Manual Pages for UNIX Operating System command usage for man ufs

File Systems                                             ufs(7FS)



NAME
     ufs - UFS file system

SYNOPSIS
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DESCRIPTION
     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  con-
     tents 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  sys-
     tem. 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  modi-
                 fied  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.


     FSSTABLE    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.





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File Systems                                             ufs(7FS)



     FSBAD       Indicates that this file system contains  incon-
                 sistent 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 sys-
                 tem 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  vari-
     able  (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
     overhead.


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




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File Systems                                             ufs(7FS)



         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 mul-
              titerabyte UFS file system.

  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  transac-
              tion  log  eliminates  the need to run fsck after a
              system crash or an unclean shutdown.

         2.   UFS logging often provides  a  significant  perfor-
              mance  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 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 system. The log is  con-
     tinually  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  -




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File Systems                                             ufs(7FS)



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

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



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Uncommitted                 |
    |_____________________________|_____________________________|


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

NOTES
     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
     /usr/include/protocols/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 avail-
     able 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.







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