fstab(4) fstab(4)
NAME
fstab - static information about filesystems
DESCRIPTION
The file /etc/fstab describes the filesystems and swapping partitions
used by the local machine. The system administrator can modify it with a
text editor. It is read by commands that mount, unmount, and check the
consistency of filesystems. The file consists of a number of lines of
the form:
filesystem directory type options frequency pass
For example:
/dev/root / xfs rw 0 0
Fields are separated by white space; a `#' as the first non-white space
character indicates a comment.
The entries from this file are accessed using the routines in
getmntent(3), which return a structure of the following form:
struct mntent {
char *mnt_fsname; /* filesystem name */
char *mnt_dir; /* filesystem path prefix */
char *mnt_type; /* e.g. xfs, nfs, proc, or ignore */
char *mnt_opts; /* rw, ro, hard, soft, etc. */
int mnt_freq; /* dump frequency, in days */
int mnt_passno; /* parallel fsck pass number */
};
This structure is defined in the <mntent.h> include file. To compile and
link a program that calls getmntent(3), follow the procedures for section
(3Y) routines as described in intro(3).
The mnt_dir field is the full pathname of the directory to be mounted on.
The mnt_type field determines how the mnt_fsname and mnt_opts fields are
interpreted. Here is a list of the filesystem types currently supported,
and the way each of them interprets these fields:
xfs mnt_fsname must be a block special device (for example,
/dev/root) or a logical volume.
efs mnt_fsname must be a block special device (for example,
/dev/root) or a logical volume.
proc mnt_fsname should be the /proc directory. See proc(4).
fd mnt_fsname should be the /dev/fd directory. See fd(4).
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hwgfs mnt_fsname should be the /hw directory. See hwgfs(4).
nfs mnt_fsname is the path on the server of the directory to be
served. (NFS option only).
cdfs A synonym for type iso9660 (see below). This type is required
for MIPS ABI compliance.
iso9660 mnt_fsname formerly was a generic SCSI device. With 6.2 plus
patches, or later releases, it is the volume partition of the
raw disk (for example, /dev/rdsk/dks0d7vol). See ds(7M). This
filesystem type is used to mount CD-ROM discs in ISO 9660 (with
or without Rock Ridge extensions) and High Sierra formats.
eoe.sw.cdrom must be installed in order to use the iso9660
filesystem type.
dos mnt_fsname is normally a floppy device, or other removable
media using the disk driver. These are located in the
directory /dev/rdsk (for example, /dev/rdsk/fds0d2.3.5). See
dksc(7M) and smfd(7M).
hfs mnt_fsname must be either a floppy device or a raw disk device.
Floppy devices are located in the directory /dev/rdsk (for
example, /dev/rdsk/fds0d2.3.5hi). See smfd(7M). Raw disk
devices are located in the directory /dev/rdsk (for example,
/dev/rdsk/dks0d4vol). See ds(7M).
swap mnt_fsname should be the full pathname to the file or block
device to be used as a swap resource.
cachefs mnt_fsname should be the filesystem name for the backing
filesystem to be mounted as a cache filesystem. This will
either be the special filename (for example, /dev/dsk/dks0d4s7)
or host:path.
rawdata mnt_fsname may be the block/char special device of the
partition or logical volume to reserve (mnt_dir is ignored).
This entry enables the system utilities (for example, mkfs,
mount, and so on) to treat the raw partition or logical volume
as 'mounted', preventing the partition from inadvertently being
overwritten. Any packages that require dedicated raw
partitions (databases and so on) should consider placing a
rawdata entry in fstab(4).
If the mnt_type is specified as ignore, then the entry is ignored. This
is useful to show disk partitions not currently used. mnt_freq is not
used in current IRIX systems.
mnt_passno can be used to control the behavior of parallel filesystem
checking on bootup, see fsck(1M).
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The mnt_opts field contains a list of comma-separated option words. Some
mnt_opts are valid for all filesystem types, while others apply to a
specific type only.
