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intro unix/linux 07
 

intro unix/linux 07

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creating and changing directories

creating and changing directories

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    intro unix/linux 07 intro unix/linux 07 Presentation Transcript

    • Lesson 7-Creating and Changing Directories
    • Overview
      • Using directories to create order.
      • Managing files in directories.
      • Using pathnames to manage files in directories.
      • Accessing files in remote directories.
      • Managing files from more than one directory.
      • Moving and removing directories and their contents.
    • Using Directories to Create Order
      • A file is a collection of information stored electronically on the hard drive of a system.
      • An inode contains all the information about each file, including the location of the actual file on the disk.
    • Using Directories to Create Order
      • The home directory.
      • Listing files in a directory.
      • Working with directories.
      • Distinguishing between files and directories.
      • Obtaining information about a directory or its contents.
    • The Home Directory
      • The “pwd” command displays the path from root to the user’s home directory.
      • The /etc/passwd file holds the user’s home directory path.
      • A file is created and listed in the current home directory by default.
    • Listing Files in a Directory
      • The “ls” command reads the names of the files listed in the current directory, and then outputs those names.
      • Each file in the directory contains only the name of that file and a number that leads to the inode for that file.
      • The “–i” option instructs ls to include the inodes in its output.
      • Inodes are small pieces of memory created on the hard disk when it is formatted.
    • Listing Files in a Directory
      • The inode has a list of addresses of the block on the disk where the data that comprise the file is actually located.
      • It addresses up to 13 data blocks on the hard drive.
      • The first ten blocks addressed from the inode contains the actual file data.
      • If a file is too large, additional blocks are allocated to fit the data.
    • Working with Directories
      • The “mkdir” command is used for creating a new directory.
      • Directories created in uppercase are listed first by the ls command.
      • Each new directory created is called a subdirectory.
      • The “cd” or “change directory” command instructs the shell to locate the directory listed as an argument.
    • Working with Directories
      • The “pwd” command outputs the absolute path from the top of the file system (root or /) to the current directory.
      • A path is a list of directory names separated by the / (slash) character.
      • The topmost directory is called the root and is symbolized by the first forward slash (/) in the pathname.
    • Working with Directories
      • The vi editor can be used for creating a file within a directory or subdirectory.
      • The cd command, without any directory name as an argument, returns to the home directory.
      • The “–R” (recursive) option used with ls descends through each subdirectory in the directory tree.
    • Distinguishing between Files and Directories
      • The “ls –F” command displays directory names with a slash appended at the end.
      • Filenames displayed with an asterisk (*) at the end are executable files.
      • The “–C” option to ls instructs ls to make several columns in the output instead of one.
    • Obtaining Information About a Directory or its Contents
      • The “ls –l” command displays the permissions and owners of files listed in a directory.
      • The “–d” option with ls command returns a listing of information about the contents of the target directory.
      • The “ls –ld” displays the permissions of the directory, and not the information about the files.
    • Managing Files in Directories
      • Moving or copying files into a subdirectory.
      • Accessing a file in a subdirectory.
      • Avoiding mistakes when moving files into directories.
      • Renaming files.
      • Removing files from subdirectories.
    • Moving or Copying Files into a Subdirectory
      • Moving a file or directory does not move the file electronically.
      • The name and the inode number are erased from the current directory and are written in the subdirectory.
    • Moving or Copying Files into a Subdirectory
      • When a file is copied, a second electronic version is created.
      • The copied file does not have the same inode number as the original.
      • The copied file has its own inode, permission, and data blocks containing the new files actual contents.
    • Accessing a File in a Subdirectory
      • To access a file in a subdirectory:
        • Locate the inode number of the file.
        • Check the permissions on the directory.
        • Get the directory’s address from the inode.
        • Identify the inode associated with the file.
        • Read the files from the data blocks.
    • Avoiding Mistakes When Moving Files into Directories
      • The mv utility takes two arguments.
      • The first argument is the name of an existing file.
      • The second argument is a new name assigned to existing file, unless the second argument is a directory.
      • A slash at the end of the second argument interprets the argument as a directory name.
    • Renaming Files
      • The command to move a file listing from the current directory to a new directory and also to change its filename is mv filename subdirectory/newfilename.
      • Moving a file just moves its listing from one directory to another.
    • Removing Files from Subdirectories
      • The “rm” command can be used for removing files form a directory or subdirectory.
      • After the rm command, the entry of the file is removed, and the data blocks listed in the inode for that file are released.
    • Using Pathnames to Manage Files in Directories
      • Accessing or creating a subdirectory.
      • Using pathnames with utilities.
      • Copying files into other directories using paths.
      • Using parent directory names.
      • Copying and moving multiple files to subdirectories.
      • Examining the full path from root to directories and files.
    • Using Pathnames to Manage Files in Directories
      • Explicitly accessing a user’s home directory.
      • Including other users’ logins in directory paths.
      • Returning to the previous directory.
    • Accessing or Creating a Subdirectory
      • Providing a full path to the cd command without any spaces can access a subdirectory.
      • Pathnames are the mechanism used to tell the shell what path to follow to access a file or directory not listed in the current directory.
      • Remote directories can also be created by specifying the relative or absolute pathname.
    • Using Pathnames with Utilities
      • Pathnames can also be used as arguments to utilities.
      • A relative path can be specified for accessing a file without changing the current directory.
    • Copying Files into Other Directories Using Paths
      • Pathnames are particularly useful with the “cp” and “mv” commands.
