Updated: 2022/Sep/29

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MOUNT(8)                    System Manager's Manual                   MOUNT(8)

     mount - mount file systems

     mount [-Aadfruvw] [-t type]
     mount [-dfruvw] {special | node}
     mount [-dfruvw] [-o options] [-t type] special node

     The mount command invokes a file system-specific program to prepare and
     graft the special device on to the file system tree at the point node, or
     to update options for an already-mounted file system.

     These programs are named "mount_<fstype>" where "<fstype>" refers to the
     file system-specific type; for example for NFS the mount program is
     called mount_nfs(8).

     The node argument is always interpreted as a directory in the name space
     of currently mounted file systems.  The special argument is interpreted
     in different ways by the programs that handle different file system
     types; for example, mount_ffs(8) interprets it as a device node,
     mount_null(8) interprets it as a directory name, mount_nfs(8) interprets
     it as reference to a remote host and a directory on that host, and
     mount_tmpfs(8) ignores it.

     The system maintains a list of currently mounted file systems.  This list
     is printed if mount is invoked with no arguments, and with no options
     that require some other behaviour.

     If exactly one of special or node is provided, then the missing
     information (including the file system type) is taken from the fstab(5)
     file.  The provided argument is looked up first in the "fs_file", then in
     the "fs_spec" column.  If the matching entry in fstab(5) has the string
     "from_mount" as its "fs_spec" field, the device or remote file system
     already mounted at the location specified by "fs_spec" will be used.

     If both special and node are provided, then fstab(5) is not used.  In
     this case, if the file system type is not specified via the -t flag, then
     mount may determine the type from the disk label (see disklabel(8)).  In
     addition, if special contains a colon (`:') or at sign (`@'), then the
     nfs type is inferred.  In NetBSD, the file system mounting policy is
     dictated by the running security models.  The default security model may
     allow unprivileged mounting; see secmodel_suser(9) and
     secmodel_extensions(9) for details.

     The options are as follows:

     -A      Causes mount to try to mount all of the file systems listed in
             the fstab(5) file except those for which the "noauto" option is

     -a      Similar to the -A flag, except that if a file system (other than
             the root file system) appears to be already mounted, mount will
             not try to mount it again.  mount assumes that a file system is
             already mounted if a file system with the same type is mounted on
             the given mount point.  More stringent checks are not possible
             because some file system types report strange values for the
             mounted-from device for mounted file systems.

     -d      Causes everything to be done except for the invocation of the
             file system-specific program.  This option is useful in
             conjunction with the -v flag to determine what the mount command
             is trying to do.

     -f      Forces the revocation of write access when trying to downgrade a
             file system mount status from read-write to read-only.

     -o      Options are specified with a -o flag followed by a comma
             separated string of options.  The following options are

             async       All I/O to the file system should be done
                         asynchronously.  In the event of a crash, it is
                         impossible for the system to verify the integrity of
                         data on a file system mounted with this option.  You
                         should only use this option if you have an
                         application-specific data recovery mechanism, or are
                         willing to recreate the file system from scratch.

             noasync     Clear async mode.

                         This flag indicates that the file system was mounted
                         by automountd(8).  Automounted file systems are
                         automatically unmounted by autounmountd(8).

             discard     Use DISCARD/TRIM commands if disk and driver support

                         EXPERIMENTAL - negatively influences filesystem
                         performance by increasing fragmentation, causes free
                         block map inconsistency on unclean shutdown, and is
                         incompatible with log.  If log option is also used,
                         discard is automatically disabled.

             extattr     Enable extended attributes, if the filesystem
                         supports them and does not enable them by default.
                         Currently this is only the case for UFS1.

             force       The same as -f; forces the revocation of write access
                         when trying to downgrade a file system mount status
                         from read-write to read-only.

             getargs     Retrieves the file system specific mount arguments
                         for the given mounted file system and prints them.

             hidden      By setting the MNT_IGNORE flag, causes the mount
                         point to be excluded from the list of file systems
                         shown by default with df(1).

