Systemd的基本概念及使用
rc.local调用简要关系：
- 树莓派启动的相关问题
- 走进Linux之systemd启动过程
- systemd 中文手册
- Systemd 入门教程：命令篇
- Systemd 入门教程：实战篇
- Systemd FAQ (简体中文)
- systemctl enable rc-local.service error
pi@raspberrypi:/etc/rcS.d $ stat /sbin/init
File: /sbin/init -> /lib/systemd/systemd
Size: 20 Blocks: 0 IO Block: 4096 symbolic link
Device: b302h/45826d Inode: 6755 Links: 1
Access: (0777/lrwxrwxrwx) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2018-11-13 14:08:59.595343944 +0000
Modify: 2018-10-28 17:02:10.000000000 +0000
Change: 2018-11-13 14:08:59.595343944 +0000
Birth: -
当作为系统实例运行时， systemd 将会按照 system.conf 配置文件 以及 system.conf.d 配置目录中的指令工作； 当作为用户实例运行时，systemd 将会按照 user.conf 配置文件 以及 user.conf.d 配置目录中的指令工作。
看懂这部分可以很好得理解为什么无图形界面是从multi-user.target启动，有图形界面从graphical.target启动。
| sysvinit | systemd target | 备注 |
|---|---|---|
| 0 | poweroff.target | 关闭系统 |
| 1,s,single | rescue.target | 单用户模式 |
| 2,4 | multi-user.target | 用户定义/域特定运行级别。默认等同于 3 |
| 3 | multi-user.target | 多用户，非图形化界面 |
| 5 | graphical.target | 多用户，图形化界面 |
| 6 | reboot.target | 重启 |
| emergency | emergency.target | 紧急shell |
pi@raspberrypi:/lib/systemd/system $ ls -al runlevel*
lrwxrwxrwx 1 root root 15 Oct 28 17:02 runlevel0.target -> poweroff.target
lrwxrwxrwx 1 root root 13 Oct 28 17:02 runlevel1.target -> rescue.target
lrwxrwxrwx 1 root root 17 Oct 28 17:02 runlevel2.target -> multi-user.target
lrwxrwxrwx 1 root root 17 Oct 28 17:02 runlevel3.target -> multi-user.target
lrwxrwxrwx 1 root root 17 Oct 28 17:02 runlevel4.target -> multi-user.target
lrwxrwxrwx 1 root root 16 Oct 28 17:02 runlevel5.target -> graphical.target
lrwxrwxrwx 1 root root 13 Oct 28 17:02 runlevel6.target -> reboot.target
- service：用于封装一个后台服务进程；
- target：用于将多个单元在逻辑上组合在一起；
- 命令行处理命令：
systemctl systemctl enable xxx.service：为对应得service在target目录(/etc/systemd/system/)创建软链接；systemctl disable xxx.service：删除软链接；
- 存放系统target目录:
/lib/systemd/systempi@raspberrypi:/ $ pkg-config systemd --variable=systemdsystemunitdir /lib/systemd/system pi@raspberrypi:/ $ ls /lib/systemd/system alsa-restore.service getty.target.wants paths.target runlevel4.target systemd-journal-flush.service alsa-state.service gldriver-test.service paxctld.service runlevel4.target.wants systemd-kexec.service alsa-utils.service graphical.target pigpiod.service runlevel5.target systemd-localed.service apply_noobs_os_config.service graphical.target.wants plymouth-halt.service runlevel5.target.wants systemd-logind.service apt-daily.service halt.service plymouth-kexec.service runlevel6.target systemd-machine-id-commit.service apt-daily.timer halt.target plymouth-log.service run-rpc_pipefs.mount systemd-modules-load.service apt-daily-upgrade.service halt.target.wants plymouth-poweroff.service sendsigs.service systemd-networkd.service apt-daily-upgrade.timer hciuart.service plymouth-quit.service serial-getty@.service systemd-networkd.socket auth-rpcgss-module.service hibernate.target plymouth-quit-wait.service shutdown.target systemd-networkd-wait-online.service autovt@.service hostname.service plymouth-read-write.service sigpwr.target systemd-poweroff.service avahi-daemon.service hwclock.service plymouth-reboot.service single.service systemd-quotacheck.service avahi-daemon.socket hybrid-sleep.target plymouth.service sleep.target systemd-random-seed.service basic.target ifup@.service plymouth-start.service slices.target systemd-reboot.service basic.target.wants initrd-cleanup.service plymouth-switch-root.service smartcard.target systemd-remount-fs.service bluealsa.service initrd-fs.target polkit.service sockets.target systemd-resolved.service bluetooth.service initrd-parse-etc.service portmap.service sockets.target.wants systemd-resolved.service.d bluetooth.target initrd-root-device.target poweroff.target sound.target systemd-rfkill.service