xref: /freebsd/share/man/man5/fstab.5 (revision 1a720cbec513210fa2e85c3882741ef2f6dc5f35)

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.Dd April 14, 2014
.Dt FSTAB 5
.Os
.Sh NAME
.Nm fstab
.Nd static information about the file systems
.Sh SYNOPSIS
.In fstab.h
.Sh DESCRIPTION
The file
.Nm
contains descriptive information about the various file
systems.
.Nm
is only read by programs, and not written;
it is the duty of the system administrator to properly create
and maintain this file.
Each file system is described on a separate line;
fields on each line are separated by tabs or spaces.
The order of records in
.Nm
is important because
.Xr fsck 8 ,
.Xr mount 8 ,
and
.Xr umount 8
sequentially iterate through
.Nm
doing their thing.
.Pp
The first field,
.Pq Fa fs_spec ,
describes the special device or
remote file system to be mounted.
The contents are decoded by the
.Xr strunvis 3
function.
This allows using spaces or tabs in the device name which would be
interpreted as field separators otherwise.
.Pp
The second field,
.Pq Fa fs_file ,
describes the mount point for the file system.
For swap partitions, this field should be specified as
.Dq none .
The contents are decoded by the
.Xr strunvis 3
function, as above.
.Pp
The third field,
.Pq Fa fs_vfstype ,
describes the type of the file system.
The system can support various file system types.
Only the root, /usr, and /tmp file systems need be statically
compiled into the kernel;
everything else will be automatically loaded at mount
time.
(Exception: the FFS cannot currently be demand-loaded.)
Some people still prefer to statically
compile other file systems as well.
.Pp
The fourth field,
.Pq Fa fs_mntops ,
describes the mount options associated with the file system.
It is formatted as a comma separated list of options.
It contains at least the type of mount (see
.Fa fs_type
below) plus any additional options appropriate to the file system type.
See the options flag
.Pq Fl o
in the
.Xr mount 8
page and the file system specific page, such as
.Xr mount_nfs 8 ,
for additional options that may be specified.
All options that can be given to the file system specific mount commands
can be used in
.Nm
as well.
They just need to be formatted a bit differently.
The arguments of the
.Fl o
option can be used without the preceding
.Fl o
flag.
Other options need both the file system specific flag and its argument,
separated by an equal sign.
For example, mounting an
.Xr msdosfs 4
filesystem, the options
.Bd -literal -offset indent
-o sync -o noatime -m 644 -M 755 -u foo -g bar
.Ed
.Pp
should be written as
.Bd -literal -offset indent
sync,noatime,-m=644,-M=755,-u=foo,-g=bar
.Ed
.Pp
in the option field of
.Nm .
.Pp
If the options
.Dq userquota
and/or
.Dq groupquota
are specified,
the file system is automatically processed by the
.Xr quotacheck 8
command, and user and/or group disk quotas are enabled with
.Xr quotaon 8 .
By default,
file system quotas are maintained in files named
.Pa quota.user
and
.Pa quota.group
which are located at the root of the associated file system.
These defaults may be overridden by putting an equal sign
and an alternative absolute pathname following the quota option.
Thus, if the user quota file for
.Pa /tmp
is stored in
.Pa /var/quotas/tmp.user ,
this location can be specified as:
.Bd -literal -offset indent
userquota=/var/quotas/tmp.user
.Ed
.Pp
If the option
.Dq failok
is specified,
the system will ignore any error which happens during the mount of that filesystem,
which would otherwise cause the system to drop into single user mode.
This option is implemented by the
.Xr mount 8
command and will not be passed to the kernel.
.Pp
If the option
.Dq noauto
is specified, the file system will not be automatically
mounted at system startup.
Note that, for network file systems
of third party types
(i.e., types supported by additional software
not included in the base system)
to be automatically mounted at system startup,
the
.Va extra_netfs_types
.Xr rc.conf 5
variable must be used to extend the
.Xr rc 8
startup script's list of network file system types.
