NFS server
NFS server
install
sudo apt install nfs-kernel-server
start
sudo systemctl start nfs-kernel-server.service
创建共享文件夹
$ sudo mkdir -p /mnt/nfs_share
修改共享文件夹权限
$ sudo chown -R nobody:nogroup /mnt/nfs_share/
$ sudo chmod 777 /mnt/nfs_share/
config
sudo vim /etc/exports
授权给指定的ip主机
/mnt/storage *(rw,sync,no_subtree_check,all_squash)
ro 只读访问
rw 读写访问
sync 所有数据在请求时写入共享
async NFS在写入数据前可以相应请求
secure NFS通过1024以下的安全TCP/IP端口发送
insecure NFS通过1024以上的端口发送
wdelay 如果多个用户要写入NFS目录，则归组写入（默认）
no_wdelay 如果多个用户要写入NFS目录，则立即写入，当使用async时，无需此设置。
hide 在NFS共享目录中不共享其子目录
no_hide 共享NFS目录的子目录
subtree_check 如果共享/usr/bin之类的子目录时，强制NFS检查父目录的权限（默认）
no_subtree_check 和上面相对，不检查父目录权限
all_squash 共享文件的UID和GID映射匿名用户anonymous，适合公用目录。
no_all_squash 保留共享文件的UID和GID（默认）
root_squash root用户的所有请求映射成如anonymous用户一样的权限（默认）
no_root_squas root用户具有根目录的完全管理访问权限
anonuid=xxx 指定NFS服务器/etc/passwd文件中匿名用户的UID
anongid=xxx 指定NFS服务器/etc/passwd文件中匿名用户的GID
修改完成后，应用修改，重启服务
#$ sudo exportfs -a
#$ sudo systemctl restart nfs-kernel-server
$ sudo exportfs -ra
修改防火墙配置，允许主机通过防火墙
$ sudo ufw allow from 192.168.43.0/24 to any port nfs
开启关闭防火墙
$ sudo ufw enable
$ sudo ufw status
NFS client
$ sudo apt install nfs-common
$ sudo mkdir -p /mnt/nfs_clientshare
$ sudo mount 192.168.43.234:/mnt/nfs_share /mnt/nfs_clientshare
192.168.43.234 为nfs server的ip
查看指定IP的主机nfs共享的文件夹有哪些
showmount -e 192.168.1.1
查看系统磁盘文件系统类型
df -T
Linux NFS Mount Entry in fstab ( /etc/fstab ) with Example
NFS stands for ‘Network File System’. This mechanism allows unix machines to
share files and directories over the network. Using this feature, a Linux
machine can mount a remote directory (residing in a NFS server machine) just
like a local directory and can access files from it.
A NFS share can be mounted on a machine by adding a line to the /etc/fstab file.
The default syntax for fstab entry of NFS mounts is as follows.
Server:/path/to/export /local_mountpoint nfs <options> 0 0
Server: This should be replaced with the exact hostname or IP address of the NFS server where the exported directory resides.
/path/to/export: This should be replaced with the exact shared directory (exported folder) path.
/local_mountpoint: This should be replaced with an existing directory in the server where you want to mount the NFS share.
Fstab NFS options
You can specify a number of mount points which you want to set on the NFS mount.
We will go through the important mount options which you may consider while mounting a NFS share.
1) soft/hard
When the mount option hard is set, if the NFS server crashes or becomes unresponsive,
the NFS requests will be retried indefinitely. You can set the mount option intr,
so that the process can be interrupted. When the NFS server comes back online,
the process can be continued from where it was while the server became unresponsive.
When the option soft is set, the process will be reported an error when the NFS
server is unresponsive after waiting for a period of time (defined by the timeo option).
In certain cases soft option can cause data corruption and loss of data.
So, it is recommended to use hard and intr options.
2) timeo=n
This option defines the time (in tenths of a second) the NFS client waits for
a response before it retries an NFS request.
3) intr
This allows NFS requests to be interrupted if the server goes down or cannot be
reached. Using the intr option is preferred to using the soft option because it
is significantly less likely to result in data corruption.
4) rsize=num and wsize=num
This defines the maximum number of bytes in each READ/WRITE request that the
NFS client can receive/send when communicating with a NFS server. The rsize/wsize
value is a positive integral multiple of 1024. Specified rsize values lower
than 1024 are replaced with 4096; values larger than 1048576 are replaced with 1048576.
If a specified value is within the supported range but not a multiple of 1024,
it is rounded down to the nearest multiple of 1024.
5) retrans=n
The number of times the NFS client retries a request before it attempts further
recovery action. If the retrans option is not specified, the NFS client tries
each request three times. The NFS client generates a "server not responding"
message after retrans retries, then attempts further recovery
(depending on whether the hard mount option is in effect).
6) noexec
Prevents execution of binaries on mounted file systems. This is useful if the
system is mounting a non-Linux file system via NFS containing incompatible binaries.
7) nosuid
Disables set-user-identifier or set-group-identifier bits. This prevents remote
users from gaining higher privileges by running a setuid program.
8) tcp
This specifies the NFS mount to use the TCP protocol.
9) udp
This specifies the NFS mount to use the UDP protocol.
Sample NFS fstab entry
A sample fstab entry for NFS share is as follows.
host.myserver.com:/home /mnt/home nfs nosuid,rw,hard,intr,rsize=8192,wsize=8192,timeo=14 0 0
This will make the export directory /home to be available on the NFS client machine.
You can mount the NFS share just like you mount a local folder.
mount /mnt/home
https://linoxide.com/file-system/example-linux-nfs-mount-entry-in-fstab-etcfstab
exports
exports(5) — Linux manual page
NAME | DESCRIPTION | EXAMPLE | FILES | SEE ALSO | COLOPHON
exports(5) File Formats Manual exports(5)
NAME top
exports - NFS server export table
DESCRIPTION top
The file /etc/exports contains a table of local physical file systems
on an NFS server that are accessible to NFS clients. The contents of
the file are maintained by the server's system administrator.
Each file system in this table has a list of options and an access
control list. The table is used by exportfs(8) to give information
to mountd(8).
The file format is similar to the SunOS exports file. Each line
contains an export point and a whitespace-separated list of clients
allowed to mount the file system at that point. Each listed client
may be immediately followed by a parenthesized, comma-separated list
of export options for that client. No whitespace is permitted between
a client and its option list.
Also, each line may have one or more specifications for default
options after the path name, in the form of a dash ("-") followed by
an option list. The option list is used for all subsequent exports on
that line only.
Blank lines are ignored. A pound sign ("#") introduces a comment to
the end of the line. Entries may be continued across newlines using a
backslash. If an export name contains spaces it should be quoted
using double quotes. You can also specify spaces or other unusual
character in the export name using a backslash followed by the
character code as three octal digits.
To apply changes to this file, run exportfs -ra or restart the NFS
server.
Machine Name Formats
NFS clients may be specified in a number of ways:
single host
You may specify a host either by an abbreviated name
recognized be the resolver, the fully qualified domain name,
an IPv4 address, or an IPv6 address. IPv6 addresses must not
be inside square brackets in /etc/exports lest they be
confused with character-class wildcard matches.
IP networks
You can also export directories to all hosts on an IP (sub-)
network simultaneously. This is done by specifying an IP
address and netmask pair as address/netmask where the netmask
can be specified in dotted-decimal format, or as a contiguous
mask length. For example, either `/255.255.252.0' or `/22'
appended to the network base IPv4 address results in identical
subnetworks with 10 bits of host. IPv6 addresses must use a
contiguous mask length and must not be inside square brackets
to avoid confusion with character-class wildcards. Wildcard
characters generally do not work on IP addresses, though they
may work by accident when reverse DNS lookups fail.
wildcards
Machine names may contain the wildcard characters * and ?, or
may contain character class lists within [square brackets].
This can be used to make the exports file more compact; for
instance, *.cs.foo.edu matches all hosts in the domain
cs.foo.edu. As these characters also match the dots in a
domain name, the given pattern will also match all hosts
within any subdomain of cs.foo.edu.
netgroups
NIS netgroups may be given as @group. Only the host part of
each netgroup members is consider in checking for membership.
Empty host parts or those containing a single dash (-) are
ignored.
anonymous
This is specified by a single * character (not to be confused
with the wildcard entry above) and will match all clients.
If a client matches more than one of the specifications above, then
the first match from the above list order takes precedence -
regardless of the order they appear on the export line. However, if a
client matches more than one of the same type of specification (e.g.
two netgroups), then the first match from the order they appear on
the export line takes precedence.
RPCSEC_GSS security
You may use the special strings "gss/krb5", "gss/krb5i", or
"gss/krb5p" to restrict access to clients using rpcsec_gss security.
However, this syntax is deprecated; on linux kernels since 2.6.23,
you should instead use the "sec=" export option:
sec= The sec= option, followed by a colon-delimited list of
security flavors, restricts the export to clients using those
flavors. Available security flavors include sys (the
default--no cryptographic security), krb5 (authentication
only), krb5i (integrity protection), and krb5p (privacy
protection). For the purposes of security flavor negotiation,
order counts: preferred flavors should be listed first. The
order of the sec= option with respect to the other options
does not matter, unless you want some options to be enforced
differently depending on flavor. In that case you may include
multiple sec= options, and following options will be enforced
only for access using flavors listed in the immediately
preceding sec= option. The only options that are permitted to
vary in this way are ro, rw, no_root_squash, root_squash, and
all_squash.
General Options
exportfs understands the following export options:
secure This option requires that requests not using gss originate on
an Internet port less than IPPORT_RESERVED (1024). This option
is on by default. To turn it off, specify insecure. (NOTE:
older kernels (before upstream kernel version 4.17) enforced
this requirement on gss requests as well.)
rw Allow both read and write requests on this NFS volume. The
default is to disallow any request which changes the
filesystem. This can also be made explicit by using the ro
option.
async This option allows the NFS server to violate the NFS protocol
and reply to requests before any changes made by that request
have been committed to stable storage (e.g. disc drive).
Using this option usually improves performance, but at the
cost that an unclean server restart (i.e. a crash) can cause
data to be lost or corrupted.
sync Reply to requests only after the changes have been committed
to stable storage (see async above).
In releases of nfs-utils up to and including 1.0.0, the async
option was the default. In all releases after 1.0.0, sync is
the default, and async must be explicitly requested if needed.
