synthetic.confsynthetic symbolic link and directory manifest

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 .

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.


Individual subsystems may add their own synthetic manifests to to avoid having to append to the content of synthetic.conf. This is similar to the mechanisms which exist for shell and manual page paths, and , 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.

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 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.

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

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

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


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

September 3, 2019 Darwin/macOS