1.\" 2.\" SPDX-License-Identifier: BSD-3-Clause 3.\" 4.\" Copyright (c) 1980, 1989, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.Dd October 28, 2025 32.Dt MOUNT 8 33.Os 34.Sh NAME 35.Nm mount 36.Nd mount file systems 37.Sh SYNOPSIS 38.Nm 39.Op Fl -libxo 40.Op Fl adflpruvw 41.Op Fl F Ar fstab 42.Op Fl o Ar options 43.Op Fl t Oo Cm no Oc Ns Ar type Ns Op , Ns Ar type ... 44.Nm 45.Op Fl -libxo 46.Op Fl dfpruvw 47.Ar special | node 48.Nm 49.Op Fl -libxo 50.Op Fl dfpruvw 51.Op Fl o Ar options 52.Op Fl t Oo Cm no Oc Ns Ar type Ns Op , Ns Ar type ... 53.Ar special node 54.Sh DESCRIPTION 55The 56.Nm 57utility calls the 58.Xr nmount 2 59system call to prepare and graft a 60.Ar special 61device or the remote node (rhost:path) on to the file system tree at the point 62.Ar node . 63If either 64.Ar special 65or 66.Ar node 67are not provided, the appropriate information is taken from the 68.Xr fstab 5 69file. 70.Pp 71The system maintains a list of currently mounted file systems. 72If no arguments are given to 73.Nm , 74this list is printed. 75.Pp 76The options are as follows: 77.Bl -tag -width indent 78.It Fl -libxo 79Generate output via 80.Xr libxo 3 81in a selection of different human and machine readable formats. 82See 83.Xr xo_options 7 84for details on command line arguments. 85.It Fl a 86All the file systems described in 87.Xr fstab 5 88are mounted. 89Exceptions are those marked as 90.Dq Li noauto , 91those marked as 92.Dq Li late 93(unless the 94.Fl l 95option was specified), 96those excluded by the 97.Fl t 98flag (see below), or if they are already mounted (except the 99root file system which is always remounted to preserve 100traditional single user mode behavior). 101.It Fl d 102Causes everything to be done except for the actual system call. 103This option is useful in conjunction with the 104.Fl v 105flag to 106determine what the 107.Nm 108command is trying to do. 109.It Fl F Ar fstab 110Specify the 111.Pa fstab 112file to use. 113.It Fl f 114Forces the revocation of write access when trying to downgrade 115a file system mount status from read-write to read-only. 116Also 117forces the R/W mount of an unclean file system (dangerous; use with 118caution). 119.It Fl L 120When used in conjunction with the 121.Fl a 122option, mount 123.Em only 124those file systems which are marked as 125.Dq Li late . 126.It Fl l 127When used in conjunction with the 128.Fl a 129option, also mount those file systems which are marked as 130.Dq Li late . 131.It Fl n 132For compatibility with some other implementations, this flag is 133currently a no-op. 134.It Fl o 135Options are specified with a 136.Fl o 137flag followed by a comma separated string of options. 138In case of conflicting options being specified, the rightmost option 139takes effect. 140The following options are available: 141.Bl -tag -width indent 142.It Cm acls 143Enable POSIX.1e Access Control Lists, or ACLs, which can be customized via the 144.Xr setfacl 1 145and 146.Xr getfacl 1 147commands. 148This flag is mutually exclusive with 149.Cm nfsv4acls 150flag. 151.It Cm async 152All I/O to the file system should be done asynchronously. 153This is a 154.Em dangerous 155flag to set, since it does not guarantee that the file system structure 156on the disk will remain consistent. 157For this reason, the 158.Cm async 159flag should be used sparingly, and only when some data recovery 160mechanism is present. 161.It Cm atime 162Update the file access time when reading from a file. 163This is the default. 164.It Cm automounted 165This flag indicates that the file system was mounted by 166.Xr automountd 8 . 167Automounted file systems are automatically unmounted by 168.Xr autounmountd 8 . 169.It Cm autoro 170Mount the file system read-write. 171If that fails with an error that suggests that the media could be read-only, 172then automatically try to mount the file system read-only. 173.It Cm current 174When used with the 175.Fl u 176flag, this is the same as specifying the options currently in effect for 177the mounted file system. 178.It Cm emptydir 179Require that the mount point directory be empty. 180.It Cm force 181The same as 182.Fl f ; 183forces the revocation of write access when trying to downgrade 184a file system mount status from read-write to read-only. 185Also 186forces the R/W mount of an unclean file system (dangerous; use with caution). 187.It Cm fstab 188When used with the 189.Fl u 190flag, this is the same as specifying all the options listed in the 191.Xr fstab 5 192file for the file system. 