To help make system administrators aware of this change,
exportfs will issue a warning if neither sync nor async is
specified.
no_wdelay
This option has no effect if async is also set. The NFS
server will normally delay committing a write request to disc
slightly if it suspects that another related write request may
be in progress or may arrive soon. This allows multiple write
requests to be committed to disc with the one operation which
can improve performance. If an NFS server received mainly
small unrelated requests, this behaviour could actually reduce
performance, so no_wdelay is available to turn it off. The
default can be explicitly requested with the wdelay option.
nohide This option is based on the option of the same name provided
in IRIX NFS. Normally, if a server exports two filesystems
one of which is mounted on the other, then the client will
have to mount both filesystems explicitly to get access to
them. If it just mounts the parent, it will see an empty
directory at the place where the other filesystem is mounted.
That filesystem is "hidden".
Setting the nohide option on a filesystem causes it not to be
hidden, and an appropriately authorised client will be able to
move from the parent to that filesystem without noticing the
change.
However, some NFS clients do not cope well with this situation
as, for instance, it is then possible for two files in the one
apparent filesystem to have the same inode number.
The nohide option is currently only effective on single host
exports. It does not work reliably with netgroup, subnet, or
wildcard exports.
This option can be very useful in some situations, but it
should be used with due care, and only after confirming that
the client system copes with the situation effectively.
The option can be explicitly disabled for NFSv2 and NFSv3 with
hide.
This option is not relevant when NFSv4 is use. NFSv4 never
hides subordinate filesystems. Any filesystem that is
exported will be visible where expected when using NFSv4.
crossmnt
This option is similar to nohide but it makes it possible for
clients to access all filesystems mounted on a filesystem
marked with crossmnt. Thus when a child filesystem "B" is
mounted on a parent "A", setting crossmnt on "A" has a similar
effect to setting "nohide" on B.
With nohide the child filesystem needs to be explicitly
exported. With crossmnt it need not. If a child of a
crossmnt file is not explicitly exported, then it will be
implicitly exported with the same export options as the
parent, except for fsid=. This makes it impossible to not
export a child of a crossmnt filesystem. If some but not all
subordinate filesystems of a parent are to be exported, then
they must be explicitly exported and the parent should not
have crossmnt set.
The nocrossmnt option can explictly disable crossmnt if it was
previously set. This is rarely useful.
no_subtree_check
This option disables subtree checking, which has mild security
implications, but can improve reliability in some
circumstances.
If a subdirectory of a filesystem is exported, but the whole
filesystem isn't then whenever a NFS request arrives, the
server must check not only that the accessed file is in the
appropriate filesystem (which is easy) but also that it is in
the exported tree (which is harder). This check is called the
subtree_check.
In order to perform this check, the server must include some
information about the location of the file in the "filehandle"
that is given to the client. This can cause problems with
accessing files that are renamed while a client has them open
(though in many simple cases it will still work).
subtree checking is also used to make sure that files inside
directories to which only root has access can only be accessed
if the filesystem is exported with no_root_squash (see below),
even if the file itself allows more general access.
As a general guide, a home directory filesystem, which is
normally exported at the root and may see lots of file
renames, should be exported with subtree checking disabled. A
filesystem which is mostly readonly, and at least doesn't see
many file renames (e.g. /usr or /var) and for which
subdirectories may be exported, should probably be exported
with subtree checks enabled.
The default of having subtree checks enabled, can be
explicitly requested with subtree_check.
From release 1.1.0 of nfs-utils onwards, the default will be
no_subtree_check as subtree_checking tends to cause more
problems than it is worth. If you genuinely require subtree
checking, you should explicitly put that option in the exports
file. If you put neither option, exportfs will warn you that
the change is pending.
insecure_locks
no_auth_nlm
This option (the two names are synonymous) tells the NFS
server not to require authentication of locking requests (i.e.
requests which use the NLM protocol). Normally the NFS server
will require a lock request to hold a credential for a user
who has read access to the file. With this flag no access
checks will be performed.
Early NFS client implementations did not send credentials with
lock requests, and many current NFS clients still exist which
are based on the old implementations. Use this flag if you
find that you can only lock files which are world readable.
The default behaviour of requiring authentication for NLM
requests can be explicitly requested with either of the
synonymous auth_nlm, or secure_locks.
mountpoint=path
mp This option makes it possible to only export a directory if it
has successfully been mounted. If no path is given (e.g.
mountpoint or mp) then the export point must also be a mount
point. If it isn't then the export point is not exported.
This allows you to be sure that the directory underneath a
mountpoint will never be exported by accident if, for example,
the filesystem failed to mount due to a disc error.
If a path is given (e.g. mountpoint=/path or mp=/path) then
the nominated path must be a mountpoint for the exportpoint to
be exported.
fsid=num|root|uuid
NFS needs to be able to identify each filesystem that it
exports. Normally it will use a UUID for the filesystem (if
the filesystem has such a thing) or the device number of the
device holding the filesystem (if the filesystem is stored on
the device).
As not all filesystems are stored on devices, and not all
filesystems have UUIDs, it is sometimes necessary to
explicitly tell NFS how to identify a filesystem. This is
done with the fsid= option.
For NFSv4, there is a distinguished filesystem which is the
root of all exported filesystem. This is specified with
fsid=root or fsid=0 both of which mean exactly the same thing.
Other filesystems can be identified with a small integer, or a
UUID which should contain 32 hex digits and arbitrary
punctuation.
Linux kernels version 2.6.20 and earlier do not understand the
UUID setting so a small integer must be used if an fsid option
needs to be set for such kernels. Setting both a small number
and a UUID is supported so the same configuration can be made
to work on old and new kernels alike.
nordirplus
This option will disable READDIRPLUS request handling. When
set, READDIRPLUS requests from NFS clients return
NFS3ERR_NOTSUPP, and clients fall back on READDIR. This
option affects only NFSv3 clients.
refer=path@host[+host][:path@host[+host]]
A client referencing the export point will be directed to
choose from the given list an alternative location for the
filesystem. (Note that the server must have a mountpoint
here, though a different filesystem is not required; so, for
example, mount --bind /path /path is sufficient.)
replicas=path@host[+host][:path@host[+host]]
If the client asks for alternative locations for the export
point, it will be given this list of alternatives. (Note that
actual replication of the filesystem must be handled
elsewhere.)
pnfs This option enables the use of the pNFS extension if the
protocol level is NFSv4.1 or higher, and the filesystem
supports pNFS exports. With pNFS clients can bypass the
server and perform I/O directly to storage devices. The
default can be explicitly requested with the no_pnfs option.
security_label
With this option set, clients using NFSv4.2 or higher will be
able to set and retrieve security labels (such as those used
by SELinux). This will only work if all clients use a
consistent security policy. Note that early kernels did not
support this export option, and instead enabled security
labels by default.
User ID Mapping
nfsd bases its access control to files on the server machine on the
uid and gid provided in each NFS RPC request. The normal behavior a
user would expect is that she can access her files on the server just
as she would on a normal file system. This requires that the same
uids and gids are used on the client and the server machine. This is
not always true, nor is it always desirable.
Very often, it is not desirable that the root user on a client
machine is also treated as root when accessing files on the NFS
server. To this end, uid 0 is normally mapped to a different id: the
so-called anonymous or nobody uid. This mode of operation (called
`root squashing') is the default, and can be turned off with
no_root_squash.
By default, exportfs chooses a uid and gid of 65534 for squashed
access. These values can also be overridden by the anonuid and
anongid options. Finally, you can map all user requests to the
anonymous uid by specifying the all_squash option.
Here's the complete list of mapping options:
root_squash
Map requests from uid/gid 0 to the anonymous uid/gid. Note
that this does not apply to any other uids or gids that might
be equally sensitive, such as user bin or group staff.
no_root_squash
Turn off root squashing. This option is mainly useful for
diskless clients.
all_squash
Map all uids and gids to the anonymous user. Useful for NFS-
exported public FTP directories, news spool directories, etc.
The opposite option is no_all_squash, which is the default
setting.
anonuid and anongid
These options explicitly set the uid and gid of the anonymous
account. This option is primarily useful for PC/NFS clients,
where you might want all requests appear to be from one user.
As an example, consider the export entry for /home/joe in the
example section below, which maps all requests to uid 150
(which is supposedly that of user joe).
Subdirectory Exports
Normally you should only export only the root of a filesystem. The
NFS server will also allow you to export a subdirectory of a
filesystem, however, this has drawbacks:
First, it may be possible for a malicious user to access files on the
filesystem outside of the exported subdirectory, by guessing
filehandles for those other files. The only way to prevent this is
by using the no_subtree_check option, which can cause other problems.
Second, export options may not be enforced in the way that you would
expect. For example, the security_label option will not work on
subdirectory exports, and if nested subdirectory exports change the
security_label or sec= options, NFSv4 clients will normally see only
the options on the parent export. Also, where security options
differ, a malicious client may use filehandle-guessing attacks to
access the files from one subdirectory using the options from
another.
Extra Export Tables
After reading /etc/exports exportfs reads files in the /etc/exports.d
directory as extra export tables. Only files ending in .exports are
considered. Files beginning with a dot are ignored. The format for
extra export tables is the same as /etc/exports
EXAMPLE top
# sample /etc/exports file
/ master(rw) trusty(rw,no_root_squash)
/projects proj*.local.domain(rw)
/usr *.local.domain(ro) @trusted(rw)
/home/joe pc001(rw,all_squash,anonuid=150,anongid=100)
/pub *(ro,insecure,all_squash)
/srv/www -sync,rw server @trusted @external(ro)
/foo 2001:db8:9:e54::/64(rw) 192.0.2.0/24(rw)
/build buildhost[0-9].local.domain(rw)
The first line exports the entire filesystem to machines master and
trusty. In addition to write access, all uid squashing is turned off
for host trusty. The second and third entry show examples for
wildcard hostnames and netgroups (this is the entry `@trusted'). The
fourth line shows the entry for the PC/NFS client discussed above.
Line 5 exports the public FTP directory to every host in the world,
executing all requests under the nobody account. The insecure option
in this entry also allows clients with NFS implementations that don't
use a reserved port for NFS. The sixth line exports a directory
read-write to the machine 'server' as well as the `@trusted'
netgroup, and read-only to netgroup `@external', all three mounts
with the `sync' option enabled. The seventh line exports a directory
to both an IPv6 and an IPv4 subnet. The eighth line demonstrates a
character class wildcard match.
FILES top
/etc/exports /etc/exports.d
状态验证
/etc/init.d/nfs-kernel-server status
service nfs-kernel-server status
nfsstat(8) System Manager's Manual nfsstat(8)
NAME top
nfsstat - list NFS statistics
SYNOPSIS top
nfsstat [OPTION]...
DESCRIPTION top
The nfsstat displays statistics kept about NFS client and server
activity.
OPTIONS top
-s, --server
Print only server-side statistics. The default is to print
both server and client statistics.
-c, --client
Print only client-side statistics.