bootlogd.service initrd-root-fs.target poweroff.target.wants ssh.service systemd-rfkill.socket bootlogs.service initrd-switch-root.service printer.target ssh@.service systemd-suspend.service bootmisc.service initrd-switch-root.target proc-fs-nfsd.mount ssh.socket systemd-sysctl.service bthelper@.service initrd-switch-root.target.wants procps.service sshswitch.service systemd-timedated.service busnames.target initrd.target proc-sys-fs-binfmt_misc.automount stop-bootlogd.service systemd-timesyncd.service busnames.target.wants initrd-udevadm-cleanup-db.service proc-sys-fs-binfmt_misc.mount stop-bootlogd-single.service systemd-timesyncd.service.d checkfs.service kexec.target quotaon.service sudo.service systemd-tmpfiles-clean.service checkroot-bootclean.service kexec.target.wants raspberrypi-net-mods.service suspend.target systemd-tmpfiles-clean.timer checkroot.service keyboard-setup.service rc-local.service swap.target systemd-tmpfiles-setup-dev.service console-getty.service killprocs.service rc.local.service sys-fs-fuse-connections.mount systemd-tmpfiles-setup.service console-setup.service kmod.service rc-local.service.d sysinit.target systemd-udevd-control.socket container-getty@.service kmod-static-nodes.service rc.service sysinit.target.wants systemd-udevd-kernel.socket cron.service lightdm.service rcS.service sys-kernel-config.mount systemd-udevd.service cryptdisks-early.service local-fs-pre.target reboot.service sys-kernel-debug.mount systemd-udev-settle.service cryptdisks.service local-fs.target reboot.target syslog.socket systemd-udev-trigger.service cryptsetup-pre.target local-fs.target.wants reboot.target.wants systemd-ask-password-console.path systemd-update-utmp-runlevel.service cryptsetup.target machine.slice regenerate_ssh_host_keys.service systemd-ask-password-console.service systemd-update-utmp.service ctrl-alt-del.target module-init-tools.service remote-fs-pre.target systemd-ask-password-plymouth.path systemd-user-sessions.service dbus-org.freedesktop.hostname1.service motd.service remote-fs.target systemd-ask-password-plymouth.service system.slice dbus-org.freedesktop.locale1.service mountall-bootclean.service rescue.service systemd-ask-password-wall.path system-update.target dbus-org.freedesktop.login1.service mountall.service rescue.target systemd-ask-password-wall.service system-update.target.wants dbus-org.freedesktop.network1.service mountdevsubfs.service rescue.target.wants systemd-backlight@.service timers.target dbus-org.freedesktop.resolve1.service mountkernfs.service rmnologin.service systemd-binfmt.service timers.target.wants dbus-org.freedesktop.timedate1.service mountnfs-bootclean.service rpcbind.service systemd-exit.service time-sync.target dbus.service mountnfs.service rpcbind.socket systemd-fsckd.service triggerhappy.service dbus.socket multi-user.target rpcbind.target systemd-fsckd.socket triggerhappy.socket debug-shell.service multi-user.target.wants rpc-gssd.service systemd-fsck-root.service udev.service default.target networking.service rpc-statd-notify.service systemd-fsck@.service udisks2.service dev-hugepages.mount network-online.target rpc-statd.service systemd-halt.service umountfs.service dev-mqueue.mount network-pre.target rpc-svcgssd.service systemd-hibernate-resume@.service umountnfs.service dhcpcd.service network.target rpi-display-backlight.service systemd-hibernate.service umountroot.service emergency.service nfs-client.target rsync.service systemd-hostnamed.service umount.target emergency.target nfs-common.service rsyslog.service systemd-hwdb-update.service urandom.service exit.target nfs-config.service runlevel0.target systemd-hybrid-sleep.service usb_modeswitch@.service fake-hwclock.service nfs-idmapd.service runlevel1.target systemd-initctl.service user@.service final.target nfs-utils.service runlevel1.target.wants systemd-initctl.socket user.slice fuse.service nss-lookup.target runlevel2.target systemd-journald-audit.socket wifi-country.service getty@.service nss-user-lookup.target runlevel2.target.wants systemd-journald-dev-log.socket wpa_supplicant.service getty-static.service packagekit-offline-update.service runlevel3.target systemd-journald.service wpa_supplicant@.service getty.target packagekit.service runlevel3.target.wants systemd-journald.socket x11-common.service - 存放用户target目录:
/usr/lib/systemd/userpi@raspberrypi:/ $ pkg-config systemd --variable=systemduserunitdir /usr/lib/systemd/user pi@raspberrypi:/ $ ls /usr/lib/systemd/user basic.target exit.target gpg-agent-ssh.socket gvfs-goa-volume-monitor.service printer.target ssh-agent.service bluetooth.target glib-pacrunner.service graphical-session-pre.target gvfs-gphoto2-volume-monitor.service shutdown.target systemd-exit.service busnames.target gpg-agent-browser.socket graphical-session-pre.target.wants gvfs-metadata.service smartcard.target timers.target dbus.service gpg-agent-extra.socket graphical-session.target gvfs-mtp-volume-monitor.service sockets.target dbus.socket gpg-agent.service gvfs-afc-volume-monitor.service gvfs-udisks2-volume-monitor.service sockets.target.wants default.target gpg-agent.socket gvfs-daemon.service paths.target sound.target pi@raspberrypi:/ $
在系统启动时，systemd 默认启动 default.target 单元， 该单元中应该包含所有你想在开机时默认启动的单元。 但实际上，它通常只是一个指向 graphical.target (图形界面) 或 multi-user.target (命令行界面，常用于嵌入式或服务器环境， 一般是 graphical.target 的一个子集)的符号连接。
此外在/etc/systemd/system目录下还可以看到诸如*.wants 的目录，放在该目录下的配置单元文件等同于在[Unit]小节中的 wants 关键字，即本单元启动时，还需要启动这些单元。
目前跟得是非图形界面得树莓派系统版本；
/etc/systemd/system/default.targetpi@raspberrypi:/etc/systemd/system $ systemctl get-default # 获取默认target名称 multi-user.target pi@raspberrypi:/etc/systemd/system $ ls -al default.target lrwxrwxrwx 1 root root 37 Dec 6 00:22 default.target -> /lib/systemd/system/multi-user.target/lib/systemd/system/multi-user.target# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. [Unit] Description=Multi-User System Documentation=man:systemd.special(7) # Requires字段则表示"强依赖"关系，即如果该服务启动失败或异常退出，那么sshd.service也必须退出。 # Wants字段：表示sshd.service与sshd-keygen.service之间存在"弱依赖"关系，即如果"sshd-keygen.service"启动失败或停止运行，不影响sshd.service继续执行。 # required 是强依赖；want 则是弱依赖 Requires=basic.target # Conflicts字段：冲突字段。如果rescue.service或rescue.target正在运行，multi-user.target就不能运行，反之亦然。这里指定的 Unit 不能与当前 Unit 同时运行 Conflicts=rescue.service rescue.target # 当前target需要在这些target之后启动，也就是会转到先去处理那些target，出了After，还有Before是同样得意思 After=basic.target rescue.service rescue.target # AllowIsolate：允许使用systemctl isolate命令切换到default.target AllowIsolate=yes/lib/systemd/system/basic.target# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. [Unit] Description=Basic System Documentation=man:systemd.special(7) Requires=sysinit.target Wants=sockets.target timers.target paths.target slices.target After=sysinit.target sockets.target paths.target slices.target tmp.mount # We support /var, /tmp, /var/tmp, being on NFS, but we don't pull in # remote-fs.target by default, hence pull them in explicitly here. Note that we # require /var and /var/tmp, but only add a Wants= type dependency on /tmp, as # we support that unit being masked, and this should not be considered an error. RequiresMountsFor=/var /var/tmp Wants=tmp.mount/lib/systemd/system/sysinit.target# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. [Unit] Description=System Initialization Documentation=man:systemd.special(7) Conflicts=emergency.service emergency.target Wants=local-fs.target swap.target After=local-fs.target swap.target emergency.service emergency.targetlib/systemd/system/local-fs.target# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. [Unit] Description=Local File Systems Documentation=man:systemd.special(7) DefaultDependencies=no Conflicts=shutdown.target After=local-fs-pre.target OnFailure=emergency.target OnFailureJobMode=replace-irreversiblylib/systemd/system/local-fs-pre.target# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. [Unit] Description=Local File Systems (Pre) Documentation=man:systemd.special(7) RefuseManualStart=yes
