Default Directories for Root (/) and /usr File Systems

Table 40-1 describes all the directories contained in the default root (/) and /usr file systems.

Table 40-1 //usr (1 of 6)

Directory	Description
Directories in the root (/) file system:
/	Root of the overall file system name space
/dev	Primary location for special files
/dev/dsk	Block disk devices
/dev/pts	pty slave devices
/dev/rdsk	Raw disk devices

Table 40-1 //usr (2 of 6)

Directory	Description
/dev/rmt	Raw tape devices
/dev/sad	Entry points for the STREAMS Administrative Driver
/dev/term	Terminal devices
/etc	Host-specific system administrative configuration files and databases
/etc/acct	Accounting system configuration information
/etc/cron.d	Configuration information for cron
/etc/default	Defaults information for various programs
/etc/dfs	Configuration information for exported file systems
/etc/fs	Binaries organized by file system types for operations required before /usr is mounted.
/etc/inet	Configuration files for Internet services
/etc/init.d	Scripts for changing between run levels
/etc/lp	Configuration information for the printer subsystem
/etc/mail	Mail subsystem configuration
/etc/net	Configuration information for TI (transport-independent) network services
/etc/opt	Configuration information for optional packages
/etc/rc0.d	Scripts for entering/leaving run level 0
/etc/rc1.d	Scripts for entering/leaving run level 1
/etc/rc2.d	Scripts for entering/leaving run level 2
/etc/rc3.d	Scripts for entering/leaving run level 3
/etc/rcS.d	Scripts for bringing the system up in single user mode
/etc/saf	Service access facility files (including FIFOs)
/etc/skel	Default profile scripts for new user accounts
/etc/sm	Status monitor information
/etc/sm.bak	Backup copy of status monitor information
/etc/tm	Trademark files; contents displayed at boot time

Table 40-1 //usr (3 of 6)

Directory	Description
/etc/uucp	uucp configuration information
/export	Default root of the exported file system tree
/home	Default root of a subtree for user directories
/kernel	Subtree of platform-independent loadable kernel modules required as part of the boot process. It includes the generic part of the core kernel that is platform independent, /kernel/genunix. See Table 40-2 for the /kernel directory structure.
/mnt	Convenient, temporary mount point for file systems
/opt	Root of a subtree for add-on application packages
/opt/SUNWspro	Mount/installation point for unbundled language products
/sbin	Essential executables used in the booting process and in manual system failure recovery
/stand	Standalone programs
/tmp	Temporary files; cleared during boot sequence
/usr	Mount point for /usr file system
/var	Root of a subtree of varying files
/var/adm	System logging and accounting files
/var/crash	Default depository for kernel crash dumps
/var/cron	cron's log file
/var/lp	Line printer subsystem logging information
/var/mail	Directory where users' mail is kept
/var/news	Community service messages (note: not the same as USENET-style news)
/var/nis	NIS+ databases
/var/opt	Root of a subtree for varying files associated with software packages
/var/preserve	Backup files for vi and ex

Table 40-1 //usr (4 of 6)

Directory	Description
/var/sadm	Databases maintained by the software package management utilities
/var/saf	saf (service access facility) logging and accounting files
/var/spool	Directories for spooled temporary files
/var/spool/cron	cron and at spool files
/var/spool/locks	Spooling lock files
/var/spool/lp	Line printer spool files
/var/spool/mqueue	Mail queued for delivery
/var/spool/pkg	Spooled packages
/var/spool/uucp	Queued uucp jobs
/var/spool/uucppublic	Files deposited by uucp
/var/tmp	Directory for temporary files; not cleared during boot sequence
/var/uucp	c log and status files
/var/yp	NIS databases (for backwards compatibility with NIS and unnecessary after full transition to NIS+)
Directories in the /usr file system
bin	Location for standard system commands
demo	Demo programs and data
games	An empty directory, which is a remnant of the SunOS 4.x software
include	Header files (for C programs, etc.)
kernel	Additional modules
kvm	Implementation architecture-specific binaries and libraries

Table 40-1 //usr (5 of 6)