-n, --nfs
Print only NFS statistics. The default is to print both NFS
and RPC information.
-2 Print only NFS v2 statistics. The default is to only print
information about the versions of NFS that have non-zero
counts.
-3 Print only NFS v3 statistics. The default is to only print
information about the versions of NFS that have non-zero
counts.
-4 Print only NFS v4 statistics. The default is to only print
information about the versions of NFS that have non-zero
counts.
-m, --mounts
Print information about each of the mounted NFS file systems.
If this option is used, all other options are ignored.
-r, --rpc
Print only RPC statistics.
-o facility
Display statistics for the specified facility, which must be
one of:
nfs NFS protocol information, split up by RPC call.
rpc General RPC information.
net Network layer statistics, such as the number of
received packets, number of TCP connections, etc.
fh Usage information on the server's file handle cache,
including the total number of lookups, and the number
of hits and misses.
rc Usage information on the server's request reply cache,
including the total number of lookups, and the number
of hits and misses.
io Usage information on the server's io statistics; bytes
read and written.
ra Usage information on the server's read ahead cache,
including the ra cache size, the depth of ra cache
hits, and ra cache misses.
all Display all of the above facilities.
-v, --verbose
This is equivalent to -o all.
-l, --list
Print information in list form.
-S, --since file
Instead of printing current statistics, nfsstat imports
statistics from file and displays the difference between those
and the current statistics. Valid input files may be in the
form of /proc/net/rpc/nfs (raw client stats),
/proc/net/rpc/nfsd (raw server stats), or saved output from
nfsstat itself (client and/or server stats). Any statistics
missing from a saved nfsstat output file are treated as
zeroes.
-Z[interval], --sleep=[interval]
Instead of printing current statistics and immediately
exiting, nfsstat takes a snapshot of the current statistics
and pauses until it receives SIGINT (typically from Ctrl-C),
at which point it takes another snapshot and displays the
difference between the two. If interval is specified, nfsstat
will print the number of NFS calls made since the previous
report. Stats will be printed repeatedly every interval
seconds.
EXAMPLES top
nfsstat -o all -234
Show all information about all versions of NFS.
nfsstat --verbose -234
Same as above.
nfsstat -o all
Show all information about active versions of NFS.
nfsstat --nfs --server -3
Show statistics for NFS version 3 server.
nfsstat -m
Show information about mounted NFS filesystems.
DISPLAY top
The Flags output from the -m option is the same as the flags give to
the mount command.
FILES top
/proc/net/rpc/nfsd
procfs-based interface to kernel NFS server statistics.
/proc/net/rpc/nfs
procfs-based interface to kernel NFS client statistics.
/proc/mounts
procfs-based interface to the mounted filesystems.
mount
NAME top
mount - mount a filesystem
SYNOPSIS top
mount [-h|-V]
mount [-l] [-t fstype]
mount -a [-fFnrsvw] [-t fstype] [-O optlist]
mount [-fnrsvw] [-o options] device|mountpoint
mount [-fnrsvw] [-t fstype] [-o options] device mountpoint
mount --bind|--rbind|--move olddir newdir
mount
--make-{shared|slave|private|unbindable|rshared|rslave|rprivate|runbindable}
mountpoint
DESCRIPTION top
All files accessible in a Unix system are arranged in one big tree,
the file hierarchy, rooted at /. These files can be spread out over
several devices. The mount command serves to attach the filesystem
found on some device to the big file tree. Conversely, the umount(8)
command will detach it again. The filesystem is used to control how
data is stored on the device or provided in a virtual way by network
or other services.
The standard form of the mount command is:
mount -t type device dir
This tells the kernel to attach the filesystem found on device (which
is of type type) at the directory dir. The option -t type is
optional. The mount command is usually able to detect a filesystem.
The root permissions are necessary to mount a filesystem by default.
See section "Non-superuser mounts" below for more details. The
previous contents (if any) and owner and mode of dir become
invisible, and as long as this filesystem remains mounted, the
pathname dir refers to the root of the filesystem on device.
If only the directory or the device is given, for example:
mount /dir
then mount looks for a mountpoint (and if not found then for a
device) in the /etc/fstab file. It's possible to use the --target or
--source options to avoid ambiguous interpretation of the given
argument. For example:
mount --target /mountpoint
The same filesystem may be mounted more than once, and in some cases
(e.g., network filesystems) the same filesystem may be mounted on the
same mountpoint multiple times. The mount command does not implement
any policy to control this behavior. All behavior is controlled by
the kernel and it is usually specific to the filesystem driver. The
exception is --all, in this case already mounted filesystems are
ignored (see --all below for more details).
Listing the mounts
The listing mode is maintained for backward compatibility only.
For more robust and customizable output use findmnt(8), especially in
your scripts. Note that control characters in the mountpoint name
are replaced with '?'.
The following command lists all mounted filesystems (of type type):
mount [-l] [-t type]
The option -l adds labels to this listing. See below.
Indicating the device and filesystem
Most devices are indicated by a filename (of a block special device),
like /dev/sda1, but there are other possibilities. For example, in
the case of an NFS mount, device may look like knuth.cwi.nl:/dir.
The device names of disk partitions are unstable; hardware
reconfiguration, and adding or removing a device can cause changes in
names. This is the reason why it's strongly recommended to use
filesystem or partition identifiers like UUID or LABEL. Currently
supported identifiers (tags):
LABEL=label
Human readable filesystem identifier. See also -L.
UUID=uuid
Filesystem universally unique identifier. The format of
the UUID is usually a series of hex digits separated by
hyphens. See also -U.
Note that mount(8) uses UUIDs as strings. The UUIDs
from the command line or from fstab(5) are not
converted to internal binary representation. The
string representation of the UUID should be based on
lower case characters.
PARTLABEL=label
Human readable partition identifier. This identifier
is independent on filesystem and does not change by
mkfs or mkswap operations It's supported for example
for GUID Partition Tables (GPT).
PARTUUID=uuid
Partition universally unique identifier. This
identifier is independent on filesystem and does not
change by mkfs or mkswap operations It's supported for
example for GUID Partition Tables (GPT).
ID=id Hardware block device ID as generated by udevd. This
identifier is usually based on WWN (unique storage
identifier) and assigned by the hardware manufacturer.
See ls /dev/disk/by-id for more details, this directory
and running udevd is required. This identifier is not
recommended for generic use as the identifier is not
strictly defined and it depends on udev, udev rules and
hardware.
The command lsblk --fs provides an overview of filesystems, LABELs
and UUIDs on available block devices. The command blkid -p <device>
provides details about a filesystem on the specified device.
Don't forget that there is no guarantee that UUIDs and labels are
really unique, especially if you move, share or copy the device. Use
lsblk -o +UUID,PARTUUID to verify that the UUIDs are really unique in
your system.
The recommended setup is to use tags (e.g. UUID=uuid) rather than
/dev/disk/by-{label,uuid,id,partuuid,partlabel} udev symlinks in the
/etc/fstab file. Tags are more readable, robust and portable. The
mount(8) command internally uses udev symlinks, so the use of
symlinks in /etc/fstab has no advantage over tags. For more details
see libblkid(3).
The proc filesystem is not associated with a special device, and when
mounting it, an arbitrary keyword—for example, proc—can be used
instead of a device specification. (The customary choice none is
less fortunate: the error message `none already mounted' from mount
can be confusing.)
The files /etc/fstab, /etc/mtab and /proc/mounts
The file /etc/fstab (see fstab(5)), may contain lines describing what
devices are usually mounted where, using which options. The default
location of the fstab(5) file can be overridden with the --fstab path
command-line option (see below for more details).
The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all filesystems mentioned in
fstab (of the proper type and/or having or not having the proper
options) to be mounted as indicated, except for those whose line
contains the noauto keyword. Adding the -F option will make mount
fork, so that the filesystems are mounted in parallel.
When mounting a filesystem mentioned in fstab or mtab, it suffices to
specify on the command line only the device, or only the mount point.
The programs mount and umount traditionally maintained a list of
currently mounted filesystems in the file /etc/mtab. The support for
regular classic /etc/mtab is completely disabled at compile time by
default, because on current Linux systems it is better to make
/etc/mtab a symlink to /proc/mounts instead. The regular mtab file
maintained in userspace cannot reliably work with namespaces,
containers and other advanced Linux features. If the regular mtab
support is enabled, then it's possible to use the file as well as the
symlink.
If no arguments are given to mount, the list of mounted filesystems
is printed.
If you want to override mount options from /etc/fstab, you have to
use the -o option:
mount device|dir -o options
and then the mount options from the command line will be appended to
the list of options from /etc/fstab. This default behaviour can be
changed using the --options-mode command-line option. The usual
behavior is that the last option wins if there are conflicting ones.
The mount program does not read the /etc/fstab file if both device
(or LABEL, UUID, ID, PARTUUID or PARTLABEL) and dir are specified.
For example, to mount device foo at /dir:
mount /dev/foo /dir
This default behaviour can be changed by using the
--options-source-force command-line option to always read
configuration from fstab. For non-root users mount always reads the
fstab configuration.
Non-superuser mounts
Normally, only the superuser can mount filesystems. However, when
fstab contains the user option on a line, anybody can mount the
corresponding filesystem.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 filesystem found on an inserted CDROM
using the command:
mount /cd
Note that mount is very strict about non-root users and all paths
specified on command line are verified before fstab is parsed or a
helper program is executed. It's strongly recommended to use a valid
mountpoint to specify filesystem, otherwise mount may fail. For
example it's a bad idea to use NFS or CIFS source on command line.
Since util-linux 2.35, mount does not exit when user permissions are
inadequate according to libmount's internal security rules. Instead,
it drops suid permissions and continues as regular non-root user.
This behavior supports use-cases where root permissions are not
necessary (e.g., fuse filesystems, user namespaces, etc).
For more details, see fstab(5). Only the user that mounted a
filesystem can unmount it again. If any user should be able to
unmount it, then use users instead of user in the fstab line. The
owner option is similar to the user option, with the restriction that
the user must be the owner of the special file. This may be useful
e.g. for /dev/fd if a login script makes the console user owner of
this device. The group option is similar, with the restriction that
the user must be a member of the group of the special file.
Bind mount operation
Remount part of the file hierarchy somewhere else. The call is:
mount --bind olddir newdir
or by using this fstab entry:
/olddir /newdir none bind
After this call the same contents are accessible in two places.
It is important to understand that "bind" does not create any second-
class or special node in the kernel VFS. The "bind" is just another
operation to attach a filesystem. There is nowhere stored information
that the filesystem has been attached by a "bind" operation. The
olddir and newdir are independent and the olddir may be unmounted.
