path: root/share/man/man7/ffs.7

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.Dd August 25, 2019
.Dt FFS 7
.Os
.Sh NAME
.Nm ffs
.Nd Berkeley fast file system
.Sh SYNOPSIS
In the kernel configuration file:
.Cd "options FFS"
.Cd "options QUOTA"
.Cd "options SOFTUPDATES"
.Cd "options SUIDDIR"
.Cd "options UFS_ACL"
.Cd "options UFS_DIRHASH"
.Cd "options UFS_EXTATTR"
.Cd "options UFS_EXTATTR_AUTOSTART"
.Cd "options UFS_GJOURNAL"
.Pp
In
.Xr fstab 5 :
.Bd -literal -compact
/dev/disk0a	/mnt ufs rw 1 1
.Ed
.Sh DESCRIPTION
The Berkeley fast file system
provides facilities to store file system data onto a disk device.
.Nm
has been optimized over the years
for speed and reliability
and is the default
.Fx
file system.
.Ss Quotas
.Bl -tag -width 2n
.It Cd "options QUOTA"
This option allows system administrators
to set limits on disk usage
on a per-user basis.
Quotas can be used only on file systems
mounted with the
.Cm quota
option;
see
.Xr quota 1
and
.Xr edquota 8 .
.El
.Ss Soft Updates
.Bl -tag -width 2n
.It Cd "options SOFTUPDATES"
The soft updates feature tracks writes to the disk
and enforces metadata update dependencies
(e.g., updating free block maps)
to ensure that the file system remains consistent.
.Pp
To create a new file system with the soft updates
enabled,
use
.Xr newfs 8
command:
.Pp
.D1 Nm newfs Fl U Ar fs
.Pp
.Ar fs
can be either a mount point listed in
.Xr fstab 5
.Pq e.g. , Pa /usr ,
or a disk device
.Pq e.g., Pa /dev/da0a .
.Pp
It is possible to enable soft updates on an
.Em unmounted
file system by using
.Xr tunefs 8
command:
.Pp
.D1 Nm tunefs Fl n Cm enable Ar fs
.Pp
Soft updates can also add journaling that reduces the time spent by
.Xr fsck_ffs 8
cleaning up a filesystem after a crash from several minutes to a few seconds.
The journal is placed in an inode named
.Pa .sujournal ,
and is kept as a circular log of segments containing
records that describe metadata operations.
.Pp
To create a new file system with both the soft updates
and soft updates journaling enabled,
use the following command:
.Pp
.D1 Nm newfs Fl j Ar fs
.Pp
This runs
.Xr tunefs 8
command after
.Xr newfs 8
command with
.Fl U
flag enabled.
It is possible to enable soft updates journaling on an
.Em unmounted
file system by using
.Xr tunefs 8
command:
.Pp
.D1 Nm tunefs Fl j Cm enable Ar fs
.Pp
This flag automatically enables the soft updates feature
when it is not enabled.
Note that this
.Xr tunefs 8
command will fail if a file
.Pa .sujournal
already exists before enabling the soft updates journaling.
.El
.Ss File Ownership Inheritance
.Bl -tag -width 2n
.It Cd "options SUIDDIR"
For use in file sharing environments
on networks including
.Tn "Microsoft Windows"
and
.Tn "Apple Macintosh"
computers,
this option allows files on file systems
mounted with the
.Cm suiddir
option
to inherit the ownership of its directory,
i.e.,
.Dq "if it's my directory, it must be my file."
.El
.Ss Access Control Lists
.Bl -tag -width 2n
.It Cd "options UFS_ACL"
Access control lists allow the association of
fine-grained discretionary access control information
with files and directories.
This option requires the presence of the
.Dv UFS_EXTATTR
option, and it is recommended that
.Dv UFS_EXTATTR_AUTOSTART
is included as well,
so that ACLs are enabled atomically upon mounting the file system.
.El
.Pp
In order to enable support for ACLs,
two extended attributes must be available in the
.Dv EXTATTR_NAMESPACE_SYSTEM
namespace:
.Pa posix1e.acl_access ,
which holds the access ACL,
and
.Pa posix1e.acl_default ,
which holds the default ACL for directories.
