Installation guide

Improvements in autofs Version 5 over Version 4
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autofs uses /etc/auto.master (master map) as its default primary configuration file. This can
be changed to use another supported network source and name using the autofs configuration (in
/etc/sysconfig/autofs) in conjunction with the Name Service Switch (NSS) mechanism. An
instance of the autofs version 4 daemon was run for each mount point configured in the master map
and so it could be run manually from the command line for any given mount point. This is not possible
with autofs version 5, because it uses a single daemon to manage all configured mount points; as
such, all automounts must be configured in the master map. This is in line with the usual requirements
of other industry standard automounters. Mount point, hostname, exported directory, and options can
all be specified in a set of files (or other supported network sources) rather than configuring them
manually for each host.
10.3.1. Improvements in autofs Version 5 over Version 4
autofs version 5 features the following enhancements over version 4:
Direct map support
Direct maps in autofs provide a mechanism to automatically mount file systems at arbitrary
points in the file system hierarchy. A direct map is denoted by a mount point of /- in the master
map. Entries in a direct map contain an absolute path name as a key (instead of the relative path
names used in indirect maps).
Lazy mount and unmount support
Multi-mount map entries describe a hierarchy of mount points under a single key. A good example
of this is the -hosts map, commonly used for automounting all exports from a host under "/
net/host" as a multi-mount map entry. When using the "-hosts" map, an 'ls' of "/net/host"
will mount autofs trigger mounts for each export from host and mount and expire them as they
are accessed. This can greatly reduce the number of active mounts needed when accessing a
server with a large number of exports.
Enhanced LDAP support
The Lightweight Directory Access Protocol (LDAP) support in autofs version 5 has been
enhanced in several ways with respect to autofs version 4. The autofs configuration file (/
etc/sysconfig/autofs) provides a mechanism to specify the autofs schema that a site
implements, thus precluding the need to determine this via trial and error in the application itself.
In addition, authenticated binds to the LDAP server are now supported, using most mechanisms
supported by the common LDAP server implementations. A new configuration file has been
added for this support: /etc/autofs_ldap_auth.conf. The default configuration file is self-
documenting, and uses an XML format.
Proper use of the Name Service Switch (nsswitch) configuration.
The Name Service Switch configuration file exists to provide a means of determining from where
specific configuration data comes. The reason for this configuration is to allow administrators the
flexibility of using the back-end database of choice, while maintaining a uniform software interface
to access the data. While the version 4 automounter is becoming increasingly better at handling
the NSS configuration, it is still not complete. Autofs version 5, on the other hand, is a complete
implementation.
Refer to man nsswitch.conf for more information on the supported syntax of this file. Please
note that not all NSS databases are valid map sources and the parser will reject ones that are
invalid. Valid sources are files, yp, nis, nisplus, ldap, and hesiod.
Multiple master map entries per autofs mount point
One thing that is frequently used but not yet mentioned is the handling of multiple master map
entries for the direct mount point /-. The map keys for each entry are merged and behave as one
map.