled rescue.service static rhel-autorelabel-mark.service static rhel-autorelabel.service static rhel-configure.service static rhel-dmesg.service disabled rhel-domainname.service disabled rhel-import-state.service static rhel-loadmodules.service static rhel-readonly.service static rsyncd.service disabled rsyslog.service enabled serial-getty@.service disabled spice-vdagentd.service enabled sshd-keygen.service static sshd.service enabled sshd@.service static svnserve.service disabled systemd-ask-password-console.service static systemd-ask-password-plymouth.service static systemd-ask-password-wall.service static systemd-backlight@.service static systemd-binfmt.service static systemd-fsck-root.service static systemd-fsck@.service static systemd-halt.service static systemd-hibernate.service static systemd-hostnamed.service static systemd-hybrid-sleep.service static systemd-initctl.service static systemd-journal-flush.service static systemd-journald.service static systemd-kexec.service static systemd-localed.service static systemd-logind.service static systemd-machined.service static systemd-modules-load.service static systemd-nspawn@.service disabled systemd-poweroff.service static systemd-quotacheck.service static systemd-random-seed.service static systemd-readahead-collect.service enabled systemd-readahead-done.service static systemd-readahead-drop.service enabled systemd-readahead-replay.service enabled systemd-reboot.service static systemd-remount-fs.service static systemd-shutdownd.service static systemd-suspend.service static systemd-sysctl.service static systemd-timedated.service static systemd-tmpfiles-clean.service static systemd-tmpfiles-setup-dev.service static systemd-tmpfiles-setup.service static systemd-udev-settle.service static systemd-udev-trigger.service static systemd-udevd.service static systemd-update-utmp-runlevel.service static systemd-update-utmp.service static systemd-user-sessions.service static systemd-vconsole-setup.service static tcsd.service disabled teamd@.service static tuned.service enabled wacom-inputattach@.service static wpa_supplicant.service disabled -.slice static machine.slice static system.slice static user.slice static dbus.socket static rsyncd.socket disabled sshd.socket disabled syslog.socket static systemd-initctl.socket static systemd-journald.socket static systemd-shutdownd.socket static systemd-udevd-control.socket static systemd-udevd-kernel.socket static basic.target static bluetooth.target static cryptsetup.target static ctrl-alt-del.target disabled default.target enabled emergency.target static final.target static getty.target static graphical.target disabled halt.target disabled hibernate.target static hybrid-sleep.target static initrd-fs.target static initrd-root-fs.target static initrd-switch-root.target static initrd.target static iprutils.target disabled kexec.target disabled local-fs-pre.target static local-fs.target static multi-user.target enabled network-online.target static network.target static nss-lookup.target static nss-user-lookup.target static paths.target static poweroff.target disabled printer.target static reboot.target disabled remote-fs-pre.target static remote-fs.target enabled rescue.target disabled rpcbind.target static runlevel0.target disabled runlevel1.target disabled runlevel2.target disabled runlevel3.target disabled runlevel4.target disabled runlevel5.target disabled runlevel6.target disabled shutdown.target static sigpwr.target static sleep.target static slices.target static smartcard.target static sockets.target static sound.target static spice-vdagentd.target static suspend.target static swap.target static sysinit.target static system-update.target static time-sync.target static timers.target static umount.target static systemd-readahead-done.timer static systemd-tmpfiles-clean.timer static 209 unit files listed.
例えば、yum install httpdでApacheをインストールすると、以下のように登録されます。
$ systemctl list-unit-files | grep httpd httpd.service disabled
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