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diff --git a/man2/mount.2 b/man2/mount.2 new file mode 100644 index 0000000..916b68c --- /dev/null +++ b/man2/mount.2 @@ -0,0 +1,971 @@ +.\" Copyright (C) 1993 Rickard E. Faith <faith@cs.unc.edu> +.\" and Copyright (C) 1994 Andries E. Brouwer <aeb@cwi.nl> +.\" and Copyright (C) 2002, 2005, 2016 Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com> +.\" Modified 2001-10-13 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" Added note on historical behavior of MS_NOSUID +.\" Modified 2002-05-16 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" Extensive changes and additions +.\" Modified 2002-05-27 by aeb +.\" Modified 2002-06-11 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" Enhanced descriptions of MS_MOVE, MS_BIND, and MS_REMOUNT +.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" 2005-05-18, mtk, Added MNT_EXPIRE, plus a few other tidy-ups. +.\" 2008-10-06, mtk: move umount*() material into separate umount.2 page. +.\" 2008-10-06, mtk: Add discussion of namespaces. +.\" +.TH mount 2 2023-04-03 "Linux man-pages 6.05.01" +.SH NAME +mount \- mount filesystem +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B "#include <sys/mount.h>" +.PP +.BI "int mount(const char *" source ", const char *" target , +.BI " const char *" filesystemtype ", unsigned long " mountflags , +.BI " const void *_Nullable " data ); +.fi +.SH DESCRIPTION +.BR mount () +attaches the filesystem specified by +.I source +(which is often a pathname referring to a device, +but can also be the pathname of a directory or file, +or a dummy string) to the location (a directory or file) +specified by the pathname in +.IR target . +.PP +Appropriate privilege (Linux: the +.B CAP_SYS_ADMIN +capability) is required to mount filesystems. +.PP +Values for the +.I filesystemtype +argument supported by the kernel are listed in +.I /proc/filesystems +(e.g., "btrfs", "ext4", "jfs", "xfs", "vfat", "fuse", +"tmpfs", "cgroup", "proc", "mqueue", "nfs", "cifs", "iso9660"). +Further types may become available when the appropriate modules +are loaded. +.PP +The +.I data +argument is interpreted by the different filesystems. +Typically it is a string of comma-separated options +understood by this filesystem. +See +.BR mount (8) +for details of the options available for each filesystem type. +This argument may be specified as NULL, if there are no options. +.PP +A call to +.BR mount () +performs one of a number of general types of operation, +depending on the bits specified in +.IR mountflags . +The choice of which operation to perform is determined by +testing the bits set in +.IR mountflags , +with the tests being conducted in the order listed here: +.IP \[bu] 3 +Remount an existing mount: +.I mountflags +includes +.BR MS_REMOUNT . +.IP \[bu] +Create a bind mount: +.I mountflags +includes +.BR MS_BIND . +.IP \[bu] +Change the propagation type of an existing mount: +.I mountflags +includes one of +.BR MS_SHARED , +.BR MS_PRIVATE , +.BR MS_SLAVE , +or +.BR MS_UNBINDABLE . +.IP \[bu] +Move an existing mount to a new location: +.I mountflags +includes +.BR MS_MOVE . +.IP \[bu] +Create a new mount: +.I mountflags +includes none of the above flags. +.PP +Each of these operations is detailed later in this page. +Further flags may be specified in +.I mountflags +to modify the behavior of +.BR mount (), +as described below. +.\" +.SS Additional mount flags +The list below describes the additional flags that can be specified in +.IR mountflags . +Note that some operation types ignore some or all of these flags, +as described later in this page. +.\" +.\" FIXME 2.6.25 Added MS_I_VERSION, which needs to be documented. +.\" commit 7a224228ed79d587ece2304869000aad1b8e97dd +.\" (This is a per-superblock flag) +.\" +.TP +.BR 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 +.BR chattr (1).) +.TP +.BR MS_LAZYTIME " (since Linux 4.0)" +.\" commit 0ae45f63d4ef8d8eeec49c7d8b44a1775fff13e8 +.\" commit fe032c422c5ba562ba9c2d316f55e258e03259c6 +.