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ufs(7fs)

ufs(7FS)                         File Systems                         ufs(7FS)



NAME
       ufs - UFS file system

SYNOPSIS
       #include <sys/param.h>


       #include <sys/types.h>


       #include <sys/fs/ufs_fs.h>


       #include <sys/fs/ufs_inode.h>


DESCRIPTION
       UFS  is an optional disk-based file system for the Oracle Solaris envi‐
       ronment. 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 con‐
       tents replace the contents of the directory upon which it is mounted.


       Subsequent  sections  of  this  manpage provide details of the UFS file
       systems.

   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:

       FSCLEAN     Indicates an undamaged, cleanly unmounted file system.


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


       FSSTABLE    Indicates an idle mounted file system. A mounted file  sys‐
                   tem  with  this state flag indicates that neither user data
                   nor metadata would be lost if power to the system is inter‐
                   rupted.


       FSBAD       Indicates  that this file system contains inconsistent file
                   system data.


       FSLOG       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 FSACTIVE, FSSTABLE, or FSCLEAN.



       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  ter‐
       abyte.  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 overhead.


       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
                  system.

   UFS Logging
       UFS  logging bundles the multiple metadata changes that comprise a com‐
       plete UFS operation  into  a  transaction.  Sets  of  transactions  are
       recorded  in an on-disk log and are applied to the actual UFS file sys‐
       tem'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 sin‐
                  gle  updates,  thereby  reducing the number of overhead disk
                  operations.


       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 sys‐
       tem. 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).

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




       tab()  box;  cw(2.75i)  |cw(2.75i)  lw(2.75i)   |lw(2.75i)   ATTRIBUTE
       TYPEATTRIBUTE VALUE _ Interface StabilityUncommitted


SEE ALSO
       df(1M),  fsck(1M),  fsck_ufs(1M),  fstyp(1M), lockfs(1M), mkfs_ufs(1M),
       newfs(1M),   ufsdump(1M),   ufsrestore(1M),    tunefs(1M),    mount(2),
       attributes(5)


       Writing Device Drivers for Oracle Solaris 11.2

NOTES
       For  information  about  internal  UFS  structures,  see  newfs(1M) and
       mkfs_ufs(1M). For information about the  ufsdump  and  ufsrestore  com‐
       mands,   see   ufsdump(1M),   ufsrestore(1M),  and  /usr/include/proto‐
       cols/dumprestore.h.


       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 frag‐
       ments 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 frag‐
       ments and the degree of fragmentation. To correct a fragmentation prob‐
       lem, run ufsdump(1M) and ufsrestore(1M) on the ufs filesystem.



SunOS 5.11                        21 Dec 2010                         ufs(7FS)
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