Options valid on all filesystems (the default is rw) are:
rw Read/write.
ro Read-only.
noauto Ignore this entry during a mount -a command, to allow the
definition of fstab entries for commonly-used filesystems that
should not be automatically mounted.
grpid Causes a file created within the filesystem to have the group
ID of its parent directory, not the creating process's group
ID.
nosuid Setuid execution not allowed for non-superusers. This option
has no effect for the superuser.
nodev Access to character and block special files is disallowed.
mac-default=label
On systems with Mandatory Access Control, use the specified
label for all files on the specified file system that do not
have a MAC label.
mac-ip=label
On systems with Mandatory Access Control, use the specified
label for communications to other systems regarding this file
system.
A number of filesystem types also support the debug option, but the
meaning varies with the filesystem type.
Options specific only to xfs, efs and nfs filesystems are:
quota Disk quota accounting enabled, and limits enforced.
Options specific to xfs filesystems are:
biosize The biosize (buffered I/O size) option can be used to set the
default preferred buffered I/O size for filesystem. The
default preferred I/O size is 64K. The biosize option can be
used to decrease the preferred I/O size. The size must be
expressed as the log (base2) of the desired I/O size. Valid
values for this option are 14 through 16, inclusive (e.g. 16K,
32K, and 64K bytes). On machines with 4K size pages, 13 (8
Kbytes) is also a valid size. The preferred buffered I/O size
can also be altered on a per-file basis using the fcntl system
call. See fcntl(2) for further details.
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dmi Enable the Data Management Interface event callouts.
logbufs Set the number of in memory log buffers. Valid numbers range
from 2-8 inclusive. The default value is 8 buffers for
filesystems with a blocksize of 64K, 4 buffers for filesystems
with a blocksize of 32K, 3 buffers for filesystems with a
blocksize of 16K, and 2 buffers for all other configurations.
Increasing the number of buffers may increase performance on
some workloads at the cost of the memory used for the extra log
buffers and their associated control structures.
noalign Data allocations will not be aligned at stripe unit boundaries.
noatime Access timestamps are not updated when a file is read.
norecovery
The filesystem will be mounted without running log recovery.
If the filesystem was not cleanly unmounted, it is likely to be
inconsistent when mounted in norecovery mode. Some files or
directories may not be accessible because of this. Filesystems
mounted norecovery must be mounted read-only or the mount will
fail.
osyncisdsync
Make writes to files opened with the O_SYNC flag set behave as
if the O_DSYNC flag had been used instead. This can result in
better performance without compromising data safety. However
if this option in effect, timestamp updates from O_SYNC writes
can be lost if the system crashes.
qnoenforce
Disk quota accounting enabled, but limits are not enforced.
sunit=value
Used to specify the stripe unit for a RAID device or a xlv
stripe volume. value has to be specified in 512-byte block
units. If this option is not specified and the filesystem was
made on a stripe volume or the stripe unit was specified for
the RAID device at mkfs time, then the mount system call will
restore the value from the superblock. For filesystems that are
made directly on RAID devices, this option can be used to
override the information in the superblock if the underlying
disk layout changes after the filesystem has been mkfsed. If
the filesystem is made on a xlv volume, then this will be done
implicitly.
swidth=value
Used to specify the stripe width for a RAID device or a xlv
stripe volume. value has to be specified in 512-byte block
units. If this option is not specified, and the filesystem was
made on a stripe volume or the stripe width was specified for
the RAID device at mkfs time, then the mount system call will
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restore the value from the superblock. For filesystems that are
made directly on RAID devices, this option can be used to
override the information in the superblock if the underlying
disk layout changes after the filesystem has been mkfsed. If
the filesystem is made on a xlv volume, then this will be done
implicitly. This option is required if the -o sunit option has
been specified. Also it has to be a multiple of the sunit
option.
wsync All operations that modify the filesystem are synchronous
except for writes to user files (e.g. create, unlink, mv,
truncate, etc.). This option can be used in conjunction with
exporting a filesystem -wsync to obtain NFS write-synchronous
semantics, if so desired. See exports(4) for further
information.