193.It Cm late 194This file system should be skipped when 195.Nm 196is run with the 197.Fl a 198flag but without the 199.Fl l 200flag. 201.It Cm mountprog Ns = Ns Aq Ar program 202Force 203.Nm 204to use the specified program to mount the file system, instead of calling 205.Xr nmount 2 206directly. 207For example: 208.Bd -literal 209mount -t foofs -o mountprog=/mydir/fooprog /dev/cd0 /mnt 210.Ed 211.It Cm multilabel 212Enable multi-label Mandatory Access Control, or MAC, on the specified file 213system. 214If the file system supports multilabel operation, individual labels will 215be maintained for each object in the file system, rather than using a 216single label for all objects. 217An alternative to the 218.Fl l 219flag in 220.Xr tunefs 8 . 221See 222.Xr mac 4 223for more information, which cause the multilabel mount flag to be set 224automatically at mount-time. 225.It Cm nfsv4acls 226Enable NFSv4 ACLs, which can be customized via the 227.Xr setfacl 1 228and 229.Xr getfacl 1 230commands. 231This flag is mutually exclusive with 232.Cm acls 233flag. 234.It Cm noasync 235Metadata I/O should be done synchronously, while data I/O should be done 236asynchronously. 237This is the default. 238.It Cm noatime 239Do not update the file access time when reading from a file. 240This option 241is useful on file systems where there are large numbers of files and 242performance is more critical than updating the file access time (which is 243rarely ever important). 244This option is currently only supported on local file systems. 245.It Cm noauto 246This file system should be skipped when 247.Nm 248is run with the 249.Fl a 250flag. 251.It Cm noclusterr 252Disable read clustering. 253.It Cm noclusterw 254Disable write clustering. 255.It Cm nocover 256Do not mount if the requested mount point is already 257the root of a mount point. 258.It Cm noexec 259Do not allow execution of any binaries on the mounted file system. 260This option is useful for a server that has file systems containing 261binaries for architectures other than its own. 262Note: This option was not designed as a security feature and no 263guarantee is made that it will prevent malicious code execution; for 264example, it is still possible to execute scripts which reside on a 265.Cm noexec 266mounted partition. 267.It Cm nosuid 268Do not allow set-user-identifier or set-group-identifier bits to take effect. 269Note: this option is worthless if a public available suid or sgid 270wrapper is installed on your system. 271It is set automatically when the user does not have super-user privileges. 272.It Cm nosymfollow 273Do not follow symlinks on the mounted file system. 274.Pp 275This option is intended to be used when mounting file systems 276from untrusted external storage systems or public writable /tmp file systems. 277You can still create or remove symlinks, or read the value of a symbolic link. 278.It Cm ro 279Mount the filesystem read-only, even the super-user may not write it. 280Equivalent to 281.Fl r . 282.It Cm rw 283Mount the filesystem read-write. 284.It Cm snapshot 285Take a snapshot of the specified filesystem. 286When this option is used, all other options are ignored. 287The 288.Fl u 289flag is required with this option. 290.Pp 291Snapshot files must be created in the file system that is being 292snapshotted. 293You may create up to 20 snapshots per file system. 294Active snapshots are recorded in the superblock, so they persist across unmount 295and remount operations and across system reboots. 296When you are done with a snapshot, it can be removed with the 297.Xr rm 1 298command. 299Snapshots may be removed in any order, however you may not get back all the 300space contained in the snapshot as another snapshot may claim some of the blocks 301that it is releasing. 302Note that the schg flag is set on snapshots to ensure that not even the root 303user can write to them. 304The unlink command makes an exception for snapshot files in that it allows them 305to be removed even though they have the schg flag set, so it is not necessary to 306clear the schg flag before removing a snapshot file. 307.Pp 308Once you have taken a snapshot, there are three interesting things that you can 309do with it: 310.Pp 311.Bl -enum -compact 312.It 313Run 314.Xr fsck 8 315on the snapshot file. 316Assuming that the file system was clean when it was mounted, you should always 317get a clean (and unchanging) result from running fsck on the snapshot. 