Directory	Description
lib	Various program libraries, architecture-dependent databases, and binaries not invoked directly by the user
lib/acct	Accounting scripts and binaries
lib/class	Scheduling class-specific directories containing executables for priocntl and dispadmin commands
lib/font	troff font description files
lib/fs	File system type-dependent modules; not invoked directly by the user
lib/iconv	Conversion tables for iconv(1)
lib/libp	Profiled libraries
lib/locale	Internationalization localization databases
lib/lp	Line printer subsystem databases and back-end executables
lib/mail	Auxiliary programs for the mail subsystem
lib/netsvc	Internet network services
lib/nfs	Auxiliary programs and daemons related to NFS
lib/pics	PIC archives needed to build the run-time linker
lib/refer	Auxiliary refer-related programs
lib/sa	Scripts and commands for the system activity report package
lib/saf	Auxiliary programs and daemons related to the service access facility
lib/uucp	Auxiliary uucp-related programs and daemons
lib/zoneinfo	Time zone information
local	Commands local to a site
old	Programs that are being phased out
openwin	Mount/installation point for OpenWindows software
sadm	Various files and directories related to system administration; see specifics below

Table 40-1 //usr (6 of 6)

Directory	Description
sadm/bin	"valtools" binaries for use by FMLI scripts
sadm/install	Executables and scripts for pkg management
sbin	Executables for system administration
sbin/static	Statically linked version of selected programs from /usr/bin and /usr/sbin
share	Architecture-independent sharable files
share/lib	Architecture-independent databases
share/lib/keytables	Keyboard layout description tables
share/lib/mailx	mailx-related help files
share/lib/nterm	nroff terminal tables
share/lib/pub	Various data files
share/lib/spell	Auxiliary spell-related databases and scripts
share/lib/tabset	Tab setting escape sequences
share/lib/terminfo	terminfo-style terminal description files
share/lib/tmac	[nt]roff macro packages
share/src	Source code for kernel, libraries, and utilities
ucb	Berkeley compatibility package binaries
ucbinclude	Berkeley compatibility package header files
ucblib	Berkeley compatibility package libraries

The /kernel Directory

The /kernel directory contains platform-dependent information that needs to reside in the root (/) file system. These directories are described in Table 40-2.

Table 40-2 /kernel

Directory	Description
/platform	Subtree of platform-specific objects which need to reside on the root filesystem. It contains a series of directories, one per supported platform. The semantics of the series of directories is equivalent to root (/).
/platform/*/kernel	Platform-dependent objects with semantics equivalent to /kernel. It includes the file unix, the core kernel that is platform dependent. See kernel(1M).
/platform/*/lib	Platform-dependent objects with semantics equivalent to /lib.
/platform/*/sbin	Platform-dependent objects with semantics equivalent to /sbin.

The Structure of UFS File System Cylinder Groups

When you create a UFS file system, the disk slice is divided into cylinder groups, which are then divided into blocks to control and organize the structure of the files within the cylinder group. A cylinder group has one or more consecutive disk cylinders. Each type of block has a specific function in the file system. A UFS file system has these four types of blocks:

• Boot block - Used to store information used when booting the system
• Superblock - Used to store much of the information about the file system
• Inode - Used to store all information about a file except its name
• Storage or data block - Used to store data for each file

This section provides additional information about the organization and function of these blocks.

The Boot Block

The boot block stores the procedures used in booting the system. If a file system is not to be used for booting, the boot block is left blank. The boot block appears only in the first cylinder group (cylinder group 0) and is the first 8 Kbytes in a slice.

The Superblock

The superblock stores much of the information about the file system. A few of the more important things it contains are:

• Size and status of the file system
• Label (file system name and volume name)
• Size of the file system logical block
• Date and time of the last update
• Cylinder group size
• Number of data blocks in a cylinder group
• Summary data block
• File system state: clean, stable, or active
• Path name of the last mount point

The superblock is located at the beginning of the disk slice, and is replicated in each cylinder group. Because the superblock contains critical data, multiple superblocks are made when the file system is created. Each of the superblock replicas is offset by a different amount from the beginning of its cylinder group. For multiple-platter disk drives, the offsets are calculated so that a superblock appears on each platter of the drive. That way, if the first platter is lost, an alternate superblock can always be retrieved. Except for the leading blocks in the first cylinder group, the leading blocks created by the offsets are used for data storage.

