Shared Subtree Operations (Continued) and Command-Line Options

mirrors propagate to the other mirror. A slave mount receives propagation from its master, but not vice versa. A private mount carries no propagation abilities. An unbindable mount is a private mount which cannot be cloned through a bind operation. The detailed semantics are documented in Documentation/filesystems/sharedsubtree.txt file in the kernel source tree; see also mount_namespaces(7). Supported operations are: mount --make-shared mountpoint mount --make-slave mountpoint mount --make-private mountpoint mount --make-unbindable mountpoint The following commands allow one to recursively change the type of all the mounts under a given mountpoint. mount --make-rshared mountpoint mount --make-rslave mountpoint mount --make-rprivate mountpoint mount --make-runbindable mountpoint mount does not read fstab(5) when a --make-* operation is requested. All necessary information has to be specified on the command line. Note that the Linux kernel does not allow changing multiple propagation flags with a single mount(2) system call, and the flags cannot be mixed with other mount options and operations. Since util-linux 2.23 the mount command can be used to do more propagation (topology) changes by one mount(8) call and do it also together with other mount operations. The propagation flags are applied by additional mount(2) system calls when the preceding mount operations were successful. Note that this use case is not atomic. It is possible to specify the propagation flags in fstab(5) as mount options (private, slave, shared, unbindable, rprivate, rslave, rshared, runbindable). For example: mount --make-private --make-unbindable /dev/sda1 /foo is the same as: mount /dev/sda1 /foo mount --make-private /foo mount --make-unbindable /foo COMMAND-LINE OPTIONS The full set of mount options used by an invocation of mount is determined by first extracting the mount options for the filesystem from the fstab table, then applying any options specified by the -o argument, and finally applying a -r or -w option, when present. The mount command does not pass all command-line options to the /sbin/mount.suffix mount helpers. The interface between mount and the mount helpers is described below in the EXTERNAL HELPERS section. Command-line options available for the mount command are: -a, --all Mount all filesystems (of the given types) mentioned in fstab (except for those whose line contains the noauto keyword). The filesystems are mounted following their order in fstab. The mount command compares filesystem source, target (and fs root for bind mount or btrfs) to detect already mounted filesystems. The kernel table with already mounted filesystems is cached during mount --all. This means that all duplicated fstab entries will be mounted. The correct functionality depends on /proc (to detect already mounted filesystems) and on /sys (to evaluate filesystem tags like UUID= or LABEL=). It’s strongly recommended to mount /proc and /sys filesystems before mount -a is executed, or keep /proc and /sys at the beginning of fstab. The option --all is possible to use for remount operation too. In this case all filters (-t and -O) are applied to the table of already mounted filesystems. Since version 2.35 it is possible to use the command line option -o to alter mount options from fstab (see also --options-mode). Note that it is a bad practice to use mount -a for fstab checking. The recommended solution

This section continues the explanation of shared subtree operations, specifically the propagation flags and their behavior. It details how the 'mount' command can handle multiple propagation changes in one call, even with other mount operations. The section also mentions that these propagation flags can be specified in fstab as mount options. The section then transitions to command-line options for the 'mount' command. It outlines how mount options are determined by combining options from fstab and the command line. Finally, the section discusses the '-a' or '--all' option, which mounts all filesystems mentioned in fstab, explaining its functionality and dependencies on /proc and /sys. It also touches on its usage for remounting and modifying mount options from fstab.