UFS(7FS) File Systems UFS(7FS)


ufs - UFS file system


#include <sys/param.h>

#include <sys/types.h>

#include <sys/fs/ufs_fs.h>

#include <sys/fs/ufs_inode.h>


UFS is the default disk-based file system for the Solaris environment.
The UFS file system is hierarchical, starting with its root directory (/)
and continuing downward through a number of directories. The root of a
UFS file system is inode 2. A UFS file system's root contents replace the
contents of the directory upon which it is mounted.

Subsequent sections of this manpage provide details of the UFS file

State Flags (fs_state and fs_clean)
UFS uses state flags to identify the state of the file system. fs_state
is FSOKAY - fs_time. fs_time is the timestamp that indicates when the
last system write occurred. fs_state is updated whenever fs_clean
changes. Some fs_clean values are:

Indicates an undamaged, cleanly unmounted file system.

Indicates a mounted file system that has modified data in
memory. A mounted file system with this state flag indicates
that user data or metadata would be lost if power to the
system is interrupted.

Indicates an idle mounted file system. A mounted file system
with this state flag indicates that neither user data nor
metadata would be lost if power to the system is interrupted.

Indicates that this file system contains inconsistent file
system data.

Indicates that the file system has logging enabled. A file
system with this flag set is either mounted or unmounted. If
a file system has logging enabled, the only flags that it can
have are FSLOG or FSBAD. A non-logging file system can have

It is not necessary to run the fsck command on unmounted file systems
with a state of FSCLEAN, FSSTABLE, or FSLOG. mount(2) returns ENOSPC if
an attempt is made to mount a UFS file system with a state of FSACTIVE
for read/write access.

As an additional safeguard, fs_clean should be trusted only if fs_state
contains a value equal to FSOKAY - fs_time, where FSOKAY is a constant
integer defined in the /usr/include/sys/fs/ufs_fs.h file. Otherwise,
fs_clean is treated as though it contains the value of FSACTIVE.

Extended Fundamental Types (EFT)
Extended Fundamental Types (EFT) provide 32-bit user ID (UID), group ID
(GID), and device numbers.

If a UID or GID contains an extended value, the short variable (ic_suid,
ic_sgid) contains the value 65535 and the corresponding UID or GID is in
ic_uid or ic_gid. Because numbers for block and character devices are
stored in the first direct block pointer of the inode (ic_db[0]) and the
disk block addresses are already 32 bit values, no special encoding
exists for device numbers (unlike UID or GID fields).

Multiterabyte File System

A multiterabyte file system enables creation of a UFS file system up to
approximately 16 terabytes of usable space, minus approximately one
percent overhead. A sparse file can have a logical size of one terabyte.
However, the actual amount of data that can be stored in a file is
approximately one percent less than one terabyte because of file system

On-disk format changes for a multiterabyte UFS file system include:

o The magic number in the superblock changes from FS_MAGIC to
MTB_UFS_MAGIC. For more information, see the
/usr/include/sys/fs/ufs_fs file.

o The fs_logbno unit is a sector for UFS that is less than 1
terabyte in size and fragments for a multiterabyte UFS file

UFS Logging

UFS logging bundles the multiple metadata changes that comprise a
complete UFS operation into a transaction. Sets of transactions are
recorded in an on-disk log and are applied to the actual UFS file
system's metadata.

UFS logging provides two advantages:

1. A file system that is consistent with the transaction log
eliminates the need to run fsck after a system crash or an
unclean shutdown.

2. UFS logging often provides a significant performance
improvement. This is because a file system with logging
enabled converts multiple updates to the same data into single
updates, thereby reducing the number of overhead disk

The UFS log is allocated from free blocks on the file system and is sized
at approximately 1 Mbyte per 1 Gbyte of file system, up to 256 Mbytes.
The log size may be larger (up to a maximum of 512 Mbytes), depending
upon the number of cylinder groups present in the file system. The log is
continually flushed as it fills up. The log is also flushed when the file
system is unmounted or as a result of a lockfs(1M) command.

Mounting UFS File Systems

You can mount a UFS file system in various ways using syntax similar to
the following:

1. Use mount from the command line:

# mount -F ufs /dev/dsk/c0t0d0s7 /export/home

2. Include an entry in the /etc/vfstab file to mount the file
system at boot time:

/dev/dsk/c0t0d0s7 /dev/rdsk/c0t0d0s7 /export/home ufs 2 yes -

For more information on mounting UFS file systems, see mount_ufs(1M).


See attributes(5) for a description of the following attributes:

|Interface Stability | Uncommitted |


df(1M), fsck(1M), fsck_ufs(1M), fstyp(1M), lockfs(1M), mkfs_ufs(1M),
newfs(1M), ufsdump(1M), ufsrestore(1M), tunefs(1M), mount(2),

Writing Device Drivers


For information about internal UFS structures, see newfs(1M) and
mkfs_ufs(1M). For information about the ufsdump and ufsrestore commands,
see ufsdump(1M), ufsrestore(1M), and

If you experience difficulty in allocating space on the ufs filesystem,
it may be due to framentation. Fragmentation can occur when you do not
have sufficient free blocks to satisfy an allocation request even though
df(1M) indicates that enough free space is available. (This may occur
because df only uses the available fragment count to calculate available
space, but the file system requires contiguous sets of fragments for most
allocations). If you suspect that you have exhausted contiguous
fragments on your file system, you can use the fstyp(1M) utility with
the -v option. In the fstyp output, look at the nbfree (number of
blocks free) and nffree (number of fragments free) fields. On unmounted
filesystems, you can use fsck(1M) and observe the last line of output,
which reports, among other items, the number of fragments and the degree
of fragmentation. To correct a fragmentation problem, run ufsdump(1M) and
ufsrestore(1M) on the ufs filesystem.

June 18, 2009 UFS(7FS)