A summary information block is kept with the superblock. It is not replicated, but is grouped with the first superblock, usually in cylinder group 0. The summary block records changes that take place as the file system is used, and lists the number of inodes, directories, fragments, and storage blocks within the file system.

Inodes

An inode contains all the information about a file except its name, which is kept in a directory. An inode is 128 bytes. The inode information is kept in the cylinder information block, and contains:

• The type of the file

  · Regular

  · Directory

  · Block special

  · Character special

  · Symbolic link

  · FIFO, also known as named pipe

  · Socket

• The mode of the file (the set of read-write-execute permissions)
• The number of hard links to the file
• The User ID of the owner of the file
• The Group ID to which the file belongs
• The number of bytes in the file
• An array of 15 disk-block addresses
• The date and time the file was last accessed
• The date and time the file was last modified
• The date and time the file was created

The array of 15 disk addresses (0 to 14) point to the data blocks that store the contents of the file. The first 12 are direct addresses; that is, they point directly to the first 12 logical storage blocks of the contents of the file. If the file is larger than 12 logical blocks, the 13th address points to an indirect block, which contains direct block addresses instead of file contents. The 14th address points to a double indirect block, which contains addresses of indirect blocks. The 15th address is for triple indirect addresses, if they are ever needed. Figure 40-1 shows this chaining of address blocks starting from the inode.

Figure 40-1

Data Blocks

The rest of the space allocated to the file system is occupied by data blocks, also called storage blocks. The size of these data blocks is determined at the time a file system is created. Data blocks are allocated, by default, in two sizes: an 8-Kbyte logical block size, and a 1-Kbyte fragmentation size.

For a regular file, the data blocks contain the contents of the file. For a directory, the data blocks contain entries that give the inode number and the file name of the files in the directory.

Free Blocks

Blocks not currently being used as inodes, as indirect address blocks, or as storage blocks are marked as free in the cylinder group map. This map also keeps track of fragments to prevent fragmentation from degrading disk performance.

To give you an idea of the appearance of a typical UFS file system, Figure 40-2 shows a series of cylinder groups in a generic UFS file system.

Figure 40-2

Deciding on Custom File System Parameters

Before you choose to alter the default file system parameters assigned by the newfs command, you need to understand them. This section describes each of these parameters:

• Block size
• Fragment size
• Minimum free space
• Rotational delay
• Optimization type
• Number of inodes

Logical Block Size

The logical block size is the size of the blocks that the UNIX kernel uses to read or write files. The logical block size is usually different from the physical block size (usually 512 bytes), which is the size of the smallest block that the disk controller can read or write.

You can specify the logical block size of the file system. After the file system is created, you cannot change this parameter without rebuilding the file system. You can have file systems with different logical block sizes on the same disk.

By default, the logical block size is 8192 bytes (8 Kbytes) for UFS file systems. The UFS file system supports block sizes of 4096 or 8192 bytes (4 or 8 Kbytes). 8 Kbytes is the recommended logical block size.

To choose the best logical block size for your system, consider both the performance desired and the available space. For most UFS systems, an 8-Kbyte file system provides the best performance, offering a good balance between disk performance and use of space in primary memory and on disk.

As a general rule, to increase efficiency, use a larger logical block size for file systems where most of the files are very large. Use a smaller logical block size for file systems where most of the files are very small. You can use the quot -c file-system command on a file system to display a complete report on the distribution of files by block size.

Fragment Size

As files are created or expanded, they are allocated disk space in either full logical blocks or portions of logical blocks called fragments. When disk space is needed to hold a data for a file, full blocks are allocated first, and then one or more fragments of a block are allocated for the remainder. For small files allocation begins with fragments.

The ability to allocate fragments of blocks to files, rather than just whole blocks, saves space by reducing fragmentation of disk space resulting from unused holes in blocks.

