filesystem(7) UNIX System V filesystem(7)
NAME
filesystem - file system organization
SYNOPSIS
/
/usr
DESCRIPTION
The System V file system tree is organized for administrative
convenience. Distinct areas within the file system tree are provided for
files that are private to one machine, files that can be shared by
multiple machines of a common architecture, files that can be shared by
all machines, and home directories. This organization allows sharable
files to be stored on one machine but accessed by many machines using a
remote file access mechanism such as RFS or NFS. Grouping together
similar files makes the file system tree easier to upgrade and manage.
The file system tree consists of a root file system and a collection of
mountable file systems. The mount(1M) program attaches mountable file
systems to the file system tree at mount points (directory entries) in
the root file system or other previously mounted file systems. Two file
systems, / (the root) and /usr, must be mounted in order to have a
completely functional system. The root file system is mounted
automatically by the kernel at boot time; the /usr file system is mounted
by the /etc/rc.boot script, which is run as part of the booting process.
The root file system contains files that are unique to each machine. It
contains the following directories:
/dev Character and block special files. These device files provide
hooks into hardware devices or operating system facilities.
Typically, device files are built to match the kernel and
hardware configuration of the machine.
/dev/term Terminal devices.
/dev/pts Pseudo-terminal devices.
/dev/xt Devices used by layers.
/dev/sxt Shell layers device files used by shl.
/etc Machine-specific administrative configuration files and system
administration databases. /etc may be viewed as the home
directory of a machine, the directory that in a sense defines
the machine's identity. Executable programs are no longer
kept in /etc.
/home Root of a subtree for user directories.
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/mnt Temporary mount point for file systems. This is an empty
directory on which file systems may be temporarily mounted.
/opt Root of a subtree for add-on application packages.
/proc Root of a subtree for the process file system.
/sbin Essential executables used in the booting process and in manual
system recovery. The full complement of utilities is
available only after /usr is mounted,
/tmp Temporary files; initialized to empty during the boot
operation.
/var Root of a subtree for varying files. Varying files are files
that are unique to a machine but that can grow to an arbitrary
(that is, variable) size. An example is a log file.
/var/adm System logging and accounting files.
/var/cron cron's log file.
/var/mail Where users' mail is kept.
/var/opt Top-level directory used by application packages.
/var/preserve
Backup files for vi(1) and ex(1).
/var/spool Subdirectories for files used in printer spooling, mail
delivery, cron(1), at(1), etc.
/var/tmp Transitory files; initialized to empty during the boot
operation.
Because it is desirable to keep the root file system small and not
volatile, on disk-based systems larger file systems are often mounted on
/home, /opt, /usr, and /var.
The file system mounted on /usr contains architecture-dependent and
architecture-independent sharable files. The subtree rooted at
/usr/share contains architecture-independent sharable files; the rest of
the /usr tree contains architecture-dependent files. By mounting a
common remote file system, a group of machines with a common architecture
may share a single /usr file system. A single /usr/share file system can
be shared by machines of any architecture. A machine acting as a file
server may export many different /usr file systems to support several
different architectures and operating system releases. Clients usually
mount /usr read-only so that they don't accidentally change any shared
files. The /usr file system contains the following subdirectories:
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/usr/bin Most system utilities.
/usr/sbin Executables for system administration.
/usr/games Game binaries and data.
/usr/include
Include header files (for C programs, etc).
/usr/lib Program libraries, various architecture-dependent databases,
and executables not invoked directly by the user (system
daemons, etc).
/usr/share Subtree for architecture-independent sharable files.
/usr/share/man
Subdirectories for on-line reference manual pages (if
present).
/usr/share/lib
Architecture-independent databases.
/usr/src Source code for utilities and libraries.
/usr/ucb Berkeley compatibility package binaries.
/usr/ucbinclude
Berkeley compatibility package header files.
/usr/ucblib
Berkeley compatibility package libraries.
A machine with disks may export root file systems, swap files, and /usr
file systems to diskless or partially-disked machines that mount them
into the standard file system hierarchy. The standard directory tree for
sharing these file systems from a server is:
/export The default root of the exported file system tree.
/export/exec/architecture-name
The exported /usr file system supporting architecture-name
for the current release.
/export/exec/architecture-name.release-name
The exported /usr file system supporting architecture-name
for System V release-name.
/export/exec/share
The exported common /usr/share directory tree.
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/export/exec/share.release-name
The exported common /usr/share directory tree for System V
release-name.
/export/root/hostname
The exported root file system for hostname.
/export/swap/hostname
The exported swap file for hostname.
/export/var/hostname
The exported /var directory tree for hostname.
SEE ALSO
fsck(1M), init(1M), mknod(1M), mount(1M), intro(4)
at(1), sh(1), vi(1) in the User's Reference Manual
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