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NAME

       mount - mount file system

SYNOPSIS

       #include <sys/mount.h>

       int mount(const char *source, const char *target,
                 const char *filesystemtype, unsigned long mountflags,
                 const void *data);

DESCRIPTION

       mount()  attaches the file system specified by source (which is often a
       device name, but can also be a  directory  name  or  a  dummy)  to  the
       directory specified by target.

       Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required
       to mount file systems.

       Since Linux 2.4 a single file system can be visible at  multiple  mount
       points, and multiple mounts can be stacked on the same mount point.

       Values  for  the  filesystemtype  argument  supported by the kernel are
       listed in  /proc/filesystems  (like  "minix",  "ext2",  "ext3",  "jfs",
       "xfs",  "reiserfs",  "msdos",  "proc", "nfs", "iso9660" etc.).  Further
       types may become available when the appropriate modules are loaded.

       The mountflags argument may have the magic number  0xC0ED  (MS_MGC_VAL)
       in  the top 16 bits (this was required in kernel versions prior to 2.4,
       but is no longer required and ignored if specified), and various  mount
       flags   (as  defined  in  <linux/fs.h>  for  libc4  and  libc5  and  in
       <sys/mount.h> for glibc2) in the low order 16 bits:

       MS_BIND (Linux 2.4 onwards)
              Perform a bind mount, making  a  file  or  a  directory  subtree
              visible  at another point within a file system.  Bind mounts may
              cross file system boundaries  and  span  chroot(2)  jails.   The
              filesystemtype  and  data arguments are ignored.  Up until Linux
              2.6.26, mountflags was also ignored (the bind mount has the same
              mount  options  as  the  underlying  mount  point).  Since Linux
              2.6.26, the MS_RDONLY flag is honored when making a bind  mount.

       MS_DIRSYNC (since Linux 2.5.19)
              Make  directory  changes on this file system synchronous.  (This
              property can be obtained for individual directories or  subtrees
              using chattr(1).)

       MS_MANDLOCK
              Permit   mandatory   locking  on  files  in  this  file  system.
              (Mandatory locking must still be enabled on a per-file basis, as
              described in fcntl(2).)

       MS_MOVE
              Move  a  subtree.   source specifies an existing mount point and
              target specifies the new location.  The move is  atomic:  at  no
              point is the subtree unmounted.  The filesystemtype, mountflags,
              and data arguments are ignored.

       MS_NOATIME
              Do not update access times for (all types of) files on this file
              system.

       MS_NODEV
              Do  not  allow  access  to  devices (special files) on this file
              system.

       MS_NODIRATIME
              Do not update access times for directories on this file  system.
              This  flag  provides  a  subset of the functionality provided by
              MS_NOATIME; that is, MS_NOATIME implies MS_NODIRATIME.

       MS_NOEXEC
              Do not allow programs to be executed from this file system.

       MS_NOSUID
              Do not honor set-user-ID and set-group-ID  bits  when  executing
              programs from this file system.

       MS_RDONLY
              Mount file system read-only.

       MS_RELATIME (Since Linux 2.6.20)
              When  a  file  on  this file system is accessed, only update the
              file’s last access time (atime) if the current value of atime is
              less  than or equal to the file’s last modification time (mtime)
              or last status change time (ctime).  This option is  useful  for
              programs,  such  as  mutt(1),  that need to know when a file has
              been read since it was last modified.

       MS_REMOUNT
              Remount an existing  mount.   This  allows  you  to  change  the
              mountflags  and  data  of  an  existing  mount without having to
              unmount and remount the file system.  source and  target  should
              be  the  same  values  specified  in  the  initial mount() call;
              filesystemtype is ignored.

              The   following   mountflags   can   be   changed:    MS_RDONLY,
              MS_SYNCHRONOUS, MS_MANDLOCK; before kernel 2.6.16, the following
              could  also  be  changed:  MS_NOATIME  and  MS_NODIRATIME;  and,
              additionally,  before kernel 2.4.10, the following could also be
              changed: MS_NOSUID, MS_NODEV, MS_NOEXEC.

       MS_SILENT (since Linux 2.6.17)
              Suppress the display of certain (printk()) warning  messages  in
              the  kernel log.  This flag supersedes the misnamed and obsolete
              MS_VERBOSE flag (available since Linux 2.4.12),  which  has  the
              same meaning.

