Help! Invalid Sibling Link without Startup disk or DiskWarrior

You may be able to repair the disk so that you can mount it for purposes of extracting its data. Boot single user mode and at the root# prompt type

fsck_hfs -rf /dev/disk0s1

followed by the Return or Enter key. Substitute your disk device name for /disk0s1 in the above.

To see a list of devices, type ls /dev

It may take a long time to complete and may not be able to repair the disk. If and when it eventually finishes with ***** REBOOT NOW ***** it means what it says. Just force it to shut down.

Even if it repairs successfully, the disk error is likely to recur. Take that opportunity to back up or save your important documents.

Don't be concerned about that. If you are uncertain there is no harm in using disk0s1. Repeat with disk0s2 and so forth.

If you did not partition your hard disk the damaged boot volume is probably disk0s2.

Remember it will take a long time, perhaps an hour or more, and may not be successful. If you are concerned your system has become unresponsive just press the Return key. A blank line should appear. When fsck finishes the root# prompt will reappear and pressing the Return key will result in another root# prompt.

It sounds as though your HD cannot be repaired. Just make sure you are typing the command correctly.

There are a total of two spaces in it.

Type

fsck_hfs

Then a space, then

-rf

Then another space, then

/dev/disk0s2

Then the Return key.

If it still replies "volume Macintosh HD could not be repaired" that is all you can do. There is no harm in trying it repeatedly until you decide to give up.

Your options are narrow. You need to purchase at minimum a thumb drive and attempt to backup as much of your user data as possible in Safe Mode. You also need to acquire a new "start-up" DVD from Apple. Once, your data is backed up then reformat the hard drive and install a new operating system from the DVD.

Afaik, given the hints by John Galt didn't work for you, you have no other choice but DiskWarrior and you'd better backup everything while you still can. I see you can't afford DW, but that's it (and you can't be certain even DW will do the trick). This quote is from the Alsoft Support Batabase:

Product DiskWarrior Question Is DiskWarrior capable of repairing an "Invalid Sibling Link" error? Answer This is an error you definitely don't want. It indicates that parts of your directory, and therefore some of your files and folders, are inaccessible. Mac OS Standard (HFS) and Mac OS Extended (HFS Plus) disk directories have a very complex structure. Each file or folder (item) on a disk has an entry in the disk's directory. These entries are in order of enclosing folder and then item name. This is similar to a yellow pages directory being ordered by type of business and then business name. Just like a yellow pages directory, the disk directory has pages except that its pages are called nodes. Unlike the yellow pages, nodes are dynamic and change as you add and delete items. It's sort of like a realtime yellow pages. Imagine that the pages of the yellow pages are not in order and at the bottom of each page it says "Continued on page n," where n is the page that contains the next set of listings for the particular type of business that you're looking up. Well nodes are not arranged in order and each node has a reference, or link, to the next node that contains the next set of ordered items. This link is what is referred to as the sibling link. A sibling link error is a bad link to another node. Either the link refers to the wrong node or it refers to an invalid node. As I said, a sibling link error makes some of your items inaccessible and can even prevent a disk from mounting. Sibling errors are notoriously difficult for some of the patching type of disk repair utilities to repair. Sometimes the repairs fail and the directory is damaged further. If a disk with a sibling link error is still mountable, I would advise backing up the accessible files and folders on the disk before attempting to repair it with that type of disk repair utility.

Call Apple at the number shown in the Apple Online Store and explain that you require a replacement System Install DVD. They will require your Mac's serial number. It is printed on the case exterior, on the bottom. It is a mix of letters and numbers and the print is very small, so it can be challenging to read even without dyslexia.

Troubleshooting a Mac is a challenge without that disc, but it seems everything you did already verified that its hard disk requires replacement anyway. Disk Warrior may or may not be successful, and it's a lot of money to spend for something that may not work. Even if it is capable of repairing the disk so that you can start your Mac, and retrieve whatever data remains intact, some irretrievable data loss has already occurred. Ideally, that data will not be important to you.