+assumes the file
+.I /etc/krb5.keytab
+contains principals and keys that can be used to obtain machine credentials.
+.P
+.B rpc.gssd
+searches in the following order for a principal to use.
+The first matching credential is used.
+For the search, <hostname> and <REALM> are replaced with the local
+system's hostname and Kerberos realm.
+.sp
+ <HOSTNAME>$@<REALM>
+.br
+ root/<hostname>@<REALM>
+.br
+ nfs/<hostname>@<REALM>
+.br
+ host/<hostname>@<REALM>
+.br
+ root/<anyname>@<REALM>
+.br
+ nfs/<anyname>@<REALM>
+.br
+ host/<anyname>@<REALM>
+.sp
+The <anyname> entries match on the service name and realm, but ignore the hostname.
+These can be used if a principal matching the local host's name is not found.
+.P
+Note that the first principal in the search order is a user principal
+that enables Kerberized NFS when the local system is joined
+to an Active Directory domain using Samba.
+A password for this principal must be provided in the local system's keytab.
+.P
+You can specify another keytab by using the
+.B -k
+option if
+.I /etc/krb5.keytab
+does not exist or does not provide one of these principals.
+.SS Credentials for UID 0
+UID 0 is a special case.
+By default
+.B rpc.gssd
+uses the system's machine credentials for UID 0 accesses
+that require GSS authentication.
+This limits the privileges of the root user
+when accessing network resources that require authentication.
+.P
+Specify the
+.B -n
+option when starting
+.B rpc.gssd
+if you'd like to force the root user to obtain a user credential
+rather than use the local system's machine credential.
+.P
+When
+.B -n
+is specified,
+the kernel continues to request a GSS context established
+with a machine credential for NFSv4 operations,
+such as SETCLIENTID or RENEW, that manage state.
+If
+.B rpc.gssd
+cannot obtain a machine credential (say, the local system has
+no keytab), NFSv4 operations that require machine credentials will fail.
+.SS Encryption types
+A realm administrator can choose to add keys encoded in a number of different
+encryption types to the local system's keytab.
+For instance, a host/ principal might have keys for the
+.BR aes256-cts-hmac-sha1-96 ,
+.BR aes128-cts-hmac-sha1-96 ,
+.BR des3-cbc-sha1 ", and"
+.BR arcfour-hmac " encryption types."
+This permits
+.B rpc.gssd
+to choose an appropriate encryption type that the target NFS server
+supports.
+.P
+These encryption types are stronger than legacy single-DES encryption types.
+To interoperate in environments where servers support
+only weak encryption types,
+you can restrict your client to use only single-DES encryption types
+by specifying the
+.B -l
+option when starting
+.BR rpc.gssd .