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(2) UNIX File System

The UNIX File System

Files and directories live in the file system and have a "location", the location is called the "path". Absolute pathnames are unique to a system.
When logged in you have a current working directory (pwd -- print working directory). The current directory is initially set to your home directory ($HOME).
A "path" can be absolute or relative
Absolute Path
- Absolute path is unique
- Starts with root directory (/), or
- Can start with a home directory (~) or (~username)
Relative Path
- Any pathname which is not an absolute path is interpreted as relative to the current directory.
- May start with the name of a subdirectory. E.g. cd classes
- May explicitly specify the current directory (./)
- May specify the parent directory using ../, or higher up the directory tree, by stacking the ".." (../../..)
Multiple file systems make up the complete directory hierarchy
Symbolic Links
- Symbolic links are files that point to other files or directories, similar to aliases in MacOS or shortcuts in Windows. ls -li shows links. There is only one 'real' file.
- Good for sharing things while maintaining only one copy
- ln -s real_file link_name
  e.g.
  ln -s hosts1 h1
  ln -s ~richard/public/sendmail mail-notes
- Symbolic links can form loops, which is not usually what you wanted - be careful.
- Symbolic links make it possible to refer to the same file using many different pathnames - sometimes confusing.
Hard Links
It is possible to have multiple names for the same file. These are called hard links and unlike symbolic links, there is no distinction between the "real" file and other links to it - they are all equivalent. Hard links tend to be confusing.

slide02.src last modified Feb 8, 2011

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