Quiz 1 Key COP 5615 8/31/2010 1. (3) How does the operating system know that it can garbage collect an inode in Unix? 2. (2) Why must distributed systems have more tightly coupled software than network operating systems? KEY 1. The inode has a reference count that reflects the number of directories that point to it (i.e., the number of hard links to the file). When a hard link is created to the file, the reference count is incremented; when a directory entry is deleted (unlinked), the reference count of the inode is decremented. When the reference count reaches zero, the inode is no longer referenced by any directory. (1) However, even if no directory references a file, a process may have opened the file and not yet closed it. The System File Table (SFT) contains all the information on open files, including the inode number and another reference count for the number of Process File Table (PFT) entries that point to the SFT entry. This reference count is initialized to one, and is incremented
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