If you are using file system extended attributes,
the following commands may be used to
allocate space for and create the necessary EA backing files
for ACLs in the root of each file system.
In these examples, the root file system is used;
see
.Sx "Extended Attributes"
for more details.
.Bd -literal -offset indent
mkdir -p /.attribute/system
cd /.attribute/system
extattrctl initattr -p / 388 posix1e.acl_access
extattrctl initattr -p / 388 posix1e.acl_default
.Ed
.Pp
On the next mount of the root file system,
the attributes will be automatically started if
.Dv UFS_EXTATTR_AUTOSTART
is included in the kernel configuration,
and ACLs will be enabled.
.Ss Directory Hashing
.Bl -tag -width 2n
.It Cd "options UFS_DIRHASH"
Implements a hash-based lookup scheme for directories
in order to speed up accesses to very large directories.
.El
.Ss Extended Attributes
.Bl -tag -width 2n
.It Cd "options UFS_EXTATTR"
Extended attributes allow the association of
additional arbitrary metadata with files and directories,
which can be assigned and retrieved from userland
as well as from within the kernel; see
.Xr extattrctl 8 .
.It Cd "options UFS_EXTATTR_AUTOSTART"
If this option is defined,
.Nm
will search for a
.Pa .attribute
subdirectory of the file system root during the mount operation.
If found, extended attribute support will be
automatically started for that file system.
.El
.Ss GEOM-based Journaling
.Bl -tag -width 2n
.It Cd "options UFS_GJOURNAL"
Implements a block level journaling of a UFS file system,
which is for both data and metadata.
To enable this,
create a
.Xr gjournal 8
GEOM provider for a block device by using the
following command:
.Pp
.D1 Nm gjournal label Ar da0
.Pp
In this example,
.Pa /dev/da0
is used as the target block device,
and
.Pa /dev/da0.journal
is created.
Then create a new file system by using
.Xr newfs 8
with the block level journaling flag and mount it:
.Pp
.D1 Nm newfs Fl J Ar /dev/da0.journal
.D1 Nm mount Fl o Cm async Ar /dev/da0.journal Ar /mnt
.Pp
.Cm async
option is not mandatory but recommended for better performance
because the journaling guarantees the consistency of an
.Cm async
mount.
.Pp
It is also possible to enable the block level journaling
on an existing file system.
To do so,
use
.Xr gjournal 8
utility to label the underlying block device and
.Xr tunefs 8
utility to enable the block level journaling flag:
.Pp
.D1 Nm gjournal label Ar da0
.D1 Nm tunefs Fl J Cm enable Ar /dev/da0.journal
.D1 Nm mount Fl o Cm async Ar /dev/da0.journal Ar /mnt
.El
.Ss Xr sysctl 8 MIBs
The following
.Xr sysctl 8
MIBs are defined for use with
.Nm :
.Bl -hang -width ".Va vfs.ffs.doreallocblk"
.It Va vfs.ffs.doasyncfree
Asynchronously write out modified i-node and indirect blocks
upon reallocating file system blocks to be contiguous.
.Pq Default: 1 .
.It Va vfs.ffs.doreallocblks
Enable support for the rearrangement of blocks
to be contiguous.
.Pq Default: 1 .
.El
.Sh SEE ALSO
.Xr quota 1 ,
.Xr acl 3 ,
.Xr extattr 3 ,
.Xr edquota 8 ,
.Xr extattrctl 8 ,
.Xr fsck_ffs 8 ,
.Xr sysctl 8 ,
.Xr tunefs 8
.Rs
.%A M. McKusick
.%A W. Joy
.%A S. Leffler
.%A R. Fabry
.%D August 1984
.%T "A Fast File System for UNIX"
.%J "ACM Transactions on Computer Systems"
.%N 2
.%V 3
.%P 181-197
.Re
.Rs
.%A M. McKusick
.%D June 2000
.%T "Soft Updates: A Technique for Eliminating Most Synchronous Writes in the Fast Filesystem"
.%J "Proceedings of the Freenix Track at the 1999 Usenix Annual Technical Conference"
.%P 71-84
.Re
.Rs
.%A M. McKusick
.%A J. Roberson
.%D May 2010
.%T "Journaled Soft-updates"
.%J "BSD Canada Conference 2010 (BSDCan)"
.Re