One can also remount a single file (on a single file). It's also
possible to use a bind mount to create a mountpoint from a regular
directory, for example:
mount --bind foo foo
The bind mount call attaches only (part of) a single filesystem, not
possible submounts. The entire file hierarchy including submounts
can be attached a second place by using:
mount --rbind olddir newdir
Note that the filesystem mount options maintained by the kernel will
remain the same as those on the original mount point. The userspace
mount options (e.g., _netdev) will not be copied by mount and it's
necessary to explicitly specify the options on the mount command
line.
Since util-linux 2.27 mount(8) permits changing the mount options by
passing the relevant options along with --bind. For example:
mount -o bind,ro foo foo
This feature is not supported by the Linux kernel; it is implemented
in userspace by an additional mount(2) remounting system call. This
solution is not atomic.
The alternative (classic) way to create a read-only bind mount is to
use the remount operation, for example:
mount --bind olddir newdir
mount -o remount,bind,ro olddir newdir
Note that a read-only bind will create a read-only mountpoint (VFS
entry), but the original filesystem superblock will still be
writable, meaning that the olddir will be writable, but the newdir
will be read-only.
It's also possible to change nosuid, nodev, noexec, noatime,
nodiratime and relatime VFS entry flags via a "remount,bind"
operation. The other flags (for example filesystem-specific flags)
are silently ignored. It's impossible to change mount options
recursively (for example with -o rbind,ro).
Since util-linux 2.31, mount ignores the bind flag from /etc/fstab on
a remount operation (if "-o remount" is specified on command line).
This is necessary to fully control mount options on remount by
command line. In previous versions the bind flag has been always
applied and it was impossible to re-define mount options without
interaction with the bind semantic. This mount(8) behavior does not
affect situations when "remount,bind" is specified in the /etc/fstab
file.
The move operation
Move a mounted tree to another place (atomically). The call is:
mount --move olddir newdir
This will cause the contents which previously appeared under olddir
to now be accessible under newdir. The physical location of the
files is not changed. Note that olddir has to be a mountpoint.
Note also that moving a mount residing under a shared mount is
invalid and unsupported. Use findmnt -o TARGET,PROPAGATION to see
the current propagation flags.
Shared subtree operations
Since Linux 2.6.15 it is possible to mark a mount and its submounts
as shared, private, slave or unbindable. A shared mount provides the
ability to create mirrors of that mount such that mounts and unmounts
within any of the mirrors propagate to the other mirror. A slave
mount receives propagation from its master, but not vice versa. A
private mount carries no propagation abilities. An unbindable mount
is a private mount which cannot be cloned through a bind operation.
The detailed semantics are documented in
Documentation/filesystems/sharedsubtree.txt file in the kernel source
tree; see also mount_namespaces(7).
Supported operations are:
mount --make-shared mountpoint
mount --make-slave mountpoint
mount --make-private mountpoint
mount --make-unbindable mountpoint
The following commands allow one to recursively change the type of
all the mounts under a given mountpoint.
mount --make-rshared mountpoint
mount --make-rslave mountpoint
mount --make-rprivate mountpoint
mount --make-runbindable mountpoint
mount(8) does not read fstab(5) when a --make-* operation is
requested. All necessary information has to be specified on the
command line.
Note that the Linux kernel does not allow changing multiple
propagation flags with a single mount(2) system call, and the flags
cannot be mixed with other mount options and operations.
Since util-linux 2.23 the mount command can be used to do more
propagation (topology) changes by one mount(8) call and do it also
together with other mount operations. This feature is EXPERIMENTAL.
The propagation flags are applied by additional mount(2) system calls
when the preceding mount operations were successful. Note that this
use case is not atomic. It is possible to specify the propagation
flags in fstab(5) as mount options (private, slave, shared,
unbindable, rprivate, rslave, rshared, runbindable).
For example:
mount --make-private --make-unbindable /dev/sda1 /foo
is the same as:
mount /dev/sda1 /foo
mount --make-private /foo
mount --make-unbindable /foo
COMMAND-LINE OPTIONS top
The full set of mount options used by an invocation of mount is
determined by first extracting the mount options for the filesystem
from the fstab table, then applying any options specified by the -o
argument, and finally applying a -r or -w option, when present.
The mount command does not pass all command-line options to the
/sbin/mount.suffix mount helpers. The interface between mount and
the mount helpers is described below in the section EXTERNAL HELPERS.
Command-line options available for the mount command are:
-a, --all
Mount all filesystems (of the given types) mentioned in fstab
(except for those whose line contains the noauto keyword).
The filesystems are mounted following their order in fstab.
The mount command compares filesystem source, target (and fs
root for bind mount or btrfs) to detect already mounted
filesystems. The kernel table with already mounted filesystems
is cached during mount --all. This means that all duplicated
fstab entries will be mounted.
The option --all is possible to use for remount operation too.
In this case all filters (-t and -O) are applied to the table
of already mounted filesystems.
Since version 2.35 is possible to use the command line option
-o to alter mount options from fstab (see also
--options-mode).
Note that it is a bad practice to use mount -a for fstab
checking. The recommended solution is findmnt --verify.
-B, --bind
Remount a subtree somewhere else (so that its contents are
available in both places). See above, under Bind mounts.
-c, --no-canonicalize
Don't canonicalize paths. The mount command canonicalizes all
paths (from the command line or fstab) by default. This
option can be used together with the -f flag for already
canonicalized absolute paths. The option is designed for
mount helpers which call mount -i. It is strongly recommended
to not use this command-line option for normal mount
operations.
Note that mount(8) does not pass this option to the
/sbin/mount.type helpers.
-F, --fork
(Used in conjunction with -a.) Fork off a new incarnation of
mount for each device. This will do the mounts on different
devices or different NFS servers in parallel. This has the
advantage that it is faster; also NFS timeouts proceed in
parallel. A disadvantage is that the order of the mount
operations is undefined. Thus, you cannot use this option if
you want to mount both /usr and /usr/spool.
-f, --fake
Causes everything to be done except for the actual system
call; if it's not obvious, this ``fakes'' mounting the
filesystem. This option is useful in conjunction with the -v
flag to determine what the mount command is trying to do. It
can also be used to add entries for devices that were mounted
earlier with the -n option. The -f option checks for an
existing record in /etc/mtab and fails when the record already
exists (with a regular non-fake mount, this check is done by
the kernel).
-i, --internal-only
Don't call the /sbin/mount.filesystem helper even if it
exists.
-L, --label label
Mount the partition that has the specified label.
-l, --show-labels
Add the labels in the mount output. mount must have
permission to read the disk device (e.g. be set-user-ID root)
for this to work. One can set such a label for ext2, ext3 or
ext4 using the e2label(8) utility, or for XFS using
xfs_admin(8), or for reiserfs using reiserfstune(8).
-M, --move
Move a subtree to some other place. See above, the subsection
The move operation.
-n, --no-mtab
Mount without writing in /etc/mtab. This is necessary for
example when /etc is on a read-only filesystem.
-N, --namespace ns
Perform the mount operation in the mount namespace specified
by ns. ns is either PID of process running in that namespace
or special file representing that namespace.
mount(8) switches to the mount namespace when it reads
/etc/fstab, writes /etc/mtab (or writes to /run/mount) and
calls the mount(2) system call, otherwise it runs in the
original mount namespace. This means that the target
namespace does not have to contain any libraries or other
requirements necessary to execute the mount(2) call.
See mount_namespaces(7) for more information.
-O, --test-opts opts
Limit the set of filesystems to which the -a option applies.
In this regard it is like the -t option except that -O is
useless without -a. For example, the command:
mount -a -O no_netdev
mounts all filesystems except those which have the option
_netdev specified in the options field in the /etc/fstab file.
It is different from -t in that each option is matched
exactly; a leading no at the beginning of one option does not
negate the rest.
The -t and -O options are cumulative in effect; that is, the
command
mount -a -t ext2 -O _netdev
mounts all ext2 filesystems with the _netdev option, not all
filesystems that are either ext2 or have the _netdev option
specified.
-o, --options opts
Use the specified mount options. The opts argument is a
comma-separated list. For example:
mount LABEL=mydisk -o noatime,nodev,nosuid
For more details, see the FILESYSTEM-INDEPENDENT MOUNT OPTIONS
and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
--options-mode mode
Controls how to combine options from fstab/mtab with options
from the command line. mode can be one of ignore, append,
prepend or replace. For example, append means that options
from fstab are appended to options from the command line. The
default value is prepend -- it means command line options are
evaluated after fstab options. Note that the last option wins
if there are conflicting ones.
--options-source source
Source of default options. source is a comma-separated list
of fstab, mtab and disable. disable disables fstab and mtab
and disables --options-source-force. The default value is
fstab,mtab.
--options-source-force
Use options from fstab/mtab even if both device and dir are
specified.
-R, --rbind
Remount a subtree and all possible submounts somewhere else
(so that its contents are available in both places). See
above, the subsection Bind mounts.
-r, --read-only
Mount the filesystem read-only. A synonym is -o ro.
Note that, depending on the filesystem type, state and kernel
behavior, the system may still write to the device. For
example, ext3 and ext4 will replay the journal if the
filesystem is dirty. To prevent this kind of write access,
you may want to mount an ext3 or ext4 filesystem with the
ro,noload mount options or set the block device itself to
read-only mode, see the blockdev(8) command.
-s Tolerate sloppy mount options rather than failing. This will
ignore mount options not supported by a filesystem type. Not
all filesystems support this option. Currently it's supported
by the mount.nfs mount helper only.
--source device
If only one argument for the mount command is given, then the
argument might be interpreted as the target (mountpoint) or
source (device). This option allows you to explicitly define
that the argument is the mount source.
--target directory
If only one argument for the mount command is given, then the
argument might be interpreted as the target (mountpoint) or
source (device). This option allows you to explicitly define
that the argument is the mount target.
--target-prefix directory
Prepend the specified directory to all mount targets. This
option can be used to follow fstab, but mount operations are
done in another place, for example:
mount --all --target-prefix /chroot -o X-mount.mkdir
mounts all from system fstab to /chroot, all missing
mountpoint are created (due to X-mount.mkdir). See also
--fstab to use an alternative fstab.
-T, --fstab path
Specifies an alternative fstab file. If path is a directory,
then the files in the directory are sorted by strverscmp(3);
files that start with "." or without an .fstab extension are
ignored. The option can be specified more than once. This
option is mostly designed for initramfs or chroot scripts
where additional configuration is specified beyond standard
system configuration.
Note that mount(8) does not pass the option --fstab to the
/sbin/mount.type helpers, meaning that the alternative fstab
files will be invisible for the helpers. This is no problem
for normal mounts, but user (non-root) mounts always require
fstab to verify the user's rights.