You define the fragment size when you create a UFS file system. The default fragment size is 1 Kbyte. Each block can be divided into 1, 2, 4, or 8 fragments, which results in fragment sizes from 8192 bytes to 512 bytes (for 4-Kbyte file systems only). The lower bound is actually tied to the disk sector size, typically 512 bytes.

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Note - The upper bound may equal the full block size, in which case the fragment is not a fragment at all. This configuration may be optimal for file systems with very large files when you are more concerned with speed than with space.

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When choosing a fragment size, look at the trade-off between time and space: a small fragment size saves space, but requires more time to allocate. As a general rule, to increase storage efficiency, use a larger fragment size for file systems where most of the files are large. Use a smaller fragment size for file systems where most of the files are small.

Minimum Free Space

The minimum free space is the percentage of the total disk space held in reserve when you create the file system. The default reserve is 10 percent. Free space is important because file access becomes less and less efficient as a file system gets full. As long as there is an adequate amount of free space, UFS file systems operate efficiently. When a file system becomes full, using up the available user space, only root can access the reserved free space.

Commands such as df report the percentage of space that is available to users, excluding the percentage allocated as the minimum free space. When the command reports that more than 100 percent of the disk space in the file system is in use, some of the reserve has been used by root.

If you impose quotas on users, the amount of space available to the users does not include the free space reserve. You can change the value of the minimum free space for an existing file system by using the tunefs command.

Rotational Delay (Gap)

The rotational delay is the expected minimum time (in milliseconds) it takes the CPU to complete a data transfer and initiate a new data transfer on the same disk cylinder. The default delay depends on the type of the disk, and is usually optimized for each disk type.

When writing a file, the UFS allocation routines try to position new blocks on the same disk cylinder as the previous block in the same file. The allocation routines also try to optimally position new blocks within tracks to minimize the disk rotation needed to access them.

To position file blocks so they are "rotationally well-behaved," the allocation routines must know how fast the CPU can service transfers and how long it takes the disk to skip over a block. Using options to the mkfs command, you can indicate how fast the disk rotates and how many disk blocks (sectors) it has per track. The allocation routines use this information to figure out how many milliseconds it takes to skip a disk block. Then using the expected transfer time (rotational delay), the allocation routines can position or place blocks so that the next block is just coming under the disk head when the system is ready to read it.

---

Note - It is not necessary to specify the rotational delay (-d option to newfs) for some devices.

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Place blocks consecutively only if your system is fast enough to read them on the same disk rotation. If the system is too slow, the disk spins past the beginning of the next block in the file and must complete a full rotation before the block can be read, which takes a lot of time. You should try to specify an appropriate value for the gap so that the head is located over the appropriate block when the next disk request occurs.

You can change the value of this parameter for an existing file system by using the tunefs command. The change applies only to subsequent block allocation, not to blocks already allocated.

Optimization Type

The optimization type is either space or time.

• Space - When you select space optimization, disk blocks are allocated to minimize fragmentation and disk use is optimized. Space is the default when you set the minimum free space to less than 10 percent.
• Time - When you select time optimization, disk blocks are allocated as quickly as possible, with less emphasis on their placement. Time is the default when you set the minimum free space to 10 percent or greater. When there is enough free space, it is relatively easy to allocate disk blocks effectively, without resulting in too much fragmentation.

You can change the value of the optimization type parameter for an existing file system using the tunefs command.

Number of Bytes per Inode

The number of inodes determines the number of files you can have in the file system: one inode for each file. The number of bytes per inode determines the total number of inodes created when the file system is made: the total size of the file system divided by the number of bytes per inode. Once the inodes are allocated, you cannot change the number without re-creating the file system.

The default number of bytes per inode is 2048 bytes (2 Kbytes), which assumes the average size of each file is 2 Kbytes or greater. Most files are larger than 2 Kbytes. If you have a file system with many symbolic links, they can lower the average file size. If your file system is going to have many small files, you can give this parameter a lower value. Note, however, that having too many inodes is much better than running out of them. If you have too few inodes, you could reach the maximum number of files on a disk slice that is practically empty.

