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/ # API File Systems _So you are seeing all kinds of weird file systems in the output of mount(8) that are not listed in `/etc/fstab`, and you wonder what those are, how you can get rid of them, or at least change their mount options._ The Linux kernel provides a number of different ways for userspace to communicate with it. For many facilities there are system calls, others are hidden behind Netlink interfaces, and even others are exposed via virtual file systems such as `/proc` or `/sys`. These file systems are programming interfaces, they are not actually backed by real, persistent storage. They simply use the file system interface of the kernel as interface to various unrelated mechanisms. Similarly, there are file systems that userspace uses for its own API purposes, to store shared memory segments, shared temporary files or sockets. In this article we want to discuss all these kind of _API file systems_. More specifically, here's a list of these file systems typical Linux systems currently have: * `/sys` for exposing kernel devices, drivers and other kernel information to userspace * `/proc` for exposing kernel settings, processes and other kernel information to userspace * `/dev` for exposing kernel device nodes to userspace * `/run` as location for userspace sockets and files * `/tmp` as location for volatile, temporary userspace file system objects (X) * `/sys/fs/cgroup` (and file systems below that) for exposing the kernel control group hierarchy * `/sys/kernel/security`, `/sys/kernel/debug` (X), `/sys/kernel/config` (X) for exposing special purpose kernel objects to userspace * `/sys/fs/selinux` for exposing SELinux security data to userspace * `/dev/shm` as location for userspace shared memory objects * `/dev/pts` for exposing kernel pseudo TTY device nodes to userspace * `/proc/sys/fs/binfmt_misc` for registering additional binary formats in the kernel (X) * `/dev/mqueue` for exposing mqueue IPC objects to userspace (X) * `/dev/hugepages` as a userspace API for allocating "huge" memory pages (X) * `/sys/fs/fuse/connections` for exposing kernel FUSE connections to userspace (X) * `/sys/firmware/efi/efivars` for exposing firmware variables to userspace All these _API file systems_ are mounted during very early boot-up of systemd and are generally not listed in `/etc/fstab`. Depending on the used kernel configuration some of these API file systems might not be available and others might exist instead. As these interfaces are important for kernel-to-userspace and userspace-to-userspace communication they are mounted automatically and without configuration or interference by the user. Disabling or changing their parameters might hence result in applications breaking as they can no longer access the interfaces they need. Even though the default settings of these file systems should normally be suitable for most setups, in some cases it might make sense to change the mount options, or possibly even disable some of these file systems. Even though normally none of these API file systems are listed in `/etc/fstab` they may be added there. If so, any options specified therein will be applied to that specific API file system. Hence: to alter the mount options or other parameters of these file systems, simply add them to `/etc/fstab` with the appropriate settings and you are done. Using this technique it is possible to change the source, type of a file system in addition to simply changing mount options. That is useful to turn `/tmp` to a true file system backed by a physical disk. It is possible to disable the automatic mounting of some (but not all) of these file systems, if that is required. These are marked with (X) in the list above. You may disable them simply by masking them: ```sh systemctl mask dev-hugepages.mount ``` This has the effect that the huge memory page API FS is not mounted by default, starting with the next boot. See [Three Levels of Off](https://0pointer.de/blog/projects/three-levels-of-off.html) for more information on masking. The systemd service [systemd-remount-fs.service](https://www.freedesktop.org/software/systemd/man/latest/systemd-remount-fs.service.html) is responsible for applying mount parameters from `/etc/fstab` to the actual mounts. ## Why are you telling me all this? I just want to get rid of the tmpfs backed /tmp! You have three options: 1. Disable any mounting on `/tmp` so that it resides on the same physical file system as the root directory. For that, execute `systemctl mask tmp.mount` 2. Mount a different, physical file system to `/tmp`. For that, simply create an entry for it in `/etc/fstab` as you would do for any other file system. 3. Keep `/tmp` but increase/decrease the size of it. For that, also just create an entry for it in `/etc/fstab` as you would do for any other `tmpfs` file system, and use the right `size=` option.