sln

sln target_file link_name
sln --help
sln --version

target_file
    The existing file or directory to which the symbolic link will point.

link_name
    The name of the new symbolic link to be created.

--help
    Display a help message and exit.

--version
    Output version information and exit.

The sln command is a utility designed to create symbolic links (symlinks) in an atomic and safe manner. Unlike the more commonly used ln -s command, sln ensures that the link creation process is robust against system crashes or interruptions. It achieves this by first creating a temporary symbolic link to the target file or directory, and then atomically renaming this temporary link to its final desired name. This two-step process guarantees that at no point is a partially created or corrupted symbolic link exposed. If an old link with the same name exists, it is replaced atomically, meaning the old link remains valid until the new one is fully in place. While ln -s is simpler and more widely used, sln offers important safety for critical system scripts or high-availability environments.

sln is not as universally available as ln(1) and may need to be installed separately on some Linux distributions. While it offers atomicity, which ln -s does not by default, this benefit is often not critical enough for its widespread adoption. Its simplicity also means it lacks many features found in ln, such as force overwriting (-f), interactive prompting (-i), or verbose output (-v).

The core advantage of sln lies in its atomic operation. It first creates a temporary symbolic link (e.g., link.tmp) pointing to the target. Once this temporary link is fully established, it is then atomically renamed to the desired link_name. This rename(2) system call is atomic on POSIX-compliant file systems, meaning the old link (if it existed) is replaced by the new one in a single, indivisible operation, preventing any state where the link is partially updated or pointing incorrectly during a crash or interruption.

The sln command was developed to address the non-atomic nature of symbolic link creation with ln -s. In older or less robust systems, an interruption during ln -s could leave a partially created or corrupt link. sln provides a safer alternative by using a temporary file and an atomic rename operation. While it served an important purpose, its usage has declined over time as ln -s has proven sufficiently robust for most modern use cases, and the overhead of sln's atomic operation is generally not warranted. It remains available in some util-linux distributions but is rarely the default choice.

ln(1), rm(1), readlink(1)