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System Management Concepts: Operating System and Devices


Understanding the /usr File System

The /usr file system contains executable files that can be shared among machines. The major subdirectories of the /usr directory are shown in the following diagram.

Figure 7-2. /usr File System. This diagram shows the major subdirectories of the /usr directory, which includes: /bin, ccs, /lib, /lpp, /adm and its /var/adm subdirectory, /mail and its /var/spool/mail subdirectory, and /man and its /usr/share/man subdirectory.

Figure basea24 not displayed.

On a standalone machine the /usr file system is a separate file system (in the /dev/hd2 logical volume). On a diskless machine or a machine with limited disk resources, a directory from a remote server is mounted with read-only permissions over the local /usr file system. The /usr file system contains read-only commands, libraries, and data.

Except for the contents of the /usr/share directory, the files and directories in the /usr file system can be shared by all machines of the same hardware architecture.

The /usr file system includes the following directories:

/usr/bin Contains ordinary commands and shell scripts. For example, the /usr/bin directory contains the ls, cat, and mkdir commands.
/usr/ccs Contains unbundled development package binaries.
/usr/include Contains include, or header, files.
/usr/lbin Contains executable files that are backends to commands.
/usr/lib Contains architecture-independent libraries with names of the form lib*.a. The /lib directory in / (root) is a symbolic link to the /usr/lib directory, so all files that were once in the /lib directory are now in the /usr/lib directory. This includes a few nonlibrary files for compatibility.
/usr/lpp Contains optionally installed products.
/usr/sbin Contains utilities used in system administration, including System Management Interface Tool (SMIT) commands. Most of the commands that once resided in the /etc directory now reside in the /usr/sbin directory.
/usr/share Contains files that can be shared among machines with different architectures. See Understanding the /usr/share Directory for more information.

Symbolic Links to the /var Directory


/usr/adm Symbolic link to the /var/adm directory
/usr/mail Symbolic link to the /var/spool/mail directory
/usr/news Symbolic link to the /var/news directory
/usr/preserve Symbolic link to the /var/preserve directory
/usr/spool Symbolic link to the /var/spool directory
/usr/tmp Symbolic link to the /var/tmp directory, because the /usr directory is potentially shared by many nodes and is read-only.

Symbolic Links to the /usr/share and /usr/lib Directory


/usr/dict Symbolic link to the /usr/share/dict directory
/usr/man Symbolic link to the /usr/share/man directory
/usr/lpd Symbolic link to the /usr/lib/lpd directory.


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