# systemd * [Systemd](https://www.ibm.com/developerworks/cn/linux/1407_liuming_init3/index.html) * [system V与systemd](https://blog.csdn.net/qinhan728/article/details/48792691) ## man systemd systemd 是linux操作系统的系统和服务管理器，作为boot启动后的第一个进程（PID=1），systemd扮演初始化系统，以及启动和维护用户空间服务。 为了兼容SysV，如果systemd初始化被调用并且进程id不是1，它将执行`telinit`，并且将同步参数到该应用，所以在正常系统登录状态下的init和telinit是等同的。更多信息通过`man telinit` 了解。 当作为系统实例启动，systemd通过`system.conf` 解析配置文件，如果作为用户进程启动，从`user.conf`解析配置文件,更多信息通过`systemd-system.conf` 了解。 ## systemd vs sysv init * 系统同时存在sysV init脚本使能和systemd service，那么到底是生谁效的？ 如果同时存在systemd 单元文件和sysVinit脚本，亦或者upstart配置文件，理论上systemd>sysv init>upstart. * 如下路径的unit 关系，哪些unit是使能的? 参考 `man systemctl `->`COMMANDS`->`Unit File Commands`-> `enable NAME...` 在`/lib/systemd/system` 保存了所有unit file，其中部分`.service` 文件包含`[install]` 部分，当调用`systemctl enable watchdog.service` 会在 `/etc/systemd/systemd`下面创建软连接。开机通过查找该路径下面的软连接启动对应服务。 ```bash $ cat watchdog.service [Install] WantedBy=multi-user.target ``` ```bash $ tree /etc/systemd/system /etc/systemd/system ├── multi-user.target.wants │   ├── watchdog.service -> /lib/systemd/system/watchdog.service ``` 可以通过`systemctl list-unit-files |grep enable `查找所有使能的unit文件，同时可以通过`systemctl preset-all `复位所有使能的unit file。 * systemd如何控制sysV init脚本? ```bash /lib/systemd/system/supervisor.service /etc/systemd/system/multi-user.target.wants/supervisor.service #软连接 ``` 如果同时存在`supervisor.service` 和对应软连接，此时启动由systemd控制，并且状态为`enable`。 ```bash $ systemctl list-unit-files |grep supervisor supervisor.service enabled ``` 如果存在`superviosr.service`不存在对应的软连接，此时启动有systemd控制，状态为`disable`,开机不启动supervisor服务。 ```bash $ systemctl list-unit-files |grep supervisor supervisor.service disabled ``` ``` /etc/init.d/supervisor /etc/rc5.d/S01supervisor ``` 如果同时存在`supervisor`和`S01supervisor` 并且不存在如上的systemd 单元文件，那么此时启动由sysVinit控制。 如上问题还是只有从`man systemctl` 当中找答案哦。 ## systemd command ```bash systemctl (1) - Control the systemd system and service manager systemd (1) - systemd system and service manager systemd-activate (8) - Test socket activation of daemons systemd-analyze (1) - Analyze system boot-up performance systemd-ask-password (1) - Query the user for a system password systemd-ask-password-console.path (8) - Query the user for system passwords on the console and via wall systemd-ask-password-console.service (8) - Query the user for system passwords on the console and via wall systemd-ask-password-wall.path (8) - Query the user for system passwords on the console and via wall systemd-ask-password-wall.service (8) - Query the user for system passwords on the console and via wall systemd-backlight (8) - Load and save the display backlight brightness at boot and shutdown systemd-backlight@.service (8) - Load and save the display backlight brightness at boot and shutdown systemd-binfmt (8) - Configure additional binary formats for executables at boot systemd-binfmt.service (8) - Configure additional binary formats for executables at boot systemd-bootchart (1) - Boot performance graphing tool systemd-cat (1) - Connect a pipeline or program's output with the journal systemd-cgls (1) - Recursively show control group contents systemd-cgtop (1) - Show top control groups by their resource usage systemd-cryptsetup (8) - Full disk decryption logic systemd-cryptsetup-generator (8) - Unit generator for /etc/crypttab systemd-cryptsetup@.service (8) - Full disk decryption logic systemd-debug-generator (8) - Generator for enabling a runtime debug shell and masking specific units at boot systemd-delta (1) - Find overridden configuration files systemd-detect-virt (1) - Detect execution in a virtualized environment systemd-efi-boot-generator (8) - Generator for automatically mounting the EFI System Partition used by the current boot to /boot systemd-escape (1) - Escape strings for usage in system unit names systemd-fsck (8) - File system checker logic systemd-fsck-root.service (8) - File system checker logic systemd-fsck@.service (8) - File system checker logic systemd-fstab-generator (8) - Unit generator for /etc/fstab systemd-getty-generator (8) - Generator for enabling getty instances on the console systemd-gpt-auto-generator (8) - Generator for automatically discovering and mounting root, /home and /srv partitions, as well as discovering and enabling swap partitions, based on GPT par... systemd-halt.service (8) - System shutdown logic systemd-hibernate.service (8) - System sleep state logic systemd-hostnamed (8) - Host name bus mechanism systemd-hostnamed.service (8) - Host name bus mechanism systemd-hybrid-sleep.service (8) - System sleep state logic systemd-inhibit (1) - Execute a program with an inhibition lock taken systemd-initctl (8) - /dev/initctl compatibility systemd-initctl.service (8) - /dev/initctl compatibility systemd-initctl.socket (8) - /dev/initctl compatibility systemd-journald (8) - Journal service systemd-journald-dev-log.socket (8) - Journal service systemd-journald.service (8) - Journal service systemd-journald.socket (8) - Journal service systemd-kexec.service (8) - System shutdown logic systemd-localed (8) - Locale bus mechanism systemd-localed.service (8) - Locale bus mechanism systemd-logind (8) - Login manager systemd-logind.service (8) - Login manager systemd-machine-id-setup (1) - Initialize the machine ID in /etc/machine-id systemd-machined (8) - Virtual machine and container registration manager systemd-machined.service (8) - Virtual machine and container registration manager systemd-modules-load (8) - Configure kernel modules to load at boot systemd-modules-load.service (8) - Configure kernel modules