s6
Software
skarnet.org

The s6-update-symlinks program

s6-update-symlinks links the content of several similar directory trees under a single tree. Its main use is to replace search paths like $PATH or $MANPATH, by creating a unique access tree based on the source trees. Name conflicts are solved by giving precedence to the last named directory. Subdirectories are created exactly as needed ; what can be shared is shared.

s6-update-symlinks is useful when one wants to combine a logical package system, like Dan Bernstein's /package and /command, with physical filesystem constraints, like /, /usr and /usr/local on separate filesystems.

Interface

     s6-update-symlinks d src1 src2 ...

• d is the destination directory. It will be created if it doesn't exist.
• src1, src2, ... are the directory containing the files to be linked.
• d and srcn must be absolute paths, else s6-update-symlinks refuses to run. Using relative paths doesn't make sense here, anyway.
• If src2 is empty, then d becomes a link to src1.
• If src1 is empty or entirely overridden by src2, then d becomes a link to src2.
• If src1/file exists but not src2/file, then d becomes a real directory and d/file a link to src1/file. Then if src2/file2 exists, d/file2 links to it.
• And so on with other src directories, and subdirs.
• If s6-update-symlinks manages to performs all the requested tasks, it exits 0. If it encounters a hard error, it exits 111. If it is unable to resolve a conflict between given sources, it exits 100.

Examples

• s6-update-symlinks /command /bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbin
  makes all files under /bin, ..., /usr/local/sbin available under /command. The programs linked are the same as the ones that would be accessed with PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin".
• s6-update-symlinks /package /initrd/package /slash/package /usr/package /usr/local/package
  builds a /package hierarchy with what it finds in the listed directories. This allows oddities like, for instance, having the daemontools sources in /usr/package/admin/daemontools/src, and the daemontools binaries in /initrd/package/admin/daemontools/bin, but accessing both through /package/admin/daemontools/.