.Pp
If the option
.Dq late
is specified, the file system will be automatically mounted
at a stage of system startup after remote mount points are mounted.
For more detail about this option,
see the
.Xr mount 8
manual page.
.Pp
If the option
.Dq update
is specified, it indicates that the status of an already mounted file
system should be changed accordingly.
This allows, for example, file systems mounted read-only to be upgraded
read-write and vice-versa.
By default, an entry corresponding to a file systems that is already
mounted is going to be skipped over when processing
.Nm ,
unless it's a root file system, in which case logic similar to
.Dq update
is applied automatically.
.Pp
The
.Dq update
option is typically used in conjunction with two
.Nm
files.
The first
.Nm
file is used to set up the initial set of file systems.
The second
.Nm
file is then run to update the initial set of file systems and
to add additional file systems.
.Pp
The type of the mount is extracted from the
.Fa fs_mntops
field and stored separately in the
.Fa fs_type
field (it is not deleted from the
.Fa fs_mntops
field).
If
.Fa fs_type
is
.Dq rw
or
.Dq ro
then the file system whose name is given in the
.Fa fs_file
field is normally mounted read-write or read-only on the
specified special file.
.Pp
If
.Fa fs_type
is
.Dq sw
then the special file is made available as a piece of swap
space by the
.Xr swapon 8
command at the end of the system reboot procedure.
For swap devices, the keyword
.Dq trimonce
triggers the delivery of a
.Dv BIO_DELETE
command to the device.
This command marks the device's blocks as unused, except those that
might store a disk label.
This marking can erase a crash dump.
To delay
.Nm swapon
for a device until after
.Nm savecore
has copied the crash dump to another location, use the
.Dq late
option.
For vnode-backed swap spaces,
.Dq file
is supported in the
.Fa fs_mntops
field.
When
.Fa fs_spec
is an
.Xr md 4
device file
.Pq Do md Dc or Do md[0-9]* Dc
and
.Dq file
is specified in
.Fa fs_mntopts ,
an
.Xr md 4
device is created with the specified file used as backing store,
and then the new device is used as swap space.
Swap entries on
.Pa .eli
devices will cause automatic creation of encrypted devices.
The
.Dq ealgo ,
.Dq aalgo ,
.Dq keylen ,
.Dq notrim ,
and
.Dq sectorsize
options may be passed to control those
.Xr geli 8
parameters.
The fields other than
.Fa fs_spec
and
.Fa fs_type
are unused.
If
.Fa fs_type
is specified as
.Dq xx
the entry is ignored.
This is useful to show disk partitions which are currently unused.
.Pp
The fifth field,
.Pq Fa fs_freq ,
is used for these file systems by the
.Xr dump 8
command to determine which file systems need to be dumped.
If the fifth field is not present, a value of zero is returned and
.Nm dump
will assume that the file system does not need to be dumped.
If the fifth field is greater than 0, then it specifies the number of days
between dumps for this file system.
.Pp
The sixth field,
.Pq Fa fs_passno ,
is used by the
.Xr fsck 8
and
.Xr quotacheck 8
programs to determine the order in which file system and quota
checks are done at reboot time.
The
.Fa fs_passno
field can be any value between 0 and
.Ql INT_MAX Ns -1 .
.Pp
The root file system should be specified with a
.Fa fs_passno
of 1, and other file systems should have a
.Fa fs_passno
of 2 or greater.
A file system with a
.Fa fs_passno
value of 1 is always checked sequentially and be completed before
another file system is processed, and it will be processed before
all file systems with a larger
.Fa fs_passno .
.Pp
For any given value of
.Fa fs_passno ,
file systems within a drive will be checked sequentially,
but file systems on different drives will be checked at the
same time to utilize parallelism available in the hardware.