318This is essentially what the background fsck process does. 319.Pp 320.It 321Run 322.Xr dump 8 323on the snapshot. 324You will get a dump that is consistent with the file system as of the timestamp 325of the snapshot. 326.Pp 327.It 328Mount the snapshot as a frozen image of the file system. 329To mount the snapshot 330.Pa /var/snapshot/snap1 : 331.Bd -literal 332mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4 333mount -r /dev/md4 /mnt 334.Ed 335.Pp 336You can now cruise around your frozen 337.Pa /var 338file system at 339.Pa /mnt . 340Everything will be in the same state that it was at the time the snapshot was 341taken. 342The one exception is that any earlier snapshots will appear as zero length 343files. 344When you are done with the mounted snapshot: 345.Bd -literal 346umount /mnt 347mdconfig -d -u 4 348.Ed 349.El 350.It Cm suiddir 351A directory on the mounted file system will respond to the SUID bit 352being set, by setting the owner of any new files to be the same 353as the owner of the directory. 354New directories will inherit the bit from their parents. 355Execute bits are removed from 356the file, and it will not be given to root. 357.Pp 358This feature is designed for use on fileservers serving PC users via 359ftp, SAMBA, or netatalk. 360It provides security holes for shell users and as 361such should not be used on shell machines, especially on home directories. 362This option requires the SUIDDIR 363option in the kernel to work. 364Only UFS file systems support this option. 365See 366.Xr chmod 2 367for more information. 368.It Cm sync 369All I/O to the file system should be done synchronously. 370.It Cm update 371The same as 372.Fl u ; 373indicate that the status of an already mounted file system should be changed. 374.It Cm union 375Causes the namespace at the mount point to appear as the union 376of the mounted file system root and the existing directory. 377Lookups will be done in the mounted file system first. 378If those operations fail due to a non-existent file the underlying 379directory is then accessed. 380All creates are done in the mounted file system. 381.It Cm untrusted 382The file system is untrusted and the kernel should use more 383extensive checks on the file-system's metadata before using it. 384This option is intended to be used when mounting file systems 385from untrusted media such as USB memory sticks or other 386externally-provided media. 387.El 388.Pp 389Any additional options specific to a file system type that is not 390one of the internally known types (see the 391.Fl t 392option) may be passed as a comma separated list; these options are 393distinguished by a leading 394.Dq \&- 395(dash). 396For example, the 397.Nm 398command: 399.Bd -literal -offset indent 400mount -t cd9660 -o -e /dev/cd0 /cdrom 401.Ed 402.Pp 403causes 404.Nm 405to execute the equivalent of: 406.Bd -literal -offset indent 407/sbin/mount_cd9660 -e /dev/cd0 /cdrom 408.Ed 409.Pp 410Options that take a value are specified using the -option=value syntax: 411.Bd -literal -offset indent 412mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt 413.Ed 414.Pp 415is equivalent to 416.Bd -literal -offset indent 417/sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt 418.Ed 419.Pp 420Additional options specific to file system types 421which are not internally known 422(see the description of the 423.Fl t 424option below) 425may be described in the manual pages for the associated 426.Pa /sbin/mount_ Ns Sy XXX 427utilities. 428.It Fl p 429Print mount information in 430.Xr fstab 5 431format. 432Implies also the 433.Fl v 434option. 435.It Fl r 436The file system is to be mounted read-only. 437Mount the file system read-only (even the super-user may not write it). 438The same as the 439.Cm ro 440argument to the 441.Fl o 442option. 443.It Fl t Oo Cm no Oc Ns Ar type Ns Op , Ns Ar type ... 444The argument following the 445.Fl t 446is used to indicate the file system type. 447The type 448.Cm ufs 449is the default. 450The 451.Fl t 452option can be used 453to indicate that the actions should only be taken on 454file systems of the specified type. 455More than one type may be specified in a comma separated list. 456The list of file system types can be prefixed with 457.Cm no 458to specify the file system types for which action should 459.Em not 460be taken. 