-t, --types fstype
The argument following the -t is used to indicate the
filesystem type. The filesystem types which are currently
supported depend on the running kernel. See /proc/filesystems
and /lib/modules/$(uname -r)/kernel/fs for a complete list of
the filesystems. The most common are ext2, ext3, ext4, xfs,
btrfs, vfat, sysfs, proc, nfs and cifs.
The programs mount and umount support filesystem subtypes.
The subtype is defined by a '.subtype' suffix. For example
'fuse.sshfs'. It's recommended to use subtype notation rather
than add any prefix to the mount source (for example
'sshfs#example.com' is deprecated).
If no -t option is given, or if the auto type is specified,
mount will try to guess the desired type. Mount uses the
blkid library for guessing the filesystem type; if that does
not turn up anything that looks familiar, mount will try to
read the file /etc/filesystems, or, if that does not exist,
/proc/filesystems. All of the filesystem types listed there
will be tried, except for those that are labeled "nodev" (e.g.
devpts, proc and nfs). If /etc/filesystems ends in a line
with a single *, mount will read /proc/filesystems afterwards.
While trying, all filesystem types will be mounted with the
mount option silent.
The auto type may be useful for user-mounted floppies.
Creating a file /etc/filesystems can be useful to change the
probe order (e.g., to try vfat before msdos or ext3 before
ext2) or if you use a kernel module autoloader.
More than one type may be specified in a comma-separated list,
for the -t option as well as in an /etc/fstab entry. The list
of filesystem types for the -t option can be prefixed with no
to specify the filesystem types on which no action should be
taken. The prefix no has no effect when specified in an
/etc/fstab entry.
The prefix no can be meaningful with the -a option. For
example, the command
mount -a -t nomsdos,smbfs
mounts all filesystems except those of type msdos and smbfs.
For most types all the mount program has to do is issue a
simple mount(2) system call, and no detailed knowledge of the
filesystem type is required. For a few types however (like
nfs, nfs4, cifs, smbfs, ncpfs) an ad hoc code is necessary.
The nfs, nfs4, cifs, smbfs, and ncpfs filesystems have a
separate mount program. In order to make it possible to treat
all types in a uniform way, mount will execute the program
/sbin/mount.type (if that exists) when called with type type.
Since different versions of the smbmount program have
different calling conventions, /sbin/mount.smbfs may have to
be a shell script that sets up the desired call.
-U, --uuid uuid
Mount the partition that has the specified uuid.
-v, --verbose
Verbose mode.
-w, --rw, --read-write
Mount the filesystem read/write. Read-write is the kernel
default and the mount default is to try read-only if the
previous mount syscall with read-write flags on write-
protected devices of filesystems failed.
A synonym is -o rw.
Note that specifying -w on the command line forces mount to
never try read-only mount on write-protected devices or
already mounted read-only filesystems.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
FILESYSTEM-INDEPENDENT MOUNT OPTIONS top
Some of these options are only useful when they appear in the
/etc/fstab file.
Some of these options could be enabled or disabled by default in the
system kernel. To check the current setting see the options in
/proc/mounts. Note that filesystems also have per-filesystem
specific default mount options (see for example tune2fs -l output for
extN filesystems).
The following options apply to any filesystem that is being mounted
(but not every filesystem actually honors them – e.g., the sync
option today has an effect only for ext2, ext3, ext4, fat, vfat, ufs
and xfs):
async All I/O to the filesystem should be done asynchronously. (See
also the sync option.)
atime Do not use the noatime feature, so the inode access time is
controlled by kernel defaults. See also the descriptions of
the relatime and strictatime mount options.
noatime
Do not update inode access times on this filesystem (e.g. for
faster access on the news spool to speed up news servers).
This works for all inode types (directories too), so it
implies nodiratime.
auto Can be mounted with the -a option.
noauto Can only be mounted explicitly (i.e., the -a option will not
cause the filesystem to be mounted).
context=context, fscontext=context, defcontext=context, and
rootcontext=context
The context= option is useful when mounting filesystems that
do not support extended attributes, such as a floppy or hard
disk formatted with VFAT, or systems that are not normally
running under SELinux, such as an ext3 or ext4 formatted disk
from a non-SELinux workstation. You can also use context= on
filesystems you do not trust, such as a floppy. It also helps
in compatibility with xattr-supporting filesystems on earlier
2.4.<x> kernel versions. Even where xattrs are supported, you
can save time not having to label every file by assigning the
entire disk one security context.
A commonly used option for removable media is
context="system_u:object_r:removable_t".
Two other options are fscontext= and defcontext=, both of
which are mutually exclusive of the context= option. This
means you can use fscontext and defcontext with each other,
but neither can be used with context.
The fscontext= option works for all filesystems, regardless of
their xattr support. The fscontext option sets the
overarching filesystem label to a specific security context.
This filesystem label is separate from the individual labels
on the files. It represents the entire filesystem for certain
kinds of permission checks, such as during mount or file
creation. Individual file labels are still obtained from the
xattrs on the files themselves. The context option actually
sets the aggregate context that fscontext provides, in
addition to supplying the same label for individual files.
You can set the default security context for unlabeled files
using defcontext= option. This overrides the value set for
unlabeled files in the policy and requires a filesystem that
supports xattr labeling.
The rootcontext= option allows you to explicitly label the
root inode of a FS being mounted before that FS or inode
becomes visible to userspace. This was found to be useful for
things like stateless Linux.
Note that the kernel rejects any remount request that includes
the context option, even when unchanged from the current
context.
Warning: the context value might contain commas, in which case
the value has to be properly quoted, otherwise mount(8) will
interpret the comma as a separator between mount options.
Don't forget that the shell strips off quotes and thus double
quoting is required. For example:
mount -t tmpfs none /mnt -o \
'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'
For more details, see selinux(8).
defaults
Use the default options: rw, suid, dev, exec, auto, nouser,
and async.
Note that the real set of all default mount options depends on
the kernel and filesystem type. See the beginning of this
section for more details.
dev Interpret character or block special devices on the
filesystem.
nodev Do not interpret character or block special devices on the
filesystem.
diratime
Update directory inode access times on this filesystem. This
is the default. (This option is ignored when noatime is set.)
nodiratime
Do not update directory inode access times on this filesystem.
(This option is implied when noatime is set.)
dirsync
All directory updates within the filesystem should be done
synchronously. This affects the following system calls:
creat, link, unlink, symlink, mkdir, rmdir, mknod and rename.
exec Permit execution of binaries.
noexec Do not permit direct execution of any binaries on the mounted
filesystem.
group Allow an ordinary user to mount the filesystem if one of that
user's groups matches the group of the device. This option
implies the options nosuid and nodev (unless overridden by
subsequent options, as in the option line group,dev,suid).
iversion
Every time the inode is modified, the i_version field will be
incremented.
noiversion
Do not increment the i_version inode field.
mand Allow mandatory locks on this filesystem. See fcntl(2).
nomand Do not allow mandatory locks on this filesystem.
_netdev
The filesystem resides on a device that requires network
access (used to prevent the system from attempting to mount
these filesystems until the network has been enabled on the
system).
nofail Do not report errors for this device if it does not exist.
relatime
Update inode access times relative to modify or change time.
Access time is only updated if the previous access time was
earlier than the current modify or change time. (Similar to
noatime, but it doesn't break mutt or other applications that
need to know if a file has been read since the last time it
was modified.)
Since Linux 2.6.30, the kernel defaults to the behavior
provided by this option (unless noatime was specified), and
the strictatime option is required to obtain traditional
semantics. In addition, since Linux 2.6.30, the file's last
access time is always updated if it is more than 1 day old.
norelatime
Do not use the relatime feature. See also the strictatime
mount option.
strictatime
Allows to explicitly request full atime updates. This makes
it possible for the kernel to default to relatime or noatime
but still allow userspace to override it. For more details
about the default system mount options see /proc/mounts.
nostrictatime
Use the kernel's default behavior for inode access time
updates.
lazytime
Only update times (atime, mtime, ctime) on the in-memory
version of the file inode.
This mount option significantly reduces writes to the inode
table for workloads that perform frequent random writes to
preallocated files.
The on-disk timestamps are updated only when:
- the inode needs to be updated for some change unrelated to
file timestamps
- the application employs fsync(2), syncfs(2), or sync(2)
- an undeleted inode is evicted from memory
- more than 24 hours have passed since the i-node was written
to disk.
nolazytime
Do not use the lazytime feature.
suid Honor set-user-ID and set-group-ID bits or file capabilities
when executing programs from this filesystem.
nosuid Do not honor set-user-ID and set-group-ID bits or file
capabilities when executing programs from this filesystem.
silent Turn on the silent flag.
loud Turn off the silent flag.
owner Allow an ordinary user to mount the filesystem if that user is
the owner of the device. This option implies the options
nosuid and nodev (unless overridden by subsequent options, as
in the option line owner,dev,suid).
remount
Attempt to remount an already-mounted filesystem. This is
commonly used to change the mount flags for a filesystem,
especially to make a readonly filesystem writable. It does
not change device or mount point.
The remount operation together with the bind flag has special
semantics. See above, the subsection Bind mounts.
The remount functionality follows the standard way the mount
command works with options from fstab. This means that mount
does not read fstab (or mtab) only when both device and dir
are specified.
mount -o remount,rw /dev/foo /dir
After this call all old mount options are replaced and
arbitrary stuff from fstab (or mtab) is ignored, except the
loop= option which is internally generated and maintained by
the mount command.
mount -o remount,rw /dir
After this call, mount reads fstab and merges these options
with the options from the command line (-o). If no mountpoint
is found in fstab, then a remount with unspecified source is
allowed.
mount allows the use of --all to remount all already mounted
filesystems which match a specified filter (-O and -t). For
example:
mount --all -o remount,ro -t vfat
remounts all already mounted vfat filesystems in read-only
mode. Each of the filesystems is remounted by "mount -o
remount,ro /dir" semantic. This means the mount command reads
fstab or mtab and merges these options with the options from
the command line.
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
sync All I/O to the filesystem should be done synchronously. In
the case of media with a limited number of write cycles (e.g.
some flash drives), sync may cause life-cycle shortening.
user Allow an ordinary user to mount the filesystem. The name of
the mounting user is written to the mtab file (or to the
private libmount file in /run/mount on systems without a
regular mtab) so that this same user can unmount the
filesystem again. This option implies the options noexec,
nosuid, and nodev (unless overridden by subsequent options, as
in the option line user,exec,dev,suid).
nouser Forbid an ordinary user to mount the filesystem. This is the
default; it does not imply any other options.
users Allow any user to mount and to unmount the filesystem, even
when some other ordinary user mounted it. This option implies
the options noexec, nosuid, and nodev (unless overridden by
subsequent options, as in the option line
users,exec,dev,suid).