       MS_SYNCHRONOUS
              Make  writes  on  this  file  system  synchronous (as though the
              O_SYNC flag to open(2) was specified for all file opens to  this
              file system).

       From  Linux  2.4  onwards, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags
       are settable on a per-mount-point basis.  From kernel  2.6.16  onwards,
       MS_NOATIME  and  MS_NODIRATIME  are  also settable on a per-mount-point
       basis.  The MS_RELATIME flag is  also  settable  on  a  per-mount-point
       basis.

       The  data  argument  is  interpreted  by  the  different  file systems.
       Typically it is a string of comma-separated options understood by  this
       file  system.   See  mount(8)  for details of the options available for
       each filesystem type.

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.

ERRORS

       The  error  values  given below result from filesystem type independent
       errors.  Each filesystem type may have its own special errors  and  its
       own special behavior.  See the kernel source code for details.

       EACCES A   component   of   a  path  was  not  searchable.   (See  also
              path_resolution(7).)  Or, mounting a  read-only  filesystem  was
              attempted  without  giving  the  MS_RDONLY  flag.  Or, the block
              device source is  located  on  a  filesystem  mounted  with  the
              MS_NODEV option.

       EBUSY  source  is  already  mounted.   Or, it cannot be remounted read-
              only, because it still holds files open  for  writing.   Or,  it
              cannot  be mounted on target because target is still busy (it is
              the working directory of some task, the mount point  of  another
              device, has open files, etc.).

       EFAULT One  of  the  pointer  arguments points outside the user address
              space.

       EINVAL source had an invalid superblock.  Or,  a  remount  (MS_REMOUNT)
              was  attempted,  but  source  was not already mounted on target.
              Or, a move (MS_MOVE) was attempted, but source was not  a  mount
              point, or was '/'.

       ELOOP  Too  many  links  encountered during pathname resolution.  Or, a
              move was attempted, while target is a descendant of source.

       EMFILE (In case no block device is required:) Table of dummy devices is
              full.

       ENAMETOOLONG
              A pathname was longer than MAXPATHLEN.

       ENODEV filesystemtype not configured in the kernel.

       ENOENT A pathname was empty or had a nonexistent component.

       ENOMEM The  kernel  could not allocate a free page to copy filenames or
              data into.

       ENOTBLK
              source is not a block device (and a device was required).

       ENOTDIR
              target, or a prefix of source, is not a directory.

       ENXIO  The major number of the block device source is out of range.

       EPERM  The caller does not have the required privileges.

CONFORMING TO

       This function is Linux-specific and should  not  be  used  in  programs
       intended to be portable.

NOTES

       The  original  MS_SYNC flag was renamed MS_SYNCHRONOUS in 1.1.69 when a
       different MS_SYNC was added to <mman.h>.

       Before Linux 2.4 an attempt to execute a  set-user-ID  or  set-group-ID
       program  on  a filesystem mounted with MS_NOSUID would fail with EPERM.
       Since Linux 2.4 the set-user-ID and set-group-ID bits are just silently
       ignored in this case.

   Per-process Namespaces
       Starting   with   kernel   2.4.19,  Linux  provides  per-process  mount
       namespaces.  A mount namespace is the set of file  system  mounts  that
       are  visible  to a process.  Mount-point namespaces can be (and usually
       are) shared between multiple processes, and changes  to  the  namespace
       (i.e.,  mounts  and  unmounts)  by one process are visible to all other
       processes sharing the same namespace.  (The pre-2.4.19 Linux  situation
       can  be  considered  as  one  in which there was a single namespace was
       shared by every process on the system.)

       A child process created by fork(2) shares its parent’s mount namespace;
       the mount namespace is preserved across an execve(2).

       A process can obtain a private mount namespace if: it was created using
       the clone() CLONE_NEWNS flag,  in  which  case  its  new  namespace  is
       initialized  to  be  a copy of the namespace of the process that called
       clone(); or it calls unshare(2) with the CLONE_NEWNS flag, which causes
       the  caller’s mount namespace to obtain a private copy of the namespace
       that it was previously sharing with other  processes,  so  that  future
       mounts  and  unmounts  by  the  caller are invisible to other processes
       (except child processes that the caller subsequently creates) and  vice
       versa.

       The Linux-specific /proc/PID/self file exposes the list of mount points
       in the mount namespace of  the  process  with  the  specified  ID;  see
       proc(5) for details.

SEE ALSO

       umount(2), path_resolution(7), mount(8), umount(8)

COLOPHON

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