461For example, the 462.Nm 463command: 464.Bd -literal -offset indent 465mount -a -t nonfs,nullfs 466.Ed 467.Pp 468mounts all file systems except those of type NFS and NULLFS. 469.Pp 470The default behavior of 471.Nm 472is to pass the 473.Fl t 474option directly to the 475.Xr nmount 2 476system call in the 477.Li fstype 478option. 479.Pp 480However, for the following file system types: 481.Cm cd9660 , 482.Cm mfs , 483.Cm msdosfs , 484.Cm nfs , 485.Cm nullfs , 486.Cm smbfs , 487.Cm udf , 488and 489.Cm unionfs 490.Nm 491will not call 492.Xr nmount 2 493directly and will instead attempt to execute a program in 494.Pa /sbin/mount_ Ns Ar type 495where 496.Ar type 497is replaced by the file system type name. 498For example, 499.Cm nfs 500file systems are mounted by the program 501.Pa /sbin/mount_nfs . 502.Pp 503Most file systems will be dynamically loaded by the kernel 504if not already present, and if the kernel module is available. 505.It Fl u 506The 507.Fl u 508flag indicates that the status of an already mounted file 509system should be changed. 510Any of the options discussed above (the 511.Fl o 512option) 513may be changed; 514also a file system can be changed from read-only to read-write 515or vice versa. 516An attempt to change from read-write to read-only will fail if any 517files on the file system are currently open for writing unless the 518.Fl f 519flag is also specified. 520The set of options is determined by applying the options specified 521in the argument to 522.Fl o 523and finally applying the 524.Fl r 525or 526.Fl w 527option. 528.It Fl v 529Verbose mode. 530If the 531.Fl v 532is used alone, show all file systems, including those that were mounted with the 533.Dv MNT_IGNORE 534flag and show additional information about each file system (including fsid 535when run by root). 536.It Fl w 537The file system object is to be read and write. 538.El 539.Sh ENVIRONMENT 540.Bl -tag -width ".Ev PATH_FSTAB" 541.It Ev PATH_FSTAB 542If the environment variable 543.Ev PATH_FSTAB 544is set, all operations are performed against the specified file. 545.Ev PATH_FSTAB 546will not be honored if the process environment or memory address space is 547considered 548.Dq tainted . 549(See 550.Xr issetugid 2 551for more information.) 552.El 553.Sh FILES 554.Bl -tag -width /etc/fstab -compact 555.It Pa /etc/fstab 556file system table 557.El 558.Sh EXAMPLES 559Remount the root filesystem with read-write permissions: 560.Pp 561.Dl mount -uw / 562.Sh DIAGNOSTICS 563Various, most of them are self-explanatory. 564.Pp 565.Dl XXXXX file system is not available 566.Pp 567The kernel does not support the respective file system type. 568Note that 569support for a particular file system might be provided either on a static 570(kernel compile-time), or dynamic basis (loaded as a kernel module by 571.Xr kldload 8 ) . 572.Sh SEE ALSO 573.Xr getfacl 1 , 574.Xr lsvfs 1 , 575.Xr setfacl 1 , 576.Xr nmount 2 , 577.Xr symlink 2 , 578.Xr acl 3 , 579.Xr getmntinfo 3 , 580.Xr libxo 3 , 581.Xr xo_options 7 , 582.Xr cd9660 4 , 583.Xr devfs 4 , 584.Xr ext2fs 4 , 585.Xr ffs 4 , 586.Xr mac 4 , 587.Xr procfs 4 , 588.Xr tarfs 4 , 589.Xr tmpfs 4 , 590.Xr fstab 5 , 591.Xr symlink 7 , 592.Xr automount 8 , 593.Xr fstyp 8 , 594.Xr kldload 8 , 595.Xr mount_cd9660 8 , 596.Xr mount_msdosfs 8 , 597.Xr mount_nfs 8 , 598.Xr mount_nullfs 8 , 599.Xr mount_smbfs 8 , 600.Xr mount_udf 8 , 601.Xr mount_unionfs 8 , 602.Xr quotacheck 8 , 603.Xr umount 8 , 604.Xr zfs 8 , 605.Xr zpool 8 606.Sh HISTORY 607A 608.Nm 609utility appeared in 610.At v1 . 611.Sh CAVEATS 612After a successful 613.Nm , 614the permissions on the original mount point determine if 615.Pa ..\& 616is accessible from the mounted file system. 617The minimum permissions for 618the mount point for traversal across the mount point in both 619directions to be possible for all users is 0111 (execute for all). 620.Pp 621Use of the 622.Nm 623is preferred over the use of the file system specific 624.Pa mount_ Ns Sy XXX 625commands. 626In particular, 627.Xr mountd 8 628gets a 629.Dv SIGHUP 630signal (that causes an update of the export list) 631only when the file system is mounted via 632.Nm . 633.Sh BUGS 634It is possible for a corrupted file system to cause a crash. 635.Pp 636The 637.Fl p 638option will not list 639.Cm userquota 640or 641.Cm groupquota 642items from 643.Xr fstab 5 644because they are not true mount options and are not information returned by 645.Xr getmntinfo 3 . 646At boot 647.Xr quotacheck 8 , 648processes these items. 649