- ssh service
pi@raspberrypi:/etc/systemd/system $ ls -al sshd.service multi-user.target.wants/ssh.service lrwxrwxrwx 1 root root 31 Dec 5 08:27 multi-user.target.wants/ssh.service -> /lib/systemd/system/ssh.service lrwxrwxrwx 1 root root 31 Dec 5 10:55 sshd.service -> /lib/systemd/system/ssh.service /lib/systemd/system/ssh.service[Unit] Description=OpenBSD Secure Shell server After=network.target auditd.service ConditionPathExists=!/etc/ssh/sshd_not_to_be_run [Service] # EnvironmentFile字段：指定当前服务的环境参数文件。该文件内部的key=value键值对，可以用$key的形式，在当前配置文件中获取。 # 所有的启动设置之前，都可以加上一个连词号（-），表示"抑制错误"，即发生错误的时候，不影响其他命令的执行。 EnvironmentFile=-/etc/default/ssh # ExecStartPre字段：启动服务之前执行的命令 ExecStartPre=/usr/sbin/sshd -t # ExecStart字段：定义启动进程时执行的命令。 ExecStart=/usr/sbin/sshd -D $SSHD_OPTS # ExecReload字段：重启服务时执行的命令 ExecReload=/usr/sbin/sshd -t ExecReload=/bin/kill -HUP $MAINPID # KillMode字段：定义 Systemd 如何停止 sshd 服务。将KillMode设为process，表示只停止主进程，不停止任何sshd 子进程，即子进程打开的 SSH session 仍然保持连接。 KillMode=process # Restart字段：定义了 sshd 退出后，Systemd 的重启方式。Restart设为on-failure，表示任何意外的失败，就将重启sshd。如果 sshd 正常停止（比如执行systemctl stop命令），它就不会重启。 Restart=on-failure RestartPreventExitStatus=255 Type=notify [Install] # WantedBy字段：表示该服务所在的 Target。 WantedBy=multi-user.target Alias=sshd.service
- 参考文档：内核引导选项
- systemd.unit=, rd.systemd.unit=：设置默认启动的单元。 默认值是 default.target 。 可用于临时修改启动目标(例如 rescue.target 或 emergency.target )。这就相当于是PC进入安全模式得功能；
- 查找线索
pi@raspberrypi:/ $ grep rc.local /etc/* -r # 检查谁调用rc.local线索 grep: /etc/dhcpcd.secret: Permission denied grep: /etc/gshadow: Permission denied grep: /etc/polkit-1/localauthority: Permission denied /etc/rc.local:# rc.local grep: /etc/security/opasswd: Permission denied grep: /etc/shadow: Permission denied grep: /etc/ssh/ssh_host_ed25519_key: Permission denied grep: /etc/ssh/ssh_host_dsa_key: Permission denied grep: /etc/ssh/ssh_host_ecdsa_key: Permission denied grep: /etc/ssh/ssh_host_rsa_key: Permission denied grep: /etc/ssl/private: Permission denied grep: /etc/sudoers: Permission denied grep: /etc/sudoers.d/010_pi-nopasswd: Permission denied grep: /etc/sudoers.d/README: Permission denied /etc/systemd/system/autologin@.service:After=rc-local.service /etc/vim/vimrc:if filereadable("/etc/vim/vimrc.local") /etc/vim/vimrc: source /etc/vim/vimrc.local pi@raspberrypi:/ $ sudo find / -iname rc-local.service # 查找一下服务 /run/systemd/generator/multi-user.target.wants/rc-local.service /lib/systemd/system/rc-local.service /sys/fs/cgroup/devices/system.slice/rc-local.service /sys/fs/cgroup/systemd/system.slice/rc-local.service pi@raspberrypi:/ $ ls -al /lib/systemd/system/rc-local.service -rw-r--r-- 1 root root 628 Oct 28 17:02 /lib/systemd/system/rc-local.service
/lib/systemd/system/rc-local.service# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. # This unit gets pulled automatically into multi-user.target by # systemd-rc-local-generator if /etc/rc.local is executable. [Unit] Description=/etc/rc.local Compatibility ConditionFileIsExecutable=/etc/rc.local After=network.target [Service] Type=forking ExecStart=/etc/rc.local start # 就是这里了 TimeoutSec=0 RemainAfterExit=yes GuessMainPID=no
