fs_mkmount - Creates a mount point for a volume
fs mkmount -dir
< volume name
] [ -help
fs mk -d
The fs mkmount
command creates a mount point for the volume named by the
argument at the location in the AFS file space specified by the
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
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
- 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 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
- 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 OpenAFS Quick
Start Guide for instructions and the chapter about volume management
in the OpenAFS 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
- 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.
- -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
- -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
- Creates a read/write mount point. Omit this flag to create
a regular mount point.
- 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.
- 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/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
The issuer must have the "i" (insert) and "a" (administer)
permissions on the ACL of the directory that is to house the mount point.
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