Once all file system checks are complete for the current
.Fa fs_passno ,
the same process will start over for the next
.Fa fs_passno .
.Pp
If the sixth field is not present or is zero,
a value of zero is returned and
.Xr fsck 8
and
.Xr quotacheck 8
will assume that the file system does not need to be checked.
.Pp
The
.Fa fs_passno
field can be used to implement finer control when
the system utilities may determine that the file system resides
on a different physical device, when it actually does not, as with a
.Xr ccd 4
device.
All file systems with a lower
.Fa fs_passno
value will be completed before starting on file systems with a
higher
.Fa fs_passno
value.
E.g. all file systems with a
.Fa fs_passno
of 2 will be completed before any file systems with a
.Fa fs_passno
of 3 or greater are started.
Gaps are allowed between the different
.Fa fs_passno
values.
E.g. file systems listed in
.Pa /etc/fstab
may have
.Fa fs_passno
values such as 0, 1, 2, 15, 100, 200, 300, and may appear in any order
within
.Pa /etc/fstab .
.Bd -literal
#define	FSTAB_RW	"rw"	/* read/write device */
#define	FSTAB_RQ	"rq"	/* read/write with quotas */
#define	FSTAB_RO	"ro"	/* read-only device */
#define	FSTAB_SW	"sw"	/* swap device */
#define	FSTAB_XX	"xx"	/* ignore totally */

struct fstab {
	char	*fs_spec;	/* block special device name */
	char	*fs_file;	/* file system path prefix */
	char	*fs_vfstype;	/* File system type, ufs, nfs */
	char	*fs_mntops;	/* Mount options ala -o */
	char	*fs_type;	/* FSTAB_* from fs_mntops */
	int	fs_freq;	/* dump frequency, in days */
	int	fs_passno;	/* pass number on parallel fsck */
};
.Ed
.Pp
The proper way to read records from
.Pa fstab
is to use the routines
.Xr getfsent 3 ,
.Xr getfsspec 3 ,
.Xr getfstype 3 ,
and
.Xr getfsfile 3 .
.Sh FILES
.Bl -tag -width /etc/fstab -compact
.It Pa /etc/fstab
The file
.Nm
resides in
.Pa /etc .
.El
.Sh EXAMPLES
.Bd -literal
# Device	Mountpoint	FStype	Options		Dump	Pass#
#
# UFS file system.
/dev/da0p2	/		ufs	rw		1	1
#
# Swap space on a block device.
/dev/da0p1	none		swap	sw		0	0
#
# Swap space using a block device with GELI encryption.
# aalgo, ealgo, keylen, sectorsize options are available
# for .eli devices.
/dev/da1p2.eli	none		swap	sw		0	0
#
# tmpfs.
tmpfs		/tmp		tmpfs	rw,size=1g,mode=1777	0 0
#
# UFS file system on a swap-backed md(4).  /dev/md10 is
# automatically created.  If it is "md", a unit number
# will be automatically selected.
md10		/scratch	mfs	rw,-s1g		0	0
#
# Swap space on a vnode-backed md(4).
md11		none		swap	sw,file=/swapfile	0 0
#
# CDROM.  "noauto" option is typically used because the
# media is removable.
/dev/cd0	/cdrom		cd9660	ro,noauto	0	0
#
# NFS-exported file system.  "serv" is an NFS server name
# or IP address.
serv:/export	/nfs		nfs	rw,noinet6	0	0
.Ed
.Sh SEE ALSO
.Xr getfsent 3 ,
.Xr getvfsbyname 3 ,
.Xr strunvis 3 ,
.Xr ccd 4 ,
.Xr dump 8 ,
.Xr fsck 8 ,
.Xr geli 8 ,
.Xr mount 8 ,
.Xr quotacheck 8 ,
.Xr quotaon 8 ,
.Xr swapon 8 ,
.Xr umount 8
.Sh HISTORY
The
.Nm
file format appeared in
.Bx 4.0 .