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   file-hierarchy    ( 7 )

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GENERAL STRUCTURE

/ The file system root. Usually writable, but this is not required. Possibly a temporary file system ("tmpfs"). Not shared with other hosts (unless read-only).

/boot/ The boot partition used for bringing up the system. On EFI systems, this is possibly the EFI System Partition (ESP), also see systemd-gpt-auto-generator(8). This directory is usually strictly local to the host, and should be considered read-only, except when a new kernel or boot loader is installed. This directory only exists on systems that run on physical or emulated hardware that requires boot loaders.

/efi/ If the boot partition /boot/ is maintained separately from the EFI System Partition (ESP), the latter is mounted here. Tools that need to operate on the EFI system partition should look for it at this mount point first, and fall back to /boot/ — if the former doesn't qualify (for example if it is not a mount point or does not have the correct file system type MSDOS_SUPER_MAGIC).

/etc/ System-specific configuration. This directory may or may not be read-only. Frequently, this directory is pre-populated with vendor-supplied configuration files, but applications should not make assumptions about this directory being fully populated or populated at all, and should fall back to defaults if configuration is missing.

/home/ The location for normal user's home directories. Possibly shared with other systems, and never read-only. This directory should only be used for normal users, never for system users. This directory and possibly the directories contained within it might only become available or writable in late boot or even only after user authentication. This directory might be placed on limited-functionality network file systems, hence applications should not assume the full set of file API is available on this directory. Applications should generally not reference this directory directly, but via the per-user $HOME environment variable, or via the home directory field of the user database.

/root/ The home directory of the root user. The root user's home directory is located outside of /home/ in order to make sure the root user may log in even without /home/ being available and mounted.

/srv/ The place to store general server payload, managed by the administrator. No restrictions are made how this directory is organized internally. Generally writable, and possibly shared among systems. This directory might become available or writable only very late during boot.

/tmp/ The place for small temporary files. This directory is usually mounted as a "tmpfs" instance, and should hence not be used for larger files. (Use /var/tmp/ for larger files.) This directory is usually flushed at boot-up. Also, files that are not accessed within a certain time may be automatically deleted.

If applications find the environment variable $TMPDIR set, they should use the directory specified in it instead of /tmp/ (see environ(7) and IEEE Std 1003.1[4] for details).

Since /tmp/ is accessible to other users of the system, it is essential that files and subdirectories under this directory are only created with mkstemp(3), mkdtemp(3), and similar calls. For more details, see Using /tmp/ and /var/tmp/ Safely[5].