             noatime     Never update the access time field for files.  This
                         option is useful for optimizing read performance on
                         file systems, and avoiding excess writes on flash-
                         based file systems.

             noauto      This file system should be skipped when mount is run
                         with the -a flag.

             nocoredump  Do not allow programs to create crash dumps (core
                         files) on the file system.  This option can be used
                         to help protect sensitive data by keeping core files
                         (which may contain sensitive data) from being created
                         on insecure file systems.  Only core files that would
                         be created by program crashes are prevented by use of
                         this flag; the behavior of savecore(8) is not

             nodev       Do not interpret character or block special devices
                         on the file system.  This option is useful for a
                         server that has file systems containing special
                         devices for architectures other than its own.

             nodevmtime  Do not update modification times on device special
                         files.  This option is useful on laptops or other
                         systems that perform power management.

             noexec      Do not allow execution of any binaries on the mounted
                         file system.  This option is useful for a server that
                         has file systems containing binaries for
                         architectures other than its own.

             nosuid      Do not allow set-user-identifier or set-group-
                         identifier bits to take effect.

             port        (NFS only) Use the specified NFS port.

             rdonly      The same as -r; mount the file system read-only (even
                         the super-user may not write it).

             reload      Reload all incore data for a file system.  This is
                         used mainly after running fsck(8) on the root file
                         system and finding things to fix.  The file system
                         must be mounted read-only.  All cached meta-data are
                         invalidated, superblock and summary information is
                         re-read from disk, all cached inactive vnodes and
                         file data are invalidated and all inode data are re-
                         read for all active vnodes.

             rump        Instead of running "mount_<fstype>" to mount the file
                         system, run "rump_<fstype>".  This uses a userspace
                         server to mount the file system and does not require
                         kernel support for the specific file system type.
                         See the -t flag and respective rump_type manual page
                         for more information.

             log         (FFS only) Mount the file system with wapbl(4) meta-
                         data journaling, also known simply as logging.  It
                         provides rapid metadata updates and eliminates the
                         need to check file system consistency after a system
                         outage.  It requires the WAPBL option to be enabled
                         in the running kernel.  See wapbl(4) for more
                         information.  This option requires the "UFS2" (level
                         4) superblock layout, which is the default for newly
                         created FFSv1 and FFSv2 file systems.  To update an
                         old file system with an earlier superblock format,
                         use the -c option of fsck_ffs(8).

                         log cannot be used together with discard.

                         A file system mounted with log can be mounted also
                         with async, but such filesystem behaves the same as
                         if async was not specified - meta-data writes use the
                         log, hence its integrity is still guaranteed.

             symperm     Recognize permission of symbolic link when reading or
                         traversing link.

             sync        All I/O to the file system should be done
                         synchronously.  This is not equivalent to the normal
                         mode in which only metadata is written synchronously.

             nosync      Clear sync mode.

             union       Causes the namespace at the mount point to appear as
                         the union of the mounted file system root (referred
                         to as the upper layer), and the existing directory
                         (referred to as the lower layer).  Name lookups will
                         be done in the upper layer first.  If a name does not
                         exist in the upper layer, then the name will be
                         looked up in the lower layer.  If a name exists in
                         both the upper and lower layers, then only the upper
                         instance is accessible.  Creation of new files is
                         done in the upper layer, except in the case of the
                         fdesc file system (see mount_fdesc(8)).

                         Note that the union option can be applied to any type
                         of file system, and is fundamentally different from
                         mount_union(8), which is a particular type of file
                         system.  Also note that the union option affects the
                         file system name space only at the mount point
                         itself; it does not apply recursively to

             update      The same as -u; indicate that the status of an
                         already mounted file system should be changed.

             Any additional options specific to a given file system type (see
             the -t option) may be passed as a comma separated list; these
             options are distinguished by a leading "-" (dash).  Options that
             take a value are specified using the syntax -option=value.  For
             example, the mount command:

                   mount -t mfs -o nosuid,-N,-s=32m swap /tmp

             causes mount to execute the equivalent of:

                   /sbin/mount_mfs -o nosuid -N -s 32m swap /tmp

     -r      The file system is to be mounted read-only.  Mount the file
             system read-only (even the super-user may not write it).  The
             same as the "rdonly" argument to the -o option.

