fs_mkmount - Creates a mount point for a volume
fs mkmount -dir <directory> -vol <volume name> [-cell <cell name>] [-rw] [-fast] [-config <config path>] [-help]
The fs mkmount command creates a mount point for the volume named by the -vol argument at the location in the /afs file namespace specified by the -dir argument. The mount point looks like a standard directory element, and serves as the volume's root directory, but is actually a special file system object that refers to a volume. On Microsoft Windows each mount point will be identified as a Reparse Point.
When the Cache Manager first encounters a given mount point during pathname traversal, it contacts the Location Server to learn which File Servers store the indicated volume, then fetches a copy of the volume's root directory from the appropriate file server machine.
It is possible, although not recommended, to create more than one mount point to a volume. Some operating systems, such as Linux, can become confused if a volume is mounted in two places within the /afs file namespace.
The Cache Manager observes three basic rules as it traverses the /afs file namespace and encounters mount points:
When the Cache Manager encounters a mount point that specifies a volume with either a .readonly or a .backup extension,
it accesses that type of volume only.
If a mount point does not have either a .backup or .readonly extension,
the Cache Manager uses Rules 2 and 3.
For example, the Cache Manager never accesses the read/write version of a volume if the mount point names the backup version. If the specified version is inaccessible, the Cache Manager reports an error.
If a mount point resides in a .readonly volume and the volume that it references has a .readonly instance,
the Cache Manager attempts to access a .readonly instance of the volume; if there is no .readonly instance,
the Cache Manager accesses the read/write copy.
The Cache Manager is thus said to prefer a read-only path through the file namespace,
accessing .readonly volume instances when they are available.
The Cache Manager always begins travering the /afs file namespace on the read-only path.
The Cache Manager will remain on the read-only path until a mount point explicitly refers to a read/write volume or a regular mount point refers to a volume that does not possess a .readonly instance.
If a mount point resides in a read/write volume and the target volume name does not have a .readonly or a .backup extension,
the Cache Manager attempts to access only the read/write version of the volume.
The access attempt fails with an error if the read/write version is inaccessible,
even if a read-only version is accessible.
In this situation the Cache Manager is said to be on a read/write path and cannot switch back to the read-only path unless the mount point target explicitly names a volume with a .readonly extension.
(Cellular mount points are an important exception to this rule, as explained in the following discussion.
There are three types of mount points, each appropriate for a different purpose because of the manner in which the Cache Manager interprets them.
When the Cache Manager crosses a regular mount point, it obeys all three of the mount point traversal rules previously described. To create a regular mount point, include only the required -dir and -vol arguments to the fs mkmount command.
When the Cache Manager crosses a read/write mount point,
it attempts to access only the volume version named in the mount point.
If the volume name is the base (read/write) form,
without a .readonly or .backup extension,
the Cache Manager accesses the read/write version of the volume,
even if a .readonly instance exists.
In other words,
the Cache Manager disregards the second mount point traversal rule when crossing a read/write mount point: it switches to the read/write path through the file namespace.
To create a read/write mount point,
include the -rw flag on the fs mkmount command.
It is conventional to create only one read/write mount point in a cell's file namespace,
using it to mount the cell's root.cell volume just below the /afs file namespace root (by convention,
/afs/.cellname).
See the Auristor Quick Start Guide for instructions and the chapter about volume management in the Auristor Administration Guide for further discussion.
Creating a read/write mount point for a read-only or backup volume is acceptable,
but unnecessary.
The first rule of mount point traversal already specifies that the Cache Manager accesses them if the volume name in a regular mount point has a .readonly or .backup extension.
When the Cache Manager crosses a cellular mount point, it accesses the indicated volume in the specified cell, which is normally a foreign cell. (If the mount point does not name a cell along with the volume, the Cache Manager accesses the volume in the cell where the mount point resides.) The Cache Manager disregards the third mount point traversal rule when crossing a regular cellular mount point: it accesses a .readonly instance of the volume if it exists, even if the volume that houses the mount point is read/write. Switching to the read-only path in this way is designed to avoid imposing undue load on the File Servers in foreign cells.
To create a regular cellular mount point,
include the -cell argument on the fs mkmount command.
It is conventional to create cellular mount points only as children of /afs,
using them to mount the root.cell volumes of foreign cells (by convention,
at /afs/foreign_cellname).
The mount point enables local users to access the foreign cell's file namespace,
assuming they have the necessary permissions on the ACL of the volume's root directory and that Location Server information for the foreign cell in the local configuration /etc/yfs/yfs-client.conf file or via DNS SRV or DNS AFSDB queries.
In the output of the fs lsmount command,
the cell name and a colon (:) appear between the initial number sign # and the volume name in a regular cellular mount point name.
Names the directory to create as a mount point. The directory must not already exist. Relative pathnames are interpreted with respect to the current working directory.
Specify the read/write path to the directory, to avoid the failure that results from attempting to create a new mount point in a read-only volume. By convention, the read/write path is indicated by placing a period before the cell name at the pathname's second level (for example, /afs/.your-cell-name.com). For further discussion of the concept of read/write and read-only paths through the filespace, see "DESCRIPTION".
Specifies the name or volume ID number of the volume to mount.
If appropriate,
add the .readonly or .backup extension to the name,
or specify the appropriate volume ID number.
Names the cell in which the volume resides (creates a cellular mount point). Provide the fully qualified domain name, or a shortened form that disambiguates it from the other cells listed in the local configuration /etc/yfs/yfs-client.conf file.
If this argument is omitted, no cell indicator appears in the mount point. When the Cache Manager interprets it, it assumes that the volume named in the mount point resides in the same cell as the volume that houses the mount point.
Creates a read/write mount point. Omit this flag to create a regular mount point.
Prevents the Cache Manager from querying the Location Server to check that the volume has a valid entry and printing a warning message if it does not. Whether or not this flag is included, the File Server creates the mount point even when the volume has no location information.
The location of the configuration file to be used. The default path is /etc/yfs/yfs-client.conf.
Prints the online help for this command. All other valid options are ignored.
The following command creates a regular mount point,
mounting the volume user.smith at /afs/your-cell-name.com/usr/smith:
% cd /afs/your-cell-name.com/usr % fs mkmount -dir smith -vol user.smith
The following commands create a read/write mount point and a regular mount point for the Example Corporation cell's root.cell volume in that cell's file tree. The second command follows the convention of putting a period at the beginning of the read/write mount point's name.
% fs mkmount -dir /afs/your-cell-name.com -vol root.cell % fs mkmount -dir /afs/.your-cell-name.com -vol root.cell -rw
The following command mounts the foreign-cell-name.com cell's root.cell volume in the your-cell-name.com cell's file tree, creating a regular cellular mount point called /afs/foreign-cell-name.com. When a Cache Manager encounters this mount point, it crosses into the foreign-cell-name.com cell on a read-only path.
% fs mkmount -dir /afs/foreign-cell-name.com -vol root.cell -c foreign-cell-name.com
The issuer must have the i (insert) and a (administer) permissions on the ACL of the directory that is to house the mount point.
fs_lsmount(1), fs_rmmount(1), yfs-client.conf(5)
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