Commands for Creating a Customized File System

This section describes the two commands you use to create a customized file system:

• newfs
• mkfs

The newfs Command Syntax, Options, and Arguments

The newfs command is a friendlier version of the mkfs command that is used to create file systems. The newfs command is located in the /usr/sbin directory.

The syntax is:

newfs [-Nv] [mkfs_options] special

Table 40-3 describes the options and arguments to the newfs command.

Table 40-3 newfs

Option	Description
N	Displays the file system parameters that would be used in creating the file system without actually creating it. This option does not display the parameters used to create an existing file system.
-v	Displays the parameters that are passed to the mkfs command and creates the file system, unless used with the -N option.
mkfs-options	Use the following options to set the parameters passed to the mkfs command. The options are listed below in the order they are passed to mkfs. Separate the options with spaces without any preceding keywords.
-s size	The size of the file system in sectors. The default is automatically determined from the disk label.
-t ntrack	The number of tracks per cylinder on the disk. The default is determined from the disk label.
-b bsize	The logical block size in bytes to use for data transfers. Specify the size of 4096 or 8192 (4 or 8 Kbytes). The default is 8192 bytes (8 Kbytes).
-f fragsize	The smallest amount of disk space in bytes that is allocated to a file. Specify the fragment size in powers of two in the range from 512 to 8192 bytes. The default is 1024 bytes (1 Kbyte).

Table 40-3 newfs(Continued)

Option	Description
-c cgsize	The number of disk cylinders per cylinder group. This number must be in the range 1 to 32. The default is 16.
-m free	The minimum percentage of free disk space to allow. The default is 10 percent.
-r rpm	The speed of the disk, in revolutions per minute. The default is 3600. This parameter is converted to revolutions per second before it is passed to mkfs.
-i nbpi	The number of bytes per inode to use in computing how may inodes to create. The default is 2048.
-o opt	Optimization type to use for allocating disk blocks to files: s for space or t for time.
-a apc	The number of alternate blocks per disk cylinder (SCSI devices only) to reserve for bad block placement. The default is 0.
-d gap	(Rotational delay) The expected minimum number of milliseconds it takes the CPU to complete a data transfer and initiate a new data transfer on the same disk cylinder. The default is 4.
-d nrpos	The number of different rotation positions in which to divide a cylinder group. The default is 8.
-C maxcontig	The maximum number of blocks, belonging to one file, that will be allocated contiguously before inserting a rotational delay. The default varies from drive to drive. Drives without internal (track) buffers (or drives/controllers that don't advertise the existence of an internal buffer) default to 1. Drives with buffers default to 7. This parameter is limited in the following way: blocksize * maxcontig must be <= maxphys maxphys is a read-only kernel variable that specifies the maximum block transfer size (in bytes) that the I/O subsystem is capable of satisfying. (This limit is enforced by mount, not by newfs or mkfs.) This parameter also controls clustering. Regardless of the value of rotdelay, clustering is enabled only when maxcontig is greater than 1. Clustering allows higher I/O rates for sequential I/O and is described in tunefs(1M).
special	The special character (raw) device file name of the partition to contain the file system. This argument is required.

Examples--newfs Command Options and Arguments

This newfs example uses the -N option to display file system information, including the backup superblocks.

# newfs -N /dev/rdsk/c0t0d0s0 /dev/rdsk/c0t0d0s0: 37260 sectors in 115 cylinders of 9 tracks, 36 sectors 19.1MB in 8 cyl groups (16 c/g, 2.65MB/g, 1216 i/g) superblock backups (for fsck -b #) at: 32, 5264, 10496, 15728, 20960, 26192, 31424, 36656, #

The Generic mkfs Command

The generic mkfs command calls a file system-specific mkfs, which then creates a file system of a specified type on a specified disk slice. Although mkfs can support different types of file systems, in practice you would use it to create UFS file systems. To make other types of file systems, you would have to write the software for the file system-specific versions of the mkfs command to use. Normally, you do not run mkfs directly; it is called by the newfs command.

This annotated example illustrates all of the arguments to the mkfs command.

The generic mkfs command is located in /usr/sbin. See mkfs(1M) for a description of the arguments and options.