     -t type
             The argument following the -t is used to indicate the file system
             type.  The type ffs is the default.  The -t option can be used to
             indicate that the actions should only be taken on file systems of
             the specified type.  More than one type may be specified in a
             comma separated list.  The list of file system types can be
             prefixed with "no" to specify the file system types for which
             action should not be taken.  For example, the mount command:

                   mount -a -t nonfs,mfs

             mounts all file systems except those of type NFS and MFS.

             mount will attempt to execute a program in /sbin/mount_XXX where
             XXX is replaced by the type name.  For example, nfs file systems
             are mounted by the program /sbin/mount_nfs.

     -u      The -u flag indicates that the status of an already mounted file
             system should be changed.  Any of the options discussed above
             (the -o option) may be changed; also a file system can be changed
             from read-only to read-write or vice versa.  An attempt to change
             from read-write to read-only will fail if any files on the file
             system are currently open for writing unless the -f flag is also
             specified.  The set of options is determined by first extracting
             the options for the file system from the fstab(5) file, then
             applying any options specified by the -o argument, and finally
             applying the -r or -w option.

     -v      Verbose mode.  If this flag is specified more than once, then the
             file system-specific mount arguments are printed for the given
             mounted file system.

     -w      The file system object is to be read and write.

     The options specific to the various file system types are described in
     the manual pages for those file systems' "mount_<fstype>" commands; for
     instance, the options specific to Berkeley Fast File System (FFS) are
     described in the mount_ffs(8) manual page.

     The particular type of file system in each partition of a disk can be
     found by examining the disk label with the disklabel(8) command.

     /etc/fstab  file system table

     Some useful examples:

           CD-ROM  mount -t cd9660 -r /dev/cd0a /cdrom

           MS-DOS  mount -t msdos /dev/fd0a /floppy

           NFS     mount -t nfs nfs-server-host:/directory/path /mount-point

           MFS (32 megabyte)
                   mount -t mfs -o nosuid,-s=32m swap /tmp

     The "noauto" directive in /etc/fstab can be used to make it easy to
     manually mount and unmount removable media using just the mountpoint
     filename, with an entry like this:

           /dev/cd0a /cdrom cd9660 ro,noauto 0 0

     That would allow a simple command like "mount /cdrom" or "umount /cdrom"
     for media using the ISO-9660 file system format in the first CD-ROM

     The error "Operation not supported by device" indicates that the mount
     for the specified file system type cannot be completed because the kernel
     lacks support for the said file system.  See options(4).

     The error "Operation not permitted" may indicate that the mount options
     include privileged options and/or do not include options that exclude
     privileged options.  One should try using at least "nodev" and "nosuid"
     in such cases:

           mount -t cd9660 -o nodev,nosuid /dev/cd0a /mnt

     df(1), mount(2), options(4), wapbl(4), fstab(5), automount(8),
     automountd(8), autounmountd(8), disklabel(8), fsck(8), mount_ados(8),
     mount_cd9660(8), mount_chfs(8), mount_ext2fs(8), mount_fdesc(8),
     mount_ffs(8), mount_filecore(8), mount_kernfs(8), mount_lfs(8),
     mount_mfs(8), mount_msdos(8), mount_nfs(8), mount_ntfs(8), mount_null(8),
     mount_overlay(8), mount_portal(8), mount_procfs(8), mount_tmpfs(8),
     mount_udf(8), mount_umap(8), mount_union(8), rump_cd9660(8), rump_efs(8),
     rump_ext2fs(8), rump_ffs(8), rump_hfs(8), rump_lfs(8), rump_msdos(8),
     rump_nfs(8), rump_ntfs(8), rump_sysvbfs(8), rump_tmpfs(8), rump_udf(8),

     A mount command appeared in Version 1 AT&T UNIX.

NetBSD 10.99                     July 10, 2022                    NetBSD 10.99