Problems twotwo level directory separate directory

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Unformatted text preview: for all users. Problems? TwoTwo-Level Directory Separate directory for each user. Path name is needed to share files Can have the same file name for different user Efficient searching No grouping capability: still fairly flat, no subdirs TreeTree-Structured Directories Advantages? Efficient searching Grouping Capability Current directory (working directory) convenience: convenience: absolute path names can get long! relative naming • cd /spell/mail/prog • cat list Acyclic Acyclic-Graph Directories Have shared subdirectories and files. Acyclic Acyclic-Graph Directories (Cont.) Two different names (aliasing) – problem? Deletes dict /count dangling pointer! Solution: Acyclic Acyclic-Graph Directories (Cont.) If delete means delete the link, when does the file actually get deleted? deleted? General General Graph Directory Types Types of Links Hard link - multiple (path) names refer to same file (actual storage) - delete/remove: uses reference counts Soft/symbolic link - linked file (target) is special – stores the path to the source file - link directories - link across filesystems: won’t work for hard links - delete source -> dangling reference Unix – man ln Protection Protection File owner/creator should be able to control: • what can be done • by whom Types of access • • • • • • Read Write Execute Append Delete List Access Access Lists and Groups (Unix) Mode of access: read, write, execute Three classes of users a) owner access 7 b) groups access 6 c) public access 1 RWX 111 RWX 110 RWX 001 Unix Unix Special Files Prompt> ls –l /etc/passwd -r--r--r-- 1 root sys 415 May 12 2004 /etc/passwd - : regular file d: directory l: symbolic link b/c: block/char devices few others File File System Layout file system info meta-data CSci CSci 5103 Operating Systems File system implementation Chap 4 FileFile-System Structure File structure • Logical storage unit • Collection of related information File system r...
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