\" commit a26f49926da938f47561f386be56a83dd37a496d +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: +.RS +.IP \[bu] 3 +the inode needs to be updated for some change unrelated to file timestamps; +.IP \[bu] +the application employs +.BR fsync (2), +.BR syncfs (2), +or +.BR sync (2); +.IP \[bu] +an undeleted inode is evicted from memory; or +.IP \[bu] +more than 24 hours have passed since the inode was written to disk. +.RE +.IP +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. +.IP +Examples of workloads where this option could be of significant benefit +include frequent random writes to preallocated files, +as well as cases where the +.B MS_STRICTATIME +mount option is also enabled. +(The advantage of combining +.B MS_STRICTATIME +and +.B MS_LAZYTIME +is that +.BR stat (2) +will return the correctly updated atime, but the atime updates +will be flushed to disk only in the cases listed above.) +.TP +.B MS_MANDLOCK +Permit mandatory locking on files in this filesystem. +(Mandatory locking must still be enabled on a per-file basis, +as described in +.BR fcntl (2).) +Since Linux 4.5, +.\" commit 95ace75414f312f9a7b93d873f386987b92a5301 +this mount option requires the +.B CAP_SYS_ADMIN +capability and a kernel configured with the +.B CONFIG_MANDATORY_FILE_LOCKING +option. +Mandatory locking has been fully deprecated in Linux 5.15, so +this flag should be considered deprecated. +.TP +.B MS_NOATIME +Do not update access times for (all types of) files on this filesystem. +.TP +.B MS_NODEV +Do not allow access to devices (special files) on this filesystem. +.TP +.B MS_NODIRATIME +Do not update access times for directories on this filesystem. +This flag provides a subset of the functionality provided by +.BR MS_NOATIME ; +that is, +.B MS_NOATIME +implies +.BR MS_NODIRATIME . +.TP +.B MS_NOEXEC +Do not allow programs to be executed from this filesystem. +.\" (Possibly useful for a filesystem that contains non-Linux executables. +.\" Often used as a security feature, e.g., to make sure that restricted +.\" users cannot execute files uploaded using ftp or so.) +.TP +.B MS_NOSUID +Do not honor set-user-ID and set-group-ID bits or file capabilities +when executing programs from this filesystem. +In addition, SELinux domain +transitions require the permission +.IR nosuid_transition , +which in turn needs +also the policy capability +.IR nnp_nosuid_transition . +.\" (This is a security feature to prevent users executing set-user-ID and +.\" set-group-ID programs from removable disk devices.) +.TP +.B MS_RDONLY +Mount filesystem read-only. +.TP +.BR MS_REC " (since Linux 2.4.11)" +Used in conjunction with +.B MS_BIND +to create a recursive bind mount, +and in conjunction with the propagation type flags to recursively change +the propagation type of all of the mounts in a subtree. +See below for further details. +.TP +.BR 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 +.BR 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 +.B MS_NOATIME +was specified), and the +.B 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. +.\" Matthew Garrett notes in the patch that added this behavior +.\" that this lets utilities such as tmpreaper (which deletes +.\" files based on last access time) work correctly. +.TP +.BR MS_SILENT " (since Linux 2.6.17)" +Suppress the display of certain +.RI ( printk ()) +warning messages in the kernel log. +This flag supersedes the misnamed and obsolete +.B MS_VERBOSE +flag (available since Linux 2.4.12), which has the same meaning. +.TP +.BR 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 +.B MS_NOATIME +and +.B MS_RELATIME +flags. +.TP +.B MS_SYNCHRONOUS +Make writes on this filesystem synchronous (as though +the +.B O_SYNC +flag to +.BR open (2) +was specified for all file opens to this filesystem). +.TP +.BR MS_NOSYMFOLLOW " (since Linux 5.10)" +.\" dab741e0e02bd3c4f5e2e97be74b39df2523fc6e +Do not follow symbolic links when resolving paths. +Symbolic links can still be created, +and +.BR readlink (1), +.BR readlink (2), +.BR realpath (1), +and +.BR realpath (3) +all still work properly. +.PP +From Linux 2.4 onward, some of the above flags are +settable on a per-mount basis, +while others apply to the superblock of the mounted filesystem, +meaning that all mounts of the same filesystem share those flags. +(Previously, all of the flags were per-superblock.) +.PP +The per-mount-point flags are as follows: +.IP \[bu] 3 +Since Linux 2.4: +.BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID +flags are settable on a per-mount-point basis. +.IP \[bu] +Additionally, since Linux 2.6.16: +.B MS_NOATIME +and +.BR MS_NODIRATIME . +.IP \[bu] +Additionally, since Linux 2.6.20: +.BR MS_RELATIME . +.PP +The following flags are per-superblock: +.BR MS_DIRSYNC , +.BR MS_LAZYTIME , +.BR MS_MANDLOCK , +.BR MS_SILENT , +and +.BR MS_SYNCHRONOUS . +.