RPCSEC_GSS makes use of certain files to store information.
When a server retrieves the client credentials associated with a request, the server can get either the client's principal name in the form of a rpc_gss_principal_t structure pointer or local UNIX credentials (UID) for that client. Services such as NFS require a local UNIX credential for access checking, but others might not. Those services can, for example, store the principal name directly in their own access control lists as a rpc_gss_principal_t structure.
The correspondence between a client's network credential (its principal name) and any local UNIX credential is not automatic. The local security administrator must be set up explicitly.
The gsscred file contains both the client's UNIX and network (for example, Kerberos V5) credentials. The network credential is the Hex-ASCII representation of the rpc_gss_principal_t structure. The gsscred file is accessed through XFN. Thus, this table can be implemented over files, NIS, or NIS+, or any future name service supported by XFN. In the XFN hierarchy, this table appears as this_org_unit/service/gsscred. Administrators can maintain the gsscred table with the use of the gsscred utility, which enables adding and deleting of users and mechanisms.
For convenience, RPCSEC_GSS uses string literals for representing mechanisms and quality of protection (QOP) parameters. The underlying mechanisms themselves, however, require mechanisms to be represented as object identifiers and QOPs as 32–bit integers. Additionally, for each mechanism, you need to specify the shared library that implements the services for that mechanism.
The /etc/gss/mech file stores the following information on all installed mechanisms on a system: the mechanism name, in ASCII; the mechanism's OID; the shared library implementing the services provided by this mechanism; and, optionally, the kernel module implementing the service. A sample line might look like this:
kerberos_v5 1.2.840.1135220.127.116.11 gl/mech_krb5.so gl_kmech_krb5
For all mechanisms installed, the /etc/gss/qop file stores all the QOPs supported by each mechanism, both as an ASCII string and as its corresponding 32–bit integer.
Both /etc/gss/mech and /etc/gss/qop are created when security mechanisms are first installed on a given system.
Many of the in-kernel RPC routines use non-string values to represent mechanism and QOP. Therefore, applications can use the rpc_gss_mech_to_oid() and rpc_gss_qop_to_num() functions to get the non-string equivalents for these parameters, should they need to maximize use of those in-kernel routines.