to load at boot systemd-networkd (8) - Network manager systemd-networkd-wait-online (8) - Wait for network to come online systemd-networkd-wait-online.service (8) - Wait for network to come online systemd-networkd.service (8) - Network manager systemd-notify (1) - Notify service manager about start-up completion and other daemon status changes systemd-nspawn (1) - Spawn a namespace container for debugging, testing and building systemd-path (1) - List and query system and user paths systemd-poweroff.service (8) - System shutdown logic systemd-quotacheck (8) - File system quota checker logic systemd-quotacheck.service (8) - File system quota checker logic systemd-random-seed (8) - Load and save the system random seed at boot and shutdown systemd-random-seed.service (8) - Load and save the system random seed at boot and shutdown systemd-readahead (8) - Disk read ahead logic systemd-readahead-collect.service (8) - Disk read ahead logic systemd-readahead-done.service (8) - Disk read ahead logic systemd-readahead-done.timer (8) - Disk read ahead logic systemd-readahead-replay.service (8) - Disk read ahead logic systemd-reboot.service (8) - System shutdown logic systemd-remount-fs (8) - Remount root and kernel file systems systemd-remount-fs.service (8) - Remount root and kernel file systems systemd-resolved (8) - Network Name Resolution manager systemd-resolved.service (8) - Network Name Resolution manager systemd-rfkill (8) - Load and save the RF kill switch state at boot and shutdown systemd-rfkill@.service (8) - Load and save the RF kill switch state at boot and shutdown systemd-run (1) - Run programs in transient scope or service units systemd-shutdown (8) - System shutdown logic systemd-shutdownd (8) - Scheduled shutdown service systemd-shutdownd.service (8) - Scheduled shutdown service systemd-shutdownd.socket (8) - Scheduled shutdown service systemd-sleep (8) - System sleep state logic systemd-sleep.conf (5) - Suspend and hibernation configuration file systemd-socket-proxyd (8) - Bidirectionally proxy local sockets to another (possibly remote) socket. systemd-suspend.service (8) - System sleep state logic systemd-sysctl (8) - Configure kernel parameters at boot systemd-sysctl.service (8) - Configure kernel parameters at boot systemd-system-update-generator (8) - Generator for redirecting boot to offline update mode systemd-system.conf (5) - System and session service manager configuration file systemd-sysusers (8) - Allocate system users and groups systemd-sysusers.service (8) - Allocate system users and groups systemd-timedated (8) - Time and date bus mechanism systemd-timedated.service (8) - Time and date bus mechanism systemd-timesyncd (8) - Network Time Synchronization systemd-timesyncd.service (8) - Network Time Synchronization systemd-tmpfiles (8) - Creates, deletes and cleans up volatile and temporary files and directories systemd-tmpfiles-clean.service (8) - Creates, deletes and cleans up volatile and temporary files and directories systemd-tmpfiles-clean.timer (8) - Creates, deletes and cleans up volatile and temporary files and directories systemd-tmpfiles-setup-dev.service (8) - Creates, deletes and cleans up volatile and temporary files and directories systemd-tmpfiles-setup.service (8) - Creates, deletes and cleans up volatile and temporary files and directories systemd-tty-ask-password-agent (1) - List or process pending systemd password requests systemd-udevd (8) - Device event managing daemon systemd-udevd-control.socket (8) - Device event managing daemon systemd-udevd-kernel.socket (8) - Device event managing daemon systemd-udevd.service (8) - Device event managing daemon systemd-update-utmp (8) - Write audit and utmp updates at bootup, runlevel changes and shutdown systemd-update-utmp-runlevel.service (8) - Write audit and utmp updates at bootup, runlevel changes and shutdown systemd-update-utmp.service (8) - Write audit and utmp updates at bootup, runlevel changes and shutdown systemd-user-sessions (8) - Permit user logins after boot, prohibit user logins at shutdown systemd-user-sessions.service (8) - Permit user logins after boot, prohibit user logins at shutdown systemd-user.conf (5) - System and session service manager configuration file systemd.automount (5) - Automount unit configuration systemd.device (5) - Device unit configuration systemd.directives (7) - Index of configuration directives systemd.exec (5) - Execution environment configuration systemd.index (7) - List all manpages from the systemd project systemd.journal-fields (7) - Special journal fields systemd.kill (5) - Process killing procedure configuration systemd.link (5) - Network device configuration systemd.mount (5) - Mount unit configuration systemd.netdev (5) - Virtual Network Device configuration systemd.network (5) - Network configuration systemd.path (5) - Path unit configuration systemd.preset (5) - Service enablement presets systemd.resource-control (5) - Resource control unit settings systemd.scope (5) - Scope unit configuration systemd.service (5) - Service unit configuration systemd.slice (5) - Slice unit configuration systemd.snapshot (5) - Snapshot unit configuration systemd.socket (5) - Socket unit configuration systemd.special (7) - Special systemd units systemd.swap (5) - Swap unit configuration systemd.target (5) - Target unit configuration systemd.time (7) - Time and date specifications systemd.timer (5) - Timer unit configuration systemd.unit (5) - Unit configuration ``` ## systemd source review * https://github.com/systemd/systemd * https://github.com/systemd/systemd/releases