\" And MS_I_VERSION? +The initial settings of these flags are determined on the first +mount of the filesystem, and will be shared by all subsequent mounts +of the same filesystem. +Subsequently, the settings of the flags can be changed +via a remount operation (see below). +Such changes will be visible via all mounts associated +with the filesystem. +.PP +Since Linux 2.6.16, +.B MS_RDONLY +can be set or cleared on a per-mount-point basis as well as on +the underlying filesystem superblock. +The mounted filesystem will be writable only if neither the filesystem +nor the mountpoint are flagged as read-only. +.\" +.SS Remounting an existing mount +An existing mount may be remounted by specifying +.B MS_REMOUNT +in +.IR mountflags . +This allows you to change the +.I mountflags +and +.I data +of an existing mount without having to unmount and remount the filesystem. +.I target +should be the same value specified in the initial +.BR mount () +call. +.PP +The +.I source +and +.I filesystemtype +arguments are ignored. +.PP +The +.I mountflags +and +.I data +arguments should match the values used in the original +.BR mount () +call, except for those parameters that are being deliberately changed. +.PP +The following +.I mountflags +can be changed: +.BR MS_LAZYTIME , +.\" FIXME +.\" MS_LAZYTIME seems to be available only on a few filesystems, +.\" and on ext4, it seems (from experiment that this flag +.\" can only be enabled (but not disabled) on a remount. +.\" The following code in ext4_remount() (kernel 4.17) seems to +.\" confirm this: +.\" +.\" if (*flags & SB_LAZYTIME) +.\" sb->s_flags |= SB_LAZYTIME; +.BR MS_MANDLOCK , +.BR MS_NOATIME , +.BR MS_NODEV , +.BR MS_NODIRATIME , +.BR MS_NOEXEC , +.BR MS_NOSUID , +.BR MS_RELATIME , +.BR MS_RDONLY , +.B MS_STRICTATIME +(whose effect is to clear the +.B MS_NOATIME +and +.B MS_RELATIME +flags), +and +.BR MS_SYNCHRONOUS . +Attempts to change the setting of the +.\" See the definition of MS_RMT_MASK in include/uapi/linux/fs.h, +.\" which excludes MS_DIRSYNC and MS_SILENT, although SB_DIRSYNC +.\" and SB_SILENT are split out as per-superblock flags in do_mount() +.\" (Linux 4.17 source code) +.B MS_DIRSYNC +and +.B MS_SILENT +flags during a remount are silently ignored. +Note that changes to per-superblock flags are visible via +all mounts of the associated filesystem +(because the per-superblock flags are shared by all mounts). +.PP +Since Linux 3.17, +.\" commit ffbc6f0ead47fa5a1dc9642b0331cb75c20a640e +if none of +.BR MS_NOATIME , +.BR MS_NODIRATIME , +.BR MS_RELATIME , +or +.B MS_STRICTATIME +is specified in +.IR mountflags , +then the remount operation preserves the existing values of these flags +(rather than defaulting to +.BR MS_RELATIME ). +.PP +Since Linux 2.6.26, the +.B MS_REMOUNT +flag can be used with +.B MS_BIND +to modify only the per-mount-point flags. +.\" See https://lwn.net/Articles/281157/ +This is particularly useful for setting or clearing the "read-only" +flag on a mount without changing the underlying filesystem. +Specifying +.I mountflags +as: +.PP +.in +4n +.EX +MS_REMOUNT | MS_BIND | MS_RDONLY +.EE +.in +.PP +will make access through this mountpoint read-only, without affecting +other mounts. +.\" +.SS Creating a bind mount +If +.I mountflags +includes +.B MS_BIND +(available since Linux 2.4), +.