NAME
fs_mkmount - Creates a mount point for a volume
SYNOPSIS
fs mkmount -dir <directory> -vol <volume name>
[-cell <cell name>] [-rw] [-fast] [-help]
fs mk -d <directory> -v <volume name>
[-c <cell name>] [-r] [-f] [-h]
DESCRIPTION
The fs mkmount command creates a mount point for the volume named by
the -vol argument at the location in the AFS file space 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 an AFS volume. When the Cache
Manager first encounters a given mount point during pathname traversal,
it contacts the VL Server to learn which file server machines house 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. The Cache Manager can become confused if a volume is
mounted in two places along the same path through the filespace.
The Cache Manager observes three basic rules as it traverses the AFS
filespace and encounters mount points:
Rule 1: Access Backup and Read-only Volumes When Specified
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.
Rule 2: Follow the Read-only Path When Possible
If a mount point resides in a read-only volume and the volume that
it references is replicated, the Cache Manager attempts to access a
read-only copy of the volume; if the referenced volume is not
replicated, the Cache Manager accesses the read/write copy. The
Cache Manager is thus said to prefer a read-only path through the
filespace, accessing read-only volumes when they are available.
The Cache Manager starts on the read-only path in the first place
because it always accesses a read-only copy of the root.afs volume
if it exists; the volume is mounted at the root of a cell’s AFS
filespace (named /afs by convention). That is, if the "root.afs"
volume is replicated, the Cache Manager attempts to access a read-
only copy of it rather than the read/write copy. This rule then
keeps the Cache Manager on a read-only path as long as each
successive volume is replicated. The implication is that both the
"root.afs" and "root.cell" volumes must be replicated for the Cache
Manager to access replicated volumes mounted below them in the AFS
filespace. The volumes are conventionally mounted at the /afs and
/afs/cellname directories, respectively.
Rule 3: Once on a Read/write Path, Stay There
If a mount point resides in a read/write volume and the volume name
does not have a ".readonly" or a ".backup" extension, the Cache
Manager attempts to access only the a 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 mount
point 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 it is replicated. 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 filespace.
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 filespace, using it to mount the cell’s
"root.cell" volume just below the AFS filespace root (by
convention, /afs/.cellname). See the IBM AFS Quick Beginnings for
instructions and the chapter about volume management in the IBM AFS
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 read-only version of the volume if it is
replicated, 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 server machines 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 at the second level in a cell’s
filespace, using them to mount foreign cells’ root.cell volumes
just below the AFS filespace root (by convention, at
/afs/foreign_cellname). The mount point enables local users to
access the foreign cell’s filespace, assuming they have the
necessary permissions on the ACL of the volume’s root directory and
that there is an entry for the foreign cell in each local client
machine’s /etc/openafs/CellServDB file. 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.
OPTIONS
-dir <directory>+
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/.abc.com). For further discussion of the
concept of read/write and read-only paths through the filespace,
see DESCRIPTION.
-vol <volume name>
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.
-cell <cell name>
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 /etc/openafs/CellServDB 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.
-rw Creates a read/write mount point. Omit this flag to create a
regular mount point.
-fast
Prevents the Volume Location (VL) Server from checking that the
volume has a VLDB 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 VLDB entry.
-help
Prints the online help for this command. All other valid options
are ignored.
EXAMPLES
The following command creates a regular mount point, mounting the
volume "user.smith" at /afs/abc.com/usr/smith:
% cd /afs/abc.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 ABC 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/abc.com -vol root.cell
% fs mkmount -dir /afs/.abc.com -vol root.cell -rw
The following command mounts the State University cell’s "root.cell"
volume in the ABC Corporation cell’s file tree, creating a regular
cellular mount point called /afs/stateu.edu. When a ABC Corporation
Cache Manager encounters this mount point, it crosses into the State
University cell on a read-only path.
% fs mkmount -dir /afs/stateu.edu -vol root.cell -c stateu.edu
PRIVILEGE REQUIRED
The issuer must have the "i" (insert) and "a" (administer) permissions
on the ACL of the directory that is to house the mount point.
SEE ALSO
CellServDB(5), fs_lsmount(1), fs_rmmount(1)
COPYRIGHT
IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.
This documentation is covered by the IBM Public License Version 1.0.
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