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       mount - mount filesystem


       #include <sys/mount.h>

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


       mount() attaches the filesystem 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

       Since  Linux 2.4 a single filesystem 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  (e.g.,  "minix",  "ext2",  "ext3",  "jfs",  "xfs", "reiserfs", "msdos",
       "proc", "nfs", "iso9660").  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 in the low order 16 bits:

       MS_BIND (Linux 2.4 onward)
              Perform a bind mount, making a file or a directory subtree visible at another point
              within a  filesystem.   Bind  mounts  may  cross  filesystem  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).

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

       MS_LAZYTIME (since Linux 4.0)
              Reduce on-disk updates of inode timestamps (atime,  mtime,  ctime)  by  maintaining
              these changes only in memory.  The on-disk timestamps are updated only when:

              (a)  the inode needs to be updated for some change unrelated to file timestamps;

              (b)  the application employs fsync(2), syncfs(2), or sync(2);

              (c)  an undeleted inode is evicted from memory; or

              (d)  more than 24 hours have passed since the inode was written to disk.

              This  mount  option  significantly  reduces  writes  needed  to  update the inode's
              timestamps, especially mtime and atime.  However, in the event of a  system  crash,
              the atime and mtime fields on disk might be out of date by up to 24 hours.

              Examples  of  workloads  where  this option could be of significant benefit include
              frequent  random  writes  to  preallocated  files,  as  well  as  cases  where  the
              MS_STRICTATIME   mount  option  is  also  enabled.   (The  advantage  of  combining
              MS_STRICTATIME and MS_LAZYTIME is that stat(2) will return  the  correctly  updated
              atime,  but  the  atime  updates  will  be flushed to disk only in the cases listed

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

              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.

              Do not update access times for (all types of) files on this filesystem.

              Do not allow access to devices (special files) on this filesystem.

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

              Do not allow programs to be executed from this filesystem.

              Do  not  honor  set-user-ID and set-group-ID bits when executing programs from this

              Mount filesystem read-only.

       MS_RELATIME (since Linux 2.6.20)
              When a file on this filesystem is accessed, update  the  file's  last  access  time
              (atime) only 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.   Since  Linux  2.6.30,  the  kernel  defaults  to  the
              behavior  provided  by  this  flag  (unless  MS_NOATIME  was  specified),  and  the
              MS_STRICTATIME flag 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.

              Remount an existing mount.  This allows you to change the mountflags and data of an
              existing mount without having to unmount and remount the filesystem.  target should
              be the same value specified in the initial mount() call; source and  filesystemtype
              are ignored.  The mountflags and data arguments should match the values used in the
              original mount() call, except for those  parameters  that  are  being  deliberately

              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_STRICTATIME (since Linux 2.6.30)
              Always update the last access time  (atime)  when  files  on  this  filesystem  are
              accessed.   (This  was  the default behavior before Linux 2.6.30.)  Specifying this
              flag overrides the effect of setting the MS_NOATIME and MS_RELATIME flags.

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

       From Linux 2.4 onward, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags are settable on a per-
       mount-point basis.  From kernel 2.6.16  onward,  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 filesystems.  Typically it is  a  string
       of comma-separated options understood by this filesystem.  See mount(8) for details of the
       options available for each filesystem type.


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


       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
       Linux 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

       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 thread, 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.

              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.

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

              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.


       The definitions of MS_DIRSYNC, MS_MOVE, MS_REC, MS_RELATIME, and MS_STRICTATIME were added
       to glibc headers in version 2.12.


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


       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  filesystem 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 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(2)
       CLONE_NEWNS  flag,  in  which  case  its  new namespace is initialized to be a copy of the
       namespace of the process that called clone(2); 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/mounts file exposes the list of mount  points  in  the  mount
       namespace of the process with the specified ID; see proc(5) for details.


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


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