/etc/systemd/system/autologin@.service# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. [Unit] Description=Getty on %I Documentation=man:agetty(8) man:systemd-getty-generator(8) Documentation=http://0pointer.de/blog/projects/serial-console.html After=systemd-user-sessions.service plymouth-quit-wait.service After=rc-local.service # If additional gettys are spawned during boot then we should make # sure that this is synchronized before getty.target, even though # getty.target didn't actually pull it in. Before=getty.target IgnoreOnIsolate=yes # On systems without virtual consoles, don't start any getty. Note # that serial gettys are covered by serial-getty@.service, not this # unit. ConditionPathExists=/dev/tty0 [Service] # the VT is cleared by TTYVTDisallocate ExecStart=-/sbin/agetty --autologin pi --noclear %I $TERM # 启动服务 Type=idle Restart=always RestartSec=0 UtmpIdentifier=%I TTYPath=/dev/%I TTYReset=yes TTYVHangup=yes TTYVTDisallocate=yes KillMode=process IgnoreSIGPIPE=no SendSIGHUP=yes # Unset locale for the console getty since the console has problems # displaying some internationalized messages. Environment=LANG= LANGUAGE= LC_CTYPE= LC_NUMERIC= LC_TIME= LC_COLLATE= LC_MONETARY= LC_MESSAGES= LC_PAPER= LC_NAME= LC_ADDRESS= LC_TELEPHONE= LC_MEASUREMENT= LC_IDENTIFICATION= [Install] WantedBy=getty.target DefaultInstance=tty1
ps aux得出来得结果不是/etc/systemd/system/autologin@.service运行的，参数不对[...省略] root 322 0.0 0.4 4180 1808 tty1 Ss+ 05:07 0:00 /sbin/agetty --noclear tty1 linux [...省略]/lib/systemd/system/getty@.servicepi@raspberrypi:/etc/systemd/system/getty.target.wants $ ls -al total 8 drwxr-xr-x 2 root root 4096 Dec 6 00:22 . drwxr-xr-x 15 root root 4096 Dec 6 00:22 .. lrwxrwxrwx 1 root root 34 Dec 6 00:22 getty@tty1.service -> /lib/systemd/system/getty@.service/lib/systemd/system/getty@.service# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. [Unit] Description=Getty on %I Documentation=man:agetty(8) man:systemd-getty-generator(8) Documentation=http://0pointer.de/blog/projects/serial-console.html After=systemd-user-sessions.service plymouth-quit-wait.service After=rc-local.service # If additional gettys are spawned during boot then we should make # sure that this is synchronized before getty.target, even though # getty.target didn't actually pull it in. Before=getty.target IgnoreOnIsolate=yes # IgnoreOnIsolate causes issues with sulogin, if someone isolates # rescue.target or starts rescue.service from multi-user.target or # graphical.target. Conflicts=rescue.service Before=rescue.service # On systems without virtual consoles, don't start any getty. Note # that serial gettys are covered by serial-getty@.service, not this # unit. ConditionPathExists=/dev/tty0 [Service] # the VT is cleared by TTYVTDisallocate ExecStart=-/sbin/agetty --noclear %I $TERM Type=idle Restart=always RestartSec=0 UtmpIdentifier=%I TTYPath=/dev/%I TTYReset=yes TTYVHangup=yes TTYVTDisallocate=yes KillMode=process IgnoreSIGPIPE=no SendSIGHUP=yes # Unset locale for the console getty since the console has problems # displaying some internationalized messages. Environment=LANG= LANGUAGE= LC_CTYPE= LC_NUMERIC= LC_TIME= LC_COLLATE= LC_MONETARY= LC_MESSAGES= LC_PAPER= LC_NAME= LC_ADDRESS= LC_TELEPHONE= LC_MEASUREMENT= LC_IDENTIFICATION= [Install] WantedBy=getty.target DefaultInstance=tty1- 由上可知
getty@tty1.service经过调用getty@.service，在getty@.service的%I = tty1；
pi@raspberrypi:~ $ systemctl show -p "Wants" multi-user.target > data
pi@raspberrypi:~ $ cat data
Wants=remote-fs.target cron.service systemd-ask-password-wall.path systemd-user-sessions.service systemd-logind.service rsync.service rc-local.service sshswitch.service dhcpcd.service gldriver-test.service triggerhappy.service avahi-daemon.service ssh.service raspberrypi-net-mods.service plymouth-quit.service nfs-client.target console-setup.service wifi-country.service dphys-swapfile.service systemd-update-utmp-runlevel.service plymouth-quit-wait.service dbus.service networking.service raspi-config.service hciuart.service rsyslog.service getty.target
pi@raspberrypi:~ $