Files Reference

Chapter 5. Directories

Directories contain directory entries. Each entry contains a file or subdirectory name and an i-node (index node reference) number. To increase speed and enhance the use of disk space, the data in a file is stored at various locations throughout the computer's memory. The i-node contains the addresses used to locate all of the scattered blocks of data associated with a file. The i-node also records other information about the file, including time of modification and access, access modes, number of links, file owner, and file type. It is possible to link several names for a file to the same i-node by creating directory entries with the ln command.

Because directories often contain information that should not be available to all users of the system, directory access can be protected. See "File Ownership and User Groups" in AIX Version 4.3 System User's Guide: Operating System and Devices for more information.

Understanding Types of Directories

Directories can be defined by the system or the system administrator, or you can define your own directories. The system-defined directories contain specific kinds of system files, such as commands. At the top of the file system hierarchy is the system-defined root directory. The root directory is represented by a / (slash) and usually contains the following standard system-related directories:

/bin	Symbolic link to the /usr/bin directory. In prior UNIX file systems, the /bin directory contained user commands that now reside in /usr/bin in the new file structure.
/dev	Contains device nodes for special files for local devices. The /dev directory contains special files for tape drives, printers, disk partitions, and terminals.
/etc	Contains configuration files that vary for each machine. Examples include: /etc/hosts /etc/passwd The /etc directory contains the files generally used in system administration. Most of the commands that used to reside in the /etc directory now reside in the /usr/sbin directory. However, for compatibility, it contains symbolic links to the new locations of some executable files. Examples include: /etc/chown is a symbolic link to the /usr/bin/chown. /etc/exportvg is a symbolic link to the /usr/sbin/exportvg.
/export	Contains the directories and files on a server that are for remote clients.
/home	Serves as a mount point for a file system containing user home directories. The /home file system contains per-user files and directories. In a standalone machine, a separate local file system is mounted over the /home directory. In a network, a server might contain user files that should be accessible from several machines. In this case, the server's copy of the /home directory is remotely mounted onto a local /home file system.
/lib	Symbolic link to the /usr/lib directory, which contains architecture-independent libraries with names in the form *lib.a**.
/sbin	Contains files needed to boot the machine and mount the /usr file system. Most of the commands used during booting come from the boot image's RAM disk file system; therefore, very few commands reside in the /sbin directory.
/tmp	Serves as a mount point for a file system that contains system-generated temporary files.
/u	Symbolic link to the /home directory.
/usr	Serves as a mount point for a file system containing files that do not change and can be shared by machines (such as executables and ASCII documentation). Standalone machines mount a separate local file system over the /usr directory. Diskless and disk-poor machines mount a directory from a remote server over the /usr file system.
/var	Serves as a mount point for files that vary on each machine. The /var file system is configured as a file system since the files it contains tend to grow. For example, it is a symbolic link to the /usr/tmp directory, which contains temporary work files.

Some directories, such as your login or home directory ($HOME), are defined and customized by the system administrator. When you log in to the operating system, the login directory is the current directory. If you change directories using the cd command without specifying a directory name, the login directory becomes the current directory.

Related Information

Files, Directories, and File Systems for Programmers in AIX General Programming Concepts: Writing and Debugging Programs introduces i-nodes, file space allocation, and file, directory, and file system subroutines.

File Systems and Directories Overview in AIX Version 4.3 System User's Guide: Operating System and Devices introduces files and directories and the commands that control them.