X-* All options prefixed with "X-" are interpreted as comments or
as userspace application-specific options. These options are
not stored in user space (e.g., mtab file), nor sent to the
mount.type helpers nor to the mount(2) system call. The
suggested format is X-appname.option.
x-* The same as X-* options, but stored permanently in user space.
This means the options are also available for umount or other
operations. Note that maintaining mount options in user
space is tricky, because it's necessary use libmount-based
tools and there is no guarantee that the options will be
always available (for example after a move mount operation or
in unshared namespace).
Note that before util-linux v2.30 the x-* options have not
been maintained by libmount and stored in user space
(functionality was the same as for X-* now), but due to the
growing number of use-cases (in initrd, systemd etc.) the
functionality has been extended to keep existing fstab
configurations usable without a change.
X-mount.mkdir[=mode]
Allow to make a target directory (mountpoint) if it does not
exit yet. The optional argument mode specifies the filesystem
access mode used for mkdir(2) in octal notation. The default
mode is 0755. This functionality is supported only for root
users or when mount executed without suid permissions. The
option is also supported as x-mount.mkdir, this notation is
deprecated since v2.30.
FILESYSTEM-SPECIFIC MOUNT OPTIONS top
This section lists options that are specific to particular
filesystems. Where possible, you should first consult filesystem-
specific manual pages for details. Some of those pages are listed in
the following table.
Filesystem(s) Manual page
btrfs btrfs(5)
cifs mount.cifs(8)
ext2, ext3, ext4 ext4(5)
fuse fuse(8)
nfs nfs(5)
tmpfs tmpfs(5)
xfs xfs(5)
Note that some of the pages listed above might be available only
after you install the respective userland tools.
The following options apply only to certain filesystems. We sort
them by filesystem. All options follow the -o flag.
What options are supported depends a bit on the running kernel.
Further information may be available in filesystem-specific files in
the kernel source subdirectory Documentation/filesystems.
Mount options for adfs
uid=value and gid=value
Set the owner and group of the files in the filesystem
(default: uid=gid=0).
ownmask=value and othmask=value
Set the permission mask for ADFS 'owner' permissions and
'other' permissions, respectively (default: 0700 and 0077,
respectively). See also
/usr/src/linux/Documentation/filesystems/adfs.rst.
Mount options for affs
uid=value and gid=value
Set the owner and group of the root of the filesystem
(default: uid=gid=0, but with option uid or gid without
specified value, the UID and GID of the current process are
taken).
setuid=value and setgid=value
Set the owner and group of all files.
mode=value
Set the mode of all files to value & 0777 disregarding the
original permissions. Add search permission to directories
that have read permission. The value is given in octal.
protect
Do not allow any changes to the protection bits on the
filesystem.
usemp Set UID and GID of the root of the filesystem to the UID and
GID of the mount point upon the first sync or umount, and then
clear this option. Strange...
verbose
Print an informational message for each successful mount.
prefix=string
Prefix used before volume name, when following a link.
volume=string
Prefix (of length at most 30) used before '/' when following a
symbolic link.
reserved=value
(Default: 2.) Number of unused blocks at the start of the
device.
root=value
Give explicitly the location of the root block.
bs=value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota|noquota|quota|usrquota
These options are accepted but ignored. (However, quota
utilities may react to such strings in /etc/fstab.)
Mount options for debugfs
The debugfs filesystem is a pseudo filesystem, traditionally mounted
on /sys/kernel/debug. As of kernel version 3.4, debugfs has the
following options:
uid=n, gid=n
Set the owner and group of the mountpoint.
mode=value
Sets the mode of the mountpoint.
Mount options for devpts
The devpts filesystem is a pseudo filesystem, traditionally mounted
on /dev/pts. In order to acquire a pseudo terminal, a process opens
/dev/ptmx; the number of the pseudo terminal is then made available
to the process and the pseudo terminal slave can be accessed as
/dev/pts/<number>.
uid=value and gid=value
This sets the owner or the group of newly created pseudo
terminals to the specified values. When nothing is specified,
they will be set to the UID and GID of the creating process.
For example, if there is a tty group with GID 5, then gid=5
will cause newly created pseudo terminals to belong to the tty
group.
mode=value
Set the mode of newly created pseudo terminals to the
specified value. The default is 0600. A value of mode=620
and gid=5 makes "mesg y" the default on newly created pseudo
terminals.
newinstance
Create a private instance of the devpts filesystem, such that
indices of pseudo terminals allocated in this new instance are
independent of indices created in other instances of devpts.
All mounts of devpts without this newinstance option share the
same set of pseudo terminal indices (i.e., legacy mode). Each
mount of devpts with the newinstance option has a private set
of pseudo terminal indices.
This option is mainly used to support containers in the Linux
kernel. It is implemented in Linux kernel versions starting
with 2.6.29. Further, this mount option is valid only if
CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel
configuration.
To use this option effectively, /dev/ptmx must be a symbolic
link to pts/ptmx. See Documentation/filesystems/devpts.txt in
the Linux kernel source tree for details.
ptmxmode=value
Set the mode for the new ptmx device node in the devpts
filesystem.
With the support for multiple instances of devpts (see
newinstance option above), each instance has a private ptmx
node in the root of the devpts filesystem (typically
/dev/pts/ptmx).
For compatibility with older versions of the kernel, the
default mode of the new ptmx node is 0000. ptmxmode=value
specifies a more useful mode for the ptmx node and is highly
recommended when the newinstance option is specified.
This option is only implemented in Linux kernel versions
starting with 2.6.29. Further, this option is valid only if
CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel
configuration.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the
msdos, umsdos and vfat filesystems.)
blocksize={512|1024|2048}
Set blocksize (default 512). This option is obsolete.
uid=value and gid=value
Set the owner and group of all files. (Default: the UID and
GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process.
The value is given in octal.
dmask=value
Set the umask applied to directories only. The default is the
umask of the current process. The value is given in octal.
fmask=value
Set the umask applied to regular files only. The default is
the umask of the current process. The value is given in
octal.
allow_utime=value
This option controls the permission check of mtime/atime.
20 If current process is in group of file's group ID, you
can change timestamp.
2 Other users can change timestamp.
The default is set from `dmask' option. (If the directory is
writable, utime(2) is also allowed. I.e. ~dmask & 022)
Normally utime(2) checks that the current process is owner of
the file, or that it has the CAP_FOWNER capability. But FAT
filesystems don't have UID/GID on disk, so the normal check is
too inflexible. With this option you can relax it.
check=value
Three different levels of pickiness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent, long
name parts are truncated (e.g. verylongname.foobar
becomes verylong.foo), leading and embedded spaces are
accepted in each name part (name and extension).
n[ormal]
Like "relaxed", but many special characters (*, ?, <,
spaces, etc.) are rejected. This is the default.
s[trict]
Like "normal", but names that contain long parts or
special characters that are sometimes used on Linux but
are not accepted by MS-DOS (+, =, etc.) are rejected.
codepage=value
Sets the codepage for converting to shortname characters on
FAT and VFAT filesystems. By default, codepage 437 is used.
conv=mode
This option is obsolete and may fail or be ignored.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File)
module cvf_module instead of auto-detection. If the kernel
supports kmod, the cvf_format=xxx option also controls on-
demand CVF module loading. This option is obsolete.
cvf_option=option
Option passed to the CVF module. This option is obsolete.
debug Turn on the debug flag. A version string and a list of
filesystem parameters will be printed (these data are also
printed if the parameters appear to be inconsistent).
discard
If set, causes discard/TRIM commands to be issued to the block
device when blocks are freed. This is useful for SSD devices
and sparse/thinly-provisioned LUNs.
dos1xfloppy
If set, use a fallback default BIOS Parameter Block
configuration, determined by backing device size. These
static parameters match defaults assumed by DOS 1.x for 160
kiB, 180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
errors={panic|continue|remount-ro}
Specify FAT behavior on critical errors: panic, continue
without doing anything, or remount the partition in read-only
mode (default behavior).
fat={12|16|32}
Specify a 12, 16 or 32 bit fat. This overrides the automatic
FAT type detection routine. Use with caution!
iocharset=value
Character set to use for converting between 8 bit characters
and 16 bit Unicode characters. The default is iso8859-1.
Long filenames are stored on disk in Unicode format.
nfs={stale_rw|nostale_ro}
Enable this only if you want to export the FAT filesystem over
NFS.
stale_rw: This option maintains an index (cache) of directory
inodes which is used by the nfs-related code to improve look-
ups. Full file operations (read/write) over NFS are supported
but with cache eviction at NFS server, this could result in
spurious ESTALE errors.
nostale_ro: This option bases the inode number and file handle
on the on-disk location of a file in the FAT directory entry.
This ensures that ESTALE will not be returned after a file is
evicted from the inode cache. However, it means that
operations such as rename, create and unlink could cause file
handles that previously pointed at one file to point at a
different file, potentially causing data corruption. For this
reason, this option also mounts the filesystem readonly.
To maintain backward compatibility, '-o nfs' is also accepted,
defaulting to stale_rw.
tz=UTC This option disables the conversion of timestamps between
local time (as used by Windows on FAT) and UTC (which Linux
uses internally). This is particularly useful when mounting
devices (like digital cameras) that are set to UTC in order to
avoid the pitfalls of local time.
time_offset=minutes
Set offset for conversion of timestamps from local time used
by FAT to UTC. I.e., minutes will be subtracted from each
timestamp to convert it to UTC used internally by Linux. This
is useful when the time zone set in the kernel via
settimeofday(2) is not the time zone used by the filesystem.
Note that this option still does not provide correct time
stamps in all cases in presence of DST - time stamps in a
different DST setting will be off by one hour.
quiet Turn on the quiet flag. Attempts to chown or chmod files do
not return errors, although they fail. Use with caution!
rodir FAT has the ATTR_RO (read-only) attribute. On Windows, the
ATTR_RO of the directory will just be ignored, and is used
only by applications as a flag (e.g. it's set for the
customized folder).
If you want to use ATTR_RO as read-only flag even for the
directory, set this option.
showexec
If set, the execute permission bits of the file will be
allowed only if the extension part of the name is .EXE, .COM,
or .BAT. Not set by default.
sys_immutable
If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag
on Linux. Not set by default.
flush If set, the filesystem will try to flush to disk more early
than normal. Not set by default.
usefree
Use the "free clusters" value stored on FSINFO. It'll be used
to determine number of free clusters without scanning disk.