Options specific to efs filesystems (the default is fsck, noquota) are:
raw=path The filesystem's raw device pathname (for example, /dev/rroot).
fsck fsck(1M) invoked with no filesystem arguments should check this
filesystem.
nofsck fsck(1M) should not check this filesystem by default.
noquota Disk quota accounting and limit enforcement disabled.
lbsize=n The number of bytes transferred in each read or synchronous
write operation.
The value assigned to the lbsize option must be a power of two
at least as large as the system page size. This value is
returned by the getpagesize(2) system call and is normally
either 4096 or 16384 depending on the system type. The current
default for lbsize is the value in the fs_sectors field of the
superblock of the filesystem. This was normally the number of
"sectors per track" in the past, but that often fictious value
is no longer used. If not set on the mkfs command line, the
maximum value of 128 sectors is used by IRIX 6.4 and later
releases. An invalid size will cause the mount to fail with
the error EINVAL. The maximum size is currently 65536. Note
that less than lbsize bytes will be transferred if there are
not lbsize contiguous bytes of the addressed portion of the
file on disk.
Options specific to dos filesystems.
partition
With a following number, as partition,#, where # is most often
either 1 or 4, is used with type 5 (extended) filesystems to specify
which partition to use. Otherwise type 5 filesystems are not
supported.
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Options specific to iso9660 filesystems (the default is rw, which has no
effect since CD-ROM discs are always read-only) are:
setx Set execute permission on every file on the mounted filesystem.
The default is to make an intelligent guess based on the first
few bytes of the file.
notranslate
Don't translate ISO 9660 filenames to UNIX filenames. The
default is to convert upper case to lower case and to truncate
the part including and after the semicolon.
cache=blocks
Set the number of 2048 byte blocks to be used for caching
directory contents. The default is to cache 128 blocks.
noext Ignore Rock Ridge extensions. The default when the noext
option is not specified is to use Rock Ridge extensions if
present.
susp Enable processing of System Use Sharing Protocol extensions to
the ISO 9660 specification. This is the default.
nosusp Disable processing of System Use Sharing Protocol extensions.
This has the same effect as the noext option.
rrip Enable processing of the Rock Ridge extensions. This is the
default.
norrip Disable processing of the Rock Ridge extensions. This is
equivalent to the noext option.
nmconv=[clm]
This option is supplied for MIPS ABI compliance; some non-IRIX
systems may implement it only for type cdfs, IRIX allows it
with type iso9660 also. Only one of the three letters c, l, or
m can be specified. This option controls filename translation.
c has the same meaning as notranslate above. l requests
translation to lower case (the IRIX default), and m suppresses
the version number (also the IRIX default).
NFS clients can mount iso9660, dos, and hfs filesystems remotely by
specifying hostname:mountpoint for filesystem and nfs for type, where an
iso9660, dos, or hfs filesystem is mounted at mountpoint on the host
hostname. In this case, the same options apply as with nfs (see below).
If the NFS option is installed, the following options are valid for nfs
filesystems:
vers=n Use NFS protocol version n. (The default is to try version 3,
falling back to version 2 if the version 3 mount fails.)
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bg If the first attempt fails, retry in the background.
fg Retry in foreground. (Default)
retry=n Set number of mount failure retries to n. (Default = 10000)
rsize=n Set read transfer size to n bytes. This value will be rounded
up to the nearest multiple of 512 bytes. The default is 8192
for NFS version 2, and 16384 or 32768 for NFS version 3. The
16KB transfer size is used when the route to the server is
known to go through a router, or when the Maximum Transmission
Unit (MTU) of the interface used to get to the server is
Ethernet-sized (about 1500 bytes) or less. The system tunable
nfs3defaultxfer can be used to reduce the upper limit of the
NFS version 3 transfer size if 16KB is still too much for
routers. For example, setting it to 8192 gives the same
default for version 3 as version 2. For NFS version 3, the
read transfer size specified by the server will be used if it
is smaller than either the default or what the user has
specified.
wsize=n Set write transfer size to n bytes. This value will be rounded
up to the nearest multiple of 512 bytes. The default is the
same as for the read size. For NFS version 3, the write
transfer size specified by the server will be used if it is
smaller than either the default or what the user has specified.
timeo=n Set NFS timeout to n tenths of a second. (Default = 11)
retrans=n Set number of NFS retransmissions to n. (Default = 5)
port=n Set server UDP port number to n. (Default = 2049)
hard Retry request until server responds. (Default)
soft Return error if server doesn't respond.
nointr Disallow requests to be interrupted by the following signals:
SIGHUP, SIGINT, SIGQUIT, SIGKILL, SIGTERM, and SIGTSTP.