\" since Linux 2.4.0-test9 +then perform a bind mount. +A bind mount makes a file or a directory subtree visible at +another point within the single directory hierarchy. +Bind mounts may cross filesystem boundaries and span +.BR chroot (2) +jails. +.PP +The +.I filesystemtype +and +.I data +arguments are ignored. +.PP +The remaining bits (other than +.BR MS_REC , +described below) in the +.I mountflags +argument are also ignored. +(The bind mount has the same mount options as +the underlying mount.) +However, see the discussion of remounting above, +for a method of making an existing bind mount read-only. +.PP +By default, when a directory is bind mounted, +only that directory is mounted; +if there are any submounts under the directory tree, +they are not bind mounted. +If the +.B MS_REC +flag is also specified, then a recursive bind mount operation is performed: +all submounts under the +.I source +subtree (other than unbindable mounts) +are also bind mounted at the corresponding location in the +.I target +subtree. +.\" +.SS Changing the propagation type of an existing mount +If +.I mountflags +includes one of +.BR MS_SHARED , +.BR MS_PRIVATE , +.BR MS_SLAVE , +or +.B MS_UNBINDABLE +(all available since Linux 2.6.15), +then the propagation type of an existing mount is changed. +If more than one of these flags is specified, an error results. +.PP +The only other flags that can be specified while changing +the propagation type are +.B MS_REC +(described below) and +.B MS_SILENT +(which is ignored). +.PP +The +.IR source , +.IR filesystemtype , +and +.I data +arguments are ignored. +.PP +The meanings of the propagation type flags are as follows: +.TP +.B MS_SHARED +Make this mount shared. +Mount and unmount events immediately under this mount will propagate +to the other mounts that are members of this mount's peer group. +Propagation here means that the same mount or unmount will automatically +occur under all of the other mounts in the peer group. +Conversely, mount and unmount events that take place under +peer mounts will propagate to this mount. +.TP +.B MS_PRIVATE +Make this mount private. +Mount and unmount events do not propagate into or out of this mount. +.TP +.B MS_SLAVE +If this is a shared mount that is a member of a peer group +that contains other members, convert it to a slave mount. +If this is a shared mount that is a member of a peer group +that contains no other members, convert it to a private mount. +Otherwise, the propagation type of the mount is left unchanged. +.IP +When a mount is a slave, +mount and unmount events propagate into this mount from +the (master) shared peer group of which it was formerly a member. +Mount and unmount events under this mount do not propagate to any peer. +.IP +A mount can be the slave of another peer group +while at the same time sharing mount and unmount events +with a peer group of which it is a member. +.TP +.B MS_UNBINDABLE +Make this mount unbindable. +This is like a private mount, +and in addition this mount can't be bind mounted. +When a recursive bind mount +.RB ( mount () +with the +.B MS_BIND +and +.B MS_REC +flags) is performed on a directory subtree, +any unbindable mounts within the subtree are automatically pruned +(i.e., not replicated) +when replicating that subtree to produce the target subtree. +.PP +By default, changing the propagation type affects only the +.I target +mount. +If the +.B MS_REC +flag is also specified in +.IR mountflags , +then the propagation type of all mounts under +.I target +is also changed. +.PP +For further details regarding mount propagation types +(including the default propagation type assigned to new mounts), see +.BR mount_namespaces (7). +.\" +.SS Moving a mount +If +.I mountflags +contains the flag +.B MS_MOVE +(available since Linux 2.4.18), +then move a subtree: +.I source +specifies an existing mount and +.I target +specifies the new location to which that mount is to be relocated. +The move is atomic: at no point is the subtree unmounted. +.PP +The remaining bits in the +.I mountflags +argument are ignored, as are the +.I filesystemtype +and +.I data +arguments. +.\" +.SS Creating a new mount +If none of +.BR MS_REMOUNT , +.BR MS_BIND , +.BR MS_MOVE , +.BR MS_SHARED , +.BR MS_PRIVATE , +.BR MS_SLAVE , +or +.B MS_UNBINDABLE +is specified in +.IR mountflags , +then +.BR mount () +performs its default action: creating a new mount. +.I source +specifies the source for the new mount, and +.I target +specifies the directory at which to create the mount point. +.PP +The +.I filesystemtype +and +.I data +arguments are employed, and further bits may be specified in +.I mountflags +to modify the behavior of the call. +.