Man: synthetic.conf(5) - synthetic symbolic link and directory manifest

synthetic.conf.5

SYNTHETIC.CONF(5)           File Formats Manual           SYNTHETIC.CONF(5)

NAME
     synthetic.conf – synthetic symbolic link and directory manifest

DESCRIPTION
     synthetic.conf describes virtual symbolic links and empty directories to be
     created at the root mount point.  Because the root mount point is read-only
     as of macOS 10.15, physical files may not be created at this location.  All
     writeable paths must reside on the data volume, which is mounted at
     /System/Volumes/Data.

     synthetic.conf provides a mechanism for some limited, user-controlled file-
     creation at /.  The synthetic entities described in this file are
     synthesized by the kernel during early system boot.  They are not
     physically present on the disk, but when the system is booted, they behave
     as if they were within certain parameters.

     synthetic.conf is intended to be used for creating mount points at / (e.g.
     for use as NFS mount points in enterprise deployments) and symbolic links
     (e.g. for creating a package manager root without modifying the system
     volume).  synthetic.conf is read by apfs.util(8) during early system boot.

FILES
     /etc/synthetic.conf

CONFIGURATION DIRECTORY
     Individual subsystems may add their own synthetic manifests to
     /etc/synthetic.d to avoid having to append to to share the content of
     synthetic.conf.  This is similar to the mechanisms which exist for shell
     and manual page paths, paths.d and manpaths.d, respectively.  If multiple
     manifests specify the same synthetic link or directory name, the one
     respected by the implementation is undefined.  The structure of these
     manifests is identical to that of synthetic.conf.

FORMAT
     synthetic.conf specifies a single synthetic entity per line.  Each line may
     have one or two columns, separated by a tab character.  If a line has a
     single column, it denotes a virtual empty directory to be created at /.  If
     a line has two columns, it denotes a symbolic link at / whose link target
     is given in the second column.

     In either case, the first column denotes the name of the entity to be
     created at /.

     A line beginning with the # character indicates a comment that is not
     parsed.

SYNTHETIC ENTITIES
     Synthetic entities may not be deleted at runtime.    In order to delete a
     synthetic entity, it must be removed from synthetic.conf, and the host must
     be rebooted.

     New files and directories may not be created within a synthetic empty
     directory.

EXAMPLES
     # create a symbolic link named "srv" at / which points to
     # "System/Volumes/Data/srv", a writeable location at the root of the data volume
     srv     /System/Volumes/Data/srv

     # create an empty directory named "foo" at / which may be mounted over
     foo

     # create a symbolic link named "baz" at / which points to "Users/me/baz"
     baz       Users/me/baz

DIRECTORIES
     /etc/synthetic.d

SEE ALSO
     reboot(2), apfs.util(8), shutdown(8)

Darwin/macOS            September 3, 2019            Darwin/macOS