      • Any command that takes a filename or directory name as an argument can be given an explicit pathname argument.
    • Using Parent Directory Names
      • A single dot is used for referring to the current directory.
      • In a directory, the .. (dot-dot) is the listing for its parent directory.
      • The parent directory is the directory located one level above the current directory.
    • Using Parent Directory Names
      • The parent directory lists the current directory’s name and inode.
      • The . and .. are the two listings that get created when a new directory is created.
    • Copying and Moving Multiple Files to Subdirectories
      • The move and copy commands are usually used with only two arguments.
      • The cp utility displays a usage error message when more than two arguments are specified and the last argument is not a directory.
      • In the cp command, if the third argument specified is a directory, then the rest of the file arguments are copied into the destination subdirectory.
    • Copying and Moving Multiple Files to Subdirectories
      • The mv and cp commands can affect multiple files when the last argument is a directory.
      • The .. (dot-dot) listing can be used in the mv command for moving files into the parent directory.
    • Examining the Full Path from Root to Directories and Files
      • A user can specify a directory’s location with the full path from the top of the file system.
      • The full path starting at root identifies a file explicitly.
      • The pathname for every file describes a particular file uniquely and absolutely.
      • The full pathname to a file is called its absolute pathname.
    • Explicitly Accessing a User’s Home Directory
      • The “ls ~” command lists all filenames listed in the home directory.
      • The C shell and all shells define the tilde (~) as the path to the user’s home directory.
      • The shell replaces the tilde (~) with the value of the path to the user’s home directory.
      • The shell replaces the tilde (~) in any command line with the absolute path from root to the user’s home directory.
    • Including Other Users’ Logins in Directory Paths
      • The “echo ~root” option displays the path to the home directory of the user root.
      • The contents of the home directory of a user are displayed if the user has appropriate permissions.
    • Returning to the Previous Directory
      • The bash and ksh shells maintain the previous directory path as the value of a variable.
      • The tcsh shell maintains a list of previous directories in a list that can be accessed.
      • The value of the variable PWD is the path to the current directory.
    • Returning to the Previous Directory
      • An alternative way of specifying the previous directory on many bash and ksh shells is to do it with a dash argument.
      • The exit command can be used for exiting from a child bash or ksh to the login shell.
      • The “popd” command instructs the shell to move the directory currently on the top of the list of directories that are added to the list.
    • Accessing Files in Remote Directories
      • A filename that includes no relative path defaults to the current directory.
      • The ./ is the default relative path that is used.
      • Every file on the system has a unique pathname from / (root).
    • Accessing Files in Remote Directories
      • The “pwd” command displays the absolute path of the present directory.
      • A path always starts at root (/) and includes the appropriate subdirectories.
    • Managing Files from More Than One Directory
      • A listing for a file in a directory is a link to the file.
      • The ls –l command at the start lists the number of data blocks used by files and directories in the current directory.
      • In a long listing entry, or record, the information for each file or directory is divided into seven fields.
      • The second field in each entry of a file indicates the number of directories where the object is listed.
    • Managing Files from More Than One Directory
      • Linking files:
        • The “ln” command can be used for linking a file to the current directory.
        • The index card of each file keeps track of the number of directories that list it.
        • Each instance of the file listed in a directory is one link.
        • Removing a file removes it from the directory listing.
    • Managing Files from More Than One Directory
      • Linking files (continued):
        • The ln utility can be used to link multiple files at a time.
        • The “ls –il” command lists the current files with link count and inodes.
        • The “–s” option to ln creates a file in the current directory that contains information required to locate the linked file.
    • Managing Files from More Than One Directory
      • Using symbolic links:
        • A symbolic link is a small file in a directory on one file system partition that points to the correct file system and the correct inode for the linked file.
        • In the long listing of the symbolic link, the initial character is an “l” for directories and files.
        • An arrow and path at the end of the listing displays the actual directory where the link points.
    • Managing Files from More Than One Directory
      • Using symbolic links (continued):
        • The ln utility provides a “–d” option for the root user to create hard links to directories.
        • Ordinary users cannot create directory hard links.
        • Ordinary users can create symbolic links to directories.
    • Managing Files from More Than One Directory
      • The administrator can divide the hard drive into partitions for installing the system.
      • The partition labeled / holds the core of the hierarchal directory tree.
      • A partition is further divided into small pieces called data blocks, which hold the actual data for the file.
    • Managing Files from More Than One Directory
      • Each partition holds a single file system and has a set of unique inode numbers for that partition.
      • The inode contains the whole of a file, including its descriptive characteristics and the addresses of the blocks where the file data resides.
    • Moving and Removing Directories and their Contents
      • Renaming a directory only changes the name of the directory, the inode number and its location remains unchanged.
      • A directory can also be moved from a different location in the hierarchal file structure without affecting the child contents of the directory.
      • The “rmdir” command is used for removing an empty directory.
      • The “–r” option instructs the rm command to recursively remove file.
      Moving and Removing Directories and their Contents
    • Summary
      • Files reside in one or more data blocks on the hard drive.
      • Each file in a directory is assigned a unique inode.
      • A directory is a special kind of file with very specific contents, namely the names of files and directories, each with its associated inode number.
      • The passwd file holds the location of a user’s home directory.
    • Summary
      • The mkdir command is used for creating remote directories.
      • The tilde (~) is interpreted as the user’s home directory.
      • The name .. (dot-dot) is interpreted as the parent directory.
      • The “rm –r dirname” command recursively removes the contents of the directory specified.