\" +.SH RETURN VALUE +On success, zero is returned. +On error, \-1 is returned, and +.I errno +is set to indicate the error. +.SH 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 Linux kernel source code for details. +.TP +.B EACCES +A component of a path was not searchable. +(See also +.BR path_resolution (7).) +.TP +.B EACCES +Mounting a read-only filesystem was attempted without giving the +.B MS_RDONLY +flag. +.IP +The filesystem may be read-only for various reasons, including: +it resides on a read-only optical disk; +it is resides on a device with a physical switch that has been set to +mark the device read-only; +the filesystem implementation was compiled with read-only support; +or errors were detected when initially mounting the filesystem, +so that it was marked read-only +and can't be remounted as read-write (until the errors are fixed). +.IP +Some filesystems instead return the error +.B EROFS +on an attempt to mount a read-only filesystem. +.TP +.B EACCES +The block device +.I source +is located on a filesystem mounted with the +.B MS_NODEV +option. +.\" mtk: Probably: write permission is required for MS_BIND, with +.\" the error EPERM if not present; CAP_DAC_OVERRIDE is required. +.TP +.B EBUSY +An attempt was made to stack a new mount directly on +top of an existing mount point that was created in this +mount namespace with the same +.I source +and +.IR target . +.TP +.B EBUSY +.I source +cannot be remounted read-only, +because it still holds files open for writing. +.TP +.B EFAULT +One of the pointer arguments points outside the user address space. +.TP +.B EINVAL +.I source +had an invalid superblock. +.TP +.B EINVAL +A remount operation +.RB ( MS_REMOUNT ) +was attempted, but +.I source +was not already mounted on +.IR target . +.TP +.B EINVAL +A move operation +.RB ( MS_MOVE ) +was attempted, but the mount tree under +.I source +includes unbindable mounts and +.I target +is a mount that has propagation type +.BR MS_SHARED . +.TP +.B EINVAL +A move operation +.RB ( MS_MOVE ) +was attempted, but the parent mount of +.I source +mount has propagation type +.BR MS_SHARED . +.TP +.B EINVAL +A move operation +.RB ( MS_MOVE ) +was attempted, but +.I source +was not a mount, or was \[aq]/\[aq]. +.TP +.B EINVAL +A bind operation +.RB ( MS_BIND ) +was requested where +.I source +referred a mount namespace magic link (i.e., a +.IR /proc/ pid /ns/mnt +magic link or a bind mount to such a link) +and the propagation type of the parent mount of +.I target +was +.BR MS_SHARED , +.\" See commit 8823c079ba7136dc1948d6f6dcb5f8022bde438e +but propagation of the requested bind mount could lead to a circular +dependency that might prevent the mount namespace from ever being freed. +.TP +.B EINVAL +.I mountflags +includes more than one of +.BR MS_SHARED , +.BR MS_PRIVATE , +.BR MS_SLAVE , +or +.BR MS_UNBINDABLE . +.TP +.B EINVAL +.I mountflags +includes +.BR MS_SHARED , +.BR MS_PRIVATE , +.BR MS_SLAVE , +or +.B MS_UNBINDABLE +and also includes a flag other than +.B MS_REC +or +.BR MS_SILENT . +.TP +.B EINVAL +An attempt was made to bind mount an unbindable mount. +.TP +.B EINVAL +In an unprivileged mount namespace +(i.e., a mount namespace owned by a user namespace +that was created by an unprivileged user), +a bind mount operation +.RB ( MS_BIND ) +was attempted without specifying +.RB ( MS_REC ), +which would have revealed the filesystem tree underneath one of +the submounts of the directory being bound. +.TP +.B ELOOP +Too many links encountered during pathname resolution. +.TP +.B ELOOP +A move operation was attempted, and +.I target +is a descendant of +.IR source . +.TP +.B EMFILE +(In case no block device is required:) +Table of dummy devices is full. +.TP +.B ENAMETOOLONG +A pathname was longer than +.BR MAXPATHLEN . +.TP +.B ENODEV +.I filesystemtype +not configured in the kernel. +.TP +.B ENOENT +A pathname was empty or had a nonexistent component. +.TP +.B ENOMEM +The kernel could not allocate a free page to copy filenames or data into. +.TP +.B ENOTBLK +.I source +is not a block device (and a device was