(Requests are interruptible by these signals, by default.)
acregmin=t
Set the regular file minimum attribute cache timeout to t
seconds. (Default = 3)
acregmax=t
Set the regular file maximum attribute cache timeout to t
seconds. (Default = 60)
acdirmin=t
Set the directory minimum attribute cache timeout to t seconds.
(Default = 30)
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acdirmax=t
Set the directory maximum attribute cache timeout to t seconds.
(Default = 60)
actimeo=t Set regular and directory minimum and maximum attribute cache
timeouts to t seconds.
noac No attribute caching.
proto=xyz Use the IP protocol xyz , where xyz is either udp or tcp . If
the specified protocol is not supported by the server, then the
mount will fail. The default is udp .
private Do not flush delayed writes on last close of an open file, and
use local file and record locking instead of a remote lock
manager.
shortuid Do not let users with userids or groupids larger than 65535
(see id(1M)) create or own files. Some versions of UNIX do not
support large userids; trying to create a file with a large
userid on such an NFS server can produce undefined and
surprising results.
symttl=t Set the time-to-live for symbolic links cached by NFS to t
seconds. symttl=0 turns off NFS symlink caching. The maximum
value for t is 3600. (Default = 3600)
asyncnlm Use asynchronous NLM RPC calls. The default is to use
synchronous NLM. Using this option requires that lockd(1M) be
running.
defxattr Use default values for system-defined extended attributes,
rather than asking the NFS server for their values. This option
does not work when noac is also specified.
doxattr Tell the NFS server that this client can be trusted to properly
handle extended attributes. This is necessary only when the
remote filesystem is exported with the noxattr option.
The bg option causes mount to run in the background if the server's
mountd(1M) does not respond. mount attempts each request retry=n times
before giving up.
Once the filesystem is mounted, each NFS request waits timeo=n tenths of
a second for a response. If no response arrives, the time-out is
multiplied by 2, up to a maximum of MAXTIMO (900), and the request is
retransmitted. When retrans=n retransmissions have been sent with no
reply a soft mounted filesystem returns an error on the request and a
hard mounted filesystem retries the request. Filesystems that are
mounted rw (read-write) should use the hard option. The number of bytes
in a read or write request can be set with the rsize and wsize options.
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In the absence of client activity that would invalidate recently acquired
file attributes, NFS holds attributes cached for an interval between
acregmin and acregmax for regular files, and between acdirmin and
acdirmax for directories. The actimeo option sets all attribute timeout
constraints to a given number of seconds. The noac option disables
attribute caching altogether.
The private option greatly improves write performance by caching data and
delaying writes on the assumption that only this client modifies files in
the remote filesystem. It should be used only if the greater risk of
lost delayed-write data in the event of a crash is acceptable given
better performance. EFS uses caching strategies similar to private NFS
The system reduces the risk of data loss for all filesystems by
automatically executing a partial sync(2) at regular intervals.
If the BDS option is installed, the following options are valid for nfs
filesystems that have BDS service enabled:
bds Turn on bulk data service for this file system.
bdsauto=size
For all read/write requests that are appropriated aligned and
are sized greater or equal to size, do BDS I/O instead of NFS
I/O.
bdswindow=size
Set the TCP protocol send and receive windows to size instead
of the default of 4Mbytes.
bdsbuffer=size
Specify the size of data buffers within the server, instead of
allowing the server to determine the best size.
