systemd中文文档 - 启动: http://systemd.cn/docs/Booting/ - 自动启动评估: http://systemd.cn/docs/Booting/AUTOMATIC_BOOT_ASSESSMENT/ - 启动组件和根文件系统探测: http://systemd.cn/docs/Booting/ROOTFS_DISCOVERY/ - 引导加载程序接口: http://systemd.cn/docs/Booting/BOOT_LOADER_INTERFACE/ - 恢复出厂设置: http://systemd.cn/docs/Booting/FACTORY_RESET/ - 挂载点可用性要求: http://systemd.cn/docs/Booting/MOUNT_REQUIREMENTS/ - TPM2 PCR测量: http://systemd.cn/docs/Booting/TPM2_PCR_MEASUREMENTS/ - Boot Loader Specification: http://systemd.cn/docs/BOOT_LOADER_SPECIFICATION/ - Discoverable Partitions: http://systemd.cn/docs/DISCOVERABLE_PARTITIONS/ - Elf Dlopen Metadata: http://systemd.cn/docs/ELF_DLOPEN_METADATA/ - Osc Context: http://systemd.cn/docs/OSC_CONTEXT/ - Package Metadata for Executable Files: http://systemd.cn/docs/PACKAGE_METADATA_FOR_EXECUTABLE_FILES/ - API File Systems: http://systemd.cn/docs/API_FILE_SYSTEMS/ - Appstream Bundle: http://systemd.cn/docs/APPSTREAM_BUNDLE/ - Backports: http://systemd.cn/docs/BACKPORTS/ - Booting Without /usr is Broken: http://systemd.cn/docs/SEPARATE_USR_IS_BROKEN/ - Code Quality Tools: http://systemd.cn/docs/CODE_QUALITY/ - Coding Style: http://systemd.cn/docs/CODING_STYLE/ - Compatibility with SysV: http://systemd.cn/docs/INCOMPATIBILITIES/ - Container Interface: http://systemd.cn/docs/CONTAINER_INTERFACE/ - Contributing: http://systemd.cn/docs/CONTRIBUTING/ - Control Group APIs and Delegation: http://systemd.cn/docs/CGROUP_DELEGATION/ - Converting Existing Users to systemd-homed: http://systemd.cn/docs/CONVERTING_TO_HOMED/ - Credentials: http://systemd.cn/docs/CREDENTIALS/ - Desktop Environment Integration: http://systemd.cn/docs/DESKTOP_ENVIRONMENTS/ - Diagnosing Boot Problems: http://systemd.cn/docs/DEBUGGING/ - File Descriptor Store: http://systemd.cn/docs/FILE_DESCRIPTOR_STORE/ - Frequently Asked Questions: http://systemd.cn/docs/FAQ/ - Governance: http://systemd.cn/docs/GOVERNANCE/ - Hacking on systemd: http://systemd.cn/docs/HACKING/ - Home Directories: http://systemd.cn/docs/HOME_DIRECTORY/ - Inhibitor Locks: http://systemd.cn/docs/INHIBITOR_LOCKS/ - Initrd Interface: http://systemd.cn/docs/INITRD_INTERFACE/ - Journal Export Formats: http://systemd.cn/docs/JOURNAL_EXPORT_FORMATS/ - Journal File Format: http://systemd.cn/docs/JOURNAL_FILE_FORMAT/ - Journal Message Catalogs: http://systemd.cn/docs/CATALOG/ - JSON Group Records: http://systemd.cn/docs/GROUP_RECORD/ - JSON User Records: http://systemd.cn/docs/USER_RECORD/ - Known Environment Variables: http://systemd.cn/docs/ENVIRONMENT/ - Locking Block Device Access: http://systemd.cn/docs/BLOCK_DEVICE_LOCKING/ - Minimal Builds: http://systemd.cn/docs/MINIMAL_BUILDS/ - My Service Can't Get Realtime!: http://systemd.cn/docs/MY_SERVICE_CANT_GET_REALTIME/ - Native Journal Protocol: http://systemd.cn/docs/JOURNAL_NATIVE_PROTOCOL/ - New Control Group Interfaces: http://systemd.cn/docs/CONTROL_GROUP_INTERFACE/ - Notes for Translators: http://systemd.cn/docs/TRANSLATORS/ - Password Agents: http://systemd.cn/docs/PASSWORD_AGENTS/ - Pax Controla Groupiana: http://systemd.cn/docs/PAX_CONTROL_GROUPS/ - Portability and Stability: http://systemd.cn/docs/PORTABILITY_AND_STABILITY/ - Portable Services Introduction: http://systemd.cn/docs/PORTABLE_SERVICES/ - Porting systemd To New Distributions: http://systemd.cn/docs/DISTRO_PORTING/ - Porting to New Architectures: http://systemd.cn/docs/PORTING_TO_NEW_ARCHITECTURES/ - Predictable Network Interface Names: http://systemd.cn/docs/PREDICTABLE_INTERFACE_NAMES/ - Presets: http://systemd.cn/docs/PRESET/ - Project IDs for Disk Quotas on Exec Directories: http://systemd.cn/docs/DISK-QUOTAS-PROJECTIDS/ - Random Seeds: http://systemd.cn/docs/RANDOM_SEEDS/ - Reporting of Security Vulnerabilities: http://systemd.cn/docs/SECURITY/ - Resource Pressure Handling: http://systemd.cn/docs/PRESSURE/ - Running Services After the Network Is Up: http://systemd.cn/docs/NETWORK_ONLINE/ - Safely Building Images: http://systemd.cn/docs/BUILDING_IMAGES/ - Socket Activation with Popular Daemons: http://systemd.cn/docs/DAEMON_SOCKET_ACTIVATION/ - Steps to a Successful Release: http://systemd.cn/docs/RELEASE/ - Storage Daemons for the Root File System: http://systemd.cn/docs/ROOT_STORAGE_DAEMONS/ - systemd Community Conduct Guidelines: http://systemd.cn/docs/CODE_OF_CONDUCT/ - systemd Coredump Handling: http://systemd.cn/docs/COREDUMP/ - systemd File Hierarchy Requirements: http://systemd.cn/docs/SYSTEMD_FILE_HIERARCHY_REQUIREMENTS/ - systemd Optimizations: http://systemd.cn/docs/OPTIMIZATIONS/ - systemd Repository Architecture: http://systemd.cn/docs/ARCHITECTURE/ - systemd-boot UEFI Boot Manager: http://systemd.cn/docs/BOOT/ - systemd-homed and JSON User/Group Record Support in Desktop Environments: http://systemd.cn/docs/USERDB_AND_DESKTOPS/ - systemd-resolved and VPNs: http://systemd.cn/docs/RESOLVED-VPNS/ - Testing systemd Using Sanitizers: http://systemd.cn/docs/TESTING_WITH_SANITIZERS/ - The Case for the /usr Merge: http://systemd.cn/docs/THE_CASE_FOR_THE_USR_MERGE/ - Tips And Tricks: http://systemd.cn/docs/TIPS_AND_TRICKS/ - User Record Blob Directories: http://systemd.cn/docs/USER_RECORD_BLOB_DIRS/ - User/Group Name Syntax: http://systemd.cn/docs/USER_NAMES/ - User/Group Record Lookup API via Varlink: http://systemd.cn/docs/USER_GROUP_API/ - Users, Groups, UIDs and GIDs on systemd Systems: http://systemd.cn/docs/UIDS-GIDS/ - Using /tmp/ and /var/tmp/ Safely: http://systemd.cn/docs/TEMPORARY_DIRECTORIES/ - Varlink API Style: http://systemd.cn/docs/VARLINK/ - VM Interface: http://systemd.cn/docs/VM_INTERFACE/ - What Settings Are Currently Available For Transient Units?: http://systemd.cn/docs/TRANSIENT-SETTINGS/ - Writing Desktop Environments: http://systemd.cn/docs/WRITING_DESKTOP_ENVIRONMENTS/ - Writing Display Managers: http://systemd.cn/docs/WRITING_DISPLAY_MANAGERS/ - Writing Network Configuration Managers: http://systemd.cn/docs/WRITING_NETWORK_CONFIGURATION_MANAGERS/ - Writing Resolver Clients: http://systemd.cn/docs/WRITING_RESOLVER_CLIENTS/ - Writing syslog Daemons Which Cooperate Nicely With systemd: http://systemd.cn/docs/SYSLOG/ - Writing VM and Container Managers: http://systemd.cn/docs/WRITING_VM_AND_CONTAINER_MANAGERS/ # The initrd Interface of systemd The Linux initrd mechanism (short for "initial RAM disk", also known as "initramfs") refers to a small file system archive that is unpacked by the kernel and contains the first userspace code that runs. It typically finds and transitions into the actual root file system to use. systemd supports both initrd and initrd-less boots. If an initrd is used, it is a good idea to pass a few bits of runtime information from the initrd to systemd in order to avoid duplicate work and to provide performance data to the administrator. In this page we attempt to roughly describe the interfaces that exist between the initrd and systemd. These interfaces are currently used by [mkosi](https://github.com/systemd/mkosi)-generated initrds, dracut and the Arch Linux initrds. * The initrd should mount `/run/` as a tmpfs and pass it pre-mounted when jumping into the main system when executing systemd. The mount options should be `mode=0755,nodev,nosuid,strictatime`. * It's highly recommended that the initrd also mounts `/usr/` (if split off) as appropriate and passes it pre-mounted to the main system, to avoid the problems described in [Booting without /usr is Broken](/SEPARATE_USR_IS_BROKEN). * If the executable `/run/initramfs/shutdown` exists systemd will use it to jump back into the initrd on shutdown. `/run/initramfs/` should be a usable initrd environment to which systemd will pivot back and the `shutdown` executable in it should be able to detach all complex storage that for example was needed to mount the root file system. It's the job of the initrd to set up this directory and executable in the right way so that this works correctly. The shutdown binary is invoked with the shutdown verb as `argv[1]`, optionally followed (in `argv[2]`, `argv[3]`, …) systemd's original command line options, for example `--log-level=` and similar. * Storage daemons run from the initrd should follow the guide on [systemd and Storage Daemons for the Root File System](/ROOT_STORAGE_DAEMONS) to survive properly from the boot initrd all the way to the point where systemd jumps back into the initrd for shutdown. One last clarification: we use the term _initrd_ very generically here describing any kind of early boot file system, regardless whether that might be implemented as an actual ramdisk, ramfs or tmpfs. We recommend using _initrd_ in this sense as a term that is unrelated to the actual backing technologies used. ## Using systemd inside an initrd It is also possible and recommended to implement the initrd itself based on systemd. Here are a few terse notes: * Provide `/etc/initrd-release` in the initrd image. The idea is that it follows the same format as the usual `/etc/os-release` but describes the initrd implementation rather than the OS. systemd uses the existence of this file as a flag whether to run in initrd mode, or not. * When run in initrd mode, systemd and its components will read a couple of additional command line arguments, which are generally prefixed with `rd.` * To transition into the main system image invoke `systemctl switch-root`. * The switch-root operation will result in a killing spree of all running processes. Some processes might need to be excluded from that, see the guide on [systemd and Storage Daemons for the Root File System](/ROOT_STORAGE_DAEMONS).