required). +.TP +.B ENOTDIR +.IR target , +or a prefix of +.IR source , +is not a directory. +.TP +.B ENXIO +The major number of the block device +.I source +is out of range. +.TP +.B EPERM +The caller does not have the required privileges. +.TP +.B EPERM +An attempt was made to modify +.RB ( MS_REMOUNT ) +the +.BR MS_RDONLY , +.BR MS_NOSUID , +or +.B MS_NOEXEC +flag, or one of the "atime" flags +.RB ( MS_NOATIME , +.BR MS_NODIRATIME , +.BR MS_RELATIME ) +of an existing mount, but the mount is locked; see +.BR mount_namespaces (7). +.TP +.B EROFS +Mounting a read-only filesystem was attempted without giving the +.B MS_RDONLY +flag. +See +.BR EACCES , +above. +.\" +.SH STANDARDS +Linux. +.SH HISTORY +The definitions of +.BR MS_DIRSYNC , +.BR MS_MOVE , +.BR MS_PRIVATE , +.BR MS_REC , +.BR MS_RELATIME , +.BR MS_SHARED , +.BR MS_SLAVE , +.BR MS_STRICTATIME , +and +.B MS_UNBINDABLE +were added to glibc headers in glibc 2.12. +.PP +Since Linux 2.4 a single filesystem can be mounted at +multiple mount points, and multiple mounts can be stacked +on the same mount point. +.\" Multiple mounts on same mount point: since Linux 2.3.99pre7. +.PP +The +.I mountflags +argument may have the magic number 0xC0ED (\fBMS_MGC_VAL\fP) +in the top 16 bits. +(All of the other flags discussed in DESCRIPTION +occupy the low order 16 bits of +.IR mountflags .) +Specifying +.B MS_MGC_VAL +was required before Linux 2.4, +but since Linux 2.4 is no longer required and is ignored if specified. +.PP +The original +.B MS_SYNC +flag was renamed +.B MS_SYNCHRONOUS +in 1.1.69 +when a different +.B MS_SYNC +was added to \fI<mman.h>\fP. +.PP +Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program +on a filesystem mounted with +.B MS_NOSUID +would fail with +.BR EPERM . +Since Linux 2.4 the set-user-ID and set-group-ID bits are +just silently ignored in this case. +.\" The change is in patch-2.4.0-prerelease. +.\" +.SH NOTES +.SS Mount namespaces +Starting with Linux 2.4.19, Linux provides mount namespaces. +A mount namespace is the set of filesystem mounts that +are visible to a process. +Mount 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.) +.PP +A child process created by +.BR fork (2) +shares its parent's mount namespace; +the mount namespace is preserved across an +.BR execve (2). +.PP +A process can obtain a private mount namespace if: +it was created using the +.BR clone (2) +.B CLONE_NEWNS +flag, +in which case its new namespace is initialized to be a +.I copy +of the namespace of the process that called +.BR clone (2); +or it calls +.BR unshare (2) +with the +.B 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. +.PP +For further details on mount namespaces, see +.BR mount_namespaces (7). +.\" +.SS Parental relationship between mounts +Each mount has a parent mount. +The overall parental relationship of all mounts defines +the single directory hierarchy seen by the processes within a mount namespace. +.PP +The parent of a new mount is defined when the mount is created. +In the usual case, +the parent of a new mount is the mount of the filesystem +containing the directory or file at which the new mount is attached. +In the case where a new mount is stacked on top of an existing mount, +the parent of the new mount is the previous mount that was stacked +at that location. +.PP +The parental relationship between mounts can be discovered via the +.IR /proc/ pid /mountinfo +file (see below). +.\" +.SS \fI/proc/\fPpid\fI/mounts\fP and \fI/proc/\fPpid\fI/mountinfo\fP +The Linux-specific +.IR /proc/ pid /mounts +file exposes the list of mounts in the mount +namespace of the process with the specified ID. +The +.IR /proc/ pid /mountinfo +file exposes even more information about mounts, +including the propagation type and mount ID information that makes it +possible to discover the parental relationship between mounts. +See +.BR proc (5) +and +.BR mount_namespaces (7) +for details of this file. +.SH SEE ALSO +.BR mountpoint (1), +.BR chroot (2), +.BR ioctl_iflags (2), +.BR mount_setattr (2), +.BR pivot_root (2), +.BR umount (2), +.BR mount_namespaces (7), +.BR path_resolution (7), +.BR findmnt (8), +.BR lsblk (8), +.BR mount (8), +.BR umount (8) |