But it's not used by default, because recent Windows don't
update it correctly in some case. If you are sure the "free
clusters" on FSINFO is correct, by this option you can avoid
scanning disk.
dots, nodots, dotsOK=[yes|no]
Various misguided attempts to force Unix or DOS conventions
onto a FAT filesystem.
Mount options for hfs
creator=cccc, type=cccc
Set the creator/type values as shown by the MacOS finder used
for creating new files. Default values: '????'.
uid=n, gid=n
Set the owner and group of all files. (Default: the UID and
GID of the current process.)
dir_umask=n, file_umask=n, umask=n
Set the umask used for all directories, all regular files, or
all files and directories. Defaults to the umask of the
current process.
session=n
Select the CDROM session to mount. Defaults to leaving that
decision to the CDROM driver. This option will fail with
anything but a CDROM as underlying device.
part=n Select partition number n from the device. Only makes sense
for CDROMs. Defaults to not parsing the partition table at
all.
quiet Don't complain about invalid mount options.
Mount options for hpfs
uid=value and gid=value
Set the owner and group of all files. (Default: the UID and
GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process.
The value is given in octal.
case={lower|asis}
Convert all files names to lower case, or leave them.
(Default: case=lower.)
conv=mode
This option is obsolete and may fail or being ignored.
nocheck
Do not abort mounting when certain consistency checks fail.
Mount options for iso9660
ISO 9660 is a standard describing a filesystem structure to be used
on CD-ROMs. (This filesystem type is also seen on some DVDs. See
also the udf filesystem.)
Normal iso9660 filenames appear in an 8.3 format (i.e., DOS-like
restrictions on filename length), and in addition all characters are
in upper case. Also there is no field for file ownership,
protection, number of links, provision for block/character devices,
etc.
Rock Ridge is an extension to iso9660 that provides all of these
UNIX-like features. Basically there are extensions to each directory
record that supply all of the additional information, and when Rock
Ridge is in use, the filesystem is indistinguishable from a normal
UNIX filesystem (except that it is read-only, of course).
norock Disable the use of Rock Ridge extensions, even if available.
Cf. map.
nojoliet
Disable the use of Microsoft Joliet extensions, even if
available. Cf. map.
check={r[elaxed]|s[trict]}
With check=relaxed, a filename is first converted to lower
case before doing the lookup. This is probably only
meaningful together with norock and map=normal. (Default:
check=strict.)
uid=value and gid=value
Give all files in the filesystem the indicated user or group
id, possibly overriding the information found in the Rock
Ridge extensions. (Default: uid=0,gid=0.)
map={n[ormal]|o[ff]|a[corn]}
For non-Rock Ridge volumes, normal name translation maps upper
to lower case ASCII, drops a trailing `;1', and converts `;'
to `.'. With map=off no name translation is done. See
norock. (Default: map=normal.) map=acorn is like map=normal
but also apply Acorn extensions if present.
mode=value
For non-Rock Ridge volumes, give all files the indicated mode.
(Default: read and execute permission for everybody.) Octal
mode values require a leading 0.
unhide Also show hidden and associated files. (If the ordinary files
and the associated or hidden files have the same filenames,
this may make the ordinary files inaccessible.)
block={512|1024|2048}
Set the block size to the indicated value. (Default:
block=1024.)
conv=mode
This option is obsolete and may fail or being ignored.
cruft If the high byte of the file length contains other garbage,
set this mount option to ignore the high order bits of the
file length. This implies that a file cannot be larger than
16 MB.
session=x
Select number of session on multisession CD.
sbsector=xxx
Session begins from sector xxx.
The following options are the same as for vfat and specifying them
only makes sense when using discs encoded using Microsoft's Joliet
extensions.
iocharset=value
Character set to use for converting 16 bit Unicode characters
on CD to 8 bit characters. The default is iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for jfs
iocharset=name
Character set to use for converting from Unicode to ASCII.
The default is to do no conversion. Use iocharset=utf8 for
UTF8 translations. This requires CONFIG_NLS_UTF8 to be set in
the kernel .config file.
resize=value
Resize the volume to value blocks. JFS only supports growing
a volume, not shrinking it. This option is only valid during
a remount, when the volume is mounted read-write. The resize
keyword with no value will grow the volume to the full size of
the partition.
nointegrity
Do not write to the journal. The primary use of this option
is to allow for higher performance when restoring a volume
from backup media. The integrity of the volume is not
guaranteed if the system abnormally ends.
integrity
Default. Commit metadata changes to the journal. Use this
option to remount a volume where the nointegrity option was
previously specified in order to restore normal behavior.
errors={continue|remount-ro|panic}
Define the behavior when an error is encountered. (Either
ignore errors and just mark the filesystem erroneous and
continue, or remount the filesystem read-only, or panic and
halt the system.)
noquota|quota|usrquota|grpquota
These options are accepted but ignored.
Mount options for msdos
See mount options for fat. If the msdos filesystem detects an
inconsistency, it reports an error and sets the file system read-
only. The filesystem can be made writable again by remounting it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument (a
struct ncp_mount_data) to the mount system call. This argument is
constructed by ncpmount(8) and the current version of mount (2.12)
does not know anything about ncpfs.
Mount options for ntfs
iocharset=name
Character set to use when returning file names. Unlike VFAT,
NTFS suppresses names that contain nonconvertible characters.
Deprecated.
nls=name
New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
uni_xlate={0|1|2}
For 0 (or `no' or `false'), do not use escape sequences for
unknown Unicode characters. For 1 (or `yes' or `true') or 2,
use vfat-style 4-byte escape sequences starting with ":".
Here 2 give a little-endian encoding and 1 a byteswapped
bigendian encoding.
posix=[0|1]
If enabled (posix=1), the filesystem distinguishes between
upper and lower case. The 8.3 alias names are presented as
hard links instead of being suppressed. This option is
obsolete.
uid=value, gid=value and umask=value
Set the file permission on the filesystem. The umask value is
given in octal. By default, the files are owned by root and
not readable by somebody else.
Mount options for overlay
Since Linux 3.18 the overlay pseudo filesystem implements a union
mount for other filesystems.
An overlay filesystem combines two filesystems - an upper filesystem
and a lower filesystem. When a name exists in both filesystems, the
object in the upper filesystem is visible while the object in the
lower filesystem is either hidden or, in the case of directories,
merged with the upper object.
The lower filesystem can be any filesystem supported by Linux and
does not need to be writable. The lower filesystem can even be
another overlayfs. The upper filesystem will normally be writable
and if it is it must support the creation of trusted.* extended
attributes, and must provide a valid d_type in readdir responses, so
NFS is not suitable.
A read-only overlay of two read-only filesystems may use any
filesystem type. The options lowerdir and upperdir are combined into
a merged directory by using:
mount -t overlay overlay \
-olowerdir=/lower,upperdir=/upper,workdir=/work /merged
lowerdir=directory
Any filesystem, does not need to be on a writable filesystem.
upperdir=directory
The upperdir is normally on a writable filesystem.
workdir=directory
The workdir needs to be an empty directory on the same
filesystem as upperdir.
Mount options for reiserfs
Reiserfs is a journaling filesystem.
conv Instructs version 3.6 reiserfs software to mount a version 3.5
filesystem, using the 3.6 format for newly created objects.
This filesystem will no longer be compatible with reiserfs 3.5
tools.
hash={rupasov|tea|r5|detect}
Choose which hash function reiserfs will use to find files
within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast and
preserves locality, mapping lexicographically close
file names to close hash values. This option should
not be used, as it causes a high probability of hash
collisions.
tea A Davis-Meyer function implemented by Jeremy
Fitzhardinge. It uses hash permuting bits in the name.
It gets high randomness and, therefore, low probability
of hash collisions at some CPU cost. This may be used
if EHASHCOLLISION errors are experienced with the r5
hash.
r5 A modified version of the rupasov hash. It is used by
default and is the best choice unless the filesystem
has huge directories and unusual file-name patterns.
detect Instructs mount to detect which hash function is in use
by examining the filesystem being mounted, and to write
this information into the reiserfs superblock. This is
only useful on the first mount of an old format
filesystem.
hashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
noborder
Disable the border allocator algorithm invented by Yury Yu.
Rupasov. This may provide performance improvements in some
situations.
nolog Disable journaling. This will provide slight performance
improvements in some situations at the cost of losing
reiserfs's fast recovery from crashes. Even with this option
turned on, reiserfs still performs all journaling operations,
save for actual writes into its journaling area.
Implementation of nolog is a work in progress.
notail By default, reiserfs stores small files and `file tails'
directly into its tree. This confuses some utilities such as
LILO(8). This option is used to disable packing of files into
the tree.
replayonly
Replay the transactions which are in the journal, but do not
actually mount the filesystem. Mainly used by reiserfsck.
resize=number
A remount option which permits online expansion of reiserfs
partitions. Instructs reiserfs to assume that the device has
number blocks. This option is designed for use with devices
which are under logical volume management (LVM). There is a
special resizer utility which can be obtained from
ftp://ftp.namesys.com/pub/reiserfsprogs.
user_xattr
Enable Extended User Attributes. See the attr(1) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual
page.
barrier=none / barrier=flush
This disables / enables the use of write barriers in the
journaling code. barrier=none disables, barrier=flush enables
(default). This also requires an IO stack which can support
barriers, and if reiserfs gets an error on a barrier write, it
will disable barriers again with a warning. Write barriers
enforce proper on-disk ordering of journal commits, making
volatile disk write caches safe to use, at some performance
penalty. If your disks are battery-backed in one way or
another, disabling barriers may safely improve performance.
Mount options for ubifs
UBIFS is a flash filesystem which works on top of UBI volumes. Note
that atime is not supported and is always turned off.
The device name may be specified as
ubiX_Y UBI device number X, volume number Y
ubiY UBI device number 0, volume number Y
ubiX:NAME
UBI device number X, volume with name NAME
ubi:NAME
UBI device number 0, volume with name NAME
Alternative ! separator may be used instead of :.
The following mount options are available:
bulk_read
Enable bulk-read. VFS read-ahead is disabled because it slows
down the filesystem. Bulk-Read is an internal optimization.
Some flashes may read faster if the data are read at one go,
rather than at several read requests. For example, OneNAND
can do "read-while-load" if it reads more than one NAND page.
no_bulk_read
Do not bulk-read. This is the default.
chk_data_crc
Check data CRC-32 checksums. This is the default.
no_chk_data_crc.
Do not check data CRC-32 checksums. With this option, the
filesystem does not check CRC-32 checksum for data, but it
does check it for the internal indexing information. This
option only affects reading, not writing. CRC-32 is always
calculated when writing the data.
compr={none|lzo|zlib}
Select the default compressor which is used when new files are
written. It is still possible to read compressed files if
mounted with the none option.
Mount options for udf
UDF is the "Universal Disk Format" filesystem defined by OSTA, the
Optical Storage Technology Association, and is often used for DVD-
ROM, frequently in the form of a hybrid UDF/ISO-9660 filesystem. It
is, however, perfectly usable by itself on disk drives, flash drives
and other block devices. See also iso9660.
uid= Make all files in the filesystem belong to the given user.
uid=forget can be specified independently of (or usually in
addition to) uid=<user> and results in UDF not storing uids to
the media. In fact the recorded uid is the 32-bit overflow uid
-1 as defined by the UDF standard. The value is given as
either <user> which is a valid user name or the corresponding
decimal user id, or the special string "forget".
gid= Make all files in the filesystem belong to the given group.
gid=forget can be specified independently of (or usually in
addition to) gid=<group> and results in UDF not storing gids
to the media. In fact the recorded gid is the 32-bit overflow
gid -1 as defined by the UDF standard. The value is given as
either <group> which is a valid group name or the
corresponding decimal group id, or the special string
"forget".
umask= Mask out the given permissions from all inodes read from the
filesystem. The value is given in octal.
mode= If mode= is set the permissions of all non-directory inodes
read from the filesystem will be set to the given mode. The
value is given in octal.
dmode= If dmode= is set the permissions of all directory inodes read
from the filesystem will be set to the given dmode. The value
is given in octal.
bs= Set the block size. Default value prior to kernel version
2.6.30 was 2048. Since 2.6.30 and prior to 4.11 it was logical
device block size with fallback to 2048. Since 4.11 it is
logical block size with fallback to any valid block size
between logical device block size and 4096.
For other details see the mkudffs(8) 2.0+ manpage, sections
COMPATIBILITY and BLOCK SIZE.
unhide Show otherwise hidden files.
undelete
Show deleted files in lists.
adinicb
Embed data in the inode. (default)
noadinicb
Don't embed data in the inode.
shortad
Use short UDF address descriptors.
longad Use long UDF address descriptors. (default)
nostrict
Unset strict conformance.
iocharset=
Set the NLS character set. This requires kernel compiled with
CONFIG_UDF_NLS option.
utf8 Set the UTF-8 character set.
Mount options for debugging and disaster recovery
novrs Ignore the Volume Recognition Sequence and attempt to mount
anyway.
session=
Select the session number for multi-session recorded optical
media. (default= last session)
anchor=
Override standard anchor location. (default= 256)
lastblock=
Set the last block of the filesystem.
Unused historical mount options that may be encountered and should be
removed
uid=ignore
Ignored, use uid=<user> instead.
gid=ignore
Ignored, use gid=<group> instead.
volume=
Unimplemented and ignored.
partition=
Unimplemented and ignored.
fileset=
Unimplemented and ignored.
rootdir=
Unimplemented and ignored.
Mount options for ufs
ufstype=value
UFS is a filesystem widely used in different operating
systems. The problem are differences among implementations.
Features of some implementations are undocumented, so its hard
to recognize the type of ufs automatically. That's why the
user must specify the type of ufs by mount option. Possible
values are:
old Old format of ufs, this is the default, read only.
(Don't forget to give the -r option.)
44bsd For filesystems created by a BSD-like system (NetBSD,
FreeBSD, OpenBSD).
ufs2 Used in FreeBSD 5.x supported as read-write.
5xbsd Synonym for ufs2.
sun For filesystems created by SunOS or Solaris on Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT station)
(currently read only).
nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
openstep
For filesystems created by OpenStep (currently read
only). The same filesystem type is also used by Mac OS
X.
onerror=value
Set behavior on error:
panic If an error is encountered, cause a kernel panic.
[lock|umount|repair]
These mount options don't do anything at present; when
an error is encountered only a console message is
printed.
Mount options for umsdos
See mount options for msdos. The dotsOK option is explicitly killed
by umsdos.
Mount options for vfat
First of all, the mount options for fat are recognized. The dotsOK
option is explicitly killed by vfat. Furthermore, there are
uni_xlate
Translate unhandled Unicode characters to special escaped
sequences. This lets you backup and restore filenames that
are created with any Unicode characters. Without this option,
a '?' is used when no translation is possible. The escape
character is ':' because it is otherwise invalid on the vfat
filesystem. The escape sequence that gets used, where u is
the Unicode character, is: ':', (u & 0x3f), ((u>>6) & 0x3f),
(u>>12).
posix Allow two files with names that only differ in case. This
option is obsolete.
nonumtail
First try to make a short name without sequence number, before
trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is
used by the console. It can be enabled for the filesystem
with this option or disabled with utf8=0, utf8=no or
utf8=false. If `uni_xlate' gets set, UTF8 gets disabled.
shortname=mode
Defines the behavior for creation and display of filenames
which fit into 8.3 characters. If a long name for a file
exists, it will always be the preferred one for display.
There are four modes:
lower Force the short name to lower case upon display; store
a long name when the short name is not all upper case.
win95 Force the short name to upper case upon display; store
a long name when the short name is not all upper case.
winnt Display the short name as is; store a long name when
the short name is not all lower case or all upper case.
mixed Display the short name as is; store a long name when
the short name is not all upper case. This mode is the
default since Linux 2.6.32.
Mount options for usbfs
devuid=uid and devgid=gid and devmode=mode
Set the owner and group and mode of the device files in the
usbfs filesystem (default: uid=gid=0, mode=0644). The mode is
given in octal.
busuid=uid and busgid=gid and busmode=mode
Set the owner and group and mode of the bus directories in the
usbfs filesystem (default: uid=gid=0, mode=0555). The mode is
given in octal.
listuid=uid and listgid=gid and listmode=mode
Set the owner and group and mode of the file devices (default:
uid=gid=0, mode=0444). The mode is given in octal.
DM-VERITY SUPPORT (experimental) top
The device-mapper verity target provides read-only transparent
integrity checking of block devices using kernel crypto API. The
mount command can open the dm-verity device and do the integrity
verification before on the device filesystem is mounted. Requires
libcryptsetup with in libmount (optionally via dlopen). If
libcryptsetup supports extracting the root hash of an already mounted
device, existing devices will be automatically reused in case of a
match. Mount options for dm-verity:
verity.hashdevice=path
Path to the hash tree device associated with the source volume
to pass to dm-verity.
verity.roothash=hex
Hex-encoded hash of the root of verity.hashdevice Mutually
exclusive with verity.roothashfile.
verity.roothashfile=path
Path to file containing the hex-encoded hash of the root of
verity.hashdevice. Mutually exclusive with verity.roothash.
verity.hashoffset=offset
If the hash tree device is embedded in the source volume,
offset (default: 0) is used by dm-verity to get to the tree.
verity.fecdevice=path
Path to the Forward Error Correction (FEC) device associated
with the source volume to pass to dm-verity. Optional.
Requires kernel built with CONFIG_DM_VERITY_FEC.
verity.fecoffset=offset
If the FEC device is embedded in the source volume, offset
(default: 0) is used by dm-verity to get to the FEC area.
Optional.
verity.fecroots=value
Parity bytes for FEC (default: 2). Optional.
verity.roothashsig=path
Path to pkcs7 signature of root hash hex string. Requires
crypt_activate_by_signed_key() from cryptsetup and kernel
built with CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG. For device
reuse, signatures have to be either used by all mounts of a
device or by none. Optional.
Supported since util-linux v2.35.
For example commands:
mksquashfs /etc /tmp/etc.squashfs
dd if=/dev/zero of=/tmp/etc.hash bs=1M count=10
veritysetup format /tmp/etc.squashfs /tmp/etc.hash
openssl smime -sign -in <hash> -nocerts -inkey private.key \
-signer private.crt -noattr -binary -outform der -out /tmp/etc.p7
mount -o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash>,\
verity.roothashsig=/tmp/etc.p7 /tmp/etc.squashfs /mnt
create squashfs image from /etc directory, verity hash device and
mount verified filesystem image to /mnt. The kernel will verify that
the root hash is signed by a key from the kernel keyring if
roothashsig is used.
LOOP-DEVICE SUPPORT top
One further possible type is a mount via the loop device. For
example, the command
mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop3
will set up the loop device /dev/loop3 to correspond to the file
/tmp/disk.img, and then mount this device on /mnt.
If no explicit loop device is mentioned (but just an option `-o loop'
is given), then mount will try to find some unused loop device and
use that, for example
mount /tmp/disk.img /mnt -o loop
The mount command automatically creates a loop device from a regular
file if a filesystem type is not specified or the filesystem is known
for libblkid, for example:
mount /tmp/disk.img /mnt
mount -t ext4 /tmp/disk.img /mnt
This type of mount knows about three options, namely loop, offset and
sizelimit, that are really options to losetup(8). (These options can
be used in addition to those specific to the filesystem type.)
Since Linux 2.6.25 auto-destruction of loop devices is supported,
meaning that any loop device allocated by mount will be freed by
umount independently of /etc/mtab.
You can also free a loop device by hand, using losetup -d or umount
-d.
Since util-linux v2.29, mount re-uses the loop device rather than
initializing a new device if the same backing file is already used
for some loop device with the same offset and sizelimit. This is
necessary to avoid a filesystem corruption.
EXIT STATUS top
mount has the following exit status values (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop
devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
The command mount -a returns 0 (all succeeded), 32 (all
failed), or 64 (some failed, some succeeded).
EXTERNAL HELPERS top
The syntax of external mount helpers is:
/sbin/mount.suffix spec dir [-sfnv] [-N namespace] [-o options]
[-t type.subtype]
where the suffix is the filesystem type and the -sfnvoN options have
the same meaning as the normal mount options. The -t option is used
for filesystems with subtypes support (for example /sbin/mount.fuse
-t fuse.sshfs).
The command mount does not pass the mount options unbindable,
runbindable, private, rprivate, slave, rslave, shared, rshared, auto,
noauto, comment, x-*, loop, offset and sizelimit to the
mount.<suffix> helpers. All other options are used in a comma-
separated list as an argument to the -o option.
ENVIRONMENT top
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file (ignored for
suid)
LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file (ignored for
suid)
LIBMOUNT_DEBUG=all
enables libmount debug output
LIBBLKID_DEBUG=all
enables libblkid debug output
LOOPDEV_DEBUG=all
enables loop device setup debug output
FILES top
See also "The files /etc/fstab, /etc/mtab and /proc/mounts" section
above.
/etc/fstab filesystem table
/run/mount libmount private runtime directory
/etc/mtab table of mounted filesystems or symlink to
/proc/mounts
/etc/mtab~ lock file (unused on systems with mtab symlink)
/etc/mtab.tmp temporary file (unused on systems with mtab
symlink)
/etc/filesystems a list of filesystem types to try