Options specific to swap resources are:
pri=t Set the priority of the swap device to t. The legal values are
from 0 to 7 inclusive.
swplo=t Set the first 512 byte block to use to t (default is 0).
length=t Set the number of 512 byte blocks to use to t (default is
entire file/partition).
maxlength=t
Set the maximum number of 512 byte blocks to grow the swap area
to t (default is to use length).
vlength=t Set the number of virtual 512 byte blocks to claim this swap
file has to t (default is to use length).
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All other options except for noauto are ignored for swap files.
If the CacheFS option is installed, the following options are valid for
cachefs filesystems:
backfstype=file_system_type
The filesystem type of the back filesystem (for example, nfs).
Any of the following filesystem types may be used as the back
filesystem: nfs, nfs3, iso9660, dos, cdfs, kfs, or hfs. If
this option is not specified, the back filesystem type is
determined from the filesystem name. Filesystem names of the
form hostname:path will be assumed to be type nfs.
backpath=path
Specifies where the back filesystem is already mounted. If
this argument is not supplied, CacheFS determines a mount point
for the back filesystem.
cachedir=directory
The name of the cache directory.
cacheid=ID
ID is a string specifying a particular instance of a cache. If
you do not specify a cache ID, CacheFS will construct one.
write-around | non-shared
Write modes for CacheFS. In the write-around mode, writes are
made to the back filesystem, and the affected file is purged
from the cache. Also in this mode, file and record locking is
performed through the back filesystem. You can use the non-
shared mode (the default) when you are sure that no one else
will be writing to the cached filesystem. In this mode, all
writes are made to both the front and the back filesystem, and
the file remains in the cache.
noconst By default, consistency checking is performed. Disable
consistency checking by specifying noconst only if you mount
the filesystem read-only.
private Causes file and record locking to be performed locally. In
addition, files remain cached when file and record locking is
performed. By default, files are not cached when file and
record locking is performed and all file and record locking is
handled by the back filesystem.
local-access
Causes the front filesystem to interpret the mode bits used for
access checking instead or having the back filesystem verify
access permissions.
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suid | nosuid
Allow (default) or disallow set-uid execution.
acregmin=n
Specifies that cached attributes are held for at least n
seconds after file modification. After n seconds, CacheFS
checks to see if the file modification time on the back
filesystem has changed. If it has, all information about the
file is purged from the cache and new data is retrieved from
the back filesystem. The default value is 30 seconds.
acregmax=n
Specifies that cached attributes are held for no more than n
seconds after file modification. After n seconds, all file
information is purged from the cache. The default value is 30
seconds.
acdirmin=n
Specifies that cached attributes are held for at least n
seconds after directory update. After n seconds, CacheFS
checks to see if the directory modification time on the back
filesystem has changed. If it has, all information about the
directory is purged from the cache and new data is retrieved
from the back filesystem. The default value is 30 seconds.
acdirmax=n
Specifies that cached attributes are held for no more than n
seconds after directory update. After n seconds, all directory
information is purged from the cache. The default value is 30
seconds.
actimeo=n Sets acregmin, acregmax, acdirmin, and acdirmax to n.
bg This option causes mount to run in the background if the back
filesystem mount times out.
disconnect
Causes the cache filesystem to operate in disconnected mode
when the back filesystem fails to respond. This causes read
accesses to files already cached to be fulfilled from the front
filesystem even when the back filesystem does not respond.
NOTES
The filesystem types nfs2, nfs3, and nfs3pref are accepted for
compatibility with earlier releases. nfs2 is equivalent to vers=2. nfs3
is equivalent to vers=3. nfs3pref is equivalent to nfs with no vers=
option.
Options used by the mount(1M) command on normal filesystems are ignored
when applied to the root filesystem, since the fstab file cannot be read
before mounting the root filesystem. These options include rw and ro
(the root filesystem cannot be mounted read-only), grpid, quota and
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qnoenforce (see quotaon(1M), dmi, wsync, noatime, noalign, sunit, swidth,
noquota, and lbsize.
FILES
/etc/fstab
SEE ALSO
cfsadmin(1M), fsck(1M), mount(1M), quotacheck(1M), quotaon(1M), swap(1M),
getmntent(3), efs(4), exports(4), fd(4), filesystems(4), mtab(4),
proc(4), xfs(4).
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