filesystem(7) 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(2) 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.
8/91 Page 1
filesystem(7) filesystem(7)
/home Root of a subtree for user directories.
/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
Page 2 8/91
filesystem(7) filesystem(7)
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:
/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.
8/91 Page 3
filesystem(7) filesystem(7)
/export/exec/share The exported common /usr/share directory
tree.
/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
at(1), sh(1), vi(1), intro(4), init(1M), mknod(1M